Optimal control strategy of UPQC for minimum operational losses

The paper deals with a new control technique for a Unified Power Quality Conditioner (UPQC), which is the most comprehensive of FACTS devices. The problems of power quality continue to gain in significance because of the proliferation of sensitive and harmonic producing loads in electrical networks, Greater awareness among customers with regard to supply integrity and a desire by suppliers to be able to guarantee a certain degree of power quality to customers is being reflected in the development of innovative power quality solutions. The UPQC, which is a combination of shunt and series compensation, is designed to cater for multiple power quality problems. The shunt compensator provides VAR compensation to the load. It also provides harmonic isolation between the load and the utility supply. The series compensator regulates the incoming voltage quality from the supply side, and keeps the load end voltage insensitive to the supply voltage problems like sag/swell or unbalance. All these quality controls are achieved simultaneously. A comprehensive control technique has been designed based on the VA loading of the two compensators, such that minimum VA loading of the two compensators is ensured. This has been achieved by pre-calculating a suitable angle of injection voltage for the series compensator. This also minimises the operational losses of the UPQC. The design details are elaborated and verified with appropriate simulation results.