Investigation on the performance of UPQC-Q for voltage sag mitigation and power quality improvement at a critical load point

The unified power quality conditioner (UPQC) is one of the major custom power solutions, which is capable of mitigating the effect of supply voltage sag at the load end or at the point of common coupling (PCC) in a distributed network. It also prevents the propagation of the load current harmonics to the utility and improves the input power factor of the load. The control of series compensator (SERC) of the UPQC is such that it injects voltage in quadrature advance to the supply current. Thus, the SERC consumes no active power at steady state. The other advantage of the proposed control scheme is that the SERC can share the lagging VAR demand of the load with the shunt compensator (SHUC) and can ease its loading. The UPQC employing this type of quadrature voltage injection in series is termed as UPQC-Q. The VA requirement issues of SERC and SHUCs of a UPQC-Q are discussed. A PC-based new hybrid control has been proposed and the performance of the UPQC-Q is verified in a laboratory prototype. The phasor diagram, control block diagram, simulations and experimental results are presented to confirm the validity of the theory.