Research On Control Technology Of Three-phase Multi-function Grid-connected Inverter

Vigorously developing renewable energy such as wind power and solar energy,and gradually replacing renewable energy with conventional energy are important ways for China and the world to solve the energy shortage and achieve sustainable development.As the penetration rate of renewable energy in the power grid continues to increase,grid faults and power quality problems have become increasingly prominent.Therefore,according to the new grid-connected requirements,photovoltaic grid-connected inverters must have low voltage ride through(LVRT)capabilities.In order to improve the utilization of grid-connected inverter capacity,the multi-function grid-connected inverter with power quality control function has attracted extensive attention from scholars at home and abroad.The three-phase multi-function grid-connected inverter is used as the research object,and its low voltage ride through and power quality control strategy is studied.In this paper,a three-phase photovoltaic grid-connected inverter mathematical model is established in the two-phase stationary coordinate system;a current loop control strategy based on quasi-proportional resonance(PR)control is adopted to realize the three-phase photovoltaic system grid-connected power generation function.And quasi-PR controller parameters is designed.In the case of grid faults,a three-phase photovoltaic grid-connected inverter low-voltage ride-through control strategy is adopted.By injecting positive and negative sequence reactive power,the positive sequence voltage of the common coupling point(PCC)is raised,and its negative value is reduced on the basis of the current limit,thereby reducing the degree of system unbalance.Considering the influence of a large number of non-linear loads in the distributed system on the power quality of the power grid,A three-phase multi-function grid-connected inverter control scheme with dual functions of low voltage ride through and power quality control is proposed,which is based on the analytic hierarchy process(AHP).According to different control objectives,the Lagrange multiplier method is used to determine the optimal compensation factor for reactive power compensation in the harmonic current compensation and low-voltage ride-through control strategy in the load current,in order to make full use of the standby capacity of the grid-connected inverter.The three-phase multi-function grid-connected inverter has achieved flexible customization for fault crossing and power quality control.Finally,based on MATLAB/Simulink and dSPACE hardware-in-the-loop simulation system,the above control strategies were simulated and experimentally verified.The simulation and experimental results prove the feasibility and practicability of the proposed control strategy.