Reducing Common-Mode Voltage and Bearing Currents in Quasi-Resonant DC-Link Inverter

In this article, a concept of separation of an inverter-fed induction motor drive from its mains supply by two transistor switches inserted in the dc-link circuit is re-examined based on the proposed parallel quasi-resonant dc-link inverter (PQRDCLI). The objective of the article is to show an advantage of the proposed topology in limiting high-frequency common-mode voltage and bearing currents. In the laboratory setup, an induction machine was equipped with hybrid ceramic bearings and an insulated clutch to measure the shaft-to-frame bearing voltage and the shaft-grounding current. Experimental tests of the PQRDCLI confirm significant reduction of common-mode voltage and shaft-to-frame bearing voltage at dc-link zero voltage notches. By controlling the output voltage slopes, the shaft-grounding brush current and the ground leakage current are also reduced. The efficiency measurement and evaluation of the proposed topology, as compared with a two-level hard switched inverter, reveal comparable efficiency of around 95% and indicate loss distributions in both inverters.