[Show abstract][Hide abstract] ABSTRACT: This paper considers the control of a 7-leg back-to-back Voltage Source Inverter (VSI) arrangement feeding a 4-wire load from a 3-phase Permanent Magnet Synchronous Generator (PMSG) operating at variable speed. The 7-leg converter is regulated using Resonant Controllers (RCs) at the load side and self-tuning resonant controllers at the generator side. The control system is augmented by a feed-forward compensation algorithm which improves the dynamic performance during transients. Experimental results, obtained from a prototype, are presented and discussed.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a topology for a three-phase generation system for an isolated unbalanced load fed by a doubly fed induction generator with a neutral wire to include single-phase loads. The challenges of unbalanced loads connected to the system are presented along with a proposal for mitigating current imbalance by employing a four-leg rectifier. The proposed compensation method is based on the sequence decomposition analysis, and thus, it is based on previous works that use current control in double synchronous reference frames. Nevertheless, a conceptual analysis is presented that vindicates the use of resonant controllers in the stationary abc frame.
No preview · Article · Jul 2015 · IEEE Transactions on Industrial Electronics
[Show abstract][Hide abstract] ABSTRACT: This paper considers the control of a seven-leg back-to-back voltage source inverter arrangement, feeding a four-wire load from a three-phase permanent-magnet synchronous generator (PMSG) operating at variable speed. The PMSG is controlled using a sensorless model reference adaptive system to obtain the rotor position angle. The seven-leg converter is regulated using resonant controllers at the load side and self-tuning resonant controllers at the generator side. The control system is augmented by a feedforward compensation algorithm that improves the dynamic performance during transients. Experimental results, which are obtained from a prototype, are presented and discussed.
No preview · Article · Jul 2015 · IEEE Transactions on Industrial Electronics
[Show abstract][Hide abstract] ABSTRACT: This paper presents a new and simple Finite Control Set Model Predictive Control (FCS-MPC) strategy of the Modular Multilevel Matrix Converter (M 3 C). This converter is one of the direct AC/AC power converters suitable for medium-voltage high-power machine drives with regenerative capacity. One of the main feature of this converter is that does not need external dc-voltage supplies and thus, all capacitor voltages have to be regulated to the desired value. Therefore, this paper provides a cost function that considers error terms related to the output current and capacitor voltages. Moreover, a compensation input current is presented in order to improve the dynamics response of the capacitor voltage average value. Simulation results illustrate that the proposed algorithm is capable to achieving good performance, even in critical operation point of the M 3 C .
[Show abstract][Hide abstract] ABSTRACT: The trend of multimegawatt wind turbines has positioning multilevel converters as a promising solution for high-power Wind Energy Conversion Systems (WECSs). Furthermore, due to the high penetration of wind energy into the electrical network, some rather strict grid regulations have been development in case of fault into the grid power. Mainly, grid codes set Low Voltage Ride Through (LVRT) requirements for grid connected WECS. In this scenario, this paper presents a novel modelation and control strategy to fulfil Low Voltage Ride Through requirements using a Modular Multilevel Matrix Converter for interfacing a high power wind turbine. Keywords—Low Voltag eRide Through, Wind Turbine, Modular Multilvel Matrix Converter.
[Show abstract][Hide abstract] ABSTRACT: The modular multilevel topologies are the next generation of power converters for applications where high power-voltage is necessary, such as traction systems, marine propulsion and Wind Energy Conversion Systems. In this paper, a new model and its respective control scheme for the Modular Multilevel Converter are proposed. The model is able to represent separately the dynamic of each port and to show the degrees of freedom in the converter, which are two circulating currents and the common mode voltage. These three degrees of freedom were used to perform energy balancing and to mitigate the voltage fluctuations at low AC frequency operation. Additionally, the proposed control strategy is extended to control two Modular Multilevel Converters in Back to Back configuration. Extensive theoretical analysis and computer simulation validate the effectiveness and viability of the presented control algorithm.
[Show abstract][Hide abstract] ABSTRACT: The high penetration of energy from wind energy conversion systems (WECSs) can have a significant influence on the stability, power quality and reliability of power systems. Therefore several countries have developed stringent grid codes in recent years in order to enhance the overall stability of power systems. In these grid codes, the capacity to fulfil low-voltage ride through (LVRT) requirements is considered an important issue for the control of WECSs. Therefore in this study, a novel voltage sag/ swell generator (VSG) based on a 4-leg matrix converter is presented. This VSG can be used to generate the symmetrical and asymmetrical faults required to test LVRT algorithms in a laboratory environment. The performance of the VSG is experimentally demonstrated and compared with the operation of other VSGs conventionally used for LVRT studies.
Full-text · Article · Dec 2014 · IET Power Electronics
[Show abstract][Hide abstract] ABSTRACT: A strategy for an indirect matrix converter with two outputs to supply energy to a vector controlled open-end winding induction machine is presented. The modulation schemes for the input and two output stages aim to reduce the virtual DC link voltage for low speed operation and eliminate the zero sequence voltage in the load.
[Show abstract][Hide abstract] ABSTRACT: In this paper an Indirect Matrix Converter (IMC) with two output stages feeding an open-end winding induction machine is presented. The IMC has the advantage of having nobulky energy storage elements and with the two output stages up to 1.5 times the input phase voltage can be obtained across the windings of the machine, without overmodulation. A vector control scheme for the machine currents is used along with a modulation strategy for the converter two-output stages to reduce the common mode voltage and compensate the phase zero sequence currents. Simulation results showing the performance of the controlscheme and the reduction of zero sequence and common mode voltages are presented and discussed.
[Show abstract][Hide abstract] ABSTRACT: The incorporation of high power rate Wind Energy Conversion Systems (WECS) have significant influence in the stability, power quality and reliability of the electrical grid. Therefore, strict grid codes have been developed during the last years in order to enhance overall stability of the systems. Thereby Low Voltage Ride Through (LVRT) requirements is a key issue for WECS. In order to test the response of WECS under grid-voltage sag conditions, a Voltage Sag Generator (VSG) is needed. This paper presents a novel Matrix Converter based VSG Prototype in order to study the fulfilment of LVRT requirements. Voltage sags/swell of variable magnitude, duration and type can be generated for the proposed VSG without using complex modulation schemes.
[Show abstract][Hide abstract] ABSTRACT: In order to avoid stability problems, LVRT requirements (Low Voltage Ride Through) demand Wind Energy Conversion Systems (WECS) to remain connected to the grid in the presence of grid voltages dips. Because 88% of the grid failures are asymmetrical, positive and negative sequence components have to be controlled to fulfill LVRT requirements. This paper present a comparison between synchronous and stationary reference frame control strategies for an active front-end converter of a grid connected WECS working under grid fault conditions. The mathematical analysis and design procedure of both control system are presented in this work. Experimental results obtained from a 3kW prototype are fully discussed in this paper. The experimental implementation is realized using a novel implementation of a voltage sag generator which is based on a 3×4 Matrix Converter.
[Show abstract][Hide abstract] ABSTRACT: Delayed signal cancellation is one of the methods used to separate the negative- and positive-sequence components in unbalanced systems. In this letter, a DSC methodology with fast convergence time is proposed and it is shown that an improved separation of the positive and negative sequences is feasible. Experimental results are presented to demonstrate the performance of the proposed methodology.
Full-text · Article · Jan 2014 · IEEE Transactions on Power Delivery
[Show abstract][Hide abstract] ABSTRACT: Generators working with variable speed, rather than fixed speed, have many advantages, which are well documented in the literature. Higher efficiency, better power to size ratio and less mechanical stress in the system are some of the characteristics of variable speed generators. In particular, variable speed diesel generators can be used to provide small highly portable generation systems for emergency vehicles and military/aerospace applications. Such systems can be used to feed stand-alone linear/non-linear loads if an adequate power converter interface is provided. Four-leg matrix converters can be used as the power electronic interface between variable speed generators and stand-alone loads. The fourth leg provides a neutral point for single phase loads and a path for the circulation of zero sequence currents. When non-linear loads are connected to the matrix converter output, relatively high harmonic distortion can be produced in the load voltage unless an appropriate control system is provided. In this paper the application of a repetitive control system to improve the quality of the load voltage is presented. Experimental results obtained from a prototype are shown and fully analysed. (c) 2013 Elsevier B.V. All rights reserved.
No preview · Article · Nov 2013 · Electric Power Systems Research
[Show abstract][Hide abstract] ABSTRACT: The Doubly-Fed Induction Generator (DFIG) is one of the most widely used generators for wind energy applications with more than 50% of installed Wind Energy Conversion Systems (WECS) using this variable speed technology. However, the conventional DFIG requires brushes and copper slip-rings to connect a power converter to the rotor windings. The use of brushes decreases the WECS’ robustness and extra maintenance is required to periodically inspect/replace these elements. In this work a new topology for a Brushless Doubly-Fed Induction Generator (BDFIG) is presented. As an alternative to conventional Voltage Source Inverters (VSI) a matrix converter is used to regulate the current supplied to the stator of the doubly-fed machine, supplying the excitation energy to the WECS. The proposed generation system is mathematically analysed in this paper and the design of the control loops is discussed. Because the power spectrum density of the wind speed is dominated by low frequency components, in this work some simplifications of the transfer functions of the system are proposed. Experimental results obtained from a 3 kW prototype of a cascaded DFIG, are presented and fully discussed.
No preview · Article · Oct 2013 · Electric Power Systems Research
[Show abstract][Hide abstract] ABSTRACT: This "Special Section on Control and Grid Integration of Wind Energy Systems - Part II" of the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS presents the more recent advances in the following topics: 1) HVDC systems for the connection of wind farms to the main power systems; 2) novel topologies for offshore wind energy systems; 3) control of WECSs: e.g., sensorless control of electrical generators, brushless doubly fed induction generators, new topologies of permanent-magnet generators, etc.; 4) grid issues: e.g., low-voltage ride-through (LVRT) control, frequency support using grid control, stability issues, etc.; 5) power converter topologies and control systems: e.g., multilevel power converters, parallel connection of multiple converters, modulations issues, etc.
Full-text · Article · Jun 2013 · IEEE Transactions on Industrial Electronics
[Show abstract][Hide abstract] ABSTRACT: Doubly fed induction generators (DFIGs), often organized in wind parks, are the most important generators used for variable-speed wind energy generation. This paper reviews the control systems for the operation of DFIGs and brushless DFIGs in wind energy applications. Control systems for stand-alone operation, connection to balanced or unbalanced grids, sensorless control, and frequency support from DFIGs and low-voltage ride-through issues are discussed.
No preview · Article · Jun 2013 · IEEE Transactions on Industrial Electronics
[Show abstract][Hide abstract] ABSTRACT: A novel frequency changing conversion scheme using three cascade multilevel converters in a Π topology is presented. The scheme resembles a direct frequency converter using the cascade converter in its simplest form (series strings of H-bridge modules equipped with a dc link capacitor) as the building block of the overall converter. This yields a highly modular implementation approach which may be attractive for large power applications such as intertie connections and variable speed drives. Frequency conversion takes place in a cascade converter which connects the input and output ports. Two other converters are placed, respectively, in parallel to the input, to remove unwanted current components from the input, and the output to regulate output voltage. Operation of this topology is explained and a scheme to control all the converters is developed, including control of converter currents, capacitor voltages, and output voltage. Experimental results, using a low-power prototype, confirm the foundations of the topology and verify its overall performance operating as a power supply at typical output frequencies (25 Hz, 162/3 Hz and dc) while being fed from a 50-Hz system. Additionally, PowerSIM simulations demonstrate that the topology may be suitable for implementing high-performance, high-power ac drive systems using vector control techniques.
No preview · Article · Jun 2013 · IEEE Transactions on Industrial Electronics
[Show abstract][Hide abstract] ABSTRACT: The increased penetration of renewable energy systems (RESs) rises the concern about the stability and power quality of the utility grid. Therefore, some rather strict grid requirements for Low Voltage Ride-Through (LVRT) have been produced. In order to verify the response of RES under grid-voltage sag conditions, a Voltage Sag Generator (VSG) is needed. This paper presents a 5 kVA Matrix Converter based VSG to test RES in order to study the fulfillment of LVRT requirements. Voltage dips of variable magnitude, duration time and type can be generated with the proposed VSG.
[Show abstract][Hide abstract] ABSTRACT: A Space Vector Modulation (SVM) strategy for an open-end load fed by an indirect matrix converter consisting on one input stage and two output stages is presented. The modulation strategy aims to reduce the instantaneous common mode voltage and dynamically compensate the phase zero sequence current.
[Show abstract][Hide abstract] ABSTRACT: In this paper an Indirect Matrix Converter (IMC) with two output stages feeding an open end load is presented. The IMC has the advantage of having no bulky energy storage elements and with the two output stages up to 1.5 times the input phase voltage can be obtained across the load without overmodulation. Two pulse width modulation strategies are presented. The first one is based on space vector modulation and suppresses the zero sequence voltage in the load. The second one is a carrier-based modulation and lower distorted input current is obtained. Results are presented and discussed.