Capacity optimization scheme of UPQC system based on an Improved Topology

In this paper, an improved topology for unified power quality conditioner (UPQC) is proposed. By adding a coupling capacitor to the LC filter branch in series side of UPQC, the improved topology can reduce the output voltage of the inverter, and provide a large part of the load-reactive power, thereby effectively reducing the overall capacity and dc-link voltage level of the UPQC system. Because of these prominent characteristics, the overall utilization and the cost performance of the device can be improved. Firstly, the circuit topology and working principle of the proposed UPQC are introduced. Secondly, the two working modes of UPQC under different working conditions are introduced in detail, including: power regulation mode under the normal steady-state condition and voltage compensation mode under the voltage sag condition. Then, the proposed topology is compared with other topologies to show its advantages in reducing overall capacity. Finally, the validity and feasibility of the proposed topology are verified by experimental results.