Hybrid variable-structure control with evolutionary optimum-tuning algorithm for fast grid-voltage regulation using inverter-based distributed generation

Fast grid-voltage regulation is a necessary requirement in a power distribution system, particularly in feeders serving voltage-sensitive loads. Severe and random voltage disturbances might be initiated by time-varying loads, nondispatchable generation, voltage transients associated with parallel connected loads, and voltage transients caused by capacitor switching. These voltage disturbances are stochastic in nature, with durations vary from a fraction of a cycle to few cycles. To ensure perfect regulation of the voltage at the point of common coupling (PCC) and provide means for rejecting voltage disturbances, the voltage control loop should offer a high disturbance rejection performance. This paper presents a newly designed grid-voltage control scheme, for the distributed generation interface, based on a hybrid linear with variable-structure control voltage controller. 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 voltage disturbances, can be rejected. To optimally tune the proposed nonlinear voltage controller, the tuning problem is formulated as a constrained optimization problem, and solved via an evolutionary search algorithm based on the particle-swarm-optimization (PSO) technique. Therefore, a simple and structured tuning methodology can be obtained. To provide accurate and robust tracking of the generated reference current trajectory, a newly designed robust deadbeat current control algorithm is adopted. Theoretical analysis and comparative evaluation tests are presented to demonstrate the effectiveness of the proposed control scheme.