Research On Control Strategy Of Virtual Synchronous Generator Under Voltage Unbalance

As more and more users are connected to the power grid,the structure of the power system becomes more and more complex,and the probability of various faults and sudden changes in the power grid is also increasing.In order to improve the stability of virtual synchronous generator(Virtual Synchronous Generator,VSG)output of virtual synchronous generator in the case of power grid failure,this dissertation mainly analyzes the current distortion and power fluctuation in the case of power grid voltage imbalance.First,this dissertation analyzes the basic structure and control principle of VSG,and introduces the VSG control algorithm.The calculation method of related parameters of LC filter and the control of active power-frequency and reactive power-voltage under island-connected and grid-connected working conditions are given.In order to output stable voltage and current,the voltage and current double closed-loop control module is adopted.Then,in order to adapt to the power change,a self-correcting fuzzy control is used for the adaptive adjustment of damping coefficient and rotational inertia.By introducing the self-correcting parameter N,the quantization factor in the virtual parameter fuzzy control is scaled,and a flexible error normalization process is formed,so that the fuzzy cybernetics domain can adapt to the angular frequency error,and provide the system with damping and inertia that can adapt to the transient state change.Then,the operation of VSG under voltage imbalance is analyzed deeply.The traditional balance current method is improved.According to the topology structure,using the inverter circuit parameters,the positive sequence reference current is calculated,reducing a group of PI controllers.The negative sequence current is controlled by Proportional Integral Reducted Order Quasi-Resonance(PIROQR)controller based on the double frequency characteristic of negative sequence component.The output current balance,active power fluctuation suppression and reactive power fluctuation suppression are realized under VSG unbalanced state.Finally,the VSG control model is built by Matlab/Simulink,and the effectiveness of the virtual parameter adaptive method based on self-correcting fuzzy control is verified when the load changes in the island-mode.And when the grid voltage is unbalanced,the improved current control method can achieve the output current balance,active power fluctuation suppression and reactive power fluctuation suppression respectively.