Research On Control Strategy Of Inverter Current Based On Virtual Synchronous Generator

With the expansion of energy demand and the surge of environmental protection pressure,renewable energy in the form of distributed generation has attracted extensive attention.As a composite system including distributed power generation,microgrid improves the absorption capacity of renewable energy and the flexibility of distributed power generation into the power grid,but its characteristics of small inertia and small damping will have an adverse impact on the system.The grid connected inverter has inertia and damping support.Due to the virtual synchronous generator（VSG）technology,the characteristics of synchronous generator are simulated,solves the shortcomings of small inertia and damping of microgrid,and reduces the impact on the system during grid connection.Taking microgrid grid connected inverter as the research object,this paper focuses on the control strategy based on VSG.Firstly,the basic principle of synchronous generator is introduced,which leads to the VSG control strategy,and the power frequency controller and excitation controller of VSG algorithm are designed.Then the three-phase full bridge inverter is modeled.In order to avoid the complexity caused by coordinate transformation and control decoupling,the current loop structure under two-phase static reference system is designed,and finally the parameters of LC filter in the main circuit are selected.VSG pre synchronization grid connection model is established.In view of the deterioration of grid connected current quality caused by grid impedance perturbation and the improvement of grid connected current tracking performance under disturbance,an H_∞robust current controller is designed.Firstly,the state space model of LC grid connected inverter including impedance perturbation is established,the impedance perturbation range is selected,the hybrid sensitivity weighting function is selected,and the generalized controlled object is established,Finally,the designed H_∞robust current controller is obtained by MATLAB programming.The controller can improve the harmonic suppression ability of grid connected current under grid impedance perturbation and improve the tracking performance of grid connected current under disturbance.Aiming at the problem that the voltage feedforward of the power grid under the weak current network will introduce a positive feedback path to the current loop and the weak current network contains a large number of background harmonics,a combined filter feedforward strategy is designed.The strategy adopts the form of low-pass filter and notch filter in series.The low-pass filter can maintain a high bandwidth response,and the notch filter can filter out a specific number of harmonics,So as to suppress the harmonic of grid connected current.Finally,in order to simulate and analyze the above control strategies,the VSG simulation model is built in Matlab/Simulink to verify the reliability and correctness of the control strategy.