A Control Scheme for PWM Voltage-Source Distributed-Generation Inverters for Fast Load-Voltage Regulation and Effective Mitigation of Unbalanced Voltage Disturbances

This paper presents a control scheme for grid-connected pulsewidth-modulated voltage-source inverters (VSIs) featuring fast load-voltage regulation and effective mitigation of unbalanced voltage disturbances. To ensure perfect regulation of the voltage at the point of common coupling (PCC) and provide means for rejecting fast and dynamic voltage disturbances, the frequency modes of the disturbances to be eliminated should be included in the stable closed-loop system. Toward this, a hybrid voltage controller combining a linear with variable-structure control element is proposed for an inverter-based distributed-generation interface to regulate the voltage at the PCC. The proposed voltage controller can embed a wide band of frequency modes through an equivalent internal model. Subsequently, a wide range of voltage perturbations, including capacitor-switching disturbances, can be rejected. To account for unbalanced voltage disturbances, a dual-sequence voltage controller is proposed. To provide accurate and robust tracking of the generated active and reactive current trajectories, a newly designed deadbeat current control algorithm is proposed. The controller is designed under the practical considerations of inherent plant delays, which are associated with the digital implementation of the control algorithm, and the uncertain nature of the current dynamics. Theoretical analysis and comparative evaluation tests are presented to demonstrate the effectiveness of the proposed control scheme.