H∞ robust control with improved harmonics suppression for inverter-based distributed generation systems

Voltage source inverter is a key element in an inverter-based distributed generation (DG) system for the integration of renewable energy resources with an existing power grid. Interconnection standards for the requirements of inverter output current quality are one of the foremost demands imposed by distribution system operators. The operation of a stabilised DG system withLCL-filter meeting current quality requirements is challenging due to variation in system parameters and non-ideal grid voltages. In this context, this study proposes a robust H-infinity controller design and modified control structure to improve current quality in the presence of distorted grid voltages. The H-infinity controller is designed based on general mixed sensitivity problem formulation to achieve robustness against system parameters variation and ensure high-quality injected current under normal grid voltage. The control performance of the designed robust controller with a feed-forward loop is investigated under distorted grid voltage. Furthermore, an inverter current compensation is proposed, employed by an additional inverter current feedback loop through the high-pass compensator. The current quality investigation with variation in different parameters and low power operation shows enhanced control performance of the proposed solution under distorted as well as normal grid voltages. The main features of the proposed scheme are the simplicity in design, easy implementation, and better harmonics rejection capability without limiting the control loop stability. The simulation and experimental results validate the effectiveness of the proposed method.