A Control Scheme of the DG Interface for Fast Load Voltage Regulation and Effective Mitigation of Unbalanced Voltage Disturbances

This paper presents a control scheme for grid-connected pulse-width-modulated (PWM) voltage-sourced 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 (VSC) element is proposed to for an inverter-based distributed generation (DG) 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, 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 current trajectory, a newly designed deadbeat current controller is adopted. Theoretical analysis and comparative evaluation tests are presented to demonstrate the effectiveness of the proposed control scheme.