Graduate Thesis Or Dissertation

Voltage analysis of PWM inverter fed induction motors

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  • Adjustable Speed Drive (ASD) systems are widely used in industry to effectively improve process efficiency and control. Typically, an ASD system consists of a motor with its speed controlled by a power electronics converter via varying the amplitude and frequency of the input voltage. However, several abnormal insulation failures of random wound motors in ASD applications have been reported. These failures were related to voltage transients caused by inverters employing fast insulated Gate Bipolar Transistors (IGBTs) combined with long cables that connect motors to inverters. This thesis further analyzes the distribution of voltage waveforms generated by a pulse-width modulated (PWM) inverter at the motor terminals and windings. Experimental work was performed at the Motor Systems and Resource Facility (MSRF) at Oregon State University on a specially made 5hp induction motor with taps from the first and second coil and from the first four and last two turns in every phase. Tests were performed with long and short cables and results are compared. A simple simulation model was created in PSpice and used to predict maximum voltage transients across coils and turns. The validation of the model is demonstrated by its capability to predict most of the experimental results.
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