Sawtooth Carrier Based Sixty-Degree PWM for Three-phase Quasi Z-source T-Type Inverter for Induction Motor Drive

In DC to AC power conversion, impedance network connected to the inverter input DC side causes buck-boost features of the inverter output voltage and prevents damage the semiconductor devices during shoot-through conditions. Blocking voltage of the main switching devices of T-type inverter is lower than traditional voltage source inverter. Moreover, upper and lower DC link voltage are no longer balance because the values and characteristics of components used in impedance network cannot be equal. In this paper, a simple boost sixty-degree PWM (SB SDPWM) based on sawtooth carrier wave is applied to three phase quasi-Z-source T-type inverter for the purpose of AC motor drive applications. This technique provides to adjust the upper and lower input DC-link voltages of the inverter by controlling the upper and lower shoot-through duty ratios. This feature cannot be achieved in fully shoot-through technique. Small scale laboratory prototype is built and tested to certify the proposed SBSD PWM and also compared with traditional simple boost sine PWM (SB SPWM) technique. STM32F4 Discovery board is used as a main controller and implemented in Matlab/Simulink with Waijung Bolcksets. According to the experimental test results, SB SDPWM control method gives lower current harmonic distortion (THD
i
) but harmonic spectrum of voltage is slightly higher than SB SPWM. Moreover, SB SDPWM method achieves higher inverter output voltage and efficiency than SPWM method.