Research On Parallel Operation Of Inverter Based On Virtual Synchronous Generator

With the increasing number of distributed generation in large.scale power grid,Inverter parallel has become the trend of power development for power system to increase capacity demand.At the same time,better control algorithms should be used in the overall control of the system.The VSG control algorithm can not only provide the same inertia and damping characteristics as the power grid,but also find the internal correlation between P-f and Q-V based on the characteristics of Inverter parallel structure.It can control the voltage and frequency of the system and enhance the stability of the power grid.Therefore,for the Inverter parallel structure of distributed generation,this paper studies the VSG control algorithm which is more optimized than the traditional algorithm.First of all,the detailed mathematical modeling analysis of the inverter system based on VSG is carried out,and the control system is designed on the basis of this research.The power control loop uses VSG control algorithm,can be achieved without communication power allocation in Inverter parallel system,and the control method according to equation Q-V droop rated voltage output voltage reference value,provide the corresponding values for the voltage loop;The collected AC quantity is converted to a constant DC quantity.The Park and Clark transformation are introduced to simplify the mathematical model analysis,and the model of voltage and current regulator in complex frequency domain is established,and the design basis of each regulation parameter is given.Secondly,through the analysis of the VSG mechanical equation and electromagnetic torque equation,a clear excitation control simulation model and an active FM simulation model are established.Simulation experiments on a single VSG control algorithm verify the influence of active power frequency modulation and reactive power regulation droop characteristics and the degree of inertia on the system's frequency dynamic characteristics.Through the analysis of the drawbacks of the traditional Inverter parallel system,the innovation of this paper is introduced: the introduction of virtual impedance in the traditional parallel control system.Through the analysis of the equivalent impedance of the circuit before and after adding the virtual impedance,it is concluded that adding virtual impedance into the system can reduce the resistance to inductance ratio of the circuit,and greatly improve the performance and the power sharing accuracy of the control system.At the end of this paper,a Inverter parallel system with virtual impedance,which is based on VSG,is proposed to simulate the Matlab/Simulink experiment.It is verified that the VSG control strategy with virtual impedance added in this paper not only applies to two Inverter parallels of the same capacity,but also applies to two Inverter parallel control systems with proportional distribution capacity.