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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