Optimal Use Of Energy-Storage For Series Connected Voltage Source Converter

Abstract

The continuous growth in the use of sensitive equipments in modern power system requires great emphasis on the quality of the power. The quality related issues like voltage sags, swells, surges, interruptions and harmonic problems lead to a great economic loss in the power industry and needs urgent actions. To ensure the reliable and stable operation of the power system, Flexible AC Transmission System (FACTS) controllers at transmission level and custom power devices at distribution level are employed. In practice, the Dynamic Voltage Restorer (DVR) is a key device for mitigation of power quality phenomena at distribution level. DVR is series connected voltage source converter and is used to inject missing voltage of controllable magnitude and phase angle between the Point of Common Coupling (PCC) and the load. Prime goal of this thesis is to optimize energy storage for series connected compensator. Active power injected by DVR is related to its energy storage so optimization of DVR active power leads to optimization of energy storage.Two types of voltage sag mitigating strategies Energy Optimization Compensation (EOC) and pre-sag considering zero phase angle jumps were studied and results were obtained by using simulation tool PSCAD/EMTDC. Two cases were considered depending upon sag depth for analyzing EOC method. When sag is shallow one, active power injected by DVR is equal to zero which reveals the optimization of energy storage. When sag is deep one, active power injected by DVR is minimum as compared to pre-sag but not zero. Effects of phase angle jump on the power and energy requirements by using EOC method were also studied. DVR energy injection increases having voltage sag of positive phase jumps whereas its energy injection reduces when voltage sag is having negative phase angle jumps.