A Novel Control Strategy For Grid-Connected Inverter System Based On LCL Filter

In order to prevent harmonic pollution in public power grid form the ripple wave caused by grid-connected inverter system, a filter would be inserted between the inverter system and the public grid. Formerly, single L filter can meet major requirements of the filtering performance. Because of the characteristics in stability,single L filter have been wildly used. With the power of grid-connected inverter growing and the demand of power quality promoting, the claim of filtering performance of the filter is increasing. Comparing with single L filter, LCL filter demonstrate its unique properties.As well as single L filter, LCL filter get the same performance in low-frequency stage, but in the high-frequency stage, LCL filter have better damping capacity and the better ability to restrain the ripple near switching frequency. Besides that, LCL filter needs smaller inductance, it means that the volume and weight of the grid-connected inverter would decreasing, costs would be saving. But, LCL filter is a three-level system,a sudden maximum gain appears at high frequency, it affect the stability of the inverter system seriously.Aiming at the problem of LCL resonance, on the basis of passive damping and active damping, a method of adding the grid-side current correction to the inverter-side current reference to strengthen it for resonance elimination. This control strategy can not only restrain LCL resonance peak, but also do not increase the extra system loss and system stable operation would be realized, On the other hand, the current into grid would e corrected and the steady state error would be reduced.This paper analyses and introduces the control strategy detailly in the theoretical level, expands it through Photovoltaic grid connected inverter and Active power filter.On the other hand, this paper studies different parameter design methods of LCL filter aiming at different application objects and applies to the prototype of physical experiment platform. Finally, the feasibility of the control strategy has been prove by the matlab simulation and experiment platform based on DSP2812.