Zero-current transition inverter for an axial flux brushless DC machine

Abstract

The motor used in this thesis is an axial flux brushless DC motor, which is an efficient energy converter. For its control it needs an electronic converter. The improved zero transition inverter (ZCT) is a very good choice for such. A full theoretical and a state plane analysis of the ZCT inverter are conducted. This scheme which came from Virginia Power Electronics Center, (VPEC) works for any PWM scheme. This improved ZCT inverter is applied to control a brushless DC motor using six-step control which makes the thesis very original. In the six step switching control , one switch in one leg is pulse width modulating while the other in the other leg is kept on for the whole period of commutation. This is done in order to minimize the switching losses in the inverter. A torough simulation of the inverter using MATLAB SIMULINK package is conducted. From this, the resonant capacitors, the auxiliary MOSFETs switches were selected and the tank inductance is computed to be 100nH. This zero current transition inverter, enables all the main switches, diodes and auxiliary switches to be turned off under zero current transition, and in the maintime provides an opportunity to achieve zero voltage turn on for the main switches. The thesis addresses also the design of a high power (14 kW) and high frequency (205 kHz) of the resonant circuit inductor. A distributed air-gap toroidal Kool Mµ core is chosen because it possesses many good magnetic characteristics, such as high resistivity, low hysteresis and eddy current losses, excellent inductance stability after high DC magnetisation. An important consideration in designing high frequency inductors is eddy current effects in the conductors. These effects include skin-effect losses and proximity-effect losses. Both effects were controlled by the use of Litz wire. The construction and part load testing of the constructed inverter completes the thesis.

Date of Award	Feb 2004
Original language	English
Supervisor	Dean Patterson (Supervisor) & Kamal Debnath (Supervisor)