Z-source inverter design, analysis, and its application in fuel cell vehicles

With its unique structure, the Z-source inverter can utilize the shoot through states to boost the output voltage, which improves the inverter reliability greatly, and provides an attractive single stage dc-ac conversion that is able to buck and boost the voltage. For applications with a variable input voltage, this inverter is a very competitive topology. This work starts with the PWM methods for the Z-source inverter. Three PWM methods are proposed with different boost ratios. In order to reduce the switching loss, a modified PWM scheme is proposed. A comparative study of the modified PWM method and a commonly used PWM method is conducted.; To facilitate closed loop controller design, a small signal model for the Z-source inverter is developed using the state space averaging and verified with simulation results. Based on this model, a closed loop controller is designed using gain scheduling method. The controller is verified with simulation and experimental results.; In order to show the strengths and weaknesses of the Z-source inverter, a comprehensive comparison of the Z-source inverter and traditional inverters for fuel cell vehicle traction drives is conducted. The switching device power, passive components requirement, constant power speed ratio, reliability, and inverter efficiency are used as bench marks for the comparison. The comparison shows that the Z-source inverter is very suitable for applications with a moderate boost ratio needed, which most fuel cell/photovoltaic sources reside in. A detailed design process of the Z-source inverter is also provided. Besides the two basic operation modes of the Z-source inverter, new operation modes have been found when the load power factor, modulation index, and the inductance of the inductors are low. The critical conditions, voltage gain, and the consequence of these operation modes are analyzed in detail.; Three configurations of Z-source inverter for fuel cell-battery hybrid vehicle traction drives are presented with the basic control methods. With a battery in the system, the effect of the undesirable operation modes is minimized. Also, control methods to totally eliminate the undesirable operation modes are proposed. A simple comparison of the three configurations is conducted.