Intelligent Unified Power Quality Conditioner with Reactive Power Sharing for Improving DC-Link Voltage and Power Quality

A three-phase, four-leg intelligent unified power quality conditioner (UPQC) is proposed to mitigate grid voltage distortions, grid current total harmonic distortion (THD), current unbalance, and lagging power factor (PF). The developed UPQC possesses the reactive power sharing capability to share the load reactive power demand between the series and shunt inverters. Moreover, when grid voltage distortions or sudden load changes occur, the power mismatch between the series and shunt inverters of the UPQC can result in DC-link voltage fluctuations and significantly degrade power quality compensation performance. Thus, DC-link voltage control of the UPQC plays a key role in regulating the power absorbed or supplied by the DC-link capacitor, stabilizing the load voltage, and improving power quality under grid voltage distortions and sudden load changes. As a result, a Legendre Petri fuzzy neural network (LPFNN) controller is employed in place of the traditional proportional-integral (PI) and fuzzy neural network (FNN) controllers for DC-link voltage control and power quality improvement. Finally, the experimental results using the developed LPFNN-controlled UPQC are provided to verify the effectiveness of regulating DC-link voltage and improving power quality compared with the PI and FNN-controlled UPQCs under grid voltage distortions and sudden load changes. The lagging PF, current THD, CUR, and settling time of the DC-link voltage are significantly improved to 0.99, 2.9%, 2.7% and 825 ms, which are superior to the PI controller (0.98, 3.6%, 3.5% and 1220 ms) and FNN controllers (0.99, 3.2%, 3.2% and 915 ms).