An improved control strategy for grid-connected voltage source inverters with an LCL filter

A novel current control strategy based on a new current feedback for grid-connected voltage source inverters with an LCL-filter is proposed in this paper. By splitting the capacitor of the LCL-filter into two parts, each with the proportional division of the capacitance, the current flowing between these two parts is measured and used as the feedback to a current regulator to stabilize and improve the system performances. Consequently, the V-I transfer function of the grid-connected inverter system with the LCL-filter is degraded from a third-order function to a first-order one, therefore the closed-loop current feedback control system can be optimized easily for minimum steady-state error and current harmonic distortion, as well as the system stability. The characteristics of the inverter system with the proposed controller are investigated and compared with those using traditional control strategies. Experimental results are provided, and the new current control strategy has been verified on a 5 kW fuel cell inverter.