Research On Power Quality Governance Of Micro-grid Based On Grid-connected Inverter

Along with development of human civilization,electricity has gradually become the cornerstone of all industry,also the lifeline of the human daily life.Due the large-scale power outage around the world,the lack of fossil energy such as coal,oil,and the seriousness of the greenhouse effect,electricity experts push forward the grid system to improve the energy structure,ensure the quality of power supply,optimize the development environment.Athough it has inproved global power structure are greatly improved,but with micro grid access to distribution network,multi-network integration rapid development,many technical problems needs to be solved.Among them,serious power quality problem which caused by discontinuity of distributed power supply in micro grid and the use of a large number of power electronic switching devices is quite significant.Based on the complexity of power quality in micro grid,this paper proposes a new harmonic and current compensation scheme of micro grid based on multi-function grid-connected inverter,which not only realizes the integration of renewable energy,but also improves the power quality function of common coupling point.It has certain economy and feasibility.This paper deeply analyzes the working principle of the inverter and the control strategy in the MG,and find many inverter system do not reach the rated capacity when it work at current transformation model.Combining with the inverter digital control features,considering using digital signal processing(DSP)chip to control it,the paper makes full use of the residual capacity of grid inverter to implement harmonic and grid instruction current compensation,abandoning the traditional governance additional equipment,finally the strategy has a fair degree of economy.Firstly,the discrete domain transfer function of the controlled object was obtained through the research and comparison of various MFGTI topologies,and its system characteristics were further analyzed.At the same time,the grid-connected and isolated island operation characteristics of the micro-grid were fully researched by combining the distributed power supply,load,energy storage and other devices in the micro-grid,and various inverter control strategies were summarized.Secondly,reference current component detection algorithm used to compensate harmonic is studied in many aspect from the time-frequency transform,coordinate transformation,and filter decomposition,artificial intelligence and so on.Then the paper analyzes the shortcomings of a variety of strategies,concluded that the algrithem based on Fourier algorithm and the instantaneous reactive power theory are better in the precision of the strategy,system design,feasibility from time-frequency conversion,coordinate conversion,filter decomposition,artificial intelligence and other aspects.After that the paper propose interconnection of instruction current calculation based on Clarke transform and discrete Fourier transform of harmonic component calculation improvement strategies by considering the accuracy,complexity,digital realization,micro network environment characteristics.The theoretical study shows that the method can accurately and selectively calculate the specific order harmonics by means of the sliding window frequency shift and phase correction,and at the same time save a lot of calculation.Finally,due to the excellent tracking performance of PR controller for specific frequency signals,the parameter selection,delay compensation and discrete digital realization of the controller are studied and designed.Based on MATLAB/Simulink software,this paper designs the model of grid-connected operation of micro grid,and conducts simulation experiments from various harmonic components,grid-connected command current and other aspects.The results have demonstrated that the proposed method are robust and accurate in the case of highly distorted environments.