Impact Of Photovoltaic Power Generation Systems On Short-Term Voltage Stability Of Power System

Short-term voltage stability of power system refers to the ability of the system to maintain voltage stability in a short time under large disturbances.Dynamic load is the main cause of short-term voltage stability at load side in power system,such as induction motor.Reasonable and clear analysis of short-term voltage stability caused by induction motors is one of the important contents of research.In addition,with the continuous development of new energy generation system,the grid-connected capacity of photovoltaic power generation system is constantly improving.The power system will be affected by the dynamic behavior of high penetration distributed photovoltaic power generation system,such as fault disconnection,low voltage ride through.Therefore,it is necessary to analyze the influence of the dynamic behavior of distributed photovoltaic power generation system on short-term voltage stability,so as to find out the behavior mode of photovoltaic power generation system which is conducive to short-term voltage stability.Based on induction motor model and simple system model,the speed-critical voltage curve and the speed-operating voltage curve are obtained respectively.Then a method based on critical voltage curve of induction motor and operating voltage curve of load side is proposed to analyze short-term voltage stability of the system.When the induction motor can run to the acceleration region or its minimum speed is still higher than the critical speed after the fault,the load side voltage can restore stability.The feasibility and correctness of the proposed method are verified by simulation experiments of different mechanical torques.Finally,the influence of induction motor parameters on short-term voltage stability is analyzed by using critical speed.The analysis results show that the smaller the parameters of induction motor load ratio,stator resistance,stator reactance,rotor reactance and excitation reactance are,the better the stability of the load side voltage is maintained.The larger the rotor resistance of the induction motor is,the better it is to keep the voltage on the load side stable.The proposed analysis method provides a basis for the subsequent analysis of the impact of photovoltaic power system dynamic behavior on short-term voltage stability.Early photovoltaic power generation systems were disconnected after large disturbances,which often resulted in serious consequences for the power system.In recent years,photovoltaic power generation systems have been equipped with low voltage ride through and dynamic voltage support capabilities to help power system recovery after large disturbances.In this paper,low voltage ride settings for distributed photovoltaic systems are presented based on the existing low voltage ride requirements of distributed power and large and medium-sized photovoltaic power plants.Using the simplified simulation system and the proposed dynamic analysis method of short-term voltage stability,the influence of dynamic behavior of distributed photovoltaic power generation system on short-term voltage stability is simulated and analyzed.The results show that the active power recovery of photovoltaic power generation system with low voltage ride through capability after fault clearance will help the system voltage recovery,and the maximum reactive power provided by photovoltaic power generation system with dynamic voltage support capability after fault clearance can also help the system voltage recovery.Photovoltaic power generation system with traditional dynamic voltage support provides reactive power after fault.Research shows that active power supply also plays a role in voltage rise.Based on the Thevenin equivalent circuit of the system,the active and reactive power allocation modes of the photovoltaic power generation system with the optimal load side voltage rise effect are derived.A method based on equivalent impedance parameter allocation for active and reactive power of photovoltaic power generation system in dynamic voltage support process is proposed.Simplified system simulation results show that the optimal dynamic voltage support mode of photovoltaic power generation system can also contribute to system voltage recovery.When the ratio of system resistance to reactance is large,this new dynamic voltage support capability will make voltage recovery faster and better than the traditional dynamic voltage support capability.This dynamic voltage support method is applied to 220kV isolated network in a city,and its effectiveness is simulated and analyzed.