Research On Power Distribution And Voltage Compensation Strategy Of Multi-inverter Parallel System

With the accelerated expansion of power,distributed generation has become an inevitable development trend.At the same time,in order to adapt to the energy development strategy,improve the penetration rate of new energy,and put forward new requirements for distributed power generation,the microgrid control technology developed in recent years has received extensive attention.Different from the traditional power grid,the micro grid can operate in the grid-connected mode and the island mode,and can achieve smooth switching between the grid-connected and island mode under the corresponding control strategy.In island mode,the system voltage and frequency are only stabilized by their internal micro-sources.However,due to the difference in line impedance between micro-sources to the common bus,the load at the local or common point of the micro-source,and the nonlinear load,there will be large fundamental and harmonic circulation in the micro-grid,thus reducing energy.The utilization rate may even threaten the safe and stable operation of the microgrid when it is serious.In this paper,the multi-inverter parallel system in island mode is taken as the research object.The parallel power distribution and voltage compensation control strategy of multi-inverter is studied.The main research contents and innovations are as follows:(1)Briefly introduce the background and significance of the research,and compare and analyze the parallel fundamental power,harmonic power distribution method and voltage compensation strategy of the inverter at the current stage.(2)The main circuit topology of current-mode and voltage-type inverters is analyzed.The parallel system and equivalent model of three-phase voltage inverter are given.Two kinds of nonlinear loads of voltage source and current source are analyzed.The equivalent model of two inverters with parallel nonlinear load is established.The mathematical model of the inverter under abc,dq and αβ coordinate system is established,and the fundamental wave and harmonic power in the case of inverter parallel connection are Analyzed.(3)The multi-inverter parallel fundamental power allocation control strategy is studied.A power distribution method based on adaptive voltage shift and a voltage drop compensation strategy are proposed.A small-signal mathematical model of two three-phase inverter parallel systems based on improved droop control is established.By setting up simulation comparison analysis under different working conditions,the results show that the proposed method is robust and can solve the loop current and output voltage amplitude drop problem of multi-inverter parallel system based on droop control.(4)The problem of unreasonable harmonic power distribution and PCC point voltage distortion between inverters in multi-inverter parallel system with non-linear load operation is studied.According to the existence of inverter harmonic equivalent transmission impedance,the voltage harmonics at PCC and the equivalent transmission impedance difference between parallel inverters cause the harmonic power to be distributed according to a predetermined ratio.Combined with virtual impedance technology and consistency algorithm,A voltage harmonic suppression method combining harmonic virtual impedance with a multi-resonance PR controller and a harmonic power distribution method based on distributed adaptive virtual impedance.(5)The system experimental platform is introduced,and the experimental platform design process is given.The power distribution control based on voltage shift,the voltage drop compensation strategy and the harmonic adaptive power distribution based on distributed adaptive virtual impedance are tested and verified.The feasibility of the method proposed in this paper.