Nonlinear current control strategy for grid-connected voltage source converters

Abstract

This work presents an enhanced proportional-integral- (PI) based current control strategy for voltage source converters (VSCs). While conventional solutions often employ the error between the desired and actual values of the current, the proposed method involves the nonlinear processing of the error signal. In particular, the square root value of the error is used to improve the steady-state performance. On the other hand, the quadratic value of the error signal is required to increase the dynamic response of the control system. This combined approach results in faster response, higher noise rejection, and achievement of proper stability margins. Unlike conventional nonlinear techniques, the introduced solution requires a simple tuning procedure and one can perform the stability analysis based on conventional figures of merit such as the gain margin (GM) and phase margin (PM) of the open-loop transfer function. The strategy is assessed by means of a grid-connected inverter used as an interface between a dc power source and the ac grid. It can be promptly extended to a wide range of practical applications involving current control loops as well. Experimental results are presented and thoroughly discussed to demonstrate the effectiveness of the proposed control technique.