A simple approach to improvement in performance of UPQCin presence of unbalanced load

This paper proposes a simple control technique for Distributed Generation fed Unified Power Quality Conditioner (UPQCdg) in presence of unbalanced load. Compensation of unbalanced load causes second order ripples in DC link voltage of UPQCdg, which leads to ripples in reference current estimated by PI controller, and eventually unbalance & harmonics in source currents. This paper proposes use of a mean block at output of PI controller to prevent ripples passing onto reference current. Selection criterion of proposed mean block is discussed. Also, a `percentage unbalance' parameter is proposed for computing unbalance in three phase quantities and comparing among different cases. Performance of proposed technique is validated using Real Time Digital Simulation (RTDS) in Opal-RT. Steady state performance of proposed technique is verified in presence of non-linear and unbalanced loads, and dynamic performance is tested during voltage sag, swell, change in load and variation in solar irradiation. RTDS results express superiority of proposed method over conventional one.