Study On The Stability Of Virtual Synchronous Generator Based On Island Mode

New energy power generation using distributed power generation technology is a supplement to centralized power generation.However,as the penetration rate of new energy power generation in medium and low-voltage distribution networks and microgrids gradually increases,it poses many challenges to maintaining the safe and stable operation of the power system.By introducing the inertia and damping characteristics of the traditional Rotational Synchronous Generator(RSG)into the inverter control system,the Virtual Synchronous Generator(VSG)control technology was born from this,effectively improving the new System stability after energy is connected to the grid.This paper takes VSG as the research object under island mode operation,mainly focusing on the mechanism of static stability and transient stability of VSG and the corresponding control strategy.This article first introduces the basic structure and core control principles of VSG,including: the main circuit topology of the VSG inverter and its control system.The core control unit of VSG includes: active power-frequency controller,reactive power-voltage controller and RSG stator voltage equation.In addition,the voltage and current double closed-loop control is introduced into the VSG control system and the dq decoupling design is carried out on it.The LC filter and voltage and current closed-loop parameters of the virtual synchronous generator are designed.Secondly,when the VSG suffers from small disturbances,the constant virtual moment of inertia cannot meet the requirements of frequency dynamic response performance in different operating periods.For this reason,this paper improves the adaptive control of the virtual moment of inertia based on the advantages of previous designs.By adjusting the virtual inertia of different periods,the frequency dynamic response characteristics of the VSG after being disturbed during island operation are improved,and the frequency is better balanced.The contradiction between rapid response and suppression of frequency oscillation.And through Matlab/Simulink simulation to compare the other two adaptive inertia control strategies,it is verified that the improved control strategy proposed in this paper can further take into account the fast response of frequency and the performance of suppressing frequency oscillation.Finally,because VSG has external power output characteristics similar to RSG,when the system fails,VSG has a transient instability risk similar to RSG.In this paper,the transient stability of the parallel virtual synchronous generator is analyzed based on the extended equal area criterion(EEAC),taking into account the current limiting link and damping coefficient of the VSG inverter.A compensation control strategy is introduced to reduce the equivalent mechanical power of the dual-machine system by compensating the reference value of the active power to achieve the goal of improving the transient stability of the parallel virtual synchronous generator.Finally,the electromagnetic transient simulation based on Matlab/Simulink verifies the stability analysis of the parallel virtual synchronous generator and the rationality of the proposed control strategy.