Multi-Level Inverter Based UPQC for PQ Enhancement of Distribution System Under Contingencies

Abstract

Distribution systems are prone to faults, voltage unbalance, and harmonics since there is a tussle of loads, particular-ly power electronic based. Unified Power Quality Conditioner (UPQC) is a versatile power conditioner dedicated to distribu-tion systems since it can mitigate almost all types of PQ issues. Conventional-UPQC (C-UPQC) is designed with three-phase VSC. However, it is unable to mitigate the unbalance in the system completely, and the distortion in voltage and current wave-forms still exists. To address the above issues, in this paper, UPQC is designed using a Multilevel Inverter (MLI) with a Neu-tral Point Clamped (NPC) based converter topology generating 5-level inverter output. In this paper, modified NPC topology is presented in which the capacitor connected across all three phases of the inverter is reduced, and a balance in capacitor voltage is obtained by employing the SPWM carrier-based modulation technique. The proposed NPC-MLI-UPQC is designed using the right shunted topology to protect the source profile from harmonics injection via non-linear loads. The control of MLI is so designed to obtain the harmonic-free output. The performance of the proposed NPC-MLI-UPQC has been analyzed for linear non-linear for the various contingencies generated due to fault conditions resulting in sag as well as swell in voltage.