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Ehsan Abdi

University of Cambridge, Department of Engineering, Alumnus

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Dr Ehsan Abdi is the founder and director of Wind Technologies Limited in Cambridge, where he has led the commercialisation of the brushless doubly-fed machine for wind power applications. He graduated from Cambridge University with the MPhil and PhD degrees in Electrical Engineering in 2003 and 2006, respectively. He obtained his BSc degree in the same subject from Sharif University of Technology in Iran in 2002. Dr Abdi has received several prestigious awards and recognitions, among which are IET Young Professional Paper Award, The Scientific Instrument Maker Award and a runner-up for the IET Innovation in Engineering Award. His main research interests include electrical machines and drives, wind power generation, and electrical measurements and instrumentation.

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University of Cambridge

University of Zaragoza

Hamma Lakhdar El-Oued University

Sharif University of Technology

Mohammad Nasser Hashemnia

Islamic Azad University Of Mashhad

Ayman Abdel-khalik

Sultan Qaboos University

Aliaksey Kerhet

University of Technology Sydney

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Papers by Ehsan Abdi

Operation of Brushless Doubly-Fed Machine for Drive Applications

pared to predictions obtained using the coupled circuit and equivalent circuit models of the BDFM.

A new optimized rotor design for brushless doubly fed machines

The brushless doubly fed machine (BDFM) is an alternative to the doubly fed induction generator, ... more The brushless doubly fed machine (BDFM) is an alternative to the doubly fed induction generator, widely used in wind turbines, without use of brush gears and slip rings. Rotor design is important for designing an optimal multi-MW BDFM. To date, nested-loop rotors have been extensively used in various BDFMs but they may not be suitable for larger machines. In this paper, different methods of BDFM rotor equivalent circuit parameters determination are presented and validated by experimental tests. Then, a design optimization of BDFM rotors is proposed based on equivalent circuit analysis with the aim of minimizing the rotor parameters. Two optimized rotors, one bar cage rotor and one nested-loop rotor were designed and built from the outcomes of the optimization method for a BDFM with frame size D180. The characteristics of the conventional and optimized rotors in terms of the rotor equivalent circuit parameters and iron saturation at rated operating conditions are compared using analytical and Finite Element Analysis (FEA) methods.

A Light Weight Rotor Design for Brushless Doubly Fed Machines

Φ Abstract -In this paper, a new optimized rotor design for Brushless Doubly Fed Machines (BDFMs)... more Φ Abstract -In this paper, a new optimized rotor design for Brushless Doubly Fed Machines (BDFMs) is proposed. The BDFM is considered as an attractive generator particularly for offshore wind power generation and also as a replacement for doubly fed slip ring induction generators. This is due to its higher reliability and lower maintenance reported in the literature. It is shown in this paper from the study of the magnetic field distribution in the rotor core that the conventional design of the BDFM rotor iron core can be modified, leading to a lighter machine. The proposed design method is supported by an analytical study and its practicality is validated using 2-D Finite Element (FE) analysis. A 250 kW experimental BDFM with frame size D400 is considered as the prototype machine.

Wireless energy harvesting for rotor instrumentation in electrical machines

In order to perform experiments on electrical machines, it is desirable to measure rotor paramete... more In order to perform experiments on electrical machines, it is desirable to measure rotor parameters such as currents and temperatures. A Bluetooth module have been developed which sends data from the rotor, however this module is battery powered, and therefore the duration of the tests is limited. This paper presents a solution to this problem, by developing a rotor-mounted power supply system which can harvest energy from leakage magnetic flux inside the machine, by fixing an external loop to the rotor and making use of induced voltages in the loop. A full-bridge rectifier, boost converter and battery charging module was developed to supply sufficient power to the Bluetooth module.

A study of rotor eccentricities effects on brushless doubly fed machines performance

This paper studies the unbalanced magnetic pull (UMP) in the Brushless Doubly-Fed Machine (BDFM).... more This paper studies the unbalanced magnetic pull (UMP) in the Brushless Doubly-Fed Machine (BDFM). Analytical study is performed to derive the UMP, then, Finite element (FE) analysis, which has been verified experimentally, is used to verify the analytical method. The BDFM with different types of rotor eccentricities including static and dynamic eccentricities, are also modeled in FE method and their resultant UMPs are obtained. The results are compared with the case at which a perfectly constructed rotor is considered. The study has been carried out on a prototype D400 250 kW BDFM.

Symmetrical Low Voltage Ride-Through of a 250 kW Brushless DFIG

The Brushless Doubly-Fed Induction Generator (Brushless DFIG) shows commercial promise for wind p... more The Brushless Doubly-Fed Induction Generator (Brushless DFIG) shows commercial promise for wind power generation due to its lower cost and higher reliability when compared with the conventional Doubly-Fed Induction Generator (DFIG). In the most recent grid codes, wind generators are required to be able to ride through a low voltage fault and meet the reactive current demand from the grid. Hence, a Low-Voltage Ride-Through (LVRT) capability is important for wind generators which are integrated into the grid. In this paper the authors propose a control strategy enabling the Brushless DFIG to successfully ride through a symmetrical voltage dip. The control strategy has been implemented on a 250 kW Brushless DFIG and the experimental results indicate that LVRT is possible without a crowbar.

Design and Testing of a 250 kW Medium-Speed Brushless DFIG

This paper presents the design and testing of a 250 kW medium-speed Brushless Doubly-Fed Inductio... more This paper presents the design and testing of a 250 kW medium-speed Brushless Doubly-Fed Induction Generator (Brushless 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. The medium-speed Brushless DFIG in combination with a simplified two-stage gearbox promises a low-cost lowmaintenance and reliable drive train for wind turbine applications.

The BDFM as a Generator in Wind Turbines

The Brushless Doubly-Fed Machine (BDFM) is attractive for use in wind turbines, especially offsho... more The Brushless Doubly-Fed Machine (BDFM) is attractive for use in wind turbines, especially offshore, as it offers high reliability by virtue of the absence of brushgear. Critical issues in the use of the BDFM in this role at a system level include the appropriate mode of operation, the sizing of associated converter and the control of the machine. At a machine level, the design of the machine and the determination of its ratings are important. Both system and machine issues are reviewed in the light of recent advances in the study of the BDFM, and preliminary comparisons are made with the well-established doubly fed wound rotor induction generator.

Derivation of a Vector Model for a Brushless Doubly-Fed Machine with Multiple Loops per Nest

The paper presents a vector model for a Brushless Doubly-Fed Machine (BDFM). The BDFM has 4 and 8... more The paper presents a vector model for a Brushless Doubly-Fed Machine (BDFM). The BDFM has 4 and 8 pole stator windings and a nested-loop rotor cage. The rotor cage has six nests equally spaced around the circumference and each nest comprises three loops. All the rotor loops are short circuited via a common end-ring at one end. The vector model is derived based on the electrical equations of the machine and appropriate vector transformations. In contrast to the stator, there is no three phase circuit in the rotor. Therefore, the vector transformations suitable for three phase circuits can not be utilised for the rotor circuit. A new vector transformation is employed for the rotor circuit quantities. The approach presented in this paper can be extended for a BDFM with any stator poles combination and any number of loops per nest. Simulation results from the model implemented in Simulink are presented.

Equivalent Circuit Parameters for Large Brushless Doubly Fed Machines (BDFMs

This paper presents analytical methods to calculate the equivalent circuit parameters for large-s... more This paper presents analytical methods to calculate the equivalent circuit parameters for large-scale brushless doubly fed machines (BDFMs) with magnetic wedges utilized for closing stator open slots. The use of magnetic wedges reduces the magnetizing currents in the machine, reflected in the values of magnetizing inductances, but also increases leakage fluxes affecting the value of series inductances in the equivalent circuit. Though such effects can be modeled by numerical models, the proposed analytical methods are particularly helpful in optimizing machine design, inverter rating, reactive power management, and grid low-voltage ride-through performance. The conventional analytical methods cannot be readily applied to the BDFM due to its complex magnetic field distribution; this paper presents analytical methods to calculate the magnetizing and leakage inductances for the BDFM with magnetic wedges used in the stator slots. The proposed methods are assessed by experimentally verified finite-element models for a 250 kW BDFM.

DESIGN AND PERFORMANCE ANALYSIS OF A 6 MW MEDIUM-SPEED BRUSHLESS DFIG

The paper presents the design and performance analysis of a 6 MW medium-speed Brushless Doubly-Fe... more The paper presents the design and performance analysis of a 6 MW medium-speed Brushless Doubly-Fed Induction Generation (Brushless DFIG) for a wind turbine drivetrain. Two machines with different frame sizes have been designed to show the flexibility of the design procedure. The mediumspeed Brushless DFIG in combination with a two stage gearbox offers a low-cost, low-maintenance and reliable drivetrain for wind turbine applications.

The Brushless Doubly-Fed Machine Vector Model in the Rotor Flux Oriented Reference Frame

The paper presents the vector model of the Brushless Doubly-Fed Machine (BDFM) in the rotor flux ... more The paper presents the vector model of the Brushless Doubly-Fed Machine (BDFM) in the rotor flux oriented reference frame. The rotor flux oriented reference frame is well known in the standard AC machines analysis and control. Similar benefits can be sought by employing this method for the BDFM. The vector model is implemented in MATLAB/SIMULINK to simulate the BDFM dynamic performance under different operating conditions. The predictions from the vector model are compared to those from the coupled circuit model in simulation. The results are shown for the cascade mode of operation.

Dynamic Analysis of the Brushless Doubly-Fed Induction Generator during Symmetrical Three-Phase Voltage Dips

The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise as replacement for ... more The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise as replacement for doublyfed slip-ring generators for wind power applications by offering reduced capital and operational costs due to its brushless operation. In order to facilitate its commercial deployment, the capabilities of the BDFIG system to comply with grid code requirements have to be assessed. This paper, for the first time, studies the performance of the BDFIG under grid fault ridethrough and presents the dynamic behaviour of the machine during three-phase symmetrical voltage dips. Both full and partial voltage dips are studied using a vector model. Simulation and experimental results are provided for a 180 frame BDFIG.

Synchronous Operation Control Of the Brushless Doubly-Fed Machine

The paper presents a novel vector control structure for the Brushless Doubly-Fed Machine (BDFM) w... more The paper presents a novel vector control structure for the Brushless Doubly-Fed Machine (BDFM) which is derived based on the machine synchronous operation. In fact, the synchronous operation of the BDFM provides an efficient approach for determining the required reference angle in the machine vector control structure. The utilization of such reference angle makes the vector control structure presented in this paper different from and, in fact, more effective than the existing rotor flux and stator flux orientation schemes proposed for the machine. The results of implementing the vector control scheme in simulations confirm the effectiveness of the proposed approach for the BDFM control.

Asymmetrical Low-Voltage Ride Through of Brushless Doubly Fed Induction Generators for the Wind Power Generation

Compared with the Doubly fed induction generators (DFIG), the brushless doubly fed induction gene... more Compared with the Doubly fed induction generators (DFIG), the brushless doubly fed induction generator (BDFIG) has a commercial potential for wind power generation due to its lower cost and higher reliability. In the most recent grid codes, wind generators are required to be capable of riding through low voltage faults. As a result of the negative sequence, induction generators response differently in asymmetrical voltage dips compared with the symmetrical dip. This paper gave a full behavior analysis of the BDFIG under different types of the asymmetrical fault and proposed a novel control strategy for the BDFIG to ride through asymmetrical low voltage dips without any extra hardware such as crowbars. The proposed control strategies are experimentally verified by a 250-kW BDFIG.

Symmetrical Low Voltage Ride-Through of the Brushless Doubly-Fed Induction Generator

The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise for wind power gene... more The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise for wind power generation due to its lower cost and higher reliability compared to the Doubly-Fed Induction Generator (DFIG). For the purposes of commercialisation, the BDFIG must meet grid codes at all times. Nowadays, all new wind generators have to ride through certain grid faults, and the Low-Voltage Ride Through (LVRT) capability has become one of the most important points on which to assess the performance a generator. This paper, for the first time, proposes a control scheme to enable the the BDFIG to ride through symmetrical voltage dips. Simulation results and experimental results on a prototype BDFIG show that the proposed scheme gives the capability to ride through low voltage faults.

Stator-Flux-Oriented Vector Control for Brushless Doubly Fed Induction Generator

Brushless doubly fed induction generators (BDFIGs) show commercial promise for wind-power generat... more Brushless doubly fed induction generators (BDFIGs) show commercial promise for wind-power generation due to their lower capital and operational costs and higher reliability as compared with doubly fed induction generators. This paper presents a vector-control scheme for a BDFIG operating as a variable-speed generator. The proposed vector controller is developed on the power-winding stator-flux frame and can be used to control both the speed and the reactive power. The machine model and the control system are developed in MATLAB. The test results show that the proposed controller has good dynamic performance when changes in speed and reactive power are applied.

Generalized Vector Model for the Brushless Doubly-Fed Machine With a Nested-Loop Rotor

This paper presents a generic vector model for the brushless doubly-fed machine (BDFM) with a nes... more This paper presents a generic vector model for the brushless doubly-fed machine (BDFM) with a nested-loop rotor. The vector model is presented for a generic p 1 /p 2 pole-pair BDFM which may have any number of loops per nest. The vector transformations utilized in the derivation of the vector model are provided in general form such that the model can be represented in any appropriate reference frames according to the specific application of the model, such as BDFM analysis, simulations, or control system synthesis. The derived vector model benefits from the feature of reduced order in comparison with the coupledcircuit model, which is the most detailed model for the BDFM, while maintaining the accuracy by including the effects of all loops in each nest. The vector model is developed in MATLAB/Simulink based on the rotor reference frames for a 180-frame-size prototype BDFM, and its predictions for the machine performance have been compared with those of the coupled-circuit model as well as verified experimentally.

High-Performance Low-Cost Rogowski Transducers and Accompanying Circuitry

Rogowski transducers have become an increasingly popular method of measuring current within proto... more Rogowski transducers have become an increasingly popular method of measuring current within prototyping applications and power electronics equipment due to their significant advantages compared to an equivalent current transformer. This paper presents a simple and practical construction technique of high-performance low-cost Rogowski transducers and accompanying circuitry. Experimental tests were carried out to show the validity of the proposed construction technique.

Stable Operation of the Brushless Doubly-Fed Machine (BDFM

A simple method of controlling the Brushless Doubly-Fed Machine (BDFM) is presented. The controll... more A simple method of controlling the Brushless Doubly-Fed Machine (BDFM) is presented. The controller comprises two Proportional-Integral (PI) modules and requires only the rotor speed feedback The machine model and the control system are developed in MATLAB. Both simulation and experimental results are presented. The performance of the system is presented in the motoring and generating operations. The experimental tests included in this paper were carried out on a 180 frame size BDFM with a nested-loop rotor.

Operation of Brushless Doubly-Fed Machine for Drive Applications

pared to predictions obtained using the coupled circuit and equivalent circuit models of the BDFM.

A new optimized rotor design for brushless doubly fed machines

The brushless doubly fed machine (BDFM) is an alternative to the doubly fed induction generator, ... more The brushless doubly fed machine (BDFM) is an alternative to the doubly fed induction generator, widely used in wind turbines, without use of brush gears and slip rings. Rotor design is important for designing an optimal multi-MW BDFM. To date, nested-loop rotors have been extensively used in various BDFMs but they may not be suitable for larger machines. In this paper, different methods of BDFM rotor equivalent circuit parameters determination are presented and validated by experimental tests. Then, a design optimization of BDFM rotors is proposed based on equivalent circuit analysis with the aim of minimizing the rotor parameters. Two optimized rotors, one bar cage rotor and one nested-loop rotor were designed and built from the outcomes of the optimization method for a BDFM with frame size D180. The characteristics of the conventional and optimized rotors in terms of the rotor equivalent circuit parameters and iron saturation at rated operating conditions are compared using analytical and Finite Element Analysis (FEA) methods.

A Light Weight Rotor Design for Brushless Doubly Fed Machines

Φ Abstract -In this paper, a new optimized rotor design for Brushless Doubly Fed Machines (BDFMs)... more Φ Abstract -In this paper, a new optimized rotor design for Brushless Doubly Fed Machines (BDFMs) is proposed. The BDFM is considered as an attractive generator particularly for offshore wind power generation and also as a replacement for doubly fed slip ring induction generators. This is due to its higher reliability and lower maintenance reported in the literature. It is shown in this paper from the study of the magnetic field distribution in the rotor core that the conventional design of the BDFM rotor iron core can be modified, leading to a lighter machine. The proposed design method is supported by an analytical study and its practicality is validated using 2-D Finite Element (FE) analysis. A 250 kW experimental BDFM with frame size D400 is considered as the prototype machine.

Wireless energy harvesting for rotor instrumentation in electrical machines

In order to perform experiments on electrical machines, it is desirable to measure rotor paramete... more In order to perform experiments on electrical machines, it is desirable to measure rotor parameters such as currents and temperatures. A Bluetooth module have been developed which sends data from the rotor, however this module is battery powered, and therefore the duration of the tests is limited. This paper presents a solution to this problem, by developing a rotor-mounted power supply system which can harvest energy from leakage magnetic flux inside the machine, by fixing an external loop to the rotor and making use of induced voltages in the loop. A full-bridge rectifier, boost converter and battery charging module was developed to supply sufficient power to the Bluetooth module.

A study of rotor eccentricities effects on brushless doubly fed machines performance

This paper studies the unbalanced magnetic pull (UMP) in the Brushless Doubly-Fed Machine (BDFM).... more This paper studies the unbalanced magnetic pull (UMP) in the Brushless Doubly-Fed Machine (BDFM). Analytical study is performed to derive the UMP, then, Finite element (FE) analysis, which has been verified experimentally, is used to verify the analytical method. The BDFM with different types of rotor eccentricities including static and dynamic eccentricities, are also modeled in FE method and their resultant UMPs are obtained. The results are compared with the case at which a perfectly constructed rotor is considered. The study has been carried out on a prototype D400 250 kW BDFM.

Symmetrical Low Voltage Ride-Through of a 250 kW Brushless DFIG

The Brushless Doubly-Fed Induction Generator (Brushless DFIG) shows commercial promise for wind p... more The Brushless Doubly-Fed Induction Generator (Brushless DFIG) shows commercial promise for wind power generation due to its lower cost and higher reliability when compared with the conventional Doubly-Fed Induction Generator (DFIG). In the most recent grid codes, wind generators are required to be able to ride through a low voltage fault and meet the reactive current demand from the grid. Hence, a Low-Voltage Ride-Through (LVRT) capability is important for wind generators which are integrated into the grid. In this paper the authors propose a control strategy enabling the Brushless DFIG to successfully ride through a symmetrical voltage dip. The control strategy has been implemented on a 250 kW Brushless DFIG and the experimental results indicate that LVRT is possible without a crowbar.

Design and Testing of a 250 kW Medium-Speed Brushless DFIG

This paper presents the design and testing of a 250 kW medium-speed Brushless Doubly-Fed Inductio... more This paper presents the design and testing of a 250 kW medium-speed Brushless Doubly-Fed Induction Generator (Brushless 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. The medium-speed Brushless DFIG in combination with a simplified two-stage gearbox promises a low-cost lowmaintenance and reliable drive train for wind turbine applications.

The BDFM as a Generator in Wind Turbines

The Brushless Doubly-Fed Machine (BDFM) is attractive for use in wind turbines, especially offsho... more The Brushless Doubly-Fed Machine (BDFM) is attractive for use in wind turbines, especially offshore, as it offers high reliability by virtue of the absence of brushgear. Critical issues in the use of the BDFM in this role at a system level include the appropriate mode of operation, the sizing of associated converter and the control of the machine. At a machine level, the design of the machine and the determination of its ratings are important. Both system and machine issues are reviewed in the light of recent advances in the study of the BDFM, and preliminary comparisons are made with the well-established doubly fed wound rotor induction generator.

Derivation of a Vector Model for a Brushless Doubly-Fed Machine with Multiple Loops per Nest

The paper presents a vector model for a Brushless Doubly-Fed Machine (BDFM). The BDFM has 4 and 8... more The paper presents a vector model for a Brushless Doubly-Fed Machine (BDFM). The BDFM has 4 and 8 pole stator windings and a nested-loop rotor cage. The rotor cage has six nests equally spaced around the circumference and each nest comprises three loops. All the rotor loops are short circuited via a common end-ring at one end. The vector model is derived based on the electrical equations of the machine and appropriate vector transformations. In contrast to the stator, there is no three phase circuit in the rotor. Therefore, the vector transformations suitable for three phase circuits can not be utilised for the rotor circuit. A new vector transformation is employed for the rotor circuit quantities. The approach presented in this paper can be extended for a BDFM with any stator poles combination and any number of loops per nest. Simulation results from the model implemented in Simulink are presented.

Equivalent Circuit Parameters for Large Brushless Doubly Fed Machines (BDFMs

This paper presents analytical methods to calculate the equivalent circuit parameters for large-s... more This paper presents analytical methods to calculate the equivalent circuit parameters for large-scale brushless doubly fed machines (BDFMs) with magnetic wedges utilized for closing stator open slots. The use of magnetic wedges reduces the magnetizing currents in the machine, reflected in the values of magnetizing inductances, but also increases leakage fluxes affecting the value of series inductances in the equivalent circuit. Though such effects can be modeled by numerical models, the proposed analytical methods are particularly helpful in optimizing machine design, inverter rating, reactive power management, and grid low-voltage ride-through performance. The conventional analytical methods cannot be readily applied to the BDFM due to its complex magnetic field distribution; this paper presents analytical methods to calculate the magnetizing and leakage inductances for the BDFM with magnetic wedges used in the stator slots. The proposed methods are assessed by experimentally verified finite-element models for a 250 kW BDFM.

DESIGN AND PERFORMANCE ANALYSIS OF A 6 MW MEDIUM-SPEED BRUSHLESS DFIG

The paper presents the design and performance analysis of a 6 MW medium-speed Brushless Doubly-Fe... more The paper presents the design and performance analysis of a 6 MW medium-speed Brushless Doubly-Fed Induction Generation (Brushless DFIG) for a wind turbine drivetrain. Two machines with different frame sizes have been designed to show the flexibility of the design procedure. The mediumspeed Brushless DFIG in combination with a two stage gearbox offers a low-cost, low-maintenance and reliable drivetrain for wind turbine applications.

The Brushless Doubly-Fed Machine Vector Model in the Rotor Flux Oriented Reference Frame

The paper presents the vector model of the Brushless Doubly-Fed Machine (BDFM) in the rotor flux ... more The paper presents the vector model of the Brushless Doubly-Fed Machine (BDFM) in the rotor flux oriented reference frame. The rotor flux oriented reference frame is well known in the standard AC machines analysis and control. Similar benefits can be sought by employing this method for the BDFM. The vector model is implemented in MATLAB/SIMULINK to simulate the BDFM dynamic performance under different operating conditions. The predictions from the vector model are compared to those from the coupled circuit model in simulation. The results are shown for the cascade mode of operation.

Dynamic Analysis of the Brushless Doubly-Fed Induction Generator during Symmetrical Three-Phase Voltage Dips

The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise as replacement for ... more The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise as replacement for doublyfed slip-ring generators for wind power applications by offering reduced capital and operational costs due to its brushless operation. In order to facilitate its commercial deployment, the capabilities of the BDFIG system to comply with grid code requirements have to be assessed. This paper, for the first time, studies the performance of the BDFIG under grid fault ridethrough and presents the dynamic behaviour of the machine during three-phase symmetrical voltage dips. Both full and partial voltage dips are studied using a vector model. Simulation and experimental results are provided for a 180 frame BDFIG.

Synchronous Operation Control Of the Brushless Doubly-Fed Machine

The paper presents a novel vector control structure for the Brushless Doubly-Fed Machine (BDFM) w... more The paper presents a novel vector control structure for the Brushless Doubly-Fed Machine (BDFM) which is derived based on the machine synchronous operation. In fact, the synchronous operation of the BDFM provides an efficient approach for determining the required reference angle in the machine vector control structure. The utilization of such reference angle makes the vector control structure presented in this paper different from and, in fact, more effective than the existing rotor flux and stator flux orientation schemes proposed for the machine. The results of implementing the vector control scheme in simulations confirm the effectiveness of the proposed approach for the BDFM control.

Asymmetrical Low-Voltage Ride Through of Brushless Doubly Fed Induction Generators for the Wind Power Generation

Compared with the Doubly fed induction generators (DFIG), the brushless doubly fed induction gene... more Compared with the Doubly fed induction generators (DFIG), the brushless doubly fed induction generator (BDFIG) has a commercial potential for wind power generation due to its lower cost and higher reliability. In the most recent grid codes, wind generators are required to be capable of riding through low voltage faults. As a result of the negative sequence, induction generators response differently in asymmetrical voltage dips compared with the symmetrical dip. This paper gave a full behavior analysis of the BDFIG under different types of the asymmetrical fault and proposed a novel control strategy for the BDFIG to ride through asymmetrical low voltage dips without any extra hardware such as crowbars. The proposed control strategies are experimentally verified by a 250-kW BDFIG.

Symmetrical Low Voltage Ride-Through of the Brushless Doubly-Fed Induction Generator

The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise for wind power gene... more The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise for wind power generation due to its lower cost and higher reliability compared to the Doubly-Fed Induction Generator (DFIG). For the purposes of commercialisation, the BDFIG must meet grid codes at all times. Nowadays, all new wind generators have to ride through certain grid faults, and the Low-Voltage Ride Through (LVRT) capability has become one of the most important points on which to assess the performance a generator. This paper, for the first time, proposes a control scheme to enable the the BDFIG to ride through symmetrical voltage dips. Simulation results and experimental results on a prototype BDFIG show that the proposed scheme gives the capability to ride through low voltage faults.

Stator-Flux-Oriented Vector Control for Brushless Doubly Fed Induction Generator

Brushless doubly fed induction generators (BDFIGs) show commercial promise for wind-power generat... more Brushless doubly fed induction generators (BDFIGs) show commercial promise for wind-power generation due to their lower capital and operational costs and higher reliability as compared with doubly fed induction generators. This paper presents a vector-control scheme for a BDFIG operating as a variable-speed generator. The proposed vector controller is developed on the power-winding stator-flux frame and can be used to control both the speed and the reactive power. The machine model and the control system are developed in MATLAB. The test results show that the proposed controller has good dynamic performance when changes in speed and reactive power are applied.

Generalized Vector Model for the Brushless Doubly-Fed Machine With a Nested-Loop Rotor

This paper presents a generic vector model for the brushless doubly-fed machine (BDFM) with a nes... more This paper presents a generic vector model for the brushless doubly-fed machine (BDFM) with a nested-loop rotor. The vector model is presented for a generic p 1 /p 2 pole-pair BDFM which may have any number of loops per nest. The vector transformations utilized in the derivation of the vector model are provided in general form such that the model can be represented in any appropriate reference frames according to the specific application of the model, such as BDFM analysis, simulations, or control system synthesis. The derived vector model benefits from the feature of reduced order in comparison with the coupledcircuit model, which is the most detailed model for the BDFM, while maintaining the accuracy by including the effects of all loops in each nest. The vector model is developed in MATLAB/Simulink based on the rotor reference frames for a 180-frame-size prototype BDFM, and its predictions for the machine performance have been compared with those of the coupled-circuit model as well as verified experimentally.

High-Performance Low-Cost Rogowski Transducers and Accompanying Circuitry

Rogowski transducers have become an increasingly popular method of measuring current within proto... more Rogowski transducers have become an increasingly popular method of measuring current within prototyping applications and power electronics equipment due to their significant advantages compared to an equivalent current transformer. This paper presents a simple and practical construction technique of high-performance low-cost Rogowski transducers and accompanying circuitry. Experimental tests were carried out to show the validity of the proposed construction technique.

Stable Operation of the Brushless Doubly-Fed Machine (BDFM

A simple method of controlling the Brushless Doubly-Fed Machine (BDFM) is presented. The controll... more A simple method of controlling the Brushless Doubly-Fed Machine (BDFM) is presented. The controller comprises two Proportional-Integral (PI) modules and requires only the rotor speed feedback The machine model and the control system are developed in MATLAB. Both simulation and experimental results are presented. The performance of the system is presented in the motoring and generating operations. The experimental tests included in this paper were carried out on a 180 frame size BDFM with a nested-loop rotor.

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