Enhancement of Common-Mode Power Extraction Through Zero-Sequence Injection in Pulse Width Modulation

In motor drive system fed by voltage source inverter (VSI), common-mode voltage (CMV) is commonly present because of pulse width modulation (PWM) techniques. It's proved to be feasible in research to collect energy from CMV and provide a DC power source for low-power sensors such as encoders. This approach can replace auxiliary power supply thus simplifying system wiring design. However, the practicality of this approach will be largely constrained by the maximum power available from CMV, as it directly affects the stable operation of sensors. This paper aims to explore methods to improve the power capacity with low cost. A common-mode (CM) power transfer model is constructed to clarify the factors influencing CM power extraction and analyze possible methods for increasing power capacity. Then, from the perspective of power source, the characteristics of CMV are analyzed including its frequency composition and RMS value. Further exploration is conducted to analyze the influence of zero-sequence injection during modulation on the characteristics of CMV. At last, a discontinuous PWM method DPWM3 is identified as the most effective PWM method to significantly enhance power capacity. Experimental results validate the accuracy of quantitative analysis and effectiveness of the proposed method.