Study On Control Strategy Of PMSG Wind Power Generation System Based On Z-source Inverter

Wind energy because of its large reserves,no pollution,mature technology has gradually become one of the focus of the new energy sources in the world.In the wind power generation system,the inverter is responsible for the conversion of DC power into AC power.But the traditional voltage inverter because of its inherent structure can only achieve buck inverter output,at the same time,in order to avoid the situation of the bridge pass through the up and down arm,so will join the dead time,which will reduce the quality of output waveform.And the z-source inverter used its own unique Z-source network to coupling with the traditional inverter,and use the pass through zero vector to achieve the system's single-stage boost or buck,from,to make up the lack of traditional voltage inverter,and expand the range of output.This article will put the three-phase Z-source inverter into permanent magnet direct-drive wind power generation system,will improve the quality of the grid.Firstly,this article analyzed the basic working principle of the three-phase Z-source inverter and the abnormal working condition of the three-phase Z-source inverter.The grid-connected parameters of the three-phase Z-source inverter have been designed.The grid topology of three-phase Z-source inverter has been analyzed,and its mathematical model have been established in three-phase stationary coordinate system and two-phase rotating coordinate system.Then,the closed-loop control strategy of Z-source capacitor voltage outer loop control and current inner loop control is adopted in this article for the situation of the normal grid voltage,so can achieve connect to network by the unit power factor for the Z source wind power generation system.In the case of the grid voltage occurs three-phase symmetry drop,this article analysis flow of power,the energy crowbar circuit in parallel with the Z source network input,so can achieve the system's low voltage through,thereby can maintain a constant Z-source capacitor voltage and obtain a stable AC side current.Then,a grid-connected control method based on the model predictive control of the three-phase Z-source inverter for the permanent magnet direct-drive wind power system is presented in this paper.For the characteristics of the three-phase Z-source inverter,the 9 switch states of the three-phase Z-source inverter are rolling calculated by the predictive model in each sample period.The appropriate switch state can be selected according to the principle of minimizing the cost function and then be delivered to the inverter bridge without a modulator.So the capacitor voltage of Z-source and the active power of the grid can be control successfully by this method,and the unity power factor running can be realized.Last,simulation model is built up in matlab/Simulink.The results show that the capacitor voltage of Z-source and the active power can be directly control with good dynamic performance by using the MPC.The correctness and validity of theoretical analysis have been verified by the simulation.