The viability of any electric vehicle is critically dependent on it having an acceptable rangeudbetween charges, a feature which is ultimately dictated by the capacity of the battery energyudstore. Considerable improvements in vehicle range are possible, however, by ensuring the mostudeffective use of this limited energy resource through the minimisation of the losses in the electricuddrive-train, i.e. the combined machine and power electronic controller. A particular considerationudis that, for the majority of the time, the electric drive-train will be operating at part load.udThe thesis investigates the operation of induction motor based electric traction drive-trains, withuda view to minimising the system loss over typical driving cycles. The study is based around aud26kW induction motor and IGBT inverter drive, which is typical of the technology used to poweruda small urban vehicle.udA potential advantage of an induction motor based drive-train is the ability to vary the level ofudexcitation field in the motor, and therefore the balance of iron and copper loss. The control ofudthe supply voltage magnitude necessitates the use of some form of modulation on the output ofudthe power converter. The method of modulation employed will influence the harmonic contentudof the supply to the motor, the level of parasitic harmonic loss in the machine and the switchingudlosses of the power semiconductors.udA theoretical study supported by experimental work on a DSP controlled drive is presented andudused to determine the most appropriate modulation strategy at a given operating point to achieveudan optimal balance between the motor copper, iron and harmonic loss and inverter switching andudconduction loss. It is shown that compared to the established method of constant flux and fixedudinverter switching frequency control, a significant reduction in the traction system loss can beudachieved. Some different modulation schemes involve varying amounts of computationaludoverhead in a DSP, the implementation of candidate modulation and control schemes has alsoudbeen investigated to ensure the defined scheme is practically realisable.
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