Download Contributions To The Analysis And Design Of Three

ABSTRACTS
This paper contributes to the analysis and design of three – phase LC resonant inverters, which
are suitable for feeding induction motors. A simplified equivalent circuit of the three-phase
inverter-motor system has been developed to lead to a comprehensive analysis. The aim of the
analysis is to predict the load current of a phase at every switching action of the inverter by using
a piecewise linear technique. The simplified equivalent circuit is obtained by transforming the
series-parallel models of the three-phase inverter-motor system at the switching intervals into
equivalent series parameters across the dc source. The significance of this method of analysis is
that it is less complicated and one is able to obtain the harmonic components of the load current
with less difficulty. The theoretical results agree reasonably with the experimental results. The
problem of discontinuity in the load current is overcome by an appropriate selection of the series
capacitors that aid commutation of the inverter thyristors. Theoretical and experimental results
are presented.
1. Introduction
LC resonant inverters operate when the voltage or current crosses zero. They are less
prone to Electromagnetic Interference (EMI). Discontinuity in the load current can be
eliminated or reduced by appropriate selection of the capacitor.
2. LC Inverter – Machine Model
+
The LC inverter-motor model developed for analysis is
given in fig.1 below.
Cs
SCR1
SCR3
SCR5
SCR6
SCR2
+
Vdc
SCR4
Cs
C
C
C
Rsa
Rsb
Rsc
Lsa
Lsb
Lsc
Fig.1 LC inverter – motor model
3. Conventional Analysis
A single-phase version of fig.1 is used to predict a phase current of the load. The
fundamental and harmonics of the load current are presented.
4. Piecewise Linear Analysis
The equivalent series parameters of the inverter-motor model are determined at every
switching action to obtain a phase current of the load.
5. Computation using Matlab
Matlab is used to obtain theoretical results.
6. Choice of Series Capacitor
The capacitor of the LC inverter is carefully selected to eliminate discontinuous
conduction mode.
7. Experimental Results
Experimental waveforms of the load’s phase current
and the voltage across the corresponding series
capacitor are presented.
8. Conclusion
The piecewise linear analysis presents results which agree reasonably with the
experimental results. The continuous conduction mode of the inverter-motor system is
determined by the value of the load current and the selection of the series capacitor.
Presenter’s profile:
 Biography
Chris C. Okoro (B.Sc.(Hons)’1973, University of Lagos. M.Sc.’1975, Imperial College,
London. Ph.D’1980, University of Birmingham, U.K). He is currently a Professor of
Electrical Machines and Power Engineering at the University of Lagos, Nigeria. His
research interests include Power Electronics and High Voltage Engineering. He presently
encourages development of prototypes of power equipment and control systems for local
applications.
He can be reached at [email protected]
Tel (Cell): +234 802 3062749
(Office): +234 15821648
(Hse): +234 18929438
Adeola O. Balogun (B.Sc.(Hons)’1998, University of Lagos, Nigeria. M.Sc.’2004,
University of Lagos, Nigeria). He is currently an Assistant Lecturer at the Electrical and
Electronics Engineering Department, University of Lagos. His research interests include
power electronics and its applications, drive systems, power flow controllers, and
renewable energy for distributed generating systems.
He can be reached at [email protected]
Tel. +234 803 3163288