Novel Loss and Harmonic Minimized Vector Modulation for a Current-Fed Quasi-Z-Source Inverter in HEV Motor Drive Application

The recently proposed current-fed quasi-Z-source inverter (QZSI) [1] can buck and boost voltage and provide bidirectional power flow [2]-[6]. A crucial criterion for the size of three-phase PWM converters is the cooling of the power semiconductors and thus determination of power dissipation at certain operating points. In the modified space vector PWM method (SVPWM) control method for this circuit, different PWM sequences can lead to different switching loss, current ripple, total harmonic distortion, and also the voltage spike on the switching devices. In order to select the best PWM sequence to obtain the best performance and efficiency, a complete analysis and calculation for the four mentioned criterions are presented for different sequences. For each criterion, the best sequences are selected to obtain better performance. Finally, the optimized PWM sequence in the modified SVPWM control for this circuit is selected with the optimized hardware design together to achieve the best efficiency at the full operation range. The optimized hardware design has been built in the lab, including the optimal design of the coupled inductor, optimal design and selection of Z-source capacitors and output capacitors, the selection of Z-source diode, and the final layout of the hardware. In order to bring the prototype into real application in a hybrid electrical vehicle [3], the inverter efficiency is measured according to the motor P-V curve. The estimated efficiency curve and experiment results are plot and compared. The best efficiency at 15 kW reaches 97.6% at unity voltage gain.