Frequency And Voltage Secondary Regulation And Power Distribution Control Method In Independent Microgrid

Building a new power system with new energy as the main body is an important means for China to orderly promote the goal of "carbon peak,carbon neutrality".Under this goal,new energy power generation will be rapidly developed in China.Distributed new energy power generation,such as photovoltaic and wind power generation,usually connect with the main grid in the form of microgrid,which can ensure the safe operation of the whole system.The microgrid has two modes of operation,the grid-connected mode,and the standalone mode.The voltage and frequency are determined by the main grid under the grid-connected mode,while the load disturbance will affect the voltage and frequency under the standalone mode.In order to maintain the voltage and frequency under the standalone mode,this paper proposes a secondary recovery control strategy for the voltage and frequency based on the virtual synchronous generator,the main contents include:(1)Firstly,this paper analyzes the control strategy of the inverter under the standalone mode.A mathematical model of three-phase two-level with dq rotating coordinate system is built;a dual-loop control structure,the voltage control loop as the outer loop and the current control loop as the inner loop is analyzed;the droop control and the virtual synchronous control is compared;a simulation model used to verify the analysis is built in MATLAB/Simulink.It is found that the output power of virtual synchronous generator varies slowly due to the existence of the virtual moment of inertia and damping factor.(2)In order to solve the voltage and frequency deviation caused by the load switching in standalone mode.this paper analyzes the performance of active power-frequency,reactive power-voltage,and describes the root cause of deviation of voltage and frequency under standalone mode.And then,a voltage and frequency recovery secondary control strategy is proposed,and the voltage and frequency can reach the rated value by the proposed control strategy.Finally,a simulation model is built in MATLAB/Simulink to verify the proposed control strategy.(3)The relationship between the output power of the inverter and the line impedance.And a power sharing control strategy is proposed based on the proposed voltage and frequency recovery secondary control strategy.a simulation model in MATLAB/Simulink is built to verify the proposed power sharing control strategy.(4)The last section summarizes the research contents of this paper and analyzes the future research direction.The secondary frequency modulation and power equalization strategies proposed in this paper can effectively improve the system stability degradation caused by large load switching or other large disturbance caused by virtual synchronous machine in an independent microgrid situation.It improves the stability of the new power system based on new energy,and improves the voltage amplitude,frequency and power of the isolated island microgrid system to a certain extent.