Title page for ETD etd-07102008-081413

Document Type Master's Dissertation
Author Chaing, Chia-Tsung
URN etd-07102008-081413
Document Title Five-level inverter employing WRPWM switching scheme
Degree MEng (Electrical Engineering)
Department Electrical, Electronic and Computer Engineering
Advisor Name Title
Prof M N Gitau Committee Chair
  • random process
  • random number
  • probability
  • power spectrum
  • multilevel inverter
  • harmonic
  • expected value
  • discrete noise power
  • continuous noise power
  • comparison
  • signal power
  • switching decision
  • switching frequency
Date 2005-09-05
Availability unrestricted
Multilevel Random Pulse Width Modulation (RPWM) schemes have drawn increasing attention in the past few years. Multilevel topologies provide high voltage and high power capabilities and random PWM schemes offer reduction in discrete harmonics spectral.

This dissertation provides a generalized theory and analysis methods of the standard five-level Weighted RPWM (WRPWM). Equations have been derived to analyze the spectral performance and average switching frequency of the WRPWM output waveform using statistical approach. A modified WRPWM scheme has been proposed. The modified WRPWM scheme is then analyzed with the equations derived from the same approach. The analyzed theoretical spectrum of the standard five-level WRPWM is then compared with the three-level WRPWM scheme and the conventional carrier based PWM scheme.

A scaled laboratory prototype diode clamping five-level inverter has been built for verification of the standard and the proposed modified WRPWM schemes. It can be seen that the experimental measurements and the theoretical analyzed results are all in good agreement. Results show the two five-level WRPWM schemes offers significant improvements on the spectrum content than the conventional carrier based PWM scheme. It was found that the five-level WRPWM schemes have successfully suppress the magnitude of third harmonic below 5% of the magnitude of fundamental component and even less for the higher order harmonic components.

Research contributions made by the dissertation are:

- The proposed modified multilevel WRPWM scheme which utilizing the switching decision redundancy of multilevel inverter to manipulate the harmonic content of the output signal.

- The derived mathematical equations of the standard and modified five-level WRPWM scheme for analytical purposes.

2005 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Please cite as follows:

Chaing, C-T 2005, Five-level inverter employing WRPWM switching scheme , MEng dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-07102008-081413/ >


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