Study And Realization Of Frequency Converter For Doubly-Fed Wind Power System Based On DSP

As energy sources consume increasing daily and environmental pollution being serious gradually, it is meaningful to exploit renewable and clean wind energy. Countries all over the world have been competing to develop the technology of this field. Among all these technologies, Variable Speed Constant Frequency (VSCF) double-fed wind power system is the most widely used. Based on this system, back to back PWM converters can realize the maximal energy capturing from the wind.Compared with conventional cycloconverters, back-to-back PWM converters have better input and output performances, less harmonic currents and a wider frequency adjustment range. The grid-side converter diverts the rotor power to or from the grid using a DC-link between the two converters. The rotor-side converter is responsible for independent regulation of active power and reactive power output from the stator of the doubly-fed induction generator (DFIG) and maximal wind energy capturing. So VSCF double-fed wind power generation system has been mainly applied nowadays. This paper takes the operation and control of VSCF double-fed wind power generator system as the research subject, focuses on the study of the rotor-side converter, develops an experimental platform of VSCF double-fed wind power generator system, which is controlled by TI’s DSP chip TMS320F2812.First, this dissertation analyzes the principle of the wind turbine’s wind energy absorption and maximal wind energy capturing, and conducts research on the vector control scheme. Then a double closed-loop PI control scheme is established, which is based on the d-q reference of the grid-side three phase PWM converter, in order to stabilize the DC voltage and realize the unit power factor operation. Then this dissertation analyzes the DFIG operation theory, including mathematic model of DFIG and coordinate transformation, which establishes the theoretical foundation for succeeding study. In order to realize decoupled control of DFIG active & reactive power and to capture the maximal wind power, field oriented vector control technique is applied to DFIG control. A general control strategy based on stator-flux oriented vector control is proposed as well. Based on the analysis of existent techniques of wind generator grid-connection, this dissertation discusses the grid-connection control principle which fits for the occasion of AC excited VSCF generator, and two kinds of control schemes which can be called grid-connection control with no-load and grid-connection control with isolated load are put forward. Meanwhile, a new idea using the DTC (Direct Torque Control) in the variable speed wind power system is proposed, which controls the double-fed machine more directly and improves the whole system’s characteristics.In order to study the control method of the dual-PWM converter, an experiment platform of VSCF doubly-fed wind power generation system is established. It is designed with intelligent power module (IPM) as the core device, together with the DSP controller, drives of the IPM, signal sampling and the protection circuit. And the control algorithm software is written by fixed-point C code that interfaces with assembly language functions so that it can be amended and replanted easily. VSCF technology, synchronizing control and power decoupled control are studied experimentally in the co-design view of hardware and software. The experimental results testify the validity of the theory and show the accuracy, stability of the experimental platform, which is beneficial for the further study on the control technology of the variable speed wind energy generation.