| To provide higher boost ratio in motor drive or PV application, a new family of switched-coupled-inductor inverters has been proposed in this work, with voltage buck-boost function. The voltage-fed switched-coupled-inductor inverter has higher boost ratio and lower active device voltage stress than Z-source inverter at the same voltage gain, and has wider voltage buck/boost range than conventional boost-converter inverter. The current-fed switched-coupled-inductor inverter is a capacitor-less solution among the buck-boost inverters, which reduces the system size significantly. Compared to traditional boost-converter-inverter, it has less switch count, and less active device current stress.;To achieve higher efficiency with a single-stage buck-boost inverter for HEV/EV motor drive application, a current-fed quasi-Z-source inverter topology has been selected and a 24kW prototype has been built in the lab. A zero vector placement technique in SVPWM has been proposed for this inverter to obtain lowest switching loss, lowest current ripple, lowest output harmonics and lowest voltage spike on the device in both constant torque and constant power operation regions, in order to achieve higher efficiency, higher power density and lower cost. A 24kW current-fed quasi-Z-source inverter has been built in the lab and tested. The full power rating efficiency reaches 97.6%, and peak efficiency reaches 98.2%, both of which have a 3%-4% improvement on traditional two stage configuration. The power density is 15.3KW/L, which also has 30% improvement on the commercial unit in HEV.;To achieve higher switching loss reduction, a Space-Vector-Pulse-Width-Amplitude Modulation (SVPWAM) method has been proposed for buck-boost current source inverter. By using this method, the switching loss is reduced by 60%, and the power density is increased by a factor of 2 to 3, with a less output harmonic distortion than normal SVPWM method. A 1 kW boost-converter-inverter prototype has been built and tested using this method. The overall system efficiency at full power rating reaches 96.7% and the whole system power density reaches 2.3 kW/L and 0.5 kW/lb, all of which are remarkable at this power rating. As a result, the proposed SVPWAM can make the buck-boost inverter suitable for applications that require high efficiency, high power density, high temperature, and low cost, such as EV motor drive or engine starter/alternator.;To implement buck-boost function on direct matrix converter, four control methods including simple maximum boost, maximum boost, maximum constant boost control and hybrid minimum stress control have been proposed for the newly proposed direct Z-source matrix converter, and verified with simulation/experiments.;Two new discontinuous operation modes have been proposed for current-fed quasi-Z-source inverter topology. Simulation and experiment results are given to verify the theoretical analysis. A transient state-space model has been built for current-fed quasi-Z-source inverter to demonstrate its fast transient response in motoring and regenerating transition. The analytical, simulated and experimental results all show that the inverter only needs several switching cycle to complete the transition, which makes it suitable for HEV/EV motor drive application. |
