State-feedback current control of VSI-based D-STATCOM for load compensation

This paper presents a closed-loop control technique for the D-STATCOM, aiming at load balancing as well as load power factor correction. Compensation for the oscillatory components of the active and reactive powers of an unbalanced load requires the D-STATCOM to inject unbalanced three-phase currents to the power network. For this purpose, the compensator current references would contain an ac component on top of the dc value in the rotating-reference-frame. As a result, the closed-loop current control of the device would become different from that under balanced condition. In this paper, a state-feedback-based current controller is proposed and the engaged pulse width modulation is enhanced by dynamically modification of the switching duty ratios to tackle the dc-side voltage oscillations effects. The whole method, including the control technique and the modulation compensation, is simulated by using PSCAD/EMTDC software to demonstrate the validity of the proposed approach.