Research On The Excitation Control Of Doubly-fed Induction Wind Generator

Energy source scarcity and environment pollution are getting more and more serious due to the dramatic development of economy, and our country is stranded in this problem as well. In order to quest the energy source without pollution that can be exploited and utilized by large scale. It stands in the breach to develop and utilize wind power. With the increasing scale of wind power generation system, the power generation technique has been focused on improving the efficiency of wind power generation. For this reason, it has the absolute advantage to adopt the technique of variable speed constant frequency (VSCF).This dissertation makes study for the excitation control of VSCF doubly-fed induction generator (DFIG) by rounded simulation analysis. First, a novel control strategy is presented for double-fed wind generator's no-load cutting-in based on the field-oriented vector control technique and integral variable structure control (IVSC) according to analyze the existing techniques of cut-in control for wind generator. The control system consists of two current controllers using IVSC and a voltage deviation controller based on changing integration rate. With this control strategy, system exhibits strong robustness to many kinds of disturbances in global range and best dynamic performance. The second, the characteristics of dual PWM converter, which is used for DFIG excitation, and the difference between rotor-side converter and grid-side converter in control and function aspects is discussed. In order to achieve the purposes of constant DC-link voltage and bidirectional power flow for the grid-side converter of double-fed wind generator, a method of hysteretic current control with voltage space vector modulation method (VSM-HCC) and voltage PI control based on changing integration rate is proposed. Furthermore, simulation study was carried out with VSCF wind generation system. At last, the research of DFIG output active and reactive power decoupled control after connected to power system is studied.An integrated simulation model of AC excited VSCF wind power generation system is founded using PSCAD. Based on this model, the simulation research of the no-load grid-connection control, the grid-side converter control and DFIG output active and reactive power decoupled control are carried out. The results of simulation testify the validity of the theory and the control strategy proposed by this dissertation.