Analysis And Design Of Quasi-Z-Source Inverter

Inverter, as an important part of the adjustable speed drive system, plays a key role in the course of energy conversion and transmission. However, the traditional inverters (VSI and CSI) have the theoretical barriers and limitations. They are either a buck (VSI) or a boost (CSI) inverter. In order to require a higher or lower output voltage, an additional DC-DC converter to boost the output voltage (VSI) or to buck the output voltage (CSI) is needed, which lowers the efficiency of system. What is more, in voltage-source inverter, the upper and lower devices of each phase leg could be gated simultaneously by EMI noise, which would destroy the circuit and decrease the reliability. To avoid the shoot-through state, dead band has to be provided in the control strategy. Nevertheless, a disadvantage of the dead band is that it can bring the waveform distortion. CSI also has some similar limitations.In order to overcome the problems of the traditional inverter, a new type inverter named Quasi-Z-source inverter was presented. It makes the shoot-through state possible by employing a unique impedance network (Z-network). And this unique impedance network allows the Quasi-Z-source inverter to buck and boost its output voltage.In this thesis, the operating principle and superiority of the Quasi-Z-source inverter are described firstly. And its Z-network parameter design is analyzed in detail. A new PWM control strategy——constant shoot-through vector current trail control is modified for Quasi-Z-source is presented in this thesis. Based on the analysis of its mathematical model, a dc-link voltage controller for Quasi-Z-source inverter has been introduced. The application of Quasi-Z-source inverter in adjustable speed drive system is analyzed. At last, the validity of theoretical analysis is verified by simulation results.