Research On Control Algorithm Of Multi-functional Grid-connected Inverter In Consideration Of Power Quality

In distributed generation system,grid-connected inverters are widely used as interfaces between renewable energy sources and middle and low-voltage distribution system.Due to the large use of nonlinear power electronic devices in modern distribution systems,coupled with the small capacity of the distribution system and the variety of loads,there exist various power quality problems at the point of common coupling.On the other hand,the random and intermittent characteristics of renewable energy output lead to the fact that grid-connected inverters are often unable to operate under rated output conditions.To solve the above problems,this paper proposes a control algorithm of multi-functional grid-connected inverter,which can effectively improve the capacity utilization of the grid connected inverter and the power quality of the distribution network.By taking three-phase three-wire LCL type grid-connected inverter as an example,the topology and current control model of a multi-functional grid-connected inverter are introduced in this paper.On this basis,a reference current generation algorithm and a corresponding control strategy are given in detail.In order to compensate the load current quickly and accurately,a kind of current control method based on modified repetitive controller is proposed in this paper.The modified repetitive controller is composed of a proportional controller and a traditional repetitive controller connected in parallel,and an equivalent controlled object is used for analyzing the stability,steady state error and dynamic performance and designing the parameters of the modified repetitive controller.By using MATLAB/Simulink simulation platform,the dynamic response performance and the steady state tracking performance of the modified repetitive controller are verified.On the basis of theoretical analysis,the hardware experiment platform of multi-functional grid-connected inverter is built afterwards.The main circuit building work includes components selection and circuit connection according to the system function requirements.And designing and developing of control system is mainly accomplished based on TMS320F28335,including the DSP minimum system designing,peripheral circuit configuration,writing and debugging software of control system.At the end of this paper,the dynamic response performance and the steady state tracking performance of the modified repetitive controller are further verified on the hardware experiment platform.And experiments of harmonic current compensation,reactive current compensation,negative sequence current compensation and dynamic improvement of power quality are also carried out.Experiment results show that the proposed modified repetitive controller can track reference current fast and accurately,and multi-functional grid-connected inverter has an excellent ability to enhance power quality.