To provide higher boost ratio in motor drive or PV application, a new family ofswitched-coupled-inductor inverters has been proposed in this work, with voltage buck-boostfunction. The voltage-fed switched-coupled-inductor inverter has higher boost ratio andlower active device voltage stress than Z-source inverter at the same voltage gain, and haswider voltage buck/boost range than conventional boost-converter inverter. The current-fedswitched-coupled-inductor inverter is a capacitor-less solution among the buck-boostinverters, which reduces the system size significantly. Compared to traditionalboost-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 driveapplication, a current-fed quasi-Z-source inverter topology has been selected and a 24kWprototype has been built in the lab. A zero vector placement technique in SVPWM has beenproposed for this inverter to obtain lowest switching loss, lowest current ripple, lowest outputharmonics and lowest voltage spike on the device in both constant torque and constant poweroperation 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 fullpower rating efficiency reaches 97.6%, and peak efficiency reaches 98.2%, both of whichhave a 3%-4% improvement on traditional two stage configuration. The power density is15.3KW/L, which also has 30% improvement on the commercial unit in HEV.To achieve higher switching loss reduction, a Space-Vector-Pulse-Width-AmplitudeModulation (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 isincreased by a factor of 2 to 3, with a less output harmonic distortion than normal SVPWMmethod. A 1 kW boost-converter-inverter prototype has been built and tested using thismethod. The overall system efficiency at full power rating reaches 96.7% and the wholesystem power density reaches 2.3 kW/L and 0.5 kW/lb, all of which are remarkable at thispower rating. As a result, the proposed SVPWAM can make the buck-boost inverter suitablefor applications that require high efficiency, high power density, high temperature, and lowcost, such as EV motor drive or engine starter/alternator.To implement buck-boost function on direct matrix converter, four control methods includingsimple maximum boost, maximum boost, maximum constant boost control and hybridminimum stress control have been proposed for the newly proposed direct Z-source matrixconverter, and verified with simulation/experiments.Two new discontinuous operation modes have been proposed for current-fed quasi-Z-sourceinverter topology. Simulation and experiment results are given to verify the theoreticalanalysis. A transient state-space model has been built for current-fed quasi-Z-source inverterto demonstrate its fast transient response in motoring and regenerating transition. Theanalytical, simulated and experimental results all show that the inverter only needs severalswitching cycle to complete the transition, which makes it suitable for HEV/EV motor driveapplication.
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