Research On Compensation Three-phase Four-wire Photovoltaic Grid-connected Inverter With Unbalanced Load

In the future diversified energy structure,the proportion of photovoltaic power generation will gradually increase.If the photovoltaic power generation can be integrated into the existing public power grid,the mutual flow of energy through the inverter needs to be realized.However,unbalanced loads can have a large impact on power quality.Based on this background,this paper studies a three-phase four-wire unbalanced compensation inverter system suitable for photovoltaic grid-connected type,which realizes the compensation for the balance of the three-phase four-wire power supply network and the energy exchange between the microgrid and the power supply network.The thesis analyzes the working principle of the three-phase four-wire inverter and designs an unbalance compensation system based on a diode-clamped three-level inverter under the condition of three-phase unbalance.The double closed-loop control method and dual carrier are adopted.The modulation strategy of SPWM,and the method of generating the zero-sequence current separation instruction signal with integrated photovoltaic grid-connected function is applied to the compensation control scheme to realize three-phase balanced compensation and active power exchange between the system and the grid.In this paper,based on the experimental system of photovoltaic grid-connected inverter with unbalanced three-phase four-wire compensation load,the main circuit hardware selection,control circuit design and DSP digital control program design of the experimental system are completed based on DSP TMS320F28335.Finally,a simulation model was built using MATLAB/Simulink software.The designed three-phase unbalance compensation was completed for purely resistively balanced loads,purely resistively unbalanced loads,inductively balanced loads,inductively unbalanced loads,and unbalanced harmonic loads.System simulation research and analysis.The simulation results show that the compensation system based on the zero-sequence current separation method achieves better three-phase unbalance compensation.The compensation device is not limited by the specific load type and has good compensation performance.At the same time,it is verified that the system can realize active exchange with the grid when there is no load.