The study of injecting voltage calculation in three-phase series power quality controller

The three-phase series power quality controller (SPQC) is a type of device designed for mitigating power disturbances. It compensates load voltage by injecting the missing voltage of the system into the line. In this paper, a novel method of calculating the injecting voltage in a three-phase SPQC is proposed. The voltage limit existing in series devices are discussed based on the phasor diagram of unbalanced voltage sags in the three-phase system. Two types of transform are put forward to increase the voltage limit of series devices. The control strategies of a 3-phase 3-wired SPQC concerning about the voltage limit are also put forward by using the transform. The control methods can both increase the compensate limit and mitigate voltage harmonics under serious unbalanced voltage conditions. Simulation and experimental results are presented to confirm that the new control method has better performance than those traditional methods especially under unknown unbalanced voltage disturbances.