Off-grid Type Inverter Control Strategy Research For Small Wind Power Systems

The rapid development of renewable energy is beneficial to solve traditional energy crisis and the environment pollution problem.As a clean energy,Wind power has drawn much attention on its technology.In order to reduce the supply pressure of the remote mountainous areas,important stations and urban areas,small and independent wind power system has been the developing direction because of its merits of clean,easy to install and maintenance.This paper focuses on the control strategy of inverter on the base of the small off-grid wind power generation system.In this paper,the various parts of the wind power system is first introduced,and the inverter technology and its control strategy is analyzed emphatically;The single-phase/three-phase inverter topology structure is determined and the mathematical model is established.The details of the inverter modulation method are presented and the LC filter is designed.Then,on the basis of the mathematical model of single-phase inverter,the inverter is controlled using compound repeat + PI control strategy.There is coupling term in the mathematical model of three-phase inverter in the dq coordinate system,which has an influence on the harmonic content of output waveform.While there is no coupling term in the ?? coordinate system and it saves the trouble of Park's Transformation.Therefore,the repeated + PI compound control strategy in the ?? coordinate system is proposed,which improves the ability of the dynamic response of the inverter control system as well as the steady-state performance.Finally the corresponding controller is designed.The single phase inverter is simulated under the repetitive control,PI control,PI compound control strategy respectively.In comparison of their results,the repeated +PI compound control strategy is verified,which can improve the overall performance of the inverter control system.The output waveforms of the three-phase inverter using repetitive control,repetitive +PI control compound control strategy are also compared It can be seen that the output waveforms are improved obviously and the dynamic and static characteristic effect is well.Besides,the harmonic content of output waveforms are analyzed under the compound control strategy and the distortion factor is less than 2%,which meets the requirement of control.