Injected voltage calculation in three-phase series power quality controllers

A three-phase series power quality controller (SPQC) is a device designed for eliminating voltage disturbances. It compensates load-voltage fluctuation by injecting an appropriate voltage into the distribution system. The maximum output voltage of an SPQC is constrained by its voltage limit, which is determined by the configuration of the SPQC and its DC link voltage. Based on discussions about unbalanced voltage sags using the phasor-diagram approach, a rotation-transform-based control strategy is designed. With the new method, the active power injected by an SPQC is minimised and the output voltages of the SPQC are kept within its voltage limit while the supply voltage distortion can be completely compensated. A two-phase compensation method especially for a 3-phase 3-wire system is also proposed in this paper. A new control strategy, a shift-transform-based control strategy for the two-phase compensation method, is designed. The new control strategy allows the compensation range of an SPQC to be significantly expanded without increasing the voltage limit of the device. The performance of the two new control strategies is verified by simulation.