DG control strategies for grid voltage unbalance compensation

With the high level penetration of power electronics interfaced Distributed Generation (DG) systems, applying these systems to compensate the grid voltage unbalance is becoming an important and interesting ancillary service for the utility. However, compensating the unbalance voltage leads to active power oscillation from the DG and may cause adverse effects of the DG operation. This paper proposes two DG control strategies for grid voltage unbalance compensation with reduced effects on the DG active power oscillation. In the first control strategy, the active power oscillation is fully cancelled at Point of Common Coupling (PCC). However, the level of unbalance compensation cannot be controlled directly in this method. Therefore, a second control strategy is proposed to minimize the active power oscillation (instead of completely cancel it) and with adjustable unbalance compensation level according to the DG available capacity. The validity of these two control strategies have been verified by case study results.