The development of a simple efficient Pulse Width Modulation (PWM) modulator has
been a goal for many research workers. In general three techniques have been used,
namely; the analogue triangular wave technique; the use of look-up tables, and the use of
Analogue to Digital converters together with analogue circuitry. The modulator
described in this thesis is based on an iterative numerical algorithm, and is thus
fundamentally different from all previous techniques. The algorithm is limited only by
the speed and precision of the associated digital circuitry and can achieve higher
modulating frequencies with greater accuracy than can be realised using any of the
methods that have previously been investigated. The use of high switching frequencies
simplifies the design of filters to reduce both unwanted harmonics and acoustic noise.
In this thesis, an equation of a multiphase digital oscillator is derived which is simple to
implement and will operate over a wide range of frequencies. The conditions for stable
oscillation are derived, and two classes of oscillator are developed. It is shown how the
frequency and amplitude of oscillations can be independently and continuously varied.
The errors in computing the amplitude and frequency are analysed, and are shown to be
cyclic. Upper bounds for the amplitude errors are derived.
Single and three phase PWM modulators are described and the implementation
procedures for their practical realisation are developed. Two specific implementations of
the algorithm are investigated and experimental results confirm theoretical analyses.
The algorithm can be incorporated in the Space Vector Modulation (SVM) method of
PWM, to improve the resolution at low speeds and to enable the SVM technique to be
applied at high gear ratios.
A 3-phase 16-bit PWM modulator was built and operated satisfactorily with a pulse
switching frequency of 20 kHz and an output frequency range of 1000:1. / Thesis (Ph.D.)-University of Natal, Durban, 1989.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/6888 |
| Date | January 1989 |
| Creators | Green, Walter Battman. |
| Contributors | Harley, Ronald G. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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