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IET Electric Power Applications

Published by Wiley and The Institution of Engineering and Technology
Online ISSN: 1751-8679
Print ISSN: 1751-8660
Discipline: Physical Sciences & Engineering
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Aims and scope

IET Electric Power Applications is a gold open access journal that publishes research covering a wide range of applications and apparatus in the power field, with a suitable balance of practice and theory, focussing on the design and development of electrical equipment.

 

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Recent publications
  • Zhongxin WanZhongxin Wan
  • Song HuangSong Huang
  • Chong ZengChong Zeng
  • Yong LiaoYong Liao
A commutation torque ripple suppression strategy for the brushless DC motor (BLDCM) with commutation time is proposed. First, a torque model considering back electromotive force (back‐EMF) variation is presented, and the cause of commutation torque ripple is analysed. The results show that the commutation torque ripple of BLDCM is inevitable even if the non‐commutation current remains steady. On this basis, the influence and quantitative relationships of non‐commutation current and commutation time on commutation torque ripple are studied. Furthermore, two impact factors are proposed to comprehensively consider their effects on commutation torque ripple. The three‐phase windings are modulated in the commutation process at individual duty cycles. The comprehensive optimisation index of commutation torque ripple for different working conditions is obtained by calculating the relative relationship of the impact factors. The optimisation index determines the proper modulation duty cycles. Therefore, the motor parameters and working conditions do not limit the strategy. Finally, the experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed strategy. The proposed strategy can reduce the commutation torque ripple by 16.28% and 21.80% and shorten the commutation time by 50.00% and 36.67% at low speed and high speed, respectively, compared with the conventional strategy.
 
  • Kong DeshanKong Deshan
  • Wang DazhiWang Dazhi
  • Li WenhuiLi Wenhui
  • [...]
  • Hua ZhongHua Zhong
Permanent magnet eddy current couplers have been widely used in large fan and pump loads to achieve the purpose of speed regulation and energy saving. In order to reduce the coupler axial volume and simplify the actuator, a novel flux adjustable axial flux permanent magnet eddy current coupler (FAAF‐PMECC) is proposed in this paper. The permanent magnet rotor is divided into three parts: the inner, middle and outer parts, where the permanent magnets are embedded in the core and the adjacent poles are magnetised in opposite directions. The middle part is the adjusting permanent magnet ring (AR), which can rotate around the shaft. The inner part and outer part are fixed permanent magnet rings (FR) that are fixed with the shaft, and the output torque can be controlled by adjusting the relative angle of AR and FR. The structure and working principle of FAAF‐PMECC are described in detail, and the output torque analytical model of the whole regulating process is established based on the magnetic equivalent circuit method. The AR regulation process is simulated by the variable reluctance model. The validation results show that the proposed structure can achieve a good speed regulation effect, and the output torque calculated by the analytical model in a certain slip speed range matches well with the output torque obtained using the 3D finite element method and experimental measurements. The sensitivity analysis of the structure parameters is also carried out. The analysis shows that the proposed coupler can achieve a wide speed range.
 
In this study, a fractional‐order integral terminal sliding mode control (FITSMC) system is proposed to control a new voice coil motor (VCM)‐driven X–Y motion stage with different thrust forces in the X–Y axes for the tracking of reference contours. First, the operation principle and dynamics of the stage are conducted based on the equivalent electrical circuit and magnetic analysis of the VCM. Subsequently, an integer‐order integral terminal sliding mode control (ITSMC) approach is designed to control the stage for contour tracking in finite time. To enhance the positioning accuracy of the ITSMC, a novel FITSMC system is further proposed by bringing in a new fractional‐order integral terminal sliding surface. However, the hitting control gain for the FITSMC is difficult to design because of the system uncertainties. To address this issue, an intelligent adaptive uncertainty observer (AUO) is proposed to directly observe the system uncertainties, thereby eliminating the need for hitting control term and attenuating the chattering phenomena of control force. Stability analysis of the proposed FITSMC and FITSMC‐AUO systems is conducted on the basis of the Lyapunov stability theory. The experimental results demonstrate the effectiveness and superiority of the proposed control systems in comparison with the existing ITSMC system in the contour tracking tests.
 
This paper presents practical implementation of a fault detection, localisation, and categorisation (FDLC) method in PV‐fed DC‐microgrid (DCMG). The DCMG is implemented by utilising a group of two DC nanogrids (DCNG) that have power control mechanism (PCM). The FDLC uses a voltage calculating circuit comprising a single voltage sensor and diode network. Moreover, the architecture is based on six statements extracted from the investigation of line to line (L–L) and line to ground (L–G) faults at a DCNG of the cluster. The PCM in the proposed system utilises a power triggering circuit for effective power flow among the different units of the DCNG considering the load demands and the resource availability. Experimentation is carried out by creating L–L/L–G faults at different points in the DCMG. Detection, localisation, and classification of faults is performed by utilising the sensor's voltage and power of the individual DCNG. FDLC offers less computational burden, perform fast detection of fault, and is capable of distinguishing between the L–L/L–G faults and uniform irradiance and partial shading conditions in the PV‐array. The proposed FDLC technique and its six statements are verified through experimental results.
 
To pursue high‐performance motor drive, the current regulators are designed directly in the discrete domain. However, few kinds of research are developed to achieve arbitrary poles placement simply. To fill this gap, the authors propose a discrete‐time current regulator consisting of two parts: the main regulator used to obtain decoupling control of dq axes currents, and the bi‐proper compensator applied to realise arbitrary poles placement. To strengthen the anti‐disturbance ability of the current regulator, the active resistance is added to the inner feedback path. Combining the active resistance, a new zero‐order‐hold equivalent motor model is developed, based on which the main regulator is designed using the zero‐pole cancellation method. Furthermore, in this way, decoupling control for the two control objectives of reference tracking and anti‐disturbance is realised. To achieve fast tracking response and negligible overshoot, an easy‐to‐implement scheme that simplifies the tuning of the current regulator is proposed based on the arbitrary poles placement. Moreover, the current regulator can be treated as a two‐degree‐of‐freedom controller with this scheme. Finally, the effectiveness and reliability of the proposed current regulator are validated by the simulation results and experimental results in an alternating current machine drive platform.
 
We propose a method to investigate the generation mechanism of the transient vibration of a pump motor induced by electromagnetic (electromagnetic (EM)) forces. Compared with the steady vibration of a pump motor, the transient vibration characterised by a wider excitation frequency spectrum and larger instantaneous amplitude makes the vulnerable structure more easily exposed to potential damage. However, transient vibration of pump motor has not been analysed and verified before. Based on the fact that EM vibration dominates the vibration of pump motors, in this study, an approach which integrates the field‐circuit coupling method and multi‐physics finite‐element (finite‐element (FE)) simulation is proposed to estimate the structural response of pump motors under transient operating conditions. To determine the factors that determine the EM forces, an analytical model describing the transient interaction between the EM and the fluid torque is first created. It was revealed that the input voltage and slip rate are two key factors that affect the transient EM forces. Then, to quantitatively describe the transient EM forces governed by a specific control scheme during the start‐up process, a field–circuit coupling model embedding in the control scheme, electrical circuit model, motor FE model, and rotor dynamic model is established. This model allows the circuit equations, rotor dynamics equations, and magnetic field equations to be solved simultaneously. The transient EM forces obtained by the field–circuit coupling model provide excitation for the structural response calculation. Subsequently, a multi‐physics FE simulation, which takes a weak coupling strategy between the EM and structural dynamics fields, is utilised to link the different physical domains. Thus, the EM forces are transferred to a structural domain to compute the structural response by adopting a direct integration method. The integration approach developed in this study was verified on the pump motors in the main cooling units of ultra‐high voltage (UHV) converter stations. The trends of dominant components of simulated signals agree with the measured signals from the pump motors. This indicates that the proposed method can be widely applied for the transient vibration analysis and mitigation for pump motors.
 
The rotor of a magnetic suspension centrifugal compressor is supported by magnetic bearing, and a power failure will cause the high‐speed rotor to fall directly onto the protective bearings, affecting the reliability of the compressor. To solve this problem, this paper proposes an abnormal power failure shutdown control method with semi‐switching modulation of the inverter. Firstly, the overall scheme of abnormal power failure shutdown control is designed, and its feasibility is analysed in detail through mathematical modelling. Secondly, aiming at the non‐linear, time‐varying and gain uncertainty characteristics of the control system, a voltage control strategy based on parametric self‐regulating sliding‐mode variable structure is proposed, and the stability is analysed. Finally, the method proposed in this paper is experimentally verified, the results show that this method does not depend on the electric angle of the motor compared to existing methods, and the rotor can achieve a zero‐drop speed shutdown, which greatly improves the reliability of the magnetic suspension centrifugal compressor.
 
Truncated region eigenfunction expansion (TREE) method is applied to the analysis of impedance change of a coil in the vicinity of the edge of a metal plate. The analysis is carried out with the second order vector potentials (SOVPs) and provided for both cylindrical and rectangular coils. By full discretisation of the eigenvalues, double series solutions are obtained for the field and coil impedance variations. To simplify the solving procedure further, a novel approach for the determination of eigenvalues is proposed by means of the 1D finite element method (FEM), which is easy to implement and works well for the plate of non‐magnetic material. Numerical results for the impedance variations of cylindrical and rectangular coils are compared with those of 3D FEM simulation, by which the efficiency and accuracy of the authors’ method are confirmed, and the former is much faster and more memory efficient.
 
In order to investigate the effects of shrink fitting on the amorphous core, a test device is designed and the magnetisation and specific iron loss characteristics of the amorphous core are measured. The specific iron loss of amorphous core increases since the eddy current loss in the stator yoke increases significantly. The iron losses of the permanent magnet synchronous motor with the amorphous stator core in consideration of the shrink fitting effects on the specific iron loss are analysed by FEA.
 
Although the voltage feedforward control based on the point of common coupling (PCC) has been widely studied in the grid‐connected inverters to suppress the harmonics in the grid current, harmonic instability still occurs when the PCC voltage contains a series of background harmonics under weak grid condition. To this end, this paper applies the grid voltage sensed by phasor measurement units instead of the PCC voltage for feedforward. Meanwhile, considering that coupling between the phase‐locked loop (PLL) and the grid impedance would cause instability under weak grid condition, a novel compensation term is introduced to eliminate the negative influence of PLL. In addition, a method to improve the transient response of the system is also proposed so that the cut‐off frequency does not change with the impedance of the grid. By analysing the output impedance of the system, it can be proved that the strategy proposed can effectively improve the stability of the system. The experimental results indicate that the harmonics in the grid current are obviously reduced and the dynamic performance of the system is improved, which verifies the analysis.
 
Performance analysis of a linear permanent magnet Vernier machine (LPMVM), which has a complex structure, is mostly based on the finite element methods, while for its optimisation or sensitivity analysis a quick mathematical technique is desirable. This paper introduces an LPMVM and its principles of operation. Then, a mixed subdomain and magnetic equivalent circuit are applied to extract magnetic field equations in various parts of the machine, in which the end‐effect in included. Besides, the electromotive force, thrust force, normal force and electric equivalent circuit are determined. An LPMVM was prototyped and tested to verify the accuracy of the proposed method.
 
Double‐sided tubular machine (DSTM) is very suitable for wave energy conversion but easily suffers from high thrust ripple. In order to get the minimum cogging force with the maximum thrust force, a new DSTM with hybrid segmented permanent magnet array is proposed and optimised by a novel iterative few‐sample multi‐objective optimisation method. The novel optimisation method is based on an iterative Taguchi method framework to obtain optimal design with only few samples. To solve the low precision problem of the iterative Taguchi method, a surrogate‐model based multi‐objective optimisation algorithm that uses a general regression neural network, a speed‐constrained multi‐objective particle swarm optimisation and an exponentially weighted moving average are embedded into this framework. The optimisation result is compared with other alternative topologies and methods, and a prototype is manufactured for testing experiment.
 
In this paper, the analytical relationship among supply voltage, current, and structure parameters of the permanent magnet (PM) motor is cleverly deduced by using an intermediate‐flux linkage. After further consideration of boundary conditions, the direct field‐circuit coupled analytical model in integrated matrix form is subsequently constructed. Using this model, the vector potentials and currents of the motor can be calculated simultaneously, and the electromagnetic performance, such as the output torque, winding flux linkage, and so on can be further calculated by the vector potentials. Because the control parameters and motor structure parameters are both considered in the derivation process, the proposed analytical model can be used to analyse the motor operation performance under different control strategies. Its validity is finally verified on a 10‐pole/12‐slot PM motor. The results of the proposed direct field‐circuit coupled analytical model are compared with those of field‐circuit coupled time‐stepping finite element model and experiment under speed‐current double closed‐loop and current closed‐loop control strategies, respectively. The results of the proposed model are proved well with finite element simulation and experimental results.
 
Transformer overheating faults have an important impact on the transformer safe and stable operation. Taking 10 kV oil‐immersed transformer as the research object, using the indirect coupling analysis method of electromagnetic thermal fluid multi‐physical field, the transformer heating characteristics under overheating faults, such as winding inter‐turn short circuit and core multi‐point grounding, are analysed, and the transformer abnormal heating state identification method is proposed based on the inversion of transformer top oil temperature rise. By inverting the transformer normal top oil temperature rise under different load rates and comparing it with the actual measured value, taking into account the top oil temperature rise inversion error, it is determined that when the top oil temperature rise measured value is higher than the inversion value by 2.9 K, it indicates the transformer is in an abnormal heating state, and the higher the deviation degree is, the deeper the degree of abnormal heating fault. The accuracy of the transformer abnormal heating state identification method is verified by the multi‐working condition temperature rise test, which can provide a certain reference for the detection and maintenance of transformer abnormal internal heating faults.
 
A novel reaching law‐based sliding mode controller is proposed for a permanent magnet synchronous motor (PMSM) speed regulation system with uncertainties and unknown load torque in this paper. The proposed reaching law is the improvement of the traditional power rate reaching law (PRL) by using a simple tuning function of the sliding variable. The tuning function is designed such that the reaching speed is fast when the system states are far away from the sliding surface, and vice versa. Theoretical analysis shows that the reaching time of the proposed reaching law is always shorter than that of the traditional PRL with the same gains. Moreover, unlike the traditional PRL and some existing auto‐tuning PRLs, the proposed reaching law can provide globally bounded reaching time independently on the initial conditions, and the reaching time can be effectively reduced by tuning the reaching law gains. Based on this novel reaching law, a disturbance observer is designed to estimate the total disturbance, and then based on the estimated disturbance and the novel reaching law, a sliding mode speed controller is designed for the robust control of PMSM speed regulation system. Simulations and experiments are carried out to demonstrate the superiority of the proposed control method.
 
Fractional‐slot concentrated‐windings are appreciated for their simple construction, short end‐winding length, high copper fill factor, low cogging torque, good field‐weakening capability and fault‐tolerant ability. However, in comparison to the conventional distributed windings, the fractional‐slot concentrated‐windings are characterised with high space magnetomotive force (MMF) harmonics, which results in undesirable effects on the machine performance, such as localised core saturation, eddy current loss in the rotor and noise and vibration. In order to improve winding characteristics, several techniques have been developed recently. This manuscript introduces the 5 new winding topologies by using the general concept of stator slot shifting. It means that, in order to cancel undesirable MMF harmonics, by doubling (or tripling or even multiplying) the slot number and dividing the winding and then relatively shifting the winding by one (or more) slots, the undesirable harmonics have been eliminated effectively. The best choice is chosen according to the lowest amount of the MMF harmonic, highest value of winding factor and torque desirable characteristics. At the end, comprehensive comparisons for the designed synchronous reluctance motor (SynRel) equipped with proposed windings and also distributed winding are presented. The analytical study and 2D FEM analysis results show that it is possible to get an ideal low space‐harmonic winding topology, and consequently, a low torque ripple for these motors.
 
The dual‐excited synchronous condenser (DESC) has two field windings whose axes are located at direct and quadrature axes respectively. The DESC has more capacity of absorbing reactive power than that of the traditional synchronous condenser (TSC). However, the q‐axis field winding distributed on the d‐axis magnetic pole surface can decrease the magnetic circuit area of the rotor core of DESC, thus it may result in the increase of the total harmonic distortion (THD) of the magnetic field and the oversaturation of the rotor magnetic circuit. In order to obtain better electromagnetic characteristics of DESC, a q‐axis field winding structure is proposed by optimising the number of slots, slot pitch and slot dimensions. The influences of the number and pitch of slot in q‐axis on the air‐gap radial flux density and THD of DESC are studied under the d‐, q‐ and dual‐axis excitation modes. The dimensions of the q‐axis slots are optimised by combining the time‐stepping finite element method and Taguchi method, and the optimal structure of q‐axis field winding is obtained. A 10‐kVar DESC is developed to verify the simulation results. This study provides theoretical basis for the design and manufacture of the DESC.
 
The design of the dry‐type on‐board traction transformer (OBTT), a new lightweight method in the traction system of electric multiple units, needs to consider the transient hot spot temperature (HST) under different railroad line operating conditions. In order to quickly calculate the transient HST of dry‐type OBTT when operating under different railroad line conditions, a calculation method (hereinafter referred to as GP‐HST method) by combining an enhanced genetic programming algorithm (GP) with computational fluid dynamics (CFD) is presented. First, intercept a section from the railroad line to be calculated and use the CFD method to calculate the transient HST of the section railroad line. Then, the enhanced GP modelling is driven by this section of railroad line measured and simulated data. Next, a calculation model with an implicit mathematical correlation between railroad line operating conditions and the dry‐type OBTT transient HST is established. Finally, the calculation model quickly calculates the transient HST of the remaining railroad line in operation. To validate the presented method, the calculation model obtained using the presented method is used to calculate the transient HST for another railroad line with significantly different operating conditions, and it is compared with the direct use of the CFD method. The calculation results show that the GP‐HST method reduces the simulation time of the CFD method from 950 to 0.25 min with a maximum error, mean absolute error, and mean relative error of 1.856 K, 0.778 K, and 0.22%, respectively, for a railroad line with a running time of about half an hour. This shows that the GP‐HST method can effectively help to improve the design efficiency of dry‐type OBTT.
 
The online monitoring of inter-turn short-circuit (ITSC) faults in excitation windings of pumped storage units is easily affected by static air-gap eccentricity (SAGE) and armature response, and the early fault characteristics cannot be easily identified effectively. To address these problems, this study proposes a frequency-resolved circulation spectrum (FRCS) fault diagnosis method for ITSC faults in excitation windings. Firstly, the equation for the same phase multi-branch circulation under SAGE compound ITSC conditions is derived based on the structural characteristics of pumped storage units and electromagnetic induction relations, and obtains the characteristic harmonics of the loop current caused by ITSC faults. Secondly, this study introduces the implementation method of FRCS, considering a pumped storage unit with a generation capacity of 334 MVA as the research object. This study develops a two-dimensional finite element simulation model, calculates the magnitude of the in-phase branch circulation at different fault levels, extracts the corresponding time and frequency domain spectrum and FRCS, and verifies the effectiveness of the proposed method based on comparative experiments. Finally, based on the MJF-30-6 Synchronous Generator Experimental Platform in the Power System Dynamic Simulation Laboratory, ITSC operation at different fault levels is simulated, and the corresponding in-phase branch current data are collected for FRCS analysis. The experimental results demonstrate that the method can effectively eliminate SAGE and armature reaction interference, identify early weak ITSC faults and visualise the severity of faults in the form of pixel dots. © 2022 The Authors. IET Electric Power Applications published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.
 
In this article, a suspension‐guided permanent magnet synchronous linear motor (SG‐PMSLM) for ropeless elevator is proposed, which can meet the requirements of high thrust and high thrust density for ropeless elevator, and reduce vibration noise and wheel‐rail wear during motor operation. The structure, working principle and electromagnetic characteristics of SG‐PMSLM are analysed. In order to improve the overall performance of SG‐PMSLM, this article aims at improving the average thrust and thrust density, reducing the thrust fluctuation of SG‐PMSLM. Firstly, the sensitivity analysis of the key structural parameters of SG‐PMSLM is conducted, and the parameters that have significant influence on the three optimisation objectives are selected as the optimisation variables. Secondly, the response surface model of three optimisation objectives is built, and the Particle Swarm Optimisation algorithm is combined to conduct the multi‐objective optimisation design for SG‐PMSLM. Thirdly, the optimised solution set is obtained for three objectives. Finite Element Analysis is used to verify that the optimised solution set has better diversity and can effectively improve SG‐PMSLM overall performance compared with the initial design. Finally, the electromagnetic performance of SG‐PMSLM is verified by experiments.
 
This paper deals with the power smoothing of the wind power plants connected to a microgrid using a hybrid energy storage system (HESS). In a HESS, the power should be distributed between the battery and capacitor such that the capacitor supplies the peaks of power and its high‐frequency fluctuations, and the battery compensates for the rest. Besides, due to the relatively low lifetime of the batteries compared to the capacitors, it is preferred to transfer power fluctuations to the capacitor as much as possible. In this paper, methods for calculating the output, battery, and capacitor powers are presented. The output power is determined based on the grid restrictions and the battery SOC. The battery and capacitor powers are decided via an adaptive low‐pass filter. The cut‐off frequency of the low‐pass filter is specified by a fuzzy controller such that not only the power spikes and high‐frequency fluctuations are transferred to the capacitor but also the battery SOC variations are reduced. The simulation results show that for the presented wind speed profile, the output power determination reduces 13.7% of the HESS exchanged energy compared to the ramp limiting method. Besides, the proposed power distribution method reduces 92.6% of the unbeneficial charges and discharges of HESS and 8% of the battery exchanged energy compared to the condition that the constant cut‐off frequency filter is utilised. The experimental results confirm the effectiveness of the proposed output power determination and HESS power distribution methods. Analysing the methods’ cost proves that although the utilisation of the capacitor bank increases the system initial investment cost, it will return after a while relying on the units’ capacity, power fluctuations, control method etc.
 
The equalisers available are difficult to give consideration to both high balance efficiency and fast balance speed, and their performances are unstable as the number of the series‐connected batteries increases, so they are unsuitable for a large‐scale battery system. A multi‐objective parallel layered equaliser based on battery working states for the large‐scale lithium‐ion battery system is presented. The equaliser has two types of balance objects and two corresponding layers, and the first layer and the second layer take the single battery and the battery unit as the balance object, respectively. The multi‐objective parallel layered balance means that multiple balance objects are selected as the balance objectives simultaneously at each layer. The balance speed is fast due to the multi‐objective parallel balance. The balance efficiency is high due to the short energy path and the complementary pulse width modulation (PWM) control in the first layer, and the double voltage value of the balance object in the second layer. Moreover, the performance of the equaliser is stable, even when the number of series‐connected batteries is large. In short, the proposed equaliser features high efficiency, fast speed, and strong scalability. Further, the experimental platform for a battery system with twelve series‐connected lithium‐ion phosphate batteries is built, and then the balance experiments have been completed. Finally, the effectiveness of the equaliser is verified by the corresponding experimental results.
 
This article presents a miniature tubular moving magnet linear oscillating actuator (MT‐MMLOA) that operates on an electro dynamic actuation mechanism. The proposed linear oscillating actuator comprises two main parts: the stator and the mover. In this topology, the stator assembly is composed of a modular C‐core structure along with a separator to prevent flux cancelation, and the mover assembly accommodates axially magnetised permanent magnets (PMs) that contribute to high thrust force generation and present a less costly actuator compared to the conventional actuator design. The finite element analysis is performed and validated experimentally. Numerous linear oscillating actuator topologies proposed previously in the literature are compared with MT‐MMLOA to analyse the electromagnetic performance. The results show that the motor constant, which is the performance parameter, is significantly increased from the conventional design. The PM volume is reduced, which is cost‐effective. The overall volume of MT‐MMLOA is also reduced due to reduction in the PM volume, which is advantageous for compactness. Consequently, the proposed MT‐MMLOA is simple in structure, less costly, and easy to fabricate.
 
The objective of this paper is to investigate the optimal design of a 120 W outer‐rotor permanent magnet synchronous machine for air‐conditioning applications to reduce the electricity consumption and machine costs. To this end, a 2‐D analytical magnetic model, combined with a teaching–learning based optimisation algorithm is employed. The objectives are to simultaneously maximise the machine efficiency and minimise the material cost. Constraints such as the required output torque, predefined machine volume, maximum allowable torque ripple and unbalanced magnetic force and limitations to avoid iron core magnetic saturation are imposed simultaneously. To find the flux density in iron parts, a new method based on the subdomain technique has been presented. To evaluate the analytical model in terms of accuracy and speed, the results of the 2‐D analytical approach are compared with those of the 2‐D and 3‐D linear/non‐linear finite element method. Finally, a prototype of the optimised machine is fabricated and the superiority of the presented approach is demonstrated.
 
Due to its simple construction, the linear induction motor (LIM) provides a linear driving force without any intermediate motion translation system. LIMs are widely used in various industrial applications, including maglev rail transit and the national defense industry. However, LIMs are affected by the end effect and suffer from problems such as low efficiencies and low power factors. To make improvements, in this paper, an ensemble multi‐objective optimal design method for a short primary double‐sided linear induction motor (SP‐DLIM) is proposed. First, a simplified Quasi‐3D equivalent circuit model (ECM) for an SP‐DLIM applicable to the model in this paper is derived. The 3‐D transient finite element method and an experimental prototype are utilised to prove that the derived ECM is accurate enough to solve the SP‐DLIM optimisation problem. Second, an ensemble multi‐objective optimal design method of SP‐DLIM is presented, with proposed design constraints and four different optimisation problems. Then, an improved differential evolutionary (IDE) algorithm is proposed to optimise the efficiency, power factor, and tooth weight of the motor. The three‐dimensional time‐stepping finite element method is utilised to verify the validity of the optimisation method. Further, a comparison of the results suggests that the IDE yields the best performance to those of other advanced heuristic algorithms.
 
Permanent magnet linear synchronous motor (PMLSM) is one of the ideal driving sources of ropeless elevators. However, such motors, whether moving magnetic or moving coil, will produce the problem of excessive cost under long travel. The permanent magnet flux switched linear motor (PMFSLM) with permanent magnets (PMs) and copper coils on the mover side greatly reduces the cost. A U‐type PMFSLM is proposed in the paper. First, a PMFSLM is proposed and investigated, quantitatively comparing with PMLSM for the ropeless elevator system. Second, aiming at the problem of flux leakage at the top of PMFSLM, a U‐type PM (UPM) structure is presented. The electromagnetic performance of PMFSLM and UPM‐FSLM have been compared and summarised. The comparison results show that UPM‐FSLM solves the defect of top flux leakage, increases thrust by 4.34%, reduces thrust ripple by 28.10%, and has better electromagnetic performance than PMFSLM. Afterwards, the elevator passenger capacity of PMFSLM and UPM‐FSLM are simulated and calculated and the feasibility is analysed. Finally, a prototype of PMFSLM has been built and measured.
 
A novel DC‐Excited Flux‐Switching Linear Motor (DC‐FSLM) is investigated in this paper, where a simple secondary is used as the machine stator. The phases and excitation windings are placed on the primary, which contributes to a low‐cost and simple structure linear motor with acceptable dynamic performance. The motor operation under dynamic load is analysed by a parametric Magnetic Equivalent Circuit (MEC), and the core saturation is modelled by the non‐linear reluctance of the flux tubes. Moreover, the end‐effect is considered by virtual zones at both entrance and exit ends of the primary. In the considered MEC, the model accuracy can be selected as desired as well as different DC‐FSLMs with various properties can be modelled. Finally, the machine capabilities and performance characteristics are discussed by simulation results, and validation is performed by the Finite Element Method (FEM).
 
This article has conducted a comprehensive study on the stator and rotor vibration characteristics of the doubly‐fed induction generator (DFIG) in the case of radial air gap eccentricity (RAGE). Differently from other previous studies, this paper not only investigates the vibration characteristics of stator and rotor in radial static air gap eccentricity (RSAGE) and radial dynamic air‐gap eccentricity (RDAGE) fault but also takes the radial hybrid air gap eccentricity (RHAGE) into account. Through theoretical derivation, the detailed expressions of stator magnetic pull per unit area (MPPUA) and rotor unbalanced magnetic pull (UMP) are obtained. The finite element analysis (FEA) and experiment based on a two pairs of poles DFIG, and the results are consistent with theoretical calculations. It is shown that RAGE will enlarge the magnitude of stator MPPUA/vibration and rotor UMP/vibration. Specifically, RSAGE will not change the frequency components of stator MPPUA/vibration but will bring new frequency components to rotor UMP/vibration. However, both stator MPPUA/vibration and rotor UMP/vibration will generate new frequency components during RDAGE fault. In addition, the effect of RHAGE is the superposition of RSAGE and RDAGE. The research conclusions obtained in this paper can be used as a supplementary criterion for diagnosing the eccentricity of DFIG.
 
The strong coupling effect between the torque system and the suspension system of the single‐winding bearingless switched reluctance motor (SWBSRM) would result in continuous interference to the system and bring difficulties to the design of the control system. Moreover, strong external disturbances will further reduce the stability of the control system. To improve the anti‐disturbance ability and enhance the robustness of the control system of SWBSRM, a design method of the entire control system based on the second‐order sliding mode (SOSM) controllers is proposed. The strongly coupled SWBSRM torque system and suspension system are linearised and decomposed through the feedback linearisation method to benefit the design of SOSM controllers. Then, combined with a super‐spiral algorithm, the super‐spiral sliding mode controllers in the outer loop for torque and suspension system are designed separately. The design of controllers considers the interference caused by the coupling effect and the influence of external disturbance. The range of gain, which can ensure the finite time convergence of the control system is determined through proof of stability. Simulation and experiment results show that the second‐order sliding mode controllers have faster response speed and control precision when suppressing coupled interference and strong external disturbance.
 
Most of the motors used in industrial fields are interior permanent magnet synchronous motors (IPMSMs). The rotor structure of IPMSM is complex, and the rotor bridge region is affected by non‐linear saturation, which increases the difficulty of modelling and calculation. The accuracy of traditional methods for the magnetic field prediction needs to be improved. An analytical model for IPMSM that accounts for the bridge saturation and the complex rotor structure is presented. This method transformed the structure of IPMSM equivalently, which makes it easier to use modelling in the polar coordinate system. Meanwhile, the bridge subdomain and the bridge saturation overflow subdomain are established separately based on the different saturation levels, and the relative permeability value of each subdomain is solved by the iterative permeability method. The magnetic field and electromagnetic performance obtained using the analytical method are compared with those of the finite element method. Finally, the analytical predictions are compared with the measured data to confirm the validity of the methods proposed.
 
Accurate position signals are essential for a vector control system. To obtain accurate position signals, high‐precision position sensors such as optical encoder and resolver are employed. However, they are usually restricted by the environmental condition and cost. Linear Hall‐effect sensors, possessing tiny size, light weight and low cost, are usually used to detect position signals. However, the position signals detected by linear Hall‐effect sensors in low cost conditions always contain a large part of high‐order harmonics, which will decrease the validity and reliability of sensor measurement. In this paper, to eliminate the influence of harmonics, a short‐distance harmonic suppression method without any low‐pass filter is proposed. The proposed method utilises three linear Hall‐effect sensors displaced a certain electrical angle to dissolve the position signal. Through simulation analysis and experimental verification, the proposed method has been proven to be effective in suppressing the third‐order and fifth‐order harmonics.
 
When the transformer is re‐energised, the remanence in the core will cause inrush current, which will have adverse impacts on the power system. In the remanence distribution calculation, not only the hysteresis characteristics of the core, but also the characteristics of the external circuit need to be considered. In this paper, an indirect field‐circuit coupling method for calculating transformer remanence distribution is presented. The residual flux density distribution at every point of the iron core, which has not been shown in previous literatures, can be obtained, and also the H‐B trajectory of the iron core. In the field calculation, the pseudo‐permeability method is modified in order to fit the field separation‐based dynamic hysteresis model. The pseudo‐permeability method and the initial value estimation method are used to speed up the iteration convergence. Furthermore, in the electric circuit topology used in the calculation, the switching process of the circuit breaker and the capacitance in the circuit are considered, and this has not been tried in the previous remanence calculation method. The remanence results are verified by comparison with the results in the literature. The remanence results can provide a basis for the impact analysis and phase control of the re‐energisation.
 
High‐frequency resonance in traction power supply systems (TPSSs) is of great concern because of its potential to cause great damage to the safety and stable operation of railroad systems; it has been demonstrated that when a locomotive generates a harmonic current with the resonant frequency of the series impedance on the traction network, a large amount of high‐frequency harmonic voltage is generated. This paper proposes a high‐frequency harmonic suppression method based on synchronous sampled carrier phase‐shift PWM modulation strategy (SSCPS‐PWM), which has the advantage of not only considering the consistency of sampling the analogue signal by multiple controllers, but also further optimising the precise synchronization between multiple converter pulses. This method generates lower high‐frequency harmonic content and is particularly suitable for the field of high‐power, low switching frequency, multi‐controller locomotive traction converters. The proposed method was simulated and compared with the traditional method for the harmonics injected by the locomotive, and a real railway line with a harsh power supply condition was selected and field tests were conducted in four sections by a 7200kW 6‐axle electric locomotive. The test results showed that the proposed method effectively reduced the high‐frequency harmonic current of the locomotive and reduced the high‐frequency resonant overvoltage in the TPSS.
 
In order to improve the power density of the permanent‐magnet synchronous machine and reduce the cost of effective materials, this paper investigated approaches of power‐density improvement and discussed the influence of flux‐weakening level and salient ratio parameters on the characteristics of torque and power for the interior permanent magnet synchronous machine (IPMSM) based on the permanent magnet (PM) minimisation. Firstly, the model of PM minimisation can be established based on the principle of equal area of stator and rotor magnetomotive force. According to the minimisation model, a formula is derived for calculation of structural parameters of the permanent magnets in the IPMSM. Besides, the relation among the interior multilayer permanent magnets is established. Then, comparing and analysing the extremum characteristics of the maximum torque output and maximum power output of the motor under different parameters, the regular influence on the IPMSM can be summarised between the parameter and the internal power factor angle. So, it can be proposed that the corresponding internal power factor angle with respect to the golden section ratio of the maximum torque output is around −35°. Finally, combined with the results of the finite element and analytical calculation, a 45 kW PM motor for electric vehicles was manufactured and tested in no‐load, load and thermal experiment, respectively. The peak torque of the prototype lasted for 94 s and reached 2.3 times the rated torque. Compared with the conventional PM motor used for the electric vehicle, the power density was increased by more than 0.5 kW/kg which can verify the correctness of the theoretical analysis.
 
Magnetically suspended control moment gyro (MSCMG) outputs gyro moment by changing the direction of the rotor angular momentum to adjust the spacecraft attitude. In the process of outputting moment, due to the moving‐gimbal effect, the power consumption of magnetic bearing occupies a large proportion in MSCMG. The existing low power control methods have problems that adjustment time is long and the effect of reducing energy consumption depends on the model accuracy. To solve these problems, the method of current adaptive adjustment‐gimbal angular velocity feedforward (CAA‐GAVF) is proposed. The CAA‐GAVF method controls rotor deflect actively so that the permanent magnet can generate moment to offset the coupling moment of moving‐gimbal effect, thus reducing the power consumption of control current. In CAA‐GAVF, the deflection angle of rotor is quickly adjusted by the feedforward of gimbal angular velocity. The current integral value is used to adjust the feedforward matrix adaptively and precisely. The experimental results show that the power consumption of CAA‐GAVF method is reduced to 43.3% of the traditional control method.
 
In large scale permanent magnet (PM) machines, such as direct drive wind power generators, stator modularity is widely used for easy manufacturing and to protect the winding from mechanical damage due to being exposed to air. Multiple three‐phase systems that use commercial inverters provide not only a fault‐tolerant operation but also price competitiveness. Although the conventional modular structure of a concentrated single‐layer or distributed winding shows good performance, a large magnetic mutual interference between coils is inevitable. Consequently, if conventional windings are applied to multiple three‐phase systems, complexity and difficulty for controlling the machine can arise. This study proposes a new magnetic isolation winding scheme for modular multiple three‐phase PM machines with a mixed layer to deal with the abovementioned limitation. For comparison, five different modular multiple‐three phase PM machines with a mixed‐layer winding (MMPM) are presented and three conventional modular types are selected. Then, several simulation results and experimental data confirm the validity of the proposed structure.
 
Real batteries used for the performance testing and evaluation of the drive systems of electric vehicles (EVs) are being replaced by battery emulators (BEs) because of the high test costs, long test cycles, and difficulty in adapting to extreme operating conditions associated with the use of real batteries. A parametric BE for a lithium‐ion battery based on a voltage source converter is presented. First, a Thevenin model of the battery is established, and a parameter identification method is proposed to obtain the relationship between the parameters of the battery model and the characteristics of the external electrical port (i.e. I–V characteristics) of the battery. Subsequently, based on the I–V characteristics, the topological structure of the power electronic device of the BE is designed, and the working modes under charging and discharging conditions are presented. Finally, an experimental prototype of the BE is designed and tested. The experimental results show that the proposed BE power converter can successfully simulate the external port voltage and current characteristics of the battery, which can replace the real battery to provide an effective test environment for the test and evaluation of the electric drive system of EVs.
 
This paper presents a novel maximum‐power‐point tracking algorithm of a vertical‐axis wind‐turbine (VAWT) generation system using neural network compensator on the basis of a digital signal processing chip. First, the mechanical power versus rotation‐speed curve of a 3‐kW VAWT generator was constructed by means of the measurement data in various wind speeds. Because the slope of the wind‐turbine output power is a non‐linear function of the generator output current, air density, wind speed, and the characteristics of the wind‐turbine generator, the analytic solution for the maximum power is difficult to obtain due to its complexity, nonlinearity, and uncertainties of parameters. The innovation of this study is to obtain the maximum power of the wind‐turbine system using a recurrent neural network (RNN) by transferring the maximum‐power‐point tracking problem into a unit‐step‐command regulation problem despite the variation of the wind speed, ambient air density, and the load electrical characteristics. The uncertainties in the system are compensated by the RNN, which is composed of three‐layer networks with three neurons and feedback loops in the hidden layer for capturing the characteristics of the wind‐turbine generator system. Without the necessity of wind speed sensor, it only needs the generator output current and rotation speed as the inputs of the input layer. This structure containing only six neurons totally is simpler than the existing work. The duty cycle of the boost converter is determined by a proportional‐integral controller, the parameters of which are determined via a genetic algorithm by the minimisation of a performance index function with the help of MATLAB simulation tool. From the simulation and experimental results, the validity of the proposed control scheme was verified under various wind speed conditions. The performance efficiency and the tip speed ratio in each case of the experiment is near the optimal values of 0.28 and 4.3, respectively. The output power achieves 2048.4 W at the wind speed of 11 m/s in the steady state.
 
This paper presents a novel speed sensorless adaptive control scheme for the uncertain permanent‐magnet synchronous motor (PMSM) drive system using a linear matrix equalities approach with a digital signal processing (DSP) chip. The dynamic model of the PMSM drive with eight error states based on the structure of speed estimator, speed and current controllers is developed. The speed controller, current controller and rotor speed and position estimators are considered simultaneously and designed together. In addition, a three‐parameter observer is also designed and the adaptive control law is derived in the light of Lyapunov stability theorem. The objective of this study is to determine the two estimation gains and the six control gains such that the closed‐loop system is stable. The stability condition of the system can be characterized in terms of some linear matrix inequalities (LMIs). The LMIs problem can be efficiently solved with the help of MATLAB simulation tool. Differently from the conventional proportional‐integral controller, a novel controller with a low‐pass filter instead of a pure integrator is proposed. By a suitable adjustment for a design parameter, the steady‐state error can also be improved. Numerical solutions of the controller and the estimator gains and simulation examples are provided to illustrate the design procedure and corresponding performances. The experimental results by using a TI TMS320F28335 DSP chip with the speed reference 400, 700, 1000 RPM, respectively and sudden change of the reference demonstrate the performance of the proposed control scheme.
 
A three‐phase to single‐phase direct AC power generation system based on the open‐winding permanent magnet synchronous generator (PMSG) with the dual‐inverter is proposed in this study for the standalone power system. The negative DC terminals of the dual‐inverter are commonly connected, and the positive DC terminals are reconstructed as the output port of the single‐phase AC power; the three‐phase AC power generated by PMSG could be converted to be the high power quality single‐phase AC power directly without any LC filters. Different from the traditional OW‐PMSG system, zero‐sequence current is employed to achieve adjustable frequency and voltage of the single‐phase AC power, and the corresponding dual voltage‐loop control strategy with the separate positive‐sequence and zero‐sequence currents regulation of PMSG is given to achieve high output performance. The effectiveness of the proposed control strategy and the output characteristics have been verified by simulation and the experiment of the prototype, and the results show that the high‐quality single‐phase AC power can be obtained at a wide speed range and at different load operating conditions.
 
The main purpose of this work is to address the problem of robust grid voltage sensor fault‐tolerant control for a single‐phase two‐level rectifier. First, considering a rectifier with disturbances and grid voltage sensor fault, the standard switched system model is constructed. Based on identical transformation, the original system is converted into an augmented system. In the augmented system, the information of the grid voltage sensor fault is included in the state vector. Second, an unknown input observer is designed for the augmented system for sensor fault estimation. The observer error is totally robust against independent deterministic disturbances. In addition, the effect of the disturbance caused by unknown disturbances or a modelling error is minimised with respect to a prescribed H∞ performance index. Finally, the sensor fault‐tolerant control is realised by fault compensation technique, which protects the rectifier from serious performance degradation in the presence of the grid voltage sensor fault. The proposed fault‐tolerant control strategy requires no supplementary hardware and all the inputs involved in the algorithm are directly available. Simulation and experimental results are exhibited to illustrate the capability of the proposed method to tolerate the grid voltage sensor fault.
 
A double‐stator swing rotating permanent magnet spherical motor (SR‐PMSM) is designed, which can realize rotation, swing and spiral motion, and is used in the multi‐degree‐of‐freedom motion fields of industrial robot joints, torque gyroscopes, panoramic photography tables and so on. The inner surface of the rotor of the motor is attached with cylindrical PM poles, and the outer surface is attached with trapezoidal PM poles. Cylindrical and trapezoidal PM poles are simple to manufacture, but the magnetic field model of a spherical motor with two kinds of PM poles is complex. Therefore, a magnetic field modelling method combining the geometric equivalence principle and analytical method is proposed. Using the method of shape approximation, according to the principle of equivalence, the key parameters of cylindrical PM poles and trapezoidal PM poles are replaced by the parameters of approximate dihedral PM poles in a spherical coordinate. Select the most suitable dihedral PM poles, establish the analytical model of the magnetic field in the spherical coordinate system and verify the analytical results by FEM method. A SR‐PMSM motor with 6/4 pole (swing) and 12/10 pole (rotation) structure was assembled, and the experimental device was set up. The experimental results show that the experimental curve, analytical curve and FEM curve are in good agreement, which proves the accuracy of the equivalent model and is suitable for the magnetic field model of cylindrical and trapezoidal PM poles of the spherical motor. The research results of magnetic field lay a foundation for further analysis of the stator–rotor composite magnetic field considering cogging effect and edge effect, and analysis of load characteristics of the motor.
 
This paper presents an analytical model of a dual‐stator spoke‐type permanent magnet (DSSTPM) synchronous machines accounting for tooth‐tips. Based on the two‐dimensional (2‐D) subdomain technique, the field domain of DSSTPM machine is divided into seven sub‐regions, that is, permanent magnet (PM), outer/inner air gaps, slots and slot openings. The magnetic field distribution and electromagnetic performance can be calculated via solving the governing functions based on boundary and interface conditions. The analytical predictions for DSSTPM machine under both open‐circuit and on‐load conditions are calculated and compared by the finite element (FE) method.
 
Electrical machine design optimization is an expensive procedure as it contains numerous variables and multiple objectives. Therefore, it might require hundreds of time‐consuming finite element analyses (FEA). Surrogate models are one of the superior alternatives that can overcome the computational burden of FEA. However, in optimization problems with sensitive input‐output relationships, surrogate models can lack accuracy or suffer from unreasonable initial FE‐computational cost. To tackle this problem, this work presents a novel strategy called Waveform‐Targeted Surrogate Modeling (WTSM) that improves the computational efficiency of surrogate‐based design optimization of electrical machines by modifying the model construction process. In this paper, an Interior Permanent Magnet Machine (IPMSM) is studied to evaluate the proposed strategy's performance compared to the conventional Black Box Modeling (BBM) method. A two‐step assessment procedure consisting of multiple scenarios has been developed to analyse the reliability of the WTSM concerning different training‐validation datasets. Meanwhile, the Kriging model and Latin‐Hypercube‐Sampling (LHS) method are employed for surrogate model construction purposes. From the discussion and the results, it can be found that the proposed WTSM strategy can significantly increase the accuracy of the surrogate modelling procedure while the required computational cost can be reduced.
 
As More/All Electric Aircraft gradually become a research hotspot, electromechanical actuators (EMAs), which can directly convert electrical energy into mechanical energy, have gained more and more attention. However, since the reliability of EMA cannot meet the requirements of actual aircrafts, the practical application of EMA is severely limited. Therefore, fault diagnosis, prognosis and health management (DPHM), which can realise condition‐based maintenance (CBM), has become the key technology in the application of EMA. The aim is to summarise the research on EMA fault modes, fault diagnosis, prognosis and health management systematically and comprehensively. First, the basic structure and common fault modes of EMAs are introduced, and the failure mechanism of EMA is studied. Then, the algorithms of DPHM for EMAs are reviewed in detail. The perception strategies of data acquisition are analysed, and the EMA fault diagnosis methods, including model‐based and data‐driven methods, are reviewed. The research of remaining useful life (RUL) prediction and fault‐tolerant control are introduced. After that, some problems of the existing research on EMA DPHM and their potential solutions are put forward. Finally, several possible developing directions of research on EMA DPHM are predicted.
 
Using multiple position sensors in the control system of Two‐Degrees of Freedom (2‐DOF) motors causes it more complicated than that of conventional 1‐DOF ones. However, employing a 2‐DOF position sensor in comparison with two independent sensors, reduces the complexity, mass and volume of the system. The common 2‐DOF sensors are able to determine the position in linear, rotational, and helical motion. Yet, they suffer from accuracy reduction due to the longitudinal end effect. Therefore, analytical modelling and the relevant compensation methods are discussed. The accuracy of the model is approved by comparing its results with those of 3D time transient finite element method. Afterwards, the model is used for compensating the end effects. Finally, the optimised 2‐DOF resolver is prototyped and tested. The result of experimental test shows the proposed resolver's success.
 
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$2,800 / £2,200 / €2,500
Article Processing Charges (APC)
27%
Acceptance rate
53 days
Submission to first decision
1.737 (2021)
Journal Impact Factor™
5 (2021)
CiteScore™