Pulse-width modulation methods are widely used for the synthesis of ac voltages at
the terminals of a voltage-sourced converter (VSC). Traditionally sinusoidal pulsewidth
modulation (SPWM) has been used. A powerful alternative for this purpose is
space-vector modulation (SVM), in which the converter is placed in a finite number
of states in order to best approximate the reference voltage. This method offers
better utilization of the dc bus voltage and provides several degrees of freedom for
enhancement of the harmonic spectrum as well as switching losses.
This thesis studies the SVM method for two- and three-level VSCs. A model
for implementation of SVM in the electromagnetic transients simulation program
PSCAD/EMTDC is developed. The model is able to generate firing pulses in linear
as well as overmodulation range and is used to study the performance of different
SVM strategies in terms of their harmonic spectra and associated converter and harmonic
losses. The model is also used to demonstrate the suitability of the method
for network applications. The thesis also employs genetic algorithms to find an optimized
SVM sequence for improved harmonic performance. An objective function
is defined that seeks to minimize the most significant harmonic components of the
generated waveform, while keeping the other harmonic components within the acceptable
range outlined in the available standards. The obtained sequence shows
great improvement over the conventionally-used SVM sequence.
| Identifer | oai:union.ndltd.org:MANITOBA/oai:mspace.lib.umanitoba.ca:1993/2819 |
| Date | 14 September 2007 |
| Creators | Mehrizi-Sani, Ali |
| Contributors | Filizadeh, Shaahin (Electrical and Computer Engineering), Gole, Ani (Electrical and Computer Engineering) Wachal, Randy (Manitoba HVDC Research Centre) |
| Source Sets | University of Manitoba Canada |
| Language | en_US |
| Detected Language | English |
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