Research On Droop Control Of Microgrid Inverter Based On Virtual Synchronous Generator Technology

The microgrid efficiently organizes distributed power generation devices,energy storage power conversion systems,and loads to avoid the adverse effects of distributed power generation instability and real-time fluctuations on the system.As a hub for the energy exchange between the energy storage device and the microgrid,the microgrid inverter has a fast response and almost no inertia.When the load changes,the frequency and voltage vary widely.If the microgrid inverter is controlled to simulate the inertia and damping characteristics of the synchronous generator,the frequency and voltage fluctuations are delayed when the load changes,and the stable operation of the system is ensured,that is,the virtual synchronous generator technology.Due to the microgrid inverter using virtual synchronous generator technology,its active-frequency regulation and reactive-voltage regulation are essentially droop control.The coefficients of the active droop curve and the reactive droop curve are constant,and the large droop coefficient makes the system frequency and voltage shift larger,which is not conducive to the stability of the system;the small droop coefficient makes the response speed of the system slow,and the adjustment time is lengthened.The dynamic performance of the system deteriorates.In the off-grid mode,when the power variation range is large,since the conventional droop control is a single-slope droop curve,the frequency and voltage offset of the micro-grid under the new steady state is large.To this end,a virtual synchronous generator control strategy with segmented droop coefficient is proposed.When the power is widely changed,the system output frequency and voltage amplitude change are smaller than the traditional control strategy.In this paper,the synchronous generator is mathematically modeled,and then the carrier three-phase voltage inverter realized by the virtual synchronous generator is studied,and the specific equivalent algorithm of the virtual synchronous generator is realized.Thirdly,in analyzing the relationship between active-frequency and reactive-voltage,and studying the influence of several important parameters on frequency characteristics,an active-frequency controller and a reactive-voltage controller are designed for the improved virtual synchronous generator control strategy.The virtual synchronous generator simulation model is established by Matlab/Simulink platform.The traditional and improved control strategies are compared to verify the effectiveness of the improved virtual synchronous generator control strategy.Finally,a 3kW microgrid inverter based on virtual synchronous generator technology is designed,and the circuit of the hardware implementation platform is designed and the control algorithm is written in software.