ABSTRACT
The Unified Power Quality Conditioner (UPQC) is relatively the latest device in the family of the custom power devices. UPQC is a versatile custom power device which consists of two inverters connected back-to-back with a common DC-link and deals with both load current and supply voltage compensation. One voltage source inverter is connected in series to inject the required voltage and another voltage source inverter is connected in shunt with the load to compensate current. Thus, the main purpose of the UPQC is to compensate for supply voltage flicker/imbalance, reactive power, negative-sequence current and harmonics. UPQC's capability of correcting the voltage and current at the point of installation on power distribution systems or industrial power systems makes it the most powerful solution to power quality issues.
The basic configurations and modes of operation of the UPQC are discussed in this chapter. It is shown that the UPQC is a combination of the shunt and series compensators connected through a common dc link. The shunt compensator, also termed as shunt voltage source inverter (shunt-VSI), compensates for the unbalance and harmonics in the load currents. The series compensator, termed as series-VSI compensates for the voltage unbalance and harmonics. Two important configurations of UPQC, i.e., left shunt UPQC and right shunt configurations are illustrated. Later on, the right shunt UPQC structure is discussed in more detail to compensate for the unbalance and harmonics in voltage and currents. The instantaneous symmetrical component theory is used to obtain the reference currents for the shunt compensator to make source currents balanced sinusoidal quantities. For voltage compensation, Type-1 and Type-2 control schemes are discussed to extract reference voltages. These reference currents and voltages are realized using appropriate switching control strategies of shunt and series inverters. The concepts are illustrated through examples with different source voltages and current conditions.
