Research On Stability Improvement And Control Methods Of Photovoltaic Grid-Integration Based On MGP System

The large-scale substitution of grid-connected converters for traditional synchronous machine power sources has led to the increasingly obvious phenomena of reduced inertia,insufficient reactive margin,and voltage instability or even collapse at the grid connection points in new energy grids.The resulting frequency and voltage stability issues on power grids cannot be ignored.Currently,the measures to improve the stability of new energy grids are basically adding compensation equipment or improving converter control.However,due to the high investment and strong pertinence of additional equipment,and the insufficient transient support capacity of converters,the existing solutions have certain limitations in terms of economy,effectiveness,or ease of implementation.To address the above issues,this paper uses a photovoltaic(PV)system as an example to study the mechanism and effects of using a motor-generator pair(MGP)to improve system stability,and proposes improved control methods.The main research contents of this article are as follows:1)The effects of MGP on improving the frequency stability of PV systems.The DC voltage feedback control method for the PV system via MGP is analyzed,the loss characteristics of the MGP system and the effects of improving the frequency stability of the PV system are studied,and the experimental verification is also conducted.Then,the reactive power transmission characteristics of MGP system under different excitation conditions are analyzed in categories;2)The effects of MGP on improving the static voltage stability of PV systems.Combined with the calculation example,the V-Q and P-V characteristic curves of the grid-connected PV and the PV-MGP system are compared and analyzed by simulation,and the key indicators of the static voltage stability of two systems are calculated.The results show that the static voltage stability and reactive power margin of the system are improved after the PV is connected to the grid through the MGP.Further,for the MGP system using automatic exciter,its improvement effect on static voltage stability is analyzed;3)The improved control method for PV-MGP systems.Based on the fuzzy control algorithm,two controllers and corresponding control strategies for PVMGP systems are proposed,and simulation models are established to verify their effects.The results show that the overshoot and recovery speed after fluctuation of the two fuzzy control strategies are superior to traditional DC voltage feedback control strategies.Through the study of this paper,the mechanism and improvement effects of the MGP on the frequency and static voltage stability of the grid-connected PV system are revealed,and combined with the improved control strategy,it lays the foundation for the better application of the MGP to PV integration.