A Unified Inner Current Control Strategy Based on the 2-DOF Theory for a Multifunctional Cascade Converter in an Integrated Microgrid System

Abstract

Wider applications of integrated microgrids have been significantly restricted by converters with the sole function of power regulation. In microgrids with distributed generation and energy storage equipment, it is crucial for converters to be capable of reactive power compensation, harmonic suppression, voltage support, and other functions simultaneously. To achieve this, it is essential to modify the discrepancy between different control modes, both in control architectures and input signals. However, previous researches have focused on the stability and robustness of the system’s operation, rather than the instantaneous tracking performance of instructions during the mode switching. Instead, a unified control strategy based on the two-degree-of-freedom theory is conceived in this paper, to impose no reconfiguration of the inner current loop, so that the inherent stability can be guaranteed. In the proposed strategy, mode transition is replaced by the readjustment of referring instructions, and the complex tuning of filter parameters is abandoned. Thus, a desirable performance in a wide range of operating conditions for the microgrid system is provided and the effects of the disturbances associated with the mode transitions are eliminated. The simulations studied in MATLAB and experimental evaluations of the prototype both corroborate the simplicity and effectiveness.