Research On Control Strategy Of Doubly-fed Wind Power Generation Converter System Under Asymmetric Grid Voltage

With the development of wind power system, more and more researchers pay attention to improve power quality. Especially, the harmonic control has become the focus. This dissertation investigates the control and operation of DFIG under asymmetric grid voltage, and the mathematical model of machine side converter (MSC) and grid side converter (GSC) are respectively carried out. Moreover, simulation and experiment results were given to validate the feasibility of the control strategies.Firstly, the operation of DFIG wind generation has been introduced. The dynamic mathematical models of DFIG and GSC under symmetric and asymmetric grid voltage are built.Secondly, the control algorithm of the GSC under symmetric and asymmetric grid voltage is investigated. The symmetrical component method is employed to analyze the vectors under asymmetric grid voltage. After setting three control objectives in the case of asymmetric control strategy, each target control instructions are given respectively. Four kinds of positive and negative sequence component separation calculation methods are investigated for the asymmetric grid voltage, and comparisons are shown among these methods after practical experiments.For the theoretical analysis of partial verification, the operation of DFIG wind generation with different control strategies is simulated in MATLAB/Simulink. According to the simulation, the response of DFIG using traditional vector under symmetric grid voltage is investigated. And the simulation results confirmed the effectiveness of dual-dq current control and coordinated control.Thirdly, the influence of asymmetric grid voltage on the MSC is analyzed. More attention is on the MSC dual-dq current control investigation. Four control targets and the current director calculation are shown in the dissertation. Besides, the impact of rotor voltage imbalance is analyzed.Finally, experiments of GSC and MSC under some operating conditions are conducted on a90kW doubly-fed asynchronous generation test platform. Furthermore, the control effect of GSC and MSC under the asymmetric grid voltage condition is compared, and different control objectives are analyzed.