A Novel Decoupling Control Approach for Improving Dynamic Performance and Stability of Multiple Grid-Connected Converters

Abstract

The control plant model of multiple grid-connected converters is a multivariable coupling model. There is complex coupling interaction between the control loops of the multiple converters, resulting in poor current control quality or interaction oscillation issues when the grid impedance is high or the number of converters is large. This paper proposes a new multivariable decoupling control method based on a summation difference coordinate for eliminating the current control interaction between multiple converters. With a summation difference coordinate transformation matrix, the multivariable model of multiple converters can be transformed to be multiple single-variable models. By designing specific current regulators for the summation current and the difference current loops in the summation difference coordinate, the summation current and each difference current can be regulated independently. Compared to the conventional methods, the proposed method can improve the current control bandwidth without introducing any high-frequency oscillation especially when the grid impedance is high or the number of converters is large. Moreover, based on the proposed approach, the classical single variable control theory is enough to design the regulator parameters for any number of converters under the new coordinate system. Experimental results of four three-phase 2kW two-level converters have validated the propose approach.