An improvement in the performance of unified power quality conditioner using dc-link voltage control

The dc link voltage of the unified power quality conditioner (UPQC) is maintained at certain preset value during the steady state. However the dc link voltage can significantly deviate from its reference during a transient event, caused by load connection/disconnection or/and supply side voltage sag/swell. During such transients, due to significant deviation in the dc link voltage, the series injected voltage magnitude varies, causing fluctuations in the load voltage magnitude. A suitable hysteresis controller is proposed for the series compensator in order to adjust the series injected voltage for a constant deviation in the dc link voltage. Besides, an adaptive dc link voltage controller is proposed which limits the dc link voltage deviation during the transient conditions. The effectiveness of the proposed control schemes have been demonstrated through simulations.