Research On Control Strategy Of Microgrid Inverter Based On Improved Virtual Synchronous Generator

As a buffer link between new energy and power grid,microgrid can concentrate multiple complementary energy sources into one system.Microgrid can solve the problems of low predictability and instability caused by the high proportion of multiple types of new energy access to the network,while improving the power quality,power supply reliability and operating economy of the power grid.Power electronics inverters,as carriers of clean energy and large grid energy interactions,have received widespread attention for their control methods.When a grid fault occurs in the grid,the microgrid inverter adopts off-grid operation mode(island operation).In this operating mode,a virtual synchronous generator(VSG)technology is often used to control the inverter.At this time,the inertia and impedance parameters of the inverter system can be optimized using VSG technology.This technology can improve the shortcomings of low damping and low inertia caused by the high proportion of new energy entering the grid.The traditional VSG control is adopted,the power electronic inverter has the operating characteristics of a synchronous generator:it supports the microgrid voltage and frequency stability,and provides inertia buffer energy for the microgrid.However,there are the following disadvantages:the control performance of power adjustment and frequency adjustment cannot be taken into account,so that the optimization of frequency adjustment will bring a large energy impact to the microgrid system.The output frequency of the microgrid inverter is susceptible to changes in the load,so that when the control system cannot obtain the command parameters of the host computer due to a communication failure,the sudden change of the load will cause the frequency to deviate from the grid standard value.In order to solve the above-mentioned shortcomings of VSG control technology,this paper systematically studies the traditional VSG technology,analyzes the influence of the moment of inertia and damping coefficient on the performance of the inverter system,and proposes an improved VSG moment of inertia adaptive control method.This method changes the value of the VSG moment of inertia in real time with reference to the change of the output frequency,so that the frequency adjustment and power adjustment of the inverter reach the optimal value of the control cycle.While establishing Matlab simulation,a microgrid inverter prototype based on DSP28335 was built to test and verify the proposed method.The results show that the control method can reduce the impact of sudden changes in load on the inverter output frequency and reduce power oscillations to reduce the energy impact of power regulation on the microgrid inverter.In order to optimize the output power quality of the inverter and improve the dynamic performance and steady-state performance of the inverter output voltage regulation,this paper proposes an improved repeated PI double-loop control method.This method embeds improved repetitive control in the current loop of the traditional voltage and current loop.The improved repetitive control is based on the repetitive control in parallel with a feedforward broadband link.Matlab simulation and prototype tests are carried out on the proposed control method.The simulation results and experimental data show that the improved repeated PI double-loop control method can effectively reduce the higher harmonic content in the bus voltage and reduce the distortion rate of the converter output current;improve the voltage and current The steady-state performance and dynamic performance of the loop improve the anti-interference performance.of the control system.Fully demonstrated the superiority and feasibility of this control method in the field of converter application.