Multiconverter Unified Power-Quality Conditioning System: MC-UPQC



This paper presents a new unified power-quality conditioning system (MC-UPQC), capable of simultaneous compensation for voltage and current in multibus/multifeeder systems. In this configuration, one shunt voltage-source converter (shunt VSC) and two or more series VSCs exist. The system can be applied to adjacent feeders to compensate for supply-voltage and load current imperfections on the main feeder and full compensation of supply voltage imperfections on the other feeders. In the proposed configuration, all converters are connected back to back on the dc side and share a common dc-link capacitor. Therefore, power can be transferred from one feeder to adjacent feeders to compensate for sag/swell and interruption. The performance of the MC-UPQC as well as the adopted control algorithm is illustrated by simulation. The results obtained in PSCAD/EMTDC on a two-bus/two-feeder system show the effectiveness of the proposed configuration.


  1. Power quality (PQ)
  3. Unified power-quality conditioner (UPQC)
  4. Voltage-source converter (VSC)



Fig. 1. Typical MC-UPQC used in a distribution system.

Fig. 2. Control block diagram of the shunt VSC.

Fig. 3. Control block diagram of the series VSC.


Fig. 4. BUS2 voltage, series compensating voltage, and load voltage in Feeder2.

Fig. 5. Nonlinear load current, compensating current, Feeder1 current, and capacitor voltage.

Fig. 6. Simulation results for an upstream fault on Feeder2: BUS2 voltage, compensating voltage, and loads L1 and L2 voltages.

Fig. 7. Simulation results for load change: nonlinear load current, Feeder1 current, load L1 voltage, load L2 voltage, and dc-link capacitor voltage.

Fig. 8. BUS1 voltage, series compensating voltage, and load voltage in Feeder1 under unbalanced source voltage.


In this paper, a new configuration for simultaneous compensation of voltage and current in adjacent feeders has been proposed. The new configuration is named multi converter unified power-quality conditioner (MC-UPQC). Compared to a conventional UPQC, the proposed topology is capable of fully protecting critical and sensitive loads against distortions, sags/swell, and interruption in two-feeder systems. The idea can be theoretically extended to multibus/multifeeder systems by adding more series VSCs. The performance of the MC-UPQC is evaluated under various disturbance conditions and it is shown that the proposed MC-UPQC offers the following advantages:

1)  power transfer between two adjacent feeders for sag/swell and interruption compensation;

2) compensation for interruptions without the need for a battery storage system and, consequently, without storage capacity limitation;

3) sharing power compensation capabilities between two adjacent feeders which are not connected.


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