The Control Strategy Research On Photovoltaic Power Generation System In Microgrid

Microgrid is constituted of the distributed generation,storage,load and control device.It is a controllable system and can be flexible and efficient to utilize PV power generation.PV power generation on grid side is changed into a control unit,so it overcomes the fluctuation of PV power generation that it directly affects grid.The control strategy of PV inverter is the key to ensure the stable operation in microgrid at different modes.At network mode,the traditional Droop control strategy of PV inverter can not guarantee the output of consistent power of PV power generation system forward and backward,and it affects the stable operation of PV inverter.This paper selects two levels three-phase PV power generation system in microgrid as the research object.The improved Droop control strategy and PQ control strategy of PV inverter are researched in microgrid.Firstly,PV microgrid model based on the equivalent control of AC type and PV-ES microgrid model based on the master-slave control of AC type are respectively designed at PSCAD platform.The DC-DC part model based on MPPT of PV power generation system is built.The simulation verifies the effectiveness of the MPPT control algorithm adopted.Secondly,PV microgrid model based on the equivalent control is established.At network mode,considering the frequency fluctuation of grid and the pressure drop of the transmission line impedance,it leads to the inconformity of the output power of PV inverter and DC-DC part,which affects the stable operation of the system.The paper adopts the improved Droop control,which is compared with the output power of PV array,and the difference value is regulated by PI unit,then it is put into the Droop control.It guarantees the stable operation of the PV inverter.In order to reduce the fluctuation of mode switch,the synchronous control in advance is proposed.The simulation results show that the improved control strategy achieves the stability of the DC voltage and the output power of P V inverter at network mode.And it satisfies the requirements of the stable operation in microgrid.The adopted synchronization control in advance implements the smoothness of mode switch,and verifis the correctness and effectiveness of the proposed control strategy.Finally,in order to efficiently make use of energy of PV-ES microgrid based on master-slave control,the PQ control strategy of PV inverter is respectively researched at the network mode and the island mode.The simulation results show that the output power of microgrid is stable at the network mode;energy storage system supports the voltage and frequency of microgrid and balance power in microgrid at island mode.They realize the control of energy and good dynamic regulatory at the network and island mode.This paper demonstrates that the PQ control strategy of PV inverter is effective.