Yongqiang Lang

Power Conversion and Control of Wind Energy Systems: Wu/Power

Preface. List of Symbols. Acronyms and Abbreviations. 1. Introduction. 1.1 Introduction. 1.2 Overview of Wind Energy Conversion Systems. 1.3 Wind Turbine Technology. 1.4 Wind Energy Conversion System Configurations. 1.5 Grid Code. 1.6 Summary. 2. Fundamentals of Wind Energy Conversion System Control. 2.1 Introduction. 2.2 Wind Turbine Components. 2.3 Wind Turbine Aerodynamics. 2.4 Maximum Power Point Tracking (MPPT) Control. 2.5 Summary. 3. Wind Generators and Modeling. 3.1 Introduction. 3.2 Reference Frame Transformation. 3.3 Induction Generator Models. 3.4 Synchronous Generators. 3.5 Summary. 4. Power Converters in Wind Energy Conversion Systems. 4.1 Introduction. 4.2 AC Voltage Controllers (Soft Starters). 4.3 Interleaved Boost Converters. 4.4 Two-Level Voltage Source Converters. 4.5 Three-Level Neutral Point Clamped Converters. 4.6 PWM Current Source Converters. 4.7 Control of Grid-Connected Inverter. 4.8 Summary. 5. Wind Energy System Configurations. 5.1 Introduction. 5.2 Fixed Speed WECS. 5.3 Variable Speed Induction Generator WECS. 5.4 Variable-speed Synchronous Generator WECS. 5.5 Summary. 6. Fixed-Speed Induction Generator WECS. 6.1 Introduction. 6.2 Configuration of Fixed-Speed Wind Energy Systems. 6.3 Operation Principle. 6.4 Grid Connection with Soft Starter. 6.5 Reactive Power Compensation. 6.6 Summary. 7. Variable-Speed Wind Energy Systems with Squirrel Cage Induction Generators. 7.1 Introduction. 7.2 Direct Field Oriented Control. 7.3 Indirect Field Oriented Control. 7.4 Direct Torque Control. 7.5 Control of Current Source Converter Interfaced WECS. 7.6 Summary. 8. Doubly-Fed Induction Generator Based WECS. 8.1 Introduction. 8.2 Super- and Sub-synchronous Operation of DFIG. 8.3 Unity Power Factor Operation of DFIG. 8.4 Leading and Lagging Power Factor Operation. 8.5 A Steady-State Performance of DFIG WECS. 8.6 DFIG WECS Start-up and Experiments. 8.7 Summary. 9. Variable-Speed Wind Energy Systems with Synchronous Generators. 9.1 Introduction. 9.2 System Configuration. 9.3 Control of Synchronous Generators. 9.4 SG Wind Energy System with Back-to-back VSC. 9.5 DC/DC Boost Converter Interfaced SG Wind Energy Systems. 9.6 Reactive Power Control of SG WECS. 9.7 Current Source Converter Based SG Wind Energy Systems. 9.8 Summary. Appendix A. Per Unit System. Appendix B. Generator Parameters. Appendix C. Problems and Answers Manual.

A Multisampling SVM Scheme for Current Source Converters With Superior Harmonic Performance

The device switching frequency of current source converters (CSCs) in high-power medium-voltage applications is usually several hundred Hz. Selective harmonic elimination (SHE) has been the dominant modulation scheme because of its capability to eliminate unwanted low-order harmonics at low switching frequencies. Conventional space vector modulation (SVM), as another CSC modulation scheme, provides variable modulation index control but its output contains low-order harmonics with high magnitudes. In this paper, a multisampling SVM (MS-SVM) is proposed to substantially suppress the low-order harmonics in practical CSC-based drives. Investigation of the switching frequency of the proposed modulation method is carried out and methods to reduce additional switchings are developed. The proposed MS-SVM method exhibits a superior low-order harmonic performance comparable to that of SHE and provides the same fast and flexible control capability as the conventional SVM. Simulation and experimental results are provided to verify the proposed methods.

A Novel Reactive Power Control Scheme for CSC Based PMSG Wind Energy System

This paper presents a reactive power control scheme for Current Source Converter (CSC) based wind energy system using a Permanent Magnetic Synchronous Generator (PMSG). The novelty of the proposed scheme is to adjust d-axis current of the PMSG to achieve reactive power control for the utility grid. The principle of the control scheme is discussed, and theoretical analysis is provided. The effectiveness of the d-axis current control and its impact on the converter operation are investigated. The analysis shows that the reactive power of the wind energy system can be regulated in a wide range, from leading to lagging, by positive or negative d-axis current. Simulation results on a 2.47 MW CSC wind energy system are carried out, and the experimental verification is performed on a 2 kW laboratory prototype.

A Multi-sampling SVM Scheme for Current Source Converter with Superior Harmonic Performance

The device switching frequency of current source converters (CSC) in high power medium voltage applications is usually several hundred hertz. Selective harmonic elimination (SHE) has been the dominant modulation scheme because of its ability to eliminate unwanted low order harmonics at low switching frequency. Conventional space vector modulation (SVM), as another CSC modulation method, provides variable modulation index but its output contains low order harmonics with high magnitudes. In this paper, a multi-sampling SVM (MS-SVM) is proposed which substantially suppresses the low order harmonics. Investigation on the switching frequency of the proposed modulation method is carried out and methods to reduce additional switchings are developed. The proposed MS-SVM method exhibits a superior low order harmonics profile comparable to that of SHE and provides the same fast and flexible control capability as the conventional SVM. Simulation and experimental results are provided to verify the proposed method.

Dynamic performance analysis and improvements of a current source converter based PMSM wind energy system

In a current source converter (CSC) based wind energy system, the dc link current plays an important role in determining the system dynamic performance. This paper proposes two control strategies that can be used to improve the dynamic performance of the dc link current in a CSC wind energy system using permanent magnet synchronous machine (PMSM). State space equations and small-signal models of the system are developed, based on which the system dynamic behavior is investigated. It is demonstrated that the dc current of the proposed wind energy system can be controlled by either the rectifier or the inverter, but the latter provides much better dynamic performance and is therefore recommended for practical implementation. The system performance can be further enhanced by introducing a damping control to suppress possible LC resonances caused by the generator- and grid-side LC filters. Computer simulation and experimental results are provided to verify the theoretical analysis.

Reactive Power Control of Current Source Converter based Wind Energy System

In this paper, a PWM current source converter is proposed for high-power wind energy system using a Permanent Magnetic Synchronous Generator (PMSG). The current source converter normally requires filter capacitors on its ac side, which may affect power factor of the system. A decoupled active/reactive power control algorithm is proposed for the grid-side power factor adjustment. The dc current reference is generated in a way to meet the requirements from both sides. In addition, Field Oriented Control theory is used for the wind generator control. Experiments on a small-scale laboratory have been carried out to verify the analysis and experimental results are presented.