Research On Harmonic Suppression Of Grid-Connected Inverter Based On FFT

Solar energy,as a new type of energy,has the characteristics of renewable,wide source and pollution-free.It is recognized as one of the important energy sources in the 21 st century.Photovoltaic solar power generation is the main way to use solar energy resources.In the process of converting solar energy into electricity,photovoltaic inverters play a bridge role in the middle.As the interface between distributed generation and power grid,photovoltaic inverters transmit distributed generation active power to the grid.At the same time,how to use grid-connected inverters to suppress harmonics generated by non-linear loads has become the current research characteristics.Based on the research of grid-connected technology of distributed generation and the principle of grid-connected inverters and active filters,a micro-inverters with harmonic suppression function is designed in this paper.Firstly,the harmonic detection method of power system based on fast Fourier transform(FFT) is introduced,and the feasibility of the improved detection method is verified by simulation.According to the characteristics of FFT operation,after the signal is sampled by AD zero-crossing sampling,the unsigned fixed points can be obtained without converting to the signed binary fixed points again,and the calculated parameters such as the fundamental wave and the amplitude and phase of each harmonic wave do not change.At the same time,the FPGA has high-speed parallel digital operation ability,so FFT is implemented on the FPGA.Preparing for subsequent experiments.Secondly,the paper elaborates the topology of the micro grid-connected inverter,i.e.its control principle,and designs a grid-connected control strategy with closed-loop PI control as the core and grid voltage as feed-forward compensation.The simulation model of grid-connected control of two-stage micro-inverters is established by Simulink,and the effectiveness of the grid-connected strategy is verified.Finally,combined with the harmonic detection method and grid-connected control method mentioned above,and according to the working principle of active filter,a harmonic compensation method is proposed.The harmonic compensation current and the fundamental current of power grid constitute the setting value of PI controller.This compensation method does not need to change the subsequent filter circuit of the inverters,but only needs to change the control algorithm of the system to realize the inverters transmission.Output harmonic suppression.Then an experimental prototype of micro-inverters is designed to verify the compensation method of harmonic compensation for grid-connected inverters.The experimental results show that it can achieve the function of harmonic suppression.