Research On Control Strategy Of Photovoltaic Grid Connected Operation Based On Virtual Synchronous Generator

There is no rotating equipment in photovoltaic power generation system,which directly shows the characteristics of low damping in operation.When a large number of photovoltaic power generation systems are connected to the grid,the oscillation time is too long and the oscillation amplitude is too large.Therefore,high penetration photovoltaic power grid is prone to reduce stability and weak interference ability.This paper studies the control strategy of grid connected operation of photovoltaic power generation system,and puts forward the control strategy that meets the requirements of system damping,which is of great significance to further improve the stability of photovoltaic high penetration power system.Based on the basic principle of photovoltaic power generation,this paper expounds the low damping problem of power system caused by the low voltage ride through function of photovoltaic power generation system.In order to overcome the problem of damping reduction caused by a large number of grid connected photovoltaic power generation systems,a control strategy based on virtual synchronous machine is proposed.Based on the analysis of the working characteristics of synchronous generator,the synchronous virtual control topology of photovoltaic system is established.The virtual topology divides the photovoltaic control system into three parts: virtual rotor,virtual high speed device and virtual exciter,and proposes the virtual control algorithm of each part.The simulation model of photovoltaic power generation system and its virtual synchronization control strategy is established,and the simulation analysis is carried out from two aspects: large disturbance during grid connected operation and low voltage ride through during fault.The simulation results show that when large disturbance or low voltage ride through occurs,the active and reactive power output fluctuation of the PV system with virtual synchronous control strategy is smaller.This means that the photovoltaic power generation system has a larger damping system,which can suppress the impact of large disturbance on the power system and make the system show stronger stability.The control strategy based on virtual synchronous generator of photovoltaic power generation system proposed in this paper can improve the damping of photovoltaic power generation system,make the photovoltaic output have the output characteristics of synchronous machine,improve the transient stability of power system,and further improve the strength of photovoltaic high penetration power system.