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Brushless Doubly-Fed Induction Machines for Wind Turbines: Developments and Research Challenges
IET Electric Power Applications
Abstract
The brushless Doubly-Fed Induction Machine (DFIM) provides an interesting alternative to the commonly applied conventional DFIM in modern multi-MW wind turbines. This paper presents a literature survey on the brushless DFIM. The evolution of the cascaded induction machine into the modern brushless DFIM is discussed, as well as several theories explaining this machines complex operating principles. Nowadays, brushless DFIM research is mainly focussed on the development of a commercially competitive brushless DFIM based drive for multi-MW wind turbine applications. An overview of the latest developments in the fields of brushless DFIM modeling, design, and control is provided. Based on this, a qualitative comparison is presented of the brushless DFIM and other well-established generator systems for wind turbines and the challenges for future research are explored.
... The brushless doubly-fed induction machine (BDFIM) is a synchronous induction machine that presents numerous advantages for future wind-power generation systems. These benefits include low maintenance requirements due to a brushless structure, the absence of permanent magnets, voltage-fault ride-through capability, and the ability to control velocity, torque, and reactive power using fractional power [1][2][3][4]. Despite these merits, its commercialization has yet to occur primarily due to control issues [5][6][7][8]. ...
... Each BDFIM is designed to continuously operate powered through two stator windings (each connected to AC voltage sources) with carefully selected pole-pair numbers −p p and p c . The rotor winding cross-couples electromagnetically the stator windings through a particular nested-loop structure with p p + p c poles [1][2][3][4][5][6]. The angular frequency of the current in the rotor winding induced by the fundamental harmonic components of the air-gap magnetic field of ordinal numbers p p and p c (with respectively, positive and negative phase sequences), fulfils the relationship [1,3,9] w p − p p Ω r frequency of rotor winding current induced by stator winding space harmonic p p of positive phase sequence ...
... The rotor winding cross-couples electromagnetically the stator windings through a particular nested-loop structure with p p + p c poles [1][2][3][4][5][6]. The angular frequency of the current in the rotor winding induced by the fundamental harmonic components of the air-gap magnetic field of ordinal numbers p p and p c (with respectively, positive and negative phase sequences), fulfils the relationship [1,3,9] w p − p p Ω r frequency of rotor winding current induced by stator winding space harmonic p p of positive phase sequence ...
The natural mode of operation for the brushless doubly-fed induction machine is a particular instance of synchronism at a so-called natural rotor velocity when one stator winding is powered by an AC and the other by a DC voltage source. Consequently, in addition to the rotating magnetic field, there exists a magnetic field that is fixed to the stator frame of reference. Analysis in this specific mode is essential as the natural velocity arises from the choice of pole numbers, thereby determining machine efficiency. However, this presents a significant challenge when it comes to mathematical modeling using complex-valued steady-state models through either equivalent-circuit or finite element analysis. This paper presents a study on the extension of the recently-proposed steady-state complex-valued finite element model for the brushless doubly-fed induction machine to enable its application in the natural operating mode. A high correlation with the data obtained from a time-stepping model is obtained for the extended model when subjected to both low and high levels of saturation of the magnetic circuit. This extension makes the whole approach applicable in all operating conditions and modes of the brushless doubly-fed induction machine. Considering the nearly two orders of magnitude lower computational costs associated with analysis via the proposed model compared to time-stepping analysis, it is particularly useful in scenarios that involve extensive computations and require multiple cases to be considered such as design sensitivity analysis, topology optimization or a connection with machine learning techniques.
... It has been widely used in the power system. Nevertheless, there exist slip-rings and brushes in DFIG, and these wear parts can lower the reliability and also add maintenance costs [1][2][3]. In contrast, a brushless doubly fed generator (BDFG) has advantages similar to conventional DFIG, but it can also overcome the disadvantages of DFIG including having no brushes and slip rings, smaller sized gearbox and better low-voltage ride through (LVRT) capability [1][2][3][4]. ...
... Nevertheless, there exist slip-rings and brushes in DFIG, and these wear parts can lower the reliability and also add maintenance costs [1][2][3]. In contrast, a brushless doubly fed generator (BDFG) has advantages similar to conventional DFIG, but it can also overcome the disadvantages of DFIG including having no brushes and slip rings, smaller sized gearbox and better low-voltage ride through (LVRT) capability [1][2][3][4]. Hence, the BDFG is capable of greatly improving the reliability of the generation system and reducing its cost. ...
... For these reasons, the BDFG is regarded as an ideal alternative for traditional DFIG. The running of the BDFG includes stand-alone [5][6][7][8] and grid-connected modes [1][2][3][9][10][11][12][13][14][15][16][17][18]. The basic topology of a grid-connected BDFG-based wind turbine (BDFGWT) is depicted in Figure 1. ...
This article presents an improved collaborative control to resist grid voltage unbalance for brushless doubly fed generator (BDFG)-based wind turbine (BDFGWT). The mathematical model of grid-connected BDFG including machine side converter (MSC) and grid side converter (GSC) in the αβ reference frame during unbalanced grid voltage condition is established. On this base, the improved collaborative control between MSC and GSC is presented. Under the control, the control objective of the whole BDFGWT system, including canceling the pulsations of electromagnetic torque and the unbalance of BDFGWT’s total currents, pulsations of BDFGWT’s total powers are capable of being realized; therefore, the control capability of BDFGWT to resist unbalanced grid voltage is greatly improved. Moreover, improved single-loop current controllers adopting PR regulators are proposed for both MSC and GSC where the sequence extractions for both MSC and GSC currents are not needed any more, and hence the proposed control is much simpler. In addition, the transient characteristics are also improved. Moreover, in order to achieve the decoupling control of current and average power, current controller also adopts the feedforward control approach. Case studies for a two MW BDFGWT system are implemented, and the results verify that the presented control is capable of effectively improving the control capability for BDFGWT to resist grid voltage unbalance and exhibit good stable and dynamic control performances.
... Because of their merits, such as decoupled control and small converter size, traditional doubly fed induction generator (DFIG)-based wind turbines have been popularly installed on wind farms over the past decades. Nevertheless, the DFIG's electric brushes and slip rings degrade system reliability and increase its maintenance cost [1][2][3][4][5][6][7][8][9]. By comparison, a new type of multiport electric machine, the brushless doubly fed generator (BDFG), not only inherits the advantages of traditional DFIG but also overcomes its aforementioned disadvantages, such as canceling the electric brushes and slip rings and having better low voltage ride-through (LVRT) capability [2][3][4][5][6][7][8][9][10]. ...
... Nevertheless, the DFIG's electric brushes and slip rings degrade system reliability and increase its maintenance cost [1][2][3][4][5][6][7][8][9]. By comparison, a new type of multiport electric machine, the brushless doubly fed generator (BDFG), not only inherits the advantages of traditional DFIG but also overcomes its aforementioned disadvantages, such as canceling the electric brushes and slip rings and having better low voltage ride-through (LVRT) capability [2][3][4][5][6][7][8][9][10]. Thus, the use of BDFG can greatly enhance the reliability of wind generation systems and lower their cost. ...
... It therefore has promising prospects in energy conversion applications. The operation of BDFG can be stand-alone [11][12][13][14][15][16] or grid-connected [1][2][3][4][5][6][7][8][9]. Usually, in stand-alone operation, the frequency and voltage are controlled for load, whereas in grid-connected operation, active and reactive power are adjusted according to the requirements of the power grid. ...
This article proposes a proportional-integral-resonant (PIR) current control strategy for a wind-driven brushless doubly fed generator (WDBDFG) during network unbalance. Firstly, four control objectives of WDBDFG, including eliminating unbalanced currents of power winding (PW), pulsations of control winding (CW) currents, torque, and PW power, are discussed and different from current controls in which the references to PW currents were computed; the CW current references are derived here. Then, an improved CW current controller using a PIR controller is proposed to achieve different control objectives. In contrast with current controls, CW currents are not involved with sequence extraction in the proposed control and can be totally regulated only in a positive synchronous reference frame. Hence, the system control structure is greatly simplified, and dynamic characteristics are improved. Furthermore, in order to obtain completely decoupled control of current and average power, feedforward control, considering all the couplings and perturbances, is also applied in CW current loops. Simulation results for a 2 MW grid-connected WDBDFG show that the proposed control is capable of achieving four control objectives, including canceling CW current distortion, PW current unbalance, pulsations of PW active power or pulsations of reactive power, and machine torque. Its dynamic process is much more smoothly and quickly than that of current controls, and therefore the proposed control has better dynamic control characteristics during network unbalance.
... It is recognized that general reviews on BDFMs are available in literature such as [6][7][8]. These reviews cover a broad array of subjects like brief histories, electromagnetic design, modelling techniques, modes of operation, and control strategies. ...
... The nested loop (NL) and cage+NL rotors, whose origins are traced to [18], are currently deemed the most suitable for BDFMs [6,30,42]. The NL rotor winding arrangement and a prototype are shown in Figure 9a,b respectively. ...
... The winding arrangement in Figure 9a differs from that in Figure 5a by the presence of a common end ring, with the rotor illustrated in Figure 5a now sometimes called an isolated loop (IL) rotor [30]. These (NL, IL, & cage+NL) rotor types have robust builds with better torque performance and lower losses, compared to wound rotors [6]. ...
Research interest on brushless doubly fed induction machines (BDFMs) is increasing, as they offer higher reliability compared to doubly fed induction generators (DFIGs) in wind turbines. At the moment, BDFMs do not have a definitive structure nor design process, as literature is rife with different approaches to designing BDFMs. In this paper, a comprehensive review of the design of BDFMs from available literature is conducted. The evolution of cascade induction machine systems to contemporary BDFMs is first illustrated. Pioneering research work in the evolution which have influences on modern BDFM designs are highlighted. Relevant research on different aspects of present day BDFM design are then discussed. BDFM design and optimization methodologies applied in available literature are also explored.
... Fig.1 shows the configuration of BDFIG based wind turbine system. As shown, the entire system mainly consists of wind turbine, gear box, BDFIG, back-to-back converter including MSC and GSC, controllers of MSC and GSC, choke inductor and coupling transformer [5], [6]. Fig. 2 shows the three phase windings of BDFIG. ...
... Fig. 2 shows the three phase windings of BDFIG. As can been, BDFIG has two separate stator windings and a specially designed rotor, the two sets of stator windings with different pole pairs are named as power windings (PW) and control windings (CW), the rotor winding (RW) can be divided into rotor power windings (RPW) and rotor control windings (RCW) which are magnetically coupled with PW and CW, respectively [5], [6]. As can be seen in Figure 1, the PW is connected to the power grid directly whereas CW is excited by MSC and GSC, which are connected through a DC link. ...
... When the rotor rotating speed works above and below ωN, the system operation is called super-synchronous and sub-synchronous, respectively [6], [24]. ...
Grid codes require wind turbines to have capability to withstand a certain grid voltage unbalance without tripping. However, existing controls for brushless doubly-fed induction generator (BDFIG) based wind turbine under grid unbalance have many problems such as difficulty in realizing decoupling control, involvement with flux or current estimations, and complex control structure. Moreover, the existing studies only focused on the control of machine side converter (MSC), but the coordinated control between MSC and grid side converter (GSC) and the control objectives of overall BDFIG wind turbine system have not yet been addressed so far. To overcome these problems and improve the control capability, this paper proposes a coordinated control strategy by considering MSC and GSC together. First, the enhanced control objectives for overall BDFIG wind turbine system are determined. Second, the simple single current closed-loop controllers without involving with any flux or current estimations are designed for MSC and GSC, respectively. Meanwhile, in current loops, all the disturbances and cross-coupling terms on dq axes are derived and used for feedforward control so as to achieve decoupling control and improve system dynamic response. Further, a fast sequence decomposition approach is employed to enhance the control characteristics of the whole system. Finally, the effectiveness of proposed control is validated through case studies for a 2 MW BDFIG based wind generation system. The results demonstrate that the proposed control can effectively achieve the control objectives of overall wind turbine system under grid voltage unbalance and provide excellent dynamic and stable performance.
... In order to avoid the issues associated with brushes and slip rings, brushless DFIMs have attracted extensive attention since they are first proposed in [8]. Various brushless DFIM versions have been developed from conventional cascaded machines to self-cascaded machines and to modern DFIMs [9], [10]. Differing from conventional DFIMs, contemporary brushless DFIMs consist of two sets of stator windings, i.e. power windings and control windings, as shown in Figure 5(b) [11]. ...
... High due to the presence of both asynchronous and synchronous torque components [9]. ...
... High since there is no heat losses from the brushes and slip rings, as well as the external resistance [9]. ...
Abstract With ever‐increasing concerns on energy crisis and environmental protection, there is a fast‐growing interest in wind power generation systems. As electric machines and drives are core components in wind turbines, it is a pressing need for researchers and engineers to develop advanced electric machines and drives for wind power generation. This paper provides a thorough review of modern electric machines and drives for wind power generation, with emphasis on machine topologies, operation principles, performance characteristics, as well as control strategies. The key features of electric machines and drives including their merits and demerits, e.g. torque/power density, efficiency, and cost, are compared and summarised. Trade‐offs involved in various presented methods and strategies are highlighted. The major challenges and difficulties, which electric machines and drives for wind power generation are facing, are discussed. Moreover, the developing trends and opportunities are revealed, while the latest development is also discussed.
... However, DFIGs suffer from incessant maintenance downtimes due to failures from their brush and slip ring assemblies [2]. Brushless doubly fed (induction) machines (BDFMs) have been identified as alternatives to DFIGs in wind turbines, as they employ similar control systems with fractionally rated converters [3]. The absence of slip rings and brushes indicates significantly better reliability than DFIGs. ...
... Different practical BDFM rotors have been presented such as the double layer wound rotor [4], the series wound (SW) rotor [5], the nested loop (NL) rotor, and the p 1 + p 2 barcage with nested loops (cage+NL) rotor. However, the NL and cage+NL rotors, whose origins are traced to [6], are deemed the most suitable [3] [4] [5]. The NL and cage+NL rotors have robust builds with lower flux leakages and losses compared to the series wound rotors. ...
... The NL and cage+NL rotors have robust builds with lower flux leakages and losses compared to the series wound rotors. Although, the cage+NL rotor has similar advantages with the NL rotor, the NL rotor is the most commonly used rotor in BDFMs [3]. ...
... The brushless doubly-fed generator (BDFG) [1][2][3] is a prospective, maintenance-free alternative to a classical doubly-fed induction generator (DFIG) in wind power applications ( Fig. 1) [4]. While offering largely competitive performance under normal operating conditions, its low-voltage-ride-through characteristics, including the potential for frequency support provision, appear to be better than the DFIG [5,6]. ...
... The rotor of an induction BDFG type (i.e. brushless doubly fed induction generator (BDFIG)) can be of special nested-loops cage or wound structure with short-circuited coils [1,2,8,9], whereas its cage-less reluctance companion, the brushless doubly-fed reluctance generator (BDFRG), may have an axially or radially laminated design [10,11] offering the superior efficiency, fewer parameter-dependent dynamic models [12], and the possibility for decoupled field-oriented control of real and reactive power [13,14] similar to DFIG [4]. More optimised hybrid rotor prototypes of higher torque densities and efficiencies have likewise been reported recently to combine the individual BDFIG and BDFRG advantages in a single machine [15][16][17]. ...
... The prevalent vector control approaches for DFIGs [4,22], BDFIGs [2,[23][24][25] or BDFRGs [13,14] are rotor position reliant and require the use of shaft encoders. Avoiding such sensors would enhance the reliability and lower the maintenance of DFIG wind turbines in particular, as frequent and disruptive brush replacements could otherwise increase their failure rates [21]. ...
An improved and more robust flux vector orientated control scheme for an emerging doubly‐fed reluctance generator without a shaft angular position or velocity sensor has been proposed, computer‐simulated, and experimentally verified. Whilst retaining the cost and other advantages of using a fractional power electronics converter rating, this promising medium‐speed brushless machine technology has been viewed by research and industrial communities as an appealing economical solution for the compromised reliability and high maintenance requirements associated with the presence of slip rings, brushes, and the failures prone three‐stage gearbox of conventional wound rotor doubly‐fed induction generators, traditionally deployed for commercial wind turbines. The comprehensive comparative simulation and test results obtained have been shown to agree very well undoubtedly demonstrating the good overall performance of the sensorless controller. A precise speed reference tracking with smooth, intrinsically decoupled real and reactive power responses of the grid‐connected winding has been achieved for the typical variable loading profiles and narrow speed ranges (e.g. around 2 : 1 or so) of a laboratory emulated wind turbine.
... Brushless doubly fed (induction) machines (BDFMs) can be used in wind energy conversion systems in a similar way to doubly fed induction generators (DFIGs). BDFMs utilise fractionally rated converters, and are capable of synchronous torque operations with power factor control, just as in DFIGs [1]. BDFMs also have superior intrinsic low-voltage ride through characteristics compared to DFIGs [2]. ...
... The NL and cage+NL rotors have robust structures with lower flux leakages and losses compared to the other potential rotor types. Also, NL and cage+NL rotors are easier to manufacture [1,4,5]. ...
... When BDFMs are operated in the synchronous doubly fed mode, which is desirable in wind power applications, the PW and CW produce rotating independent magnetic fields travelling in opposite directions [1]. These fields induce currents on the rotor which have the same frequency and phase delay in the rotor nests. ...
The brushless doubly fed induction machine (BDFM) is considered as an alternative to doubly fed induction generators (DFIGs) in wind energy conversion systems. However, BDFMs have a complex machine structure, and their operations are relatively complicated. In this study, the winding function theory is used in the development of a coupled circuit (CC) model for BDFMs with nested loop (NL) and cage+NL rotors, in order to give a robust representation of the electrical operations of BDFMs. The electrical circuit analysis of BDFMs having NL and cage+NL rotors is comprehensively detailed, with the stator and rotor inductances calculated using their winding functions. The interactions of BDFM rotor loops with stator windings are demonstrated in terms of mutual inductances. CC models of different BDFMs are simulated for synchronous doubly fed BDFM operations with an emphasis on generating regions. Also, fresh insight into the torque production in BDFMs is provided, with the rotor loops and stator winding contributions to torque magnitude and ripple examined.
... 29 It has been proposed to overcome the maintenance challenges in the DFIG since it requires no slip rings or brushes. In previous works, 29,30 it is prototyped for large wind turbines but still emerging and not yet deployed in commercial installation. 3 It offers improved voltage fault ride-through performance over the DFIG due to higher rotor inductance and enhanced reactive current injection capability. ...
... 3 It offers improved voltage fault ride-through performance over the DFIG due to higher rotor inductance and enhanced reactive current injection capability. 30 Major technical challenges of the BDFIG are higher inverter current for the magnetization of the rotor, leading to higher cost, complex winding connections in the rotor, posing manufacturing difficulties, limited slip due to singularity at super-synchronous speeds, and it only allows for low saturation; consequently, the stator and rotor cores need to be larger than that of the DFIG with similar power rating. The BDFIG has limited slip and can only be operated in the sub-synchronous speed range; thus, a 6-pole design with natural speed of 500 rpm has been proposed to be a perfect fit for MS drive system. ...
... The BDFIG has limited slip and can only be operated in the sub-synchronous speed range; thus, a 6-pole design with natural speed of 500 rpm has been proposed to be a perfect fit for MS drive system. 30 In this way, the singularity at super-synchronous speed ceases to be a disadvantage and the dimensions can be optimally sized. ...
At the end of 2018, the total global installed wind turbine capacityf DFIG with modified SM stood at approximately 592 GW; 96% of these installations are located onshore. Yet, an additional 267 GW of onshore capacity is projected to be installed by the end of 2023. This is envisaged to open up more opportunities in the development of onshore wind turbine generator (WTG). Therefore, this survey article brings together variable‐speed onshore WTG topologies, alongside their applicable drivetrains and converter technologies. Spotlight is on their merits and respective limitations which create opportunities and challenges in their deployments in commercial installations. It also evaluates and discusses a new development in the most widely deployed onshore WTG topology and concludes by identifying the single biggest development driver.
... e operation of an island is characterised by the uneven load on each phase and random behaviour. For wind turbine brushless doubly fed induction machines, developments and research challenges have been well addressed [16]. From this study, general performance (such as size, mass, efficiency, power quality, development, and maturity), system stability (such as brushes/slip rings, power electronics converters, crowbars, and vibrations), and control (power electronics rating, complexity, and grid fault and performance) for permanent magnet generator, doubly fed induction machine (DFIM), and BDFIM have been well reported. ...
... e design of a 2/6 pole, 400V, 3.5 kW BDFIM with star connection for SPW, delta-star connection for APW, and nested loop rotor was carried out using BDFIM design equations and standard output equations (15)(16)(17). Table 1 lists the machine's specifications [7]. e inner diameter of the stator is set at 190 mm to account for the availability of standard stampings. ...
Electricity generation with minimal environmental pollution is required for the world's sustainable future, and wind electric generation is one of them. Brushless doubly fed induction generator (BDFIG), which derives from cascade induction machine technology, has grown in popularity as a wind electric generator due to advantages over doubly fed induction generator (DFIG) and permanent magnet synchronous generator (PMSG) such as the absence of slip rings and brushes and high-cost permanent magnets. Wind energy research is critical for any country's economic development and long-term sustainability. As a result, an experimental setup in a laboratory is required to replicate the behaviour of a wind turbine in the steady state. is study discusses the emulation of wind turbine characteristics in the laboratory using a prototype of a separately excited DC motor mechanically coupled to a brushless doubly fed induction generator (BDFIG). e wind turbine emulator-brushless doubly fed induction machine (WTE-BDFIM) prototype was tested in the laboratory under high power and low wind speed conditions. As a result, the simulation of the same hardware con guration in MATLAB was performed to investigate the overall performance of the BDFIM-based WECS. To determine the equivalent circuit parameters of the BDFIM, which are required for simulation, tests were performed on a prototype of 3.5 kW, 2/6 pole, 400 V, star/delta-star, and BDFIM in two modes, namely, the simple induction mode and the cascade induction mode. Based on the BDFIM parameters, a MATLAB Simulink model of a BDFIG-based wind electric conversion system (WECS) is created and its performance is investigated. Results of both hardware and simulation show that BDFIG can be used as the wind electric generator over a wider speed range compared to that of DFIG, an important feature that is required to get maximum power extraction from the wind turbine.
... Unlike the conventional doubly-fed induction generator (DFIG), the rotor of the BDFG no longer needs to be supplied by the power converter, so that the brushes and slip rings associated with the rotor can be removed [2]. Based on [3] and [4], a fair comparison between the DFIG and BDFG is depicted in TABLE I to state the typical strengths and weaknesses of the two kinds of generators. In Table R1, the symbol "+" indicates the strength and the symbol "-" stands for the weakness. ...
... These strengths of the BDFG are very important for practical industrial applications. [3], [4] Metrics of interest DFIG BDFG The current BDFGs can be divided into two main categories, i.e., the single-stator BDFGs and the dual-stator BDFG. The single-stator BDFGs mainly include the brushless doubly-fed induction generator with nested-loop rotor (BDFIG-NLR) [5], [6], the brushless doubly-fed reluctance generator (BDFRG) [7], [8], the BDFIG with wound rotor (BDFIG-WR) [9], and the BDFG with hybrid rotor (BDFG-HR) [10]. ...
The brushless doubly-fed generator (BDFG) is a kind of dual-electrical-port field-modulated electrical machine containing two sets of stator windings with different pole pairs. The stator power winding undertakes most of the power inflow and outflow, and the stator control winding connected to the power converter can be utilized to regulate the machine operation status. Consequently, the rotor no longer needs to be supplied by the power converter, so that the brushes and slip rings can be removed. The BDFG can be used for grid-connected power generation as well as standalone power generation. This paper reviews recent advances of control technologies for BDFGs under different operation conditions, e.g., grid-connected ac power generation with normal and faulty grids, standalone ac power generation with normal and special loads, and dc power generation. The progresses of sensorless control technologies for BDFG-based power generation systems are also discussed. The classification and comparison are carried out to discover the similarities and differences between theses control technologies. This paper is in the hope of inspiring new, ground breakings and progresses for high-performance BDFG power generator applications.
... Universal model equivalent circuit is selected for the battery, composed of internal resistance and controlled voltage source connected in series [24]. The wind turbine is modeled as double-fed wind power generation system, with the stator winding directly connected to the network and the rotor winding connected to the converter [25]. The micro-gas turbine adopts single shaft structure with high-frequency alternating current (AC) at the motor outlet [26]. ...
... The network is divided into nine subnetworks according to the principles of network partitioning as illustrated in Figure 14. The wind turbine is modeled as double-fed wind power generation system, with the stator winding directly connected to the network and the rotor winding connected to the converter [25]. The microgas turbine adopts single shaft structure with high-frequency alternating current (AC) at the motor outlet [26]. ...
The microgrid containing a large amount of high frequency power switches and nonlinear components has put forward high requirements for power system real-time simulation technology. Multivalued coefficient prestorage can reduce the calculation steps in real-time simulation. In order to reduce the storage pressure of the multivalued coefficients, the whole network is divided into multiple subnetworks that can be simulated in parallel, and only the parameters for computing input variables and internal variables are prestored. The multiport hybrid equivalent is performed to reduce the number of simultaneous network equations. The input variables are tied to state variables of the circuit so that the iterative calculation is limited to the local network. The devised methodology is validated through simulation of a low-voltage microgrid on a field programmable gate array (FPGA)-based real-time digital simulation (FRTDS) platform at a 5 μs time step. Comparison with a power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) model shows that the proposed method is effective.
... Among variable-speed constant-frequency (VSCF) wind energy conversion systems (WECS), a brushless doubly-fed induction generator (BDFIG) is a reliable option that inherits the doubly-fed induction generator (DFIG)'s benefits of low cost structure due to the facts that no permanent magnets materials are utilized and only a fractionally rated converter is needed. Simultaneously, the absence of electric slip rings eliminates one of the main failure modes of the DFIG [1,2]. The BDFIG also has a significantly enhanced low-voltage ride-through performance in contrast with a DFIG [3]. ...
... The stator of the BDFIG is furnished with two separate stator windings, known as the PW and CW, which share one stator lamination and differ in pole pair number distribution to avoid direct coupling between the windings. The special rotor couples both stator windings [2]. In general, the PW stator connected to the point of common coupling (PCC) directly, whereas the CW stator is fed by a back-to-back voltage source converter (VSC), handling only a fraction of the rated power with limited velocity ranges. ...
In this paper, a novel voltage control strategy for stand-alone operation brushless doubly fed induction generators for variable speed constant frequency wind energy conversion systems was presented and discussed. Based on the model of the power generation system, the proposed direct flux control strategy employs a nonlinear reduced-order generalized integrator-based resonant sliding-mode control approach to directly calculate and regulate the output value of converter which the control winding stator requires so as to eliminate its instantaneous errors, without involving any synchronous rotating coordinate transformations. The stability, robustness and convergence capability of the proposed control strategy were described and analyzed. Owing to the fact no additional current control inner loops are involved, the system configuration is therefore simplified and the dynamic performance enhanced. A constant converter switching frequency was achieved by using space vector pulse width modulation, which reduces the harmonics of the generator terminal voltage. In addition, the feasibility and validity of the proposed scheme is verified by experiments, and excellent steady and transient performance is achieved.
... BDFMs are IMs with two stator windings (PW & CW) wound for dissimilar number of poles, and a special brushless rotor which enables cross-coupling between the stator windings [13]. BDFMs can be run in a synchronous mode similar to DFIGs, and also only require fractionally rated converters. ...
... They are naturally medium speed machines which have been suggested to have more reliable drivetrains due to fewer gearbox stages [1]. BDFMs also have a better intrinsic low voltage ride through performance than DFIGs [13]. The BDFM wind turbine drivetrain is illustrated in Fig. 2. ...
... To remove the problem of the slip-ring machines, some alternative solutions such as brushless doubly fed induction generators (BDFIGs) [5][6][7][8][9][10][11][12], dual-stator winding induction generators (DSWIGs) [13][14][15][16][17][18], dual-stator core induction generators (DSCIGs) [19] and cascaded doubly fed induction generators (CDFIGs) [20][21][22][23][24][25] are proposed. In the BDFIG there are a nested-loop rotor circuit and two un-coupled windings with a dissimilar number of poles in a single-frame stator. ...
... In the BDFIG there are a nested-loop rotor circuit and two un-coupled windings with a dissimilar number of poles in a single-frame stator. A nice review of emerging and developing of the B Samad Thaghipour Boroujeni s.taghipour@sku.ac.ir 1 Shahrekord University Faculty of Technology and Engineering, Shahrekord, Islamic Republic of Iran BDFIGs is reported in [5]. A simple and approximate per phase model is developed for steady-state analysis of the BDFIGs in [6]. ...
In this work, a cascaded doubly fed induction machine with a cage rotor is studied. To investigate the machine performance, a model is provided. In this model, the spatial harmonics of the rotor magnetomotive force are exactly considered. For this purpose, each rotor loop is selected as an individual circuit. The winding function theory is applied to compute the self- and mutual inductances of the rotor and stator circuits. To reduce the required simulation time, complex vector representation is adopted. Using the obtained voltage equations, the vector form of the machine state-space equations is yielded. Experimental tests are carried out to show the accuracy of the provided model. In addition, the adequacy of the proposed machine is verified by the appropriate tests.
... To eliminate problems with slip-rings, a brushless doubly-fed induction generator (BDFIG) has been invented [7]. Among all types of brushless doubly-fed induction generators, a cascaded brushless doubly-fed induction generator (CBDFIG) is widely described due to construction simplicity and as a consequence -low cost and high durability [8]. ...
... The proposed indirect torque control algorithm requires the commanded value of electromagnetic torque. The reference value of the main machine electromagnetic torque can be calculated using commanded active power (7). It should be noted that this way the average value of torque can be found. ...
This paper describes an indirect torque control algorithm for a cascaded brushless doubly-fed generator (CBDFIG). The control algorithm presented in the paper provides a possibility for CBDFIG to work with an unbalanced power grid applying different strategies: electromagnetic torque oscillations reduction, generated active power oscillation reduction, generated phase currents balancing, sinusoidal control currents under grid imbalance. The proposed control method is based on a cascaded brushless doubly-fed induction generator equivalent model and requires fewer tuning-demanding elements in comparison to classic control methods. The control algorithm presented in the paper was implemented and tested on a CBDFIG machine model in a simulation environment PSIM and on a real physical stand with a cascaded brushless doubly-fed generator.
... Nonetheless, one of its main drawbacks is the cost of maintenance actions due to the presence of brushes and rings especially when offshore. In order to solve this issue, investigations are made on brushless machines, and as a result, the Brushless Doubly Fed Induction Machine (BDFIM) could be a good candidate (Henk et al. 2013;Tim et al. 2016). In fact, compared to a DFIG of same rate, the Brushless Doubly Fed Induction Generator (BDFIG) freed of brushes is more robust and reliable. ...
... In fact, compared to a DFIG of same rate, the Brushless Doubly Fed Induction Generator (BDFIG) freed of brushes is more robust and reliable. It also has an improved low voltage ride-through capability and, due to its pole pair numbers, appears to be a medium speed drive candidate (Francisco et al. 2009;Shiyi et al. 2009;Henk et al. 2013;Tim et al. 2016). ...
The Brushless Doubly Fed Induction Generator (BDFIG) is a great attraction nowadays thanks to its high reliability and high low voltage ride-through capability. In variable speed generation systems, the most used control techniques are the vector control, direct torque/power control. Vector control is highly sensitive to parameters variations, while the two others offer high amount of ripples reducing power quality. This paper therefore proposes a Sliding Mode Power Predictive Control (SMPPC) and an Indirect Model Power Predictive Control (I-MPPC) for a simple and efficient power control of the BDFIG. The SMPPC takes current components in the αβ frame as sliding surfaces derived from the I-MPPC based on current predictions to track the desired active and reactive powers in the BDFIG. A cost function defined as currents’ quadratic errors is used to choose the appropriate voltage vector for control winding supply, and the Particle Swarm Optimization algorithm is used to determine the optimal gain for the SMPPC. Simulations on MATLAB/Simulink are carried out to show the effectiveness of the control schemes as well as their robustness to some parameters variations. More so, power compensation is used to improve the capability of the control strategy to provide sinusoidal and balanced currents under unbalanced grid conditions. The proposed methods compared to direct power control show good performances in terms of total harmonic distortion reduction, low ripples and robustness, strengthening the idea of using the BDFIG as an alternative to new generation of wind energy conversion systems.
... The NL and cage+NL rotors, originating from the cascaded induction machine, are considered most suitable due to their solid bars and high current capabilities. While both NL and cage+NL rotors offer similar advantages, NL rotors are more commonly utilized in BDFMs [4], [15]. The cage+NL rotor is more advantageous when there is a significant disparity between p 1 and p 2 , a situation not observed in the 4/6 BDFM [16]. ...
... The converter systems used here enable comprehensive control both on the rotor side and on the grid side [11]. The presence of the brush-commutator assembly, one of the significant problems of DFIGs, has been attempted to be solved with the self-cascaded DFIG topology, which began to be implemented at the end of the 1800 s [12]. Here, the rotor winding connections of two DFIGs located on the same shaft are made through the shaft itself, thereby eliminating the brush-commutator assembly. ...
In traditional electricity generation plants, large powerful synchronous, induction, and direct current generators were used. With the proliferation of microgrids focused on electricity generation from renewable energy sources in today's power grids, studies have been conducted on different types of generators. Instead of the traditional generator architecture, generators with brushless structures, particularly those utilizing magnets for excitation, have found broad applications. Flux-switching generators (FSGs) are innovative types owing to their robust structure, active stator design, and high power density capabilities. However, designs have typically relied on rare-earth element magnets. Rare-earth magnets possess negative characteristics such as price uncertainty, the potential risk of scarcity in the future, and limited geographical production, leading to research on FSGs that do not depend on rare-earth magnets. This study comprehensively examines FSGs that do not use rare-earth element magnets. The study delves into the usage areas, operational mechanisms, structural diversities, and counterparts in the literature of these generators.
... However, BDFGs excel in mechanical durability due to the absence of brushes, slip rings, and crowbars, rendering the system more reliable. Furthermore, BDFGs offer low maintenance costs and superior performance under grid faults, underscoring their significant importance in practical applications with large capacities [47], [48]. Table II compares the BDFIG, DSBDFIG, CBDFIG, and BDFRG concerning large generators. ...
While the traditional doubly-fed induction generator (DFIG) currently play a pivotal role in variable speed applications, the brushless doubly-fed generator (BDFG) has emerged as a promising alternative. This study presents a comprehensive literature survey on control strategies aimed at improving power quality in BDFGs. The discussion explores the causes of power quality issues associated with the BDFG system, delving into their negative impacts on the generator performance. Furthermore, the study provides detailed and comparative analysis of various control systems designed to address these issues, supported by qualitative and graphical results. Additionally, the research highlights power quality challenges not previously addressed in the literature, drawing attention to areas that warrant further exploration by researchers in the near future.
... T He Brushless Doubly-Fed induction Machine (BDFM) is an attractive proposition for variable speed applications, especially in wind power generation [1], [2]. Several experimental BDFMs have been built ranging from small laboratory sizes up to several hundreds of kilowatts including a 250 kW size built by the authors [3], [4] and most recently, an 800 kW machine built for hydropower generation by Chen et al. [5]. ...
This paper presents a method to estimate the BDFM equivalent circuit rotor current from rotor bar current measurements. Rotor currents are measured using a specially designed hardware that incorporates Rogowski coils and Bluetooth wireless transmission. The measurement of rotor currents enables the parameters in the BDFM's full equivalent circuit to be extracted unambiguously. In particular, stator and rotor leakage inductances can be estimated from experimental tests, which was not possible before from terminal measurement. The method is presented for a nested-loop rotor design and experimental measurements are shown for a prototype D180 frame BDFM.
... Recent advancements in electrical machines have introduced various machines as potential wind generators, such as brushless DFIGs [11,12] and various types of stator-PM machines [13][14][15]. However, it has been mentioned that a dual-field excited synchronous generator (DESG) can also be used as a variable-speed, constant-frequency wind power generator [16,17] with appropriate control. ...
Integrating wind power generators, whose frequency varies in a wide range due to varying wind speeds, into a grid is a formidable problem. At present, the use of permanent magnet synchronous generators (PMSG) and doubly fed induction generators (DFIG) as wind generators with suitable control is the best possible solution. However, a dual-field excited synchronous generator (DESG), which has two windings on the rotor, can also be used for the same purpose with appropriate control. A new control strategy, which essentially employs the d-axis and q-axis components of the alternator terminal voltage, is suggested here. This strategy essentially results in exciting the two field windings with a slip frequency. This eventually holds the stator frequency constant, irrespective of the rotor speed of the wind generator. The difference between the required frequency and the natural frequency, analogous to the rotor speed of the wind power generator, is the slip frequency. The ring modulator automatically adjusts the slip frequency depending on the actual speed of the generator’s rotor. This paper uses the ANSYS MAXWELL 2022 R1 software to design a DESG and uses a ring modulator as the control function generator for feedback with ANSYS TWIN BUILDER 2022 R1. Simulations are carried out using transient–transient co-simulation by combining both of these software tools for cases of both a constant-speed input and of a variable-speed input to the rotor of the machine. Moreover, a mathematical model of the DESG as a wind generator with the proposed controlled strategy is used to perform the stability analysis of a nine-bus three-machine system, and the results are compared with those of conventional wind generators.
... These are no permanent magnets, high reliability, good grid fault ridethrough capability, and the fractional rating of the power converter [1][2][3]. There have been many accomplishments in the area of modelling and designing the BDFIM [4][5][6][7][8][9][10][11][12][13][14]. In recent years the focus has been on improving the machine efficiency through finding new [8] and optimising existing [9][10][11][12] rotor structures. ...
A computationally efficient time‐harmonic finite element model for the steady‐state analysis of a brushless doubly fed induction machine (BDFIM) is proposed. In the model, the electromagnetic couplings of the BDFIM are described by means of the sum of two complex magnetic vector potentials that represent the two fundamental harmonic time components of the magnetic flux density distribution in the rotor frame of reference. As in an ordinary induction motor, the non‐linearity of the magnetisation characteristic is accounted for using an effective magnetic permeability. For the BDFIM, this is derived by considering the features of modulated magnetic flux density waveform. The accuracy of the approach has been validated by comparing the characteristics of a D270 machine operating in the double‐feed mode with ones obtained from the experimentally verified time‐stepping model at various operating conditions. High accuracy of the results coming from the proposed model is demonstrated even under deep saturation conditions within the magnetic circuit.
... Also, this study deals with minimizing the use of the HTS field coil, which reduces the cost of generators. A qualitative comparison for brushless DFIM, BDFRM, and others is presented in [80]. Three types of wind generators are compared, namely DFIG1G, DFIG3G, and DDPMG [81]. ...
The rated power of wind turbines has consistently enlarged as large installations can reduce energy production costs. Multi-megawatt wind turbines are frequently used in offshore and onshore facilities, and today is possible to find wind turbines rated over 15 MW. New developments in generators and power converters for multi-MW wind turbines are needed, as the trend toward upscaling the dimensions of wind turbines is expected to continue. Therefore, this paper provides a detailed review of commercially available and recently proposed multi-MW wind turbine generators and power converters. Furthermore, comparative analyses indicate the advantages and disadvantages of commercially available and promising technologies for generators and power converters at the multi-MW target.
... Only synchronous conditions are considered for the BDFM designs. Although asynchronous modes of operations are possible with BDFMs, these modes are generally undesirable, and mostly only useful for parameter identification [32], [33], [34]. The considered designs have different specifications of rotor type, power ratings, flux densities, electric loadings and pole pair combinations. ...
In this paper, it is proposed that design evaluations of brushless doubly fed machines (BDFMs) be conducted at unity power factor in the synchronous generating mode, for wind turbine applications. In the build up to this idea, differences in power output at asynchronous, synchronous motoring, and synchronous generating modes are highlighted and discussed. The changes in generated power at varying grid side power factor of BDFMs are also demonstrated. Different designs of doubly fed induction generators (DFIGs) and BDFMs are simulated to highlight these variations. Potential issues that can arise from insufficient design evaluations are discussed. Experimental measurements from a 160L frame 2/3 BDFM are also used for validation.
... The input currents in the rotor are adjusted in frequency and phase angle to compensate for speed variations of the turbine, so that the VSCF operation could be achieved [7]. Furthermore, many modern brushless DFIMs have been proposed and attracted increasing attention because of their improved robustness and reliability, as well as the reduced maintenance requirement due to the absence of brushes and slip-rings [8]. The cascaded DFIM is the basic concept of brushless DFIMs, which is simply formed by two wound-rotor induction machines affixed to the same shaft with their rotor winding connected to each other [9]. ...
A permanent magnet brushless doubly-fed electric machine is presented in this paper. This machine is developed for variable-speed constant-frequency wind energy generation applications. Differing from conventional doubly-fed electric machines based on induction machines, a permanent magnet rotor provides the magnetic field excitations for both the control winding and the power winding in the presented machine. The operating principle of the presented machine for the variable-speed constant-frequency operation is revealed in detail. Compared to a counterpart machine, the presented machine exhibits significantly improved back- electromotive force, torque/power density, torque per magnet volume, efficiency, etc. Finally, a proof-of-concept prototype of the presented machine is fabricated, and the corresponding experimental results are provided to verify the fact that the presented machine is capable of achieving the variable-speed constant-frequency function.
... Nowadays, the topology based on the DFIG and perma-nent magnet synchronous generator (PMSG) is the most popular system and the widely used in modern wind power plants. The wind power generation system based on DFIG was developed in the late 19th century where two woundrotor induction machines in cascade have been connected [10]. Since then, a variety of structures have been described, manufactured, and presented [11]- [15]. ...
The article presents the concept of a new design of a multi-phase doubly-fed induction generator (DFIG). The innovative design approach uses a five-phase power supply from the rotor side of the generator with a three-phase classic stator power supply. Modern three-phase doubly-fed induction generators are the dominant choice for Wind Energy Conversion Systems (WECS). Solutions of this type are sensitive to the loss of at least one phase of the power supply from the rotor side due to the failure of the rotor side inverter. The proposed design solution in the form of a multi-phase power supply in the rotor circuit aims to extend the range of possible failure-free operation of the generator system, thus reducing system downtime due to the failure of power electronic systems. The correctness of the adopted conceptual assumptions was confirmed by the results of laboratory tests. The main contribution is to prove that using five-phase rotor winding improves the overall reliability of the proposed electrical energy generation system significantly.
... Other exciting research studies relate to the benefits of altering the shape of blades [33][34][35][36][37] and material innovations [38,39]. Design development for generators includes: doubly fed induction generators [40][41][42][43], brushless doubly-fed induction machines [44,45], synchronous generators [46,47] and high-temperature superconducting generators [48][49][50][51][52]. At the same time, design developments for grid connections [53][54][55][56][57], monitoring and control mechanisms [58][59][60][61][62][63][64][65][66][67][68][69][70] are discussed. ...
A design process for determining the impact of the simple wake model, park (WAsP) model, and the eddy-viscosity model on the energy production of large offshore wind farms is presented in this study. This process is implemented in the system advisor model simulator. Even though wind turbine components’ electrical transients and physical stress are not covered in this simulator, four large offshore wind farms are successfully simulated. It is found that the simple wake model is more suitable for controlling wake effects on large offshore wind farms than park (WAsP) and eddy-viscosity models. This model produces higher annual energy with a better capacity factor than the other two models. Furthermore, although any generator system could test these wake models’ performance, this study uses single stage low-speed and direct-drive generators. The direct-drive generator produces higher annual energy and better capacity factor on all four offshore wind farms for all three wake models. However, this performance is for a rectangular or square layout of wind turbines on the wind farms, with row orientation 0° and every other row as offset type. This study’s findings significantly optimize wake effect control and wind turbine layout design on large offshore wind farms.
... Recently, many developed generators have been presented for WECS like the brushless doublyfed induction generator (BDFIG) [14]- [16], as well as adual excited synchronous generator (DESG) [17], [18], stator-PM machines [19], which include like axial field flux-switching PM machines, doubly salient PM machine, and stator interior permanent magnet generators; and finally the flux modulated PM machines [20], [21] such as magnetic-geared PM machines, hybrid excited flux bidirectional modulated PM machines. Because of the absence of slip rings and brushes, BDFIG is advantageous for its high efficiency, high reliability, and low maintenance cost in comparison with DFIG. ...
This paper presents a dual excited synchronous generator (DESG) as a novel suitable alternative generation system for wind energy conversion systems. A new control strategy was proposed for the DESG wind turbine system. With this control technique, the DESG could be operated as a constant-speed constant-frequency (CSCF) generation system with the benefit of adjusting the reactive power or as a variable-speed constant-frequency (VSCF) generation system with the benefits of simple control methods and lower copper losses. Using the space phasor model of the DESG, a direct relationship between the electromechanical torque and the armature reactive power in terms of the field current space phasor magnitude and the field voltage space phasor angle is provided. The proposed control strategy is based on controlling the field-current space phasor magnitude and the field-voltage space phasor phase angle to regulate the active and reactive powers of the DESG. Simulation results, based on MATLAB/SIMULINK, for a 1.1 kW DESG wind turbine system have been executed to verify the introduced control technique under various operating conditions. Also, experimental studies have been carried out to validate the simulation results using the proposed control algorithm.
... The BDFI(R)G (recent progress in [31]) thoroughly investigated since previous years (in cascaded connections) [32] due to its brushless attribute, has two windings on stator (a main one with pp pole pairs and a control one with pc pole pairs). The rotor is provided with a nested cage pr = pp+pc poles [5], as shown in Fig. 9. Again, only the control winding . ...
Variable speed generator systems (VSGs) are at work in the now 600 GW installed wind power plants (parks). Also, they are used as vehicular and on ground stand-alone generators. VSGs imply full kVA rating PWM converters in permanent magnet (PM) or in electrically excited synchronous or in cage rotor inductance generators. But, to reduce cost in absence of PMs at a reasonable initial cost (weight) and efficiency, the fractional kVA PWM converter doubly fed induction generators (DFIG) cover now about 50% of all installed power in wind generators. The present paper reviews recent progress in DFIG and various forms of brushless DFGs (doubly fed generators) characterized in terms of topology, design, performance and advanced control for healthy and faulty load conditions in the hope of inspiring new, hopefully ground breakings, progress for wind and hydro energy conversion and in vehicular and on the ground stand-alone generator applications.
... • Considering the number of components, brushes, gearbox and mechanical vibrations etc., DFIG is less reliable than others [37]. ...
In this study, a dual-port wind-energy conversion system has been proposed. A double-fed permanent-magnet synchronous generator (DFPMSG) forms the central part of the system, where the concentrated single-layer winding configuration of the generator enables electric and magnetic isolation between the ports. DFPMSG has two three-phase terminals out of the stator; one is connected directly to the grid, whereas the other is tied to the grid through a back-to-back converter. This study investigates design issues caused by the DFPMSG port with a direct grid connection. The unique design issues of the proposed system include determining the slot/pole combination using wind data and determining the minimum reactive power requirement for the port with a direct grid connection. Next, the load-sharing capability among the ports of the proposed system is presented through a detailed investigation of three schemes. Experimental work is presented for a 5-kW prototype DFPMSG system to illustrate the isolation among the ports, minimized reactive power demand on the port with direct grid connection, and load-sharing ability among the ports for different control schemes.
... However, it has been observed that the increasing power in the field of wind energy within the existing power system has introduced few new tasks in terms of grid codes for the advanced generating units, power electronic interfacing devices, and control strategies [7]. The BDFIG has excellent low voltage ride through (LVRT) handling characteristics, improved dynamic response, and most importantly, it does not contain any carbon brushes and slip rings [8]. It is worthwhile to mention here that, similar to the other wind farm machines, the speed and torque of the BDFIG needs to be regulated according to the desired operating condition through a controller with a particular control scheme. ...
Double fed induction generator (DFIG) has shown tremendous success in wind turbines due to its flexibility and ability to regulate the active and reactive power. However, the presence of brushes and slip rings affects its reliability, stability, and power quality. Furthermore, it does not provide promising outcomes in case of faults even in presence of the crowbar circuit. In contrast, the brushless doubly fed induction generator (BDFIG) is a more reliable option for wind turbines than its mentioned counterpart due to the absence of the brushes and slip rings. This research work as such attempts to improve the dynamic performance of the vector control (VC) oriented power winding (PW) stator flux-based BDFIG by optimally selecting the proportional-integral (PI) gains through internal model control (IMC) approach. The proposed control scheme is utilized to regulate the speed, torque, and reactive power of the considered BDFIG independently. Contrary to the previous literature where the "trial and error method" is generally utilized, the current research work uses the IMC for selecting the most suitable PI parameters, thus reduces the complexity, time consumption, and uncertainty in optimal selection. The considered BDFIG based wind turbine with the proposed control scheme provides a better BDFIG control design with an enhanced dynamic response as compared to that of the same with DFIG under identical operating conditions and system configurations. Keywords: BDFIG Dynamic response enhancement IMC Vector control scheme Wind energy conversion system This is an open access article under the CC BY-SA license.
... The brushless doubly-fed induction machine (BDFIM) is an alternative to the well-established doubly-fed induction generator (DFIG) for use in wind turbines since it offers improved reliability and reduced capital and maintenance costs [1]. It retains the low-cost advantage of the DFIG system as it only requires a fractionally rated converter and does not use permanent magnet materials. ...
Abstract A new fault diagnosis method for detecting the rotor eccentricity faults including static, dynamic and mixed eccentricity is proposed for brushless doubly‐fed induction machines (BDFIMs). BDFIMs are attractive alternatives for the conventional doubly‐fed induction generator (DFIG) for offshore wind power generation; therefore, paying attention to their fault detection is essential. Existing fault detection methods for conventional induction machines cannot be directly applied to the BDFIM due to its special rotor structure and stator winding configurations as well as complex magnetic field patterns. This article proposes a novel fault detection method based on motor current signal analysis to determine stator current harmonics, induced by the nested‐loop rotor slot harmonics (NRSHs), as fault indices. The analysis is performed under healthy conditions and with different types of rotor eccentricity. Finally, a sensitivity analysis is carried out to confirm the practicability of the proposed technique with various fault intensities and load conditions. Analytical winding function approach, finite element analysis and experimental tests on a prototype D180 BDFIM are used in this study to validate the proposed fault detection technique.
... As a highly reliability machine, BDFM offers the advantages of fractional rated power converter requirements and indirect control characteristics, making it a preferred device in specific fields. When working as a generator, BDFM can be applied to standalone generation [2], hydropower generation [3] and wind power generation [4]. In addition, its superiority in the field of variable speed drive systems, especially highvoltage drive systems is also significant. ...
The brushless doubly fed machine (BDFM) drive system based on a fractional unidirectional converter is a promising low-cost variable-speed drive system, which shows great potential in applications of driving fans and pumps. However, the harmonic current generated by a diode rectifier can flow into the machine and the grid under a weak grid, which will cause a 6th-order frequency torque ripple and lead to voltage distortion. A steady equivalent circuit considering the uncontrolled rectifier and the grid impedance is built firstly to study the harmonic distribution characteristics. To eliminate the influence of harmonic currents, the harmonic equivalent impedance of the machine system should be regulated to change the harmonic distribution characteristics. This paper improves the conventional control method through adding a harmonic control loop to prevent harmonic currents from being injected into the machine or the grid, which is then applied in the fundamental synchronous frame. Two indirect parameters are selected to realize the two control targets. Afterwards, the influence of the control system on the harmonic equivalent impedance of the machine system under the conventional method and the proposed method are compared. Finally, experimental results obtained from a 30 kW BDFM prototype verify the proposed method.
... Accordingly, many scholars and scientific research institutions have studied this issue in the past few years [4,5]. More specifically, studies show that these generators outperform the conventional brush doubly fed induction generators (DFIG) in the field of wind power generation [6,7]. The schematic configuration of a brushless doubly fed wind power generation system as depicted in Figure 1. ...
Abstract In the dynamics of grid‐connected operation of brushless doubly‐fed generators, grid voltage dips can cause the extreme imbalance between the voltage and the back electromotive forces in power winding. When these imbalances are combined with the influence of the inertia link composed of converter and generator, a serious over‐current and current oscillation forms in power winding and control winding. This paper gives a process analysis and proposes an improved control to the system during the low voltage ride through event. According to the mathematical model of the generators, the correlation between the power winding and control winding currents is established and then a fully equivalent simplified model is obtained accordingly. When the voltage suddenly drops to zero, the analytic expressions of power winding and control winding are calculated in the complex frequency domain and the influence factors of overshoot and oscillations are analyzed. The conventional control method relies on limited PI regulation that cannot eliminate the oscillations completely. It is found that after adjusting a proportional coefficient and eliminating the integral link of the control winding current controller, the order of the control system reduces. Therefore, the generation system can quickly recover to a steady state without oscillations. Finally, the analysis and improvement are verified by the simulation model and experimental results.
... A capacitor is placed between the back-toback converters to filter out the ripple, to provide reactive power and to maintain constant DC link voltage. Strous et al. (2017) stated that the power rating of RSC should be essentially slip times the total stator power rating. The slip of DFIG varies in the range of � 0:3. ...
In this work, a grid side converter (GSC) control with integrated shunt active filtering function using space vector pulse width modulation (SVPWM) technique is proposed to mitigate harmonics produced by the nonlinear loads. This method is focused on removal of harmonics from the grid currents by supplying compensating currents through GSC of DFIG. The proposed control technique improves power quality and reduces Total Harmonic Distortion of the grid current. Simultaneously, it is also capable to control active power and regulate DC link voltage during variable wind speeds in the presence of nonlinear loads. Performance of the proposed technique is compared with the conventional technique considering grid-connected 2.6 MW DFIG-based wind energy conversion system using MATLAB Simulink. Performance analysis has been carried out to check the behavior of the proposed SVPWM-based modified GSC control technique to mitigate the grid current harmonics considering wide variations in various parameters. The simulation results validate the effectiveness of the proposed scheme since it achieved grid current THD within limits of 5% as per IEEE-519 standards for all wind speeds. ARTICLE HISTORY
... This paper will, however, limit its scope to the brushless DFIG. The design of the brushless DFIG is not straightforward since there are more variables to consider than in conventional induction machine designs [14]. Attention has been given to some aspects of design for wind power applications as reported in [15]- [18] and several large machines have been reported. ...
The brushless doubly fed induction generator (BDFIG) is an alternative to the doubly fed induction generator (DFIG), widely used in wind turbines which avoids the need for brush gear and slip rings. The choice of pole numbers for the two stator windings present in the BDFIG sets the operating speed range but also affects the torque capability, magnetizing currents and back iron depth. Analytical expressions are developed for these effects and a comparison is made between the BDFIG and the conventional DFIG. The torque capabilities and magnetizing currents are not strongly dependent on the choice of pole numbers but the back iron depth is significantly affected. The torque density of the BDFIG is somewhat reduced compared to a similarly sized DFIG but magnetizing currents per unit torque are the same. However, the required back iron depths are greater. The work also shows that multi-megawatt machines are expected to work within the desired range of power factors at acceptable efficiencies.
The development of the novel multiphase brushless doubly-fed generator system and voltage controller for stand-alone mode configuration is proposed in this paper. The generator system is based on the new machine construction with multiphase control winding and traditional three-phase power winding. The dynamic model of multiphase brushless doubly-fed generator is presented, and the control strategy for voltage amplitude and frequency is developed. The simulation and experimental results are used to validate the performance of the topology of the multi-phase brushless double-fed generator and of the control system. The tests of the generator system have been carried out for the normal operating state of the system and for the case where one of the control phase is inactive. This situation is equivalent to a failure in the power path of the control winding.
Brushless doubly fed induction generator (BDFIG) has great potential in standalone generation applications. Currently, lots of control strategies have been proposed based on the BDFIG
d-q
model with different machine parameters ignored for simplification, but the simplification influences on model accuracy have not been discussed systematically, and the application ranges are not clear. Therefore, aiming at controller design, this article provides a comprehensive study on model simplification and parameter estimation of brushless doubly fed standalone generation. Based on the intuitive doubly fed induction generator (DFIG)-like BDFIG model and the typical electrical quantity relations widely used in standalone controller design, steady-state and dynamic parameter sensitivities of BDFIG are analyzed with operation condition fully considered. Based on the analysis, the universal BDFIG simplified
d-q
model aiming at standalone control is evaluated sufficiently, and the application range is clarified. The simplification of control analysis is illustrated, and a highly targeted and simple parameter estimation method is proposed for simplified modeling and control. Finally, simulations and experiments verify the analysis accuracy of the simplified DFIG-like BDFIG model and the feasibility of the proposed parameter estimation method.
This paper presents a technical overview for Switched Reluctance Generators (SRG) in Wind Energy Conversion System (WECS) applications. Several topics are discussed, such as the main structures and topologies for SRG converters in WECS, and the optimization control methods to improve the operational efficiency of SRGs in wind power generation systems. A comprehensive overview including the main characteristics of each SRG converter topology and control techniques were discussed. The analysis presented can also serve as a foundation for more advanced versions of SRG control techniques, providing a necessary basis to spur more and, above all, motivate the younger researchers to study magnetless electric machines, and pave the way for higher growth of wind generators based on SRGs.
This paper presents an enhanced control and operation for brushless doubly-fed induction generator (BDFIG) based wind turbine system under grid voltage unbalance by considering the controls of machine side converter(MSC) and grid side converter(GSC) together. The MSC is controlled to eliminate torque oscillations and realize decoupling control of power winding(PW) average active and reactive power while the GSC is controlled to eliminate oscillations in the total output active power. A single current closed-loop controller composed of a positive sequence current controller in the positive synchronous reference frame and a negative sequence current controller in the negative synchronous reference frame is designed for both MSC and GSC. To achieve decoupling control and improve system dynamic response, in current loops, all the disturbances and cross-coupling terms are derived and used for feedforward control. A fast sequence decomposition algorithm is employed to reduce the considerable time delays of using notch filers. In order to validate the effectiveness of proposed control, simulations for a 2WM BDFIG based wind generation system were carried out, the results demonstrated that the proposed control can effectively eliminate oscillations of BDFIG torque and total output active power, and has good dynamic and stable performance.
This paper proposes an improved vector control scheme based on the magnetizing current for the dual-stator brushless doubly-fed induction generator during the standalone operation. The conventional scheme of the standalone control chooses the control winding current as the control object for the inner current-loop, suffering from the large variation of the output voltage caused by the large output impedance. The improved scheme of this paper selects the power winding magnetizing current as the control object, which can reduce the demagnetizing influence of the load-current. Meanwhile, the design of the outer voltage-loop can be simplified because of the direct relationship between the output voltage and the power winding magnetizing current. The main work of this paper is to design an improved standalone controller to enhance the transient performance of the system. A prototype of the dual-stator brushless doubly-fed induction generator, which employs the proposed scheme, is measured for validation.
In this paper, a novel voltage control strategy of stand-alone operation brushless doubly fed induction generator for variable speed constant frequency wind energy conversion systems was presented and discussed particularly. Based on the model of the generator power system, the proposed direct flux control strategy employs a nonlinear reduced-order generalized integrator based resonant sliding-mode control scheme to directly calculate and regulated the output value of converter which control winding stator required so as to eliminate the instantaneous errors of power winding stator flux, and no involving any synchronous rotating coordinate transformations. The stability, robustness and convergence capability of the proposed control strategy were described and analyzed. Owing to no extra current control loops involved, therefore simplifying the system configuration design and enhancing the transient performance. Constant converter switching frequency was achieved by using space vector pulse width modulation, which reduce the harmonic of generator terminal voltage. In addition, experimental results prove the feasibility and validity of the proposed scheme, and excellent steady and dynamic state performance is achieved.
This paper proposes and demonstrates a fault detection method to locate inter-turn short circuits (ITSCs) in the stator windings of a brushless doubly-fed induction machine (BDFIM). The detection of ITSC is important in machine health prognostics as ITSC is an early stage fault that may lead to other faults such as coil-to-coil and coil-to-ground. BDFIM consists of power and control windings in the stator that are magnetically coupled through a nested-loop rotor winding. Existing ITSC detection algorithms use rotor slot harmonics in stator current spectra as fault indicators for only conventional doubly-fed induction machines. However, these algorithms cannot be applied to BDFIM due to its different stator/rotor winding structure. The paper primarily proposes a new analytical formulation for the nested-loop rotor slot harmonics (NRSHs) as ITSC fault indicators in BDFIMs. Using NRSHs, a detection algorithm is also proposed to detect and locate ITSC in power/control windings of BDFIMs. The proposed algorithm is verified based on numerical analysis of a BDFIM using finite element method. The accuracy of the proposed fault detection algorithm is also experimentally investigated and demonstrated using a BDFIM test rig. Both numerical and experimental test results confirm effectiveness of the proposed ITSC fault detection and location algorithm.
In this paper, the brushless DFIM based wind turbine drive-train topology is compared to the DFIG based and PM generator based drive-train topologies, that are most commonly applied in modern wind turbines. The comparison will be based on a 3.2 MW case study wind turbine. By using FE based multi-objective optimization, optimized generator designs for the different topologies are generated. Then the capital expenditures of the resulting drive-train topologies are calculated and compared. Additionally, wind turbine drive-train configurations with 1, 2 and 3 stage gearboxes as well as a direct-drive configuration are taken into account. The resulting comparison shows that the brushless DFIM based drive-train with a 2 stage gearbox configuration provides a feasible alternative in commercial wind turbine drive-train applications.
Modern wind turbines vary greatly in their drive train configurations. With the variety of options available, it can be difficult to determine which type is most suitable for on and offshore applications. A large percentage of modern drive trains consist of either doubly fed induction generators with partially rated converters or permanent magnet generators with fully rated converters. These configurations are the focus of this empirical reliability comparison. The turbine population for this analysis contains over 1800 doubly fed induction generators, partially rated converter wind turbines, and 400 permanent magnet generator fully rated converter wind turbines. The turbines analyzed are identical except for their drive train configurations and are modern MW scale turbines making this population the largest and most modern encountered in the literature review. Results of the analysis include overall failure rates, failure rates per operational year, failure rates per failure mode, and failure rates per failure cost category for the two drive train configurations. These results contribute toward deciding on the most suitable turbine type for a particular site, as well as toward cost of energy comparisons for different drive train types. A comparison between failure rates from this analysis and failure rates from similar analyses is also shown in this paper.
This paper studies the unbalanced magnetic pull in the brushless doubly fed machine (BDFM) caused by both static and dynamic rotor eccentricities. Several parallel winding designs for the two stator windings are proposed, and the practicality of such designs is discussed with respect to direct coupling between the stator windings and with rotor undesirable harmonic fields. Once practical parallel winding designs are established, their effects on reducing deflection as a result of static and dynamic eccentricities are shown and compared with series wound stator. This study has been carried out on a prototype D400 250-kW BDFM.
This paper studies the effects of magnetic wedges on the equivalent circuit parameters of the Brushless Doubly-Fed Machine (BDFM). Magnetic wedges are used in slot openings of large electrical machines to reduce magnetizing currents, but the study of their effects on the BDFM performance is not straightforward due to the complex magnetic fields in the BDFM. Equivalent circuit and FE models have been developed for a 250 kW BDFM taking into account the effects of wedges and verified experimentally.
The Brushless Double-Fed Machine (BDFM) is a type of variable speed generator or drive. Using theoretical analysis of simple BDFM rotors this paper establishes trends in how rotor structures determine the rotor's equivalent circuit resistance, leakage inductance and turns ratio. The variation in measured parameters of five prototype rotors is then analysed in light of the trends found. Both the theory and experimental results suggest a significant performance advantage in using cage+loops type rotors as opposed to the simple nested loop type more usually employed.
This paper investigates the rotor design factors that impact the performance of brushless doubly-fed reluctance machines (BDFRMs). The performance of the BDFRM relies on the ability of the rotor structure to modulate stator magnetic fields so that magnetic coupling occurs between stator windings that do not otherwise interact. This paper investigates those factors that create the desired magnetic coupling and those that can cause undesirable magnetic performance. Theoretical analysis is compared to test results from an early prototype BDFRM and then applied to the design of a new BDFRM. New designs are explored using Finite Element Analysis. A prototype, based on these investigations is under construction.
This study presents the performance analysis and testing of a 250 kW medium-speed brushless doubly-fed induction generator (DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and show the system's steady-state and dynamic performance and grid low-voltage ride-through capability. The medium-speed brushless DFIG in combination with a simplified two-stage gearbox promises a low-cost low-maintenance and reliable drivetrain for wind turbine applications.
The brushless doubly fed machine (BDFM) is a robust alternative to the doubly fed induction generator, currently widely used in wind turbines but prone to brush-gear and slip-ring failure. The rotor winding plays an important part in a BDFM, coupling the two stator windings. To date, nested-loop (NL) rotor windings have been exclusively used in practical BDFM. This approach may not be ideal for larger machines, in which form-wound series-loop rotor winding may be preferable to large section bars and end-rings. This study gives a comparative analytical and experimental study of two different brushless doubly fed 160 frame-size rotors, with NL or series-wound windings, mounted in identical rotor core laminations operating in the same stator tested at a limited voltage (200 V line). The rotors gave a performance which accords with theoretical predictions from two independent methods, giving insight into the design issues of the different rotor windings from both an electrical and manufacturing viewpoint.
Brushless doubly fed reluctance machines (BDFRMs) are a class of machines that may be controlled using a power converter that has a rating lower than the total power rating of the machine. The attractive properties of these machines have, in the past, been offset by low power density and efficiency when compared to other types of machines. Recent advances have shown that, when well designed, these machines are, in fact, capable of operation at high torque density and efficiency. However, little guidance on how to design these machines is available in the literature. This paper presents analytical approaches to design a BDFRM with desirable qualities and the use of time-stepped finite-element analysis to validate the results of the design process.
The brushless doubly fed induction generator (BDFIG) has substantial benefits, which make it an attractive alternative as a wind generator. However, it suffers from lower efficiency and larger dimensions in comparison with the doubly fed induction generator. A major part of drawbacks arises from undesirable spatial harmonics of air-gap magnetic field. Calculation of core loss is an important issue in optimal design studies to improve the performance characteristics. The iron loss is higher and has a more complex nature in BDFIGs in contrast with conventional machines. Furthermore, additional losses cannot be ignored due to a high level of spatial harmonics distortion. This paper aims to formulate core loss and stray load loss (SLL) in BDFIGs based on the design data and experimental parameters provided by electrical steel manufacturers. In addition, an analytical procedure for calculating spatial harmonic components of the stator and rotor magnetic fields is presented. The acceptable accuracy of the theoretical equations is verified by comparing the calculated core loss and SLL of a D-180 prototype BDFIG with the measured data. The results show that SLL in BDFIGs is higher than the predicted per-unit values given by standards for induction machines, e.g., IEC 60034sim2 and NEMA MG1.
This paper presents a generalized vector control system for a generic brushless doubly fed (induction) machine (BDFM) with nested-loop type rotor. The generic BDFM consists of p1/p2 pole-pair stator windings and a nested-loop rotor with N number of loops per nest. The vector control system is derived based on the basic BDFM equation in the synchronous mode accompanied with an appropriate synchronization approach to the grid. An analysis is performed for the vector control system using the generic BDFM vector model. The analysis proves the efficacy of the proposed approach in BDFM electromagnetic torque and rotor flux control. In fact, in the proposed vector control system, the BDFM torque can be controlled very effectively promising a high-performance BDFM shaft speed control system. A closed-loop shaft speed control system is composed based on the presented vector control system whose performance is examined both in simulations and experiments. The results confirm the high performance of the proposed approach in BDFM shaft speed control as well as a very close agreement between the simulations and experiments. Tests are performed on a 180-frame prototype BDFM.
Doubly-fed cascade-connected induction machines (CCIMs), whether mounted in a single frame or otherwise, are capable of developing useful torque as brushless synchronous machines over a wide speed range. Such machines exhibit instability within certain regions of operation and may be insufficiently damped within others. This paper presents some of the loci of the dominant eigenvalues of the system equations plotted as functions of the values of various design parameters of the machines. It is shown that, by appropriate design, certain areas of instability may be reduced or removed and the response improved, but that it is not possible, by design changes alone, to remove all such unstable areas, nor can the response be improved in all areas simultaneously. © 1983, The Institution of Electrical Engineers. All rights reserved.
Two sets of stator windings of the brushless doubly-fed machine (BDFM) remain unchanged to keep the characteristic of variable speed constant frequency (VSCF). However, if either set of windings are excited with a DC power source, the BDFM would operate in the variable speed variable frequency (VSVF) state. On the basis of VSVF, this paper presents a new structure design by substituting one set of windings with high-performance permanent magnets (PMs) to decrease the copper loss and increase the power density of the BDFM. The novel structure has fewer and non-rotating PMs as compared with the conventional PM machine. Waveforms of voltage and current in the single winding are improved by reducing the harmonics in the magnetic field. A prototype was designed and then tested in the finite element method (FEM) simulation and experiment. Results from simulation and experiment shows that the novel structure satisfies the basic electromagnetic theory of BDFM, although it loses the advantage of VSCF. Moreover, the newly designed BDFM is superior to the conventional PM machine in the application situations of low speed and direct drive.
The brushless Doubly-Fed Induction Machine (DFIM) has many advantages over the conventional DFIG commonly applied in wind turbines. However, due to the complex motion of the magnetic field in this machine type, the inclusion of nonlinear iron saturation in brushless DFIM models has been proven to be challenging. This paper combines a brushless DFIM Electric Equivalent Circuit (EEC) model with an analytical derived magnetic field model. The saturated magnetic field is iteratively obtained using the secant method. Saturation is included in the EEC model by introducing complex saturation factors derived from the magnetic field. This results in an EEC model that is able to accurately determine brushless DFIM operating characteristics. The model is validated by application to a case study machine and comparing the results with those derived from a finite element model.
The Brushless Doubly Fed Induction Machine (B-DFIM) shows promise for use in wind turbine drivetrains. This paper discusses the performance of this machine under symmetric low voltage dips and compares this with the performance of two other machines - the Permanent Magnet Synchronous Machine (PMSM) and the Doubly-Fed Induction Generator (DFIG). Attention is paid to the controller for the B-DFIM and protection methods for improved Low Voltage Ride Through (LVRT) performance are discussed. It is shown that the B-DFIM has an improved LVRT performance when compared with the DFIG, moreover, the B-DFIM does not require an external circuit for protection from low voltage events.
Brushless doubly-fed induction machines (BDFIM) have great potential as variable-speed generators in larger-scale wind turbines. Undesired space harmonics exist because the special rotor needs to couple both two stator windings which with different pole-pair numbers and different frequencies. These rich space harmonics lead to a bigger torque ripple comparing to the normal induction machine. This paper makes use of 2D multi-slice finite element (FE) method to study the effect of the rotor skew on the performance of the BDFIM in the cases without and with saturation. The results show the torque ripple is reduced significantly by skewing the rotor both in those two situations. But the rotor skew has negligible influence on the harmonics due to the saturation effect. Furthermore, the rotor skew has little influence on the total amount of losses. However, based on the simulation results, it redistributes the core losses along the axial direction in the BDFIM.
The brushless doubly-fed induction machine (BD-FIM) is a potentially attractive choice for a variable-speed wind generator. Using classical analytical models is not so straightforward, because the motion of the magnetic field in BDFIM is not a simple rotation. Finite element (FE) modeling makes it easier to evaluate the machine performance considering the saturation. However, for the purpose of a better convergence and an accurate calculation of the magnetic field equation and the coupled circuit equation, small time steps are utilized in the adaptive time-step solver of the transient FE model. A long computing time makes FE model be difficult to combine with an optimization program. This paper presents one possible alternative method to predict the BDFIM performance by using the magneto-static FE solutions and the space-time transformation. The simulation time then reduces significantly making it possible to search in a large design space for the optimization purpose.
The brushless Doubly-Fed Induction Machine (DFIM) without its brush-gear and slip-rings seems interesting as successor of the normal DFIG in wind turbine drivetrains. However, the brushless DFIM magnetic field has a rich space-harmonic spectrum, which causes additional torque ripple. This paper focuses on torque ripple in the brushless DFIM. The causes and origin of torque ripple are discussed and an analytical model is developed that derives the torque ripple from the air-gap magnetic field distribution. Further, a finite element method for torque ripple calculation is presented. Both methods are used to calculate the torque response of a case study machine. Results are compared and the accuracy of the analytical model is validated with good result. The analytical model is then used to further analyse the torque ripple, resulting in exact torque ripple frequencies and additional insight in the cause of the torque ripple.
Although the brushless Doubly-Fed Induction Machine (DFIM) has great potential as generator system in large-scale wind turbines, its complexity has so far retained a commercial breakthrough. This paper contributes by combining brushless DFIM Finite Element (FE) modelling with multi-objective optimization. A static brushless DFIM FE model is applied with the NSGA-II multi-objective optimization algorithm. The result is an accurate and fast brushless DFIM design optimization tool. This tool is then used to generate a machine design with optimized performance, that fits a fixed volume frame size D180. Optimization results of different brushless DFIM construction variations are compared. The best designs of each construction variation are then analysed in more detail using a time-stepping brushless DFIM FE model. This provides good insight in the effects of different construction variations on torque ripple and induced time-harmonics. The optimized design of the best construction variation will be selected to be manufactured as prototype machine.
This paper presents the analysis of a brushless doubly fed reluctance machine (BDFRM) for renewable energy applications with an emphasis on the rotor design. The BDFRM stator includes two sets of windings, i.e., the control winding (CW) and power winding (PW). The PW is connected to the grid, while the CW links the grid by a power converter of fractional rating to regulate the operating speed. This reduces the converter cost, and the brushless configuration enhances the reliability. In this paper, the reluctance rotor of the BDFRM, which is similar to that of a synchronous reluctance machine, is designed and analyzed in order to improve the performance. The influence of the total MMF and its allocation to the two stator windings are also discussed in relation to the machine performance. Finite-element analysis is used for performance simulation. The experimental study validates the proposed design for a small BDFRM.
This paper presents the development and experimental validation of a novel angular velocity observer-based field-oriented control algorithm for a promising low-cost brushless doubly fed reluctance generator (BDFRG) in wind power applications. The BDFRG has been receiving increasing attention because of the use of partially rated power electronics, the high reliability of brushless design, and competitive performance to its popular slip-ring counterpart, the doubly fed induction generator. The controller viability has been demonstrated on a BDFRG laboratory test facility for emulation of variable speed and loading conditions of wind turbines or pump drives.
The brushless DFIM is a complex machine type. Though never commercially exploited, it has a great potential as generator system in large-scale wind turbines. This paper develops an analytical magnetic field model for the brushless DFIM. Since the brushless DFIM rotor construction has a rich space harmonic spectrum, attention is paid to the effects of winding space-harmonics. The developed model is validated by FE calculations. With use of the developed model, the brushless DFIM operating principles are considered from the point of view of the magnetic field.
This paper proposes a Wound-Rotor Brushless Doubly Fed Induction Machine (WRBDFIM), an alternative Brush-less Doubly Fed Induction Machine (BDFIM) concept for wind turbine applications. The WRBDFIM consists of two separate machine winding sets different in pole-numbers, whose rotor windings are connected together. Both of the winding sets are housed in the same machine frame. The separate winding set arrangement aims to eliminate the circulating current and suppress the undesired spatial harmonics created by the conventional BDFIM. The two-phase equivalent circuit of the WRBDFIM is derived by connecting the circuits of two conventional Doubly Fed Induction Machines (DFIMs). The electrical and mechanical dynamics are identified to form the machine model for the Direct Power Vector Control (DPVC), which is proposed to regulate the generated power of the WRBDFIM without rotor position sensors. Simulation results confirm the machine dynamic model and also prove the effectiveness of the DPVC scheme that provides accurate control and fast tracking capability.
The paper deals with flux and voltage vector oriented control of a brushless doubly-fed reluctance generator (BDFRG) for grid-connected wind turbines. The BDFRG features the low operation & maintenance costs afforded by using a smaller inverter and the high reliability of brushless structure at potentially competitive performance to its popular slip-ring cousin, the doubly-fed induction generator (DFIG). The simulation and experimental studies have evaluated the two parameter independent speed and reactive power control algorithms on a custom-built BDFRG under the maximum torque per inverter ampere (MTPIA) conditions for various loading profiles.
Nowadays many wind turbines use a doubly fed induction machine (DFIM) as a generator (DFIG). The brushless DFIM (BDFIM), however, has increased fault handling capabilities and suffers less from reliability issues. This paper presents a different method of analytically evaluating the BDFIM. This is done by analyzing the flux density produced by the two stator windings and the interaction with the nested loops of the rotor. Subsequently FEM is used to verify the analytical findings and analyze the behavior of the machine. Additionally several design parameters of the BDFIM such as the pole pair combinations and the number of loops per nest are evaluated. General rules of thumb regarding these design parameters are presented.
In this paper a variable structure direct torque control based on sliding mode approach, linear PI and space vector modulation (SVM) is proposed for a brushless doubly fed induction generator. The DTC transient merits and robustness are preserved and the steady state behavior is improved by reducing the torque and flux pulsations. The presented method also guarantees maximum power point tracking (MPPT) with a desirable operation. The simulation results verify an accurate, quick and robust operation of the brushless doubly fed induction generator for wind turbine applications.
In this study, a control scheme for the stand-alone generation system based on brushless doubly-fed machine (BDFM) is presented. The output voltage amplitude and frequency are kept constant under variable rotor speed and load by regulating the amplitude and frequency of the control winding (CW) current of BDFM appropriately. The control scheme utilises a CW current vector controller as the inner loop, and a power winding voltage amplitude controller and a frequency controller as the outer loop. The proposed control scheme has been implemented on a prototype BDFM designed for the variable-speed stand-alone ship shaft generation application. Moreover, the satisfactory dynamic performance and low total harmonic distortion of the output voltage in the proposed stand-alone generation system is verified by experiments with two kinds of typical loads: three-phase induction motor load and three-phase RL inductive load.
The Brushless Doubly-Fed Machine (BDFM) shown in Fig.1 has two sets of three-phase stator windings with different pole numbers and only one rotor which contains three phases windings. The two sets stator windings are named Power Winding (PW) and Control Winding (CW), but they cannot couple with each other directly. The Rotor Winding (RW) is particularly designed to couple with both of them. The BDFM can be conceived as two distinct induction machines with the same frame, intended for operation in the self-cascaded mode. Therefore a fundamental equivalent circuit which is shown in Fig.2, using the standard per-phase model can be developed to represent the BDFM as two connected induction machines[1]. The equivalent circuit is a simple method of representing the steady-state performance of the machine. This method, however, does not give enough accuracy because it assumes linearity of the iron core and derived from the analytical solutions under basic simplified assumptions. Thus, many correction factors are needed to adjust the design solution to fit the testing results, and significant errors may be caused. With the development of numerical modeling techniques, the finite element analysis (FEA) is well suited for the precise prediction of electromagnetic device. A method based on the use of complex 2-D finite element solutions for accurately predicting the steady-state performance of BDFM is presented, and the saturation effect is considered by introducing a new method named frozen permeability[2]. Based on the new method, the magnetizing inductance and leakage inductance per phase can be worked out precisely.
Brushless doubly fed induction generators (BDFIGs) are promising alternatives to doubly fed induction generators due to high reliability and low maintenance cost for the absence of brushes and slip rings. As a typical application in offshore wind energy generation, a feedforward method is applied to the grid-voltage oriented vector control to make the active and reactive power decoupled. Another challenge in practice is how to meet the demanding requirements of grid codes. The dynamic behavior of BDFIG is analyzed in detail under unbalanced grid conditions with the proposal of four different targets. To deal with these issues, an improved vector control strategy based on the proportional-integral resonant controller (PI + R) in a single synchronous reference frame is developed. The stability and robustness of the proposed control scheme under parameters uncertainties and variations are discussed as well. The advantage of this control strategy is that it is simple and fast in transient response. The effectiveness of the proposed control strategy is validated by the experiment results of a 3-kW prototype machine.
The Brushless Doubly-Fed Reluctance Machine (BD-FRM) is a potential candidate to compete with induction and permanent magnet machines in variable speed application such as wind power. It is in research phase and much effort, mostly on its electromagnetic design, is still needed so that this machine can be used in large scale. This paper focuses on rotor design by studying the impact of geometric parameter variations on its global performance by using Finite Element Analysis (FEA). Issues with the flux barrier ending's geometry, number of rotor slots, existence of an additional interpolar flux barrier, rotor slot arc angle and duct ratio are investigated. The results show potentially good practices that should be considered on BDFRM rotor design. They may also be used as initial step for a more refined optimization process using specialized tools.
This paper proposes a novel machine termed the axial flux brushless doubly fed reluctance machine (AF-BDFRM) suitable for high torque, low speed direct drive applications. The main potential advantages of AF-BDFRM are its higher torque and power density compared to the radial flux brushless doubly fed reluctance machine (RF-BDFRM). In addition, the proposed machine utilizes a bidirectional power converter of much lower rating as compared to the machine rating depending on the range of speed variation. The proposed machine axial flux topology is composed of two stators and a reluctance iron rotor. The upper stator winding which is connected directly to the power grid, transfers active power to the grid and lower stator winding creates excitation for the machine and connects to the grid through a partially rated converter. The design principles of the proposed AF-BDFRM are studied in this paper. Furthermore, the transient 3D finite element analysis (FEA) result