S-domain modelling for HVdc converter installation transient control design.

Type of content
Theses / Dissertations
Publisher's DOI/URI
Thesis discipline
Electrical Engineering
Degree name
Doctor of Philosophy
Publisher
University of Canterbury
Journal Title
Journal ISSN
Volume Title
Language
English
Date
1998
Authors
Todd, Simon
Abstract

This thesis describes an s-domain model of an HVde converter installation suitable for transient control design. As its basis, the s-domain model utilises a Describing Function analysis defined algebraically in the frequency domain, that allows definition of converter frequency response behaviour.

To model frequency response data in the s-domain for control analysis, a direct Rational Function modelling technique is developed. The approximation is written as an overdetermined set of linear equations which may be solved in the Least Squares sense, using Singular Value Decomposition.

To develop a suitable representation for control design and analysis, a block diagram equivalent in the s-domain is required. For this purpose, the converter is considered as a driving point impedance transfer function on the DC side, and in conjunction with the DC side electrical equations, reduced to define a block diagram equivalent in the frequency domain. Separate representation of control action is achieved using the Describing Function model equation set, with each converter transfer function in this equivalent, modelled in the s-domain by Rational Function approximation. The predicted output transients using the s-domain model, are validated with time domain simulation.

Using the s-domain model and the Root Locus technique, fast transient controllers are designed for current order set-point changes, and the reduction of DC overcurrents, specifically to reduce the incidence of commutation failures following both rectifier and inverter AC system disturbances.

System variation with operating point changes is analysed, with analysis suggesting that variation is directly dependent on commutation period length and DC current magnitude. This result allows the full dynamic range of converter s-domain behaviour to be predicted for any HVdc installation.

Finally, the Rational Function modelling technique is proposed for use in Electro­ Magnetic Transients programs, to model power system Frequency Dependent Equivalents in the s-domain.

Description
Citation
Keywords
Ngā upoko tukutuku/Māori subject headings
ANZSRC fields of research
Rights
All Right Reserved