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Date of Award

4-1989

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering

Supervisor

Dr. Barna Szabados

Abstract

Variable speed AC drives have become the new standard for high performance drive systems. Very high power traction drives present a particular challenge for AC drive technology because of the simultaneous need for high-torque vibration-free operation at standstill, traction-limited dynamic braking, and high speed operation.

In this work, two independently controlled cycloconverters are used with a wound rotor machine to provide a double fed drive system that overcomes the frequency limitations of the cycloconverters and provides a stable high power drive, with potential for rapid torque response and power factor control.

A new 'Jitter' control method is derived for the firing angle control of the cycloconverter. This method effectively spreads the cycloconverter output harmonics over a broader spectrum and thus minimizes the filtering requirements.

The double fed motor (DFM) equations are applied to the DFM circle diagram and a simulation program has been written to plot the circle diagram and give a geometric interpretation of the developed torque. A new algorithm is proposed using δν, the pseudo torque angle, to give direct control of the torque using only position feed-back. A novel frequency hopping algorithm is also derived that allows the cycloconverters to be operated at high frequencies without generating harmonic torques.

A dual cycloconverter drive was built to verify the stability and torque-speed performance of such a system. Reliable operation was achieved by using bank switching sensors based on detecting the reverse bias across a series connected diode, and by short circuit detection circuits with automatic reset facilities. The control software displays system status information on the screen, with on-line parameter modification, and provides a complete range of manual and automatic modes of operation to facilitate system development and testing.

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