Coordinated Power Allocation and Robust DC Voltage Control of UPQC with Energy Storage Unit During Source Voltage Sag

The unified power quality conditioner (UPQC) combines the function of series and shunt active filters to enhance the electric power quality. Reasonable power allocation and robust DC voltage response are essential requirements of UPQC during compensating the source voltage sag. Motivated by this objective, this paper presents a control scheme for UPQC based on an improved UPQC-Q power allocation strategy and sliding mode control of DC side voltage. The prominent features of the proposed scheme are: 1) The active power needed for compensating the voltage sag is eliminated and the feeder current is reduced during the source voltage sag; 2) The VA loading of the series and shunt converters are controlled to be maintained within the rated capacity range; 3) The sliding mode control of DC voltage can effectively suppress the external disturbance and improve the robustness of UPQC during source voltage sag. Theoretical analysis and simulations in PSCAD/EMTDC are presented to validate the effectiveness of the proposed control scheme.