New Control Strategy Of LCL-type Three-phase Inverter System Based On The Correction Of Grid-side Current

Compared with single L filter,LCL filter is widely used in three-phase power grid system. Using LCL filter can diminish the volume and the power loss of filter while effectively filtering out high harmonic wave[1,2]. However,LCL filter has the resonance problem while working because of its characterof low impedance. To solve the resonance of LCL filter,people mention the methods of active damping and passive damping. The most classic method is series resistance on the Capacitor branch in the way of passive damping,which can effectively control the stability of system[3]. But it will bring a large loss and bad influence on filter effect of high frequency by series resistance in grid-connected photovoltaic system,and adding the burden of the system’s running. The most particular method is virtual resistance among the ways of active damping which replace the passive damping resistance by control arichmetic[4].However,this way brings differential,which makes control arichmetic more complex and the running of system instabale.To solve above questions, this paper methions a new control strategy of introduce the correction of grid-side current based on traditional control strategy of single induction.In an ideal situation,the current of the side of invertor is equal to the current of grid-side.So,getting the correction of grid-side current by PI controller which error coming from comparing grid-side current to setting current goes through,while current of the side of invertor is used to be feedback current in current inside loop.At last,introducing the grid current correction into controller of inner loop,this strategy can restrain LCL filter resonance and improve the current quality.To introduce the information of grid-side currect,we have to add current sensor at grid-side,which no doubt adds cost of prudence of invertor.So,this paper make up reduced-order state observer based on Modern Control Theroy,and analyzing the astringency of reduced-order state observer[5].at last,discretizing that state observer by backward euler[6].Finally,this new tragedy has been test by simulation on matlab/simulink platform and experiment on phasical experiment based on chip of DSPTMS320F2812.The result of simulation and experiment prove the effectiveness and feasibility of the new tradegy that introducing the correction of estimated grid-side current by reduced-order state observer into current inside loop.