4-Vector SVPWM for Single-Phase Transformerless UPQC With Two-Leg and Low DC Voltage

In this letter, we propose a single-phase transformerless unified power quality conditioner (UPQC) with two legs. Owing to the limited quantity of switches, the half-bridge (HB) UPQC consists of a HB dynamic voltage restorer (DVR) and an active power filter (APF). The proposed topology maintains constant switching stress under all operational scenarios by combining an HB DVR with a full-bridge (FB) APF without increasing the number of switches. To address the issue of current compensation and voltage compensation coupling caused by the shared leg, a four-vector space vector pulsewidth modulation (SVPWM) is proposed for decoupling. With the proposed SVPWM for independent control reference calculation, the effects of dc voltage and load current on voltage compensation can be eliminated by the control strategy. Finally, the effectiveness of the topology and modulation strategy are verified by the experimental results.