Roberts, Graham John (2010) Evaluation of emerging unipolar devices in the motor drive of a hybrid electric vehicle. PhD thesis, University of Warwick.

Abstract

Silicon carbide (SiC) is seen as a potential replacement power semiconductor material because it can operate at high temperatures, with reduced losses leading to high efficiency in power converter applications. The SiC Schottky diode and metal oxide field effect transistor (MOSFET) are two devices which offer improved efficiency in power conversion, with the former commercially available for a number of years and the latter currently emerging as a commercially available device. The original contribution of this thesis is the integration of models of the SiC Schottky diode and SiC MOSFET into a fast inverter simulation framework, giving a method of evaluating the benefits offered by these emerging devices to a hybrid vehicle inverter. Fast models of the SiC Schottky diode and SiC MOSFET based on device physics were implemented. These models used device design parameters and material temperature dependencies to determine device behaviour where possible, rather than relying completely on empirically determined parameters, such that a user could evaluate the benefits offered by a new SiC device design to a whole system. On-state and switching data were gathered from commercially available diodes and a prototype MOSFET to allow validation of the models. Parameter extraction methods were developed and applied to measurements of existing devices to provide an initial estimate of model parameters, then these parameters were adjusted to give a good match between measured and simulated on-state and switching data. Following validation, the models were integrated into a fast inverter simulation framework, allowing the simulation of a hybrid vehicle inverter undergoing a 35 minute load cycle, taking approximately seven minutes to complete. This is approximately five times faster than real time. The output of this simulation was a temperature profile for the Schottky diode an MOSFET, giving information that can assist in investigation of an inverter and cooling system design for a particular load cycle.

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