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Please use this identifier to cite or link to this item: https://dspace.lboro.ac.uk/2134/7205

Title: Optimal PWM switching strategy for single-phase AC-DC converters
Authors: Gitau, Michael N.
Keywords: Converter-fed traction drives
Issue Date: 1994
Publisher: © M.N. Gitau
Abstract: The thesis describes an optimal selective harmonic elimination strategy suitable for singlephase AC-DC converter-fed traction drives. The objective is to eliminate low-order supply current harmonics, including those injected into the supply due to load-side current ripple. Other advantages that the switching strategy has to offer over phase-control include improved supply power factor, reduced VA consumption for a given demand speed and load, reduced torque and speed ripple and smaller armature circuit smoothing inductance. The effect of field current boost on the dynamic response of the drive is also described. It is shown that field boost helps to reduce the speed rise-time by increasing the electromagnetic torque available during acceleration periods. Closed-loop control of a 4-quadrant DC drive is described and a comparison made between the performance of PID-control and pseudo-derivative feedback control. It is shown that pseudo-derivative feedback control has several advantages to offer, amongst which are ease of tuning of the controller gains and a superior performance following load torque disturbances. A laboratory size drive system was designed and built, and used to validate simulation predictions for both the switching strategy and pseudo-derivative feedback control. A microcontroller based hardware implementation of both the switching strategy and a digital pseudo-derivative feedback controller was adopted, with the switching strategy being implemented using an off-line approach of precalculating the switching angles and storing these in look-up tables. The armature voltage controller comprises a dual-converter employing IGBTs as switching devices. The use of IGBTs allows higher switching frequencies at significant power levels than would be possible if GTOs were used. It also simplifies the gate drive circuit design and minimises the need to use snubber circuits.
Description: A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.
URI: https://dspace.lboro.ac.uk/2134/7205
Appears in Collections:PhD Theses (Mechanical, Electrical and Manufacturing Engineering)

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