Design and optimum-tuning of a linear with variable-structure voltage control scheme for the distributed generation interface

This paper presents a control scheme for grid-connected PWM voltage source inverters (VSIs) featuring fast load voltage regulation and effective mitigation of fast voltage disturbances. To ensure perfect regulation of the voltage at the point of common coupling, and provide means for rejecting voltage disturbances, the voltage control loop should offer a high disturbance rejection performance. Toward this, a hybrid voltage controller combining a linear with variable-structure control (VSC) element is proposed to generate the reactive current reference in a grid-connected VSI. 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 transients, 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. Theoretical analysis and comparative evaluation tests are presented to demonstrate the effectiveness of the proposed control scheme.