Browsing by Author "Kiran, Aipathi Sai"

Z-source inverters eliminate the need for front-end DC-DC boost converters in applications with limited DC voltage such as solar PV, fuel cell. Quasi Z-source inverters offer advantages over Z-source inverter, such as continuous source current and lower component ratings. In these inverters, DC link voltage is boosted by using shoot through state i.e., turning ON both the switches in the inverter leg. Without affecting the output voltage harmonic distortion, this shoot through state has to be introduced. Initially, carrier based PWM techniques were modified for controlling Z-source/quasi Z-source inverters in the literature. Space vector PWM technique is very popular because of better DC bus utilization and total harmonic distortion (THD). In this thesis, conventional space vector modulation technique is modified for introducing shoot through state during the traditional zero vector time. Three such methods of modification in conventional space vector PWM are presented. In these methods, shoot through state is inserted without any extra switching operations unlike carrier based techniques. Thus, switching losses are less compared to carrier based techniques. In this thesis, bus clamping PWM methods are presented for quasi Z-source in verter. In bus clamping PWM methods, switching losses are reduced because each phase is clamped to positive or negative bus for certain duration in every cycle. Conventional bus clamping techniques are modified for introducing shoot through state needed for boosting DC link voltage in Z-source/quasi Z-source inverters. The switching losses are theoretically evaluated for different PWM methods and a minimum switching loss PWM for different power factor loads is presented. Mod ified space vector PWMs and bus clamping PWM techniques for quasi Z-source inverter are experimentally validated using FPGA platform. In this work, switching table PWM specially needed for Direct Torque Control (DTC) of induction motor fed by quasi Z-Source Inverter (qZSI) is presented. In the proposed technique, DC link voltage is boosted by incorporating shoot through state into the switching table. This simplifies the implementation of DTC using qZSI. An additional DC link voltage hysteresis controller is included along with torque and flux hysteresis controllers used in conventional DTC. The simulation results using MATLAB/simulink validate the boost capability of qZSI and torque response of the DTC.

Z-source/quasi Z-source inverters (qZSI) can eliminate DC-DC converter in conventional drive applications where DC-DC converter is coupled with voltage source inverter (VSI). Compared to Z-source inverter (ZSI), qZSI has more advantages like continuous input current and lower component ratings. In these inverters, DC link voltage is boosted by using shoot through state i.e., turning ON both the switches in the inverter leg. In this paper, conventional space vector modulation is modified for introducing shoot through state that is necessary for boosting DC link voltage, without any extra switching operations. This paper gives detailed implementation steps for this modified space vector modulation and is implemented by FPGA.

Z-source inverters eliminate the need for front-end DC-DC boost converters in applications with limited DC voltage such as solar PV, fuel cell. Quasi Z-source inverters offer advantages over Z-source inverter, such as continuous source current and lower component ratings. In this paper, switching table based Direct Torque Control (DTC) of induction motor fed by quasi Z-Source Inverter (qZSI) is presented. In the proposed technique, dc link voltage is boosted by incorporating shoot through state into the switching table. This simplifies the implementation of DTC using qZSI. An additional DC link voltage hysteresis controller is included along with torque and flux hysteresis controllers used in conventional DTC. The results validate the boost capability of qZSI and torque response of the DTC.