Common-Mode Voltage Reduction Techniques of Three-Phase Quasi Z-Source Inverter for AC Drives Yam P. Siwakoti Department of Electronic Engineering, Macquarie University, NSW-2109, Australia. Email: yam.siwakoti@mq.edu.au Graham E. Town Department of Electronic Engineering, Macquarie University, NSW-2109, Australia. Email: graham.town@mq.edu.au Abstract— This paper presents the modulation techniques to reduce the common mode voltage (CMV) and common mode current (CMC) in 3- Quasi Z-Source Inverter (q-ZSI) for AC drive systems. A modified Space Vector Pulse Width Modulation technique with reduced number of commutation per sector was used to minimize the CMV and CMC without adding extra circuitry (filters and/or leakage current isolation/bypass circuits) in a q-ZSI whilst maintaining the boost capability of q-ZSI by inserting the shoot-through vector in between the active state vector. Detailed analysis of the modified SVPWM technique to reduce the CMV and CMC of q-ZSI is presented, and performance of the proposed system has been verified using Matlab Simulink. I. INTRODUCTION Traditional 3- voltage source (VSI) based adjustable speed drives (ASD) and AC motor drives have been reported with different modulation techniques based on sine PWM and Space Vector PWM (SVPWM) for various circuit topologies with the aim of minimizing the common mode voltage (CMV) and common mode current (CMC), which can have detrimental effect on the system [1], [2] and [3]. However, VSI behaves as buck converter whose input DC voltage must be greater than the peak AC output voltage in linear modulation range for sine wave PWM (m<1) and all modified SVPWM and cannot deal with voltage sags in the power line. For 3- 230V rms drive system the VSI can only produce a maximum of 190 V rms AC in the linear modulation range, limiting the amount of output power from the motor [4]. The usual remedy is to use boost converter before the VSI, or to oversize the drive system. This multistage power conversion reduces the efficiency and reliability of the system. q-ZSI features single stage power conversion with wide range of voltage gain and ride-through capability during voltage sags, reduced line harmonics and input current ripples and has niche in AC drive systems [4]. However, the galvanic connection between the motor and the inverter cause a problem of high dv/dt CMV which cause the CMC through the parasitic capacitance (C pg ) inside the motor and motor chassis (typical value of 100-500pF), especially at high frequencies [5]. The CMC results in bearing failures, undesired electromagnetic interference, nuisance trips in the system and power loss. The Z-source Inverter (ZSI) and q-ZSI based ASD are preferred over VSI in process control and critical loads because of their buck-boost capability and good performances [6]-[9]. Analysis of CMV of the ZSI (with extra diode to This work was supported by the Australian Research Council (ARC), Triquint Semiconductor Inc., and Macquarie University, Australia.                                             Figure 1. 3- quasi Z-source Inverter for AC drives. 978-1-4673-4355-8/13/$31.00 ©2013 IEEE 2247