Research On Control Strategy Of DFIG For Wind Power Generation Under Low Switching Frequency Conditions

With the development of different types of new energy grid-connected power generation(eg,photovoltaic,wind power systems)systems,more opportunities has been brought for the application of high-power inverter has brought.However,in these high-power low-switching frequency inverter applications,on one hand,how to select the reasonable control method is used to reduce the switching frequency,on the other hand,how to obtain the better control performance to reduce switching losses is the study hot and difficult..This paper is based on the principle of finite state set model predictive control(FCS-MPC)and the difference between the two control methods,showing that the better control effect could be achieved at low switching frequency.In order to reduce the influence of the one-step delay in the predictive control on the system,one-step prediction is replaced by two-step prediction,and the results shows that the two-step prediction can improve the transient response speed of the system.In order to establish predictive current control model and predicts the value of the future time according to the predicted trajectory based on the current voltage sampling value at the time of history,the mathematical model of the doubly fed wind power generation system is established under the normal condition of the grid with a state variable of grid-connected system output current.This paper also proposes a corresponding switching frequency optimization algorithm designed to reduce the switching frequency.In the stability analysis of MPC control system,the discrete Lyapunov function is established and the stability of the control system is determined according to the equilibrium state of the system.The other is to establish MPC-DFIG doubly-fed system discretization closed-loop transfer function,the stability of the control system can be determined through the distribution of zero-pole,showing that the important reason for the stability of the control system is that the model predicts the degree of parameter matching from the analysis result.Secondly,when the harmonic voltage appears on the grid,the state feedback equation of the capacitor voltage can be added on the basis of the original model to effectively suppress the fifth and seventh harmonic currents of the stator and rotor of the doubly-fed machine,and through the control with the traditional PR Method,and the results show the advantages of multi-target control method...