Energy and Power Engineering, 2010, 10-17 doi:10.4236/epe.2010.21003 Published Online February 2010 (http://www.scirp.org/journal/epe) Copyright © 2010 SciRes EPE Three-Level Five-Phase Space Vector PWM Inverter for a Two Five-Phase Series Connected Induction Machine Drive N. R. ABJADI 1 , J. SOLTANI 2 , J. ASKARI 2 , Gh. R. Arab MARKADEH 1 1 Department of Engineering, Shahrekord University, Shahrekord, Iran 2 Department of Electrical and Computer Engineering, Isfahan University of Technology, Isfahan, Iran Email: navidabjadi@yahoo.com Abstract: This paper describes the decoupled torque and flux control of a two series connected five-phase Induction Machine (IM) drive that is supplied by a three-level five phase SVPWM inverter, using a well known phase transposition in the series connection. At the first, the decoupled torque and flux controller is developed based on variable-structure control (VSC). Then, a sliding-mode (SM) flux observer in employed to estimate the stator flux; that uses a two reference frames which result in eliminating the speed adaptation. Moreover simple control strategy is introduced for three-level SVPWM voltage source inverter (VSI) that can be easily implemented in practice for a two-series five phase IM drive. Finally, the effectiveness and capability of the proposed control method is verified by computer simulation. Keywords: multiphase systems, multilevel VSI, sliding mode control 1. Introduction In electrical drive applications, three-phase drives are widely used for their convenience. However, high-ph- ase number drives possess several advantages over conventional three-phase drives such as: reducing the amplitude and increasing the frequency of torque puls- ations, reducing the rotor harmonic currents, reducing the current per phase without increasing the voltage per phase, and lowering the dc-link current harmonics and higher reliability. By increasing the number of phases, it is also possible to increase the torque per rms ampere for the same volume machine [1]. Multi-phase machines have found wide applications in transport, textile manufacturing and aerospace since few years [2–14]. The recent research works on multi- phase machines can be categorized into multi-phase pulse width modulation (PWM) techniques for multi- phase machines [2–14], harmonic injection to produce more torque and to achieve better stability [5], fault tolerant issues of multi-phase motor drives [6], series/ parallel connected multi-phase machines [7–14]. Applications involving high power may require multiphase systems, in order to reduce stress on the switching devices. There are two approaches to supplying high power systems; one approach is the use of multilevel inverters supplying three-phase mac- hines and the other approach is multileg inverters sup- plying multiphase machines. Much more work has been done on multilevel inverters. It is interesting to note the similarity in switching schemes between the two approaches: for the multilevel inverter the additional switching devices increase the number of voltage levels, while for the multileg inverter, the additional number of switching devices increases the number of phases [15]. In [16], Kelly et al. also verified that an n-phase space vector PWM (SVPWM) scheme can be described in terms of the applying times of available switching vectors on the basis of the space vector concept. How- ever, the paper only focuses on how to realize a sinu- soidal phase voltage. As is widely known, most multi- phase motors are designed to have the nonsinusoidal back-EMF voltage. Hamid A. Toliyat have made much research on control method and running performance aim at five-phase drive [1], but their subject investigated is the system feeding with two level inverter. Another research work has been done in [17] on a multiphase two level nonsinusoidal SVPWM. The power rating of the converter should meet the required level for the machine and driven load. However, the converter ratings can not be increased over a certain range due to the limitation on the power rating of semiconductor devices. One solution to this problem is