Coordinated Control Strategy Research Of Multi-functional Grid-connected Inverter For Three-phase Four-wire System

Since the emergency of the energy crisis and social problems,utilization of the new energy has been effectively.The technology of using new energy to generate power is more and more mature,the large wind farm and photovoltaic solar plant have been established.It is one of the focused aspects to make small capacity plants access to power grid without the harmonic and reactive power influence.The emergency of the micro grid provide a useful method to access distributed generation to power grid.The micro grid contained lots of renewable energy sources,energy storage,local load,monitoring protection and control unit is a special distributed generation and a local power supply system.It is now in a wide research.To reduce the influence of the harmonic and reactive power,we normally use passive filter to compensate the demand of the grid.Because of passive filter's bad filtering effect and compensating capacity is fixed,active power filter(APF),static var compensator(SVC),static var generator(SVG)and so on has been widely used.But active filter device is always expensively,it is unsuited to be applied to small distributed generation.It is not difficult to find there are lots of grid inverters in micro power grid,if we can use grid inverter to compensate the affect of accessing micro grid to power grid when it is working in grid-connected condition,we can improve the power quality of point of common coupling without additional cost.Grid-connected inverter and APF have the same topological structure,the main difference reflected in the control strategy.The major research of this paper is using grid-connected inverter of micro grid to harness the aspects of harmonic and reactive power when it is working in grid-connected condition,aimed at decreasing the harmonic and reactive power influence for low-voltage network.The research topic of this article is using three-phase four-leg grid-connected inverter to harness affects of reactive power,harmonic and unbalanced current in micro grid.Firstly,this paper introduces the background and meaning of study,analysis some problems which exists in now research,and introduce a detailed research contents.Then,we analysis the topology structure of three-phase four-leg grid-connected inverter and establish the corresponding mathematical model.We analyze the inverter control strategy and emphasis the algorithm of command current.Command current contains two parts,one part of it is grid-connected current order,another part is harmonic current order.Grid-connected current order is used to control inverter to the function of generation using new energy,and harmonic current order is used to compensate the quality of electric energy in micro power.Finally,we make inverter get higher efficiency by using strategy of optimum compensation in inverter.This paper use MATLAB/Simulink to build the whole system,and the simulation results show these algorithms are effective,and give a simulation result of strategy of optimum compensation.Finally,we give the experiment results conducted by RT-lab.All of the results show the validity and efficiency of control strategy proposed in this paper.