Harmonic analysis of AC/DC converters using the harmonic admittance method

Rajagopal, Narayanan (1993) Harmonic analysis of AC/DC converters using the harmonic admittance method. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (14MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Phase control technique used in ac/dc converters results in the generation of harmonics which can disrupt the operation of critical and sensitive loads. In general, the level of harmonics in the system depends on the interaction between the ac network and the harmonics generated by the converter. -- This thesis develops a technique for the harmonic analysis of phase-controlled ac/dc converters connected to the ac network. The analysis method is based on the harmonic admittance model, which uses the multi-port network concept to define a relationship between the input ac voltages and currents, and the output dc voltage and current. The matrix representation of the relationships is expressed in terms of A, B, C, D parameters, which contain the harmonic components of the switching functions of the converter and the admittance of the commutating inductance. -- A single phase model of the harmonic admittance technique is first implemented. The model is used to determine the harmonics at various nodes in the system. It is shown that in addition to providing quantitative information about the harmonic levels, the model accurately predicts the operating conditions and harmonic instabilities in the system. -- The method is extended to model a three-phase system. For simplicity, the operation of the converter with commutating overlap angle less than 60° (i.e. mode-I operation) is considered. However, based on the procedure described in the thesis, the model for other modes of operation can be developed. The model is used to study the harmonic interaction in a simple HVDC system. Specifically, the distortion at the point of common coupling, the effects of ac source harmonics and unbalance in ac network impedance on the system voltages are investigated. -- The harmonic admittance models developed in the thesis are verified by EMTP simulation. The model accurately predicts the harmonics and system behaviour. It is shown that the harmonic admittance method provides an alternate tool to study the harmonic interactions in power systems with converters.

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