Torque Ripples Suppression for Six-Phase Induction Motors Under Open Phase Faults R. Kianinezhad * , B. Nahid-Mobarakeh ** , L. Baghli *** , F. Betin ** and G.A. Capolino ** Abstract- This paper introduces a new disturbance free operation method for six-phase induction motors. The machine is supposed to loss one or more phases and to have a pulsating torque. In order to improve the motor torque, we propose a new control law satisfying a condition required to have a smooth torque. The simulation and experimental results illustrate the validity and the efficiency of the proposed method for disturbance free operation of six-phase induction machines. 1 I. INTRODUCTION In the industrial applications where high reliability is required, multi-phase induction machines instead of traditional three-phase machines are used. In the multi-phase drive systems, the electric machine has more than three phases in the stator and the same number of inverter legs is in the inverter side. The advantages of multi-phase drive systems are: total rating of system is multiplied, the torque pulsations will be smoothed, the rotor harmonic losses as well as the harmonics content of the DC link current will be reduced and the loss of one or more phases, does not prevent the machine working, so improving the system reliability. The most common multi- phase machine drive structure is the six-phase induction machine (SPIM), which has six windings in the stator (Fig. 1). One of the most important faults in the electrical drives is the suppression of one or more stator phases of the motor. This case takes place when a transistor in the inverter, or one of the motor phases is opened. This fault causes other problems like disturbing the rotating MMF, and producing a high pulsating torque. As the dynamic behavior of the electrical machines is very important in the modern drive systems, it is crucial to Fig. 1. Circuit diagram of SPIM and its inverter. 1 * R. Kianinezhad is with the University of Shahid Chamran, Electrical Engineering Department, Ahvaz, Iran (e-mail: reza.kiani@scu.ac.ir). ** B. Nahid-Mobarakeh, F. Betin and G.A. Capolino are with the Centre de Robotique, Electrotechnique et Automatique (CREA), CNRS EA 3299, Université de Picardie Jules Verne, avenue F. Mitterrand, 02880 Cuffies, France (e-mail: babak.nahid@ieee.org and franck.betin@ieee.org). *** L. Baghli is with the Groupe de Recherche en Electronique et en Electrotechnique de Nancy (GREEN), CNRS UMR 7037, avenue de la forêt de Haye, 54516 Vandoeuvre-Nancy, France (e-mail: lotfi.baghli@ uhp-nancy.fr). develop a method to improve the behavior of the machine under phase fault conditions. In [1], it is shown for three-phase ac machines that during an open phase fault, a zero sequence current component is required to maintain an undisturbed rotating MMF. This zero sequence component is established by a connection between the motor neutral and the dc midpoint. In the multiphase ac machines as a result of more phases, additional degrees of freedom are available. In [2], the authors showed that for multiphase ac machines during open phase fault conditions, the neutral line is not required. In this case, the machine under fault may produce the same MMF as normal case by an appropriate choice of phase currents combination resulting to a smooth non pulsating torque. Another approach based on modifying only one phase current to eliminate the torque ripples is presented in [3]. In [4], the authors propose to choose a proper stator voltage vector according to a proper control law in order to have a non-pulsating torque. In this paper, we propose a new approach for eliminating the torque ripples. It results from our analysis of the electromagnetic torque when the machine is faulty. This analysis, given in this paper, shows that the torque is smooth if a simple condition on the stator currents is verified. This condition may be satisfied by a proper control law suppressing the torque ripples. This will be presented and tested by simulation and experimentation in this paper. This paper is organized in five sections. The model of the machine under open phase fault is presented in the next section. Then, the electromagnetic torque expression will be given in section III. It will be shown that the torque contains two components under open phase conditions: an average one and a pulsating one. The fourth section presents three control methods suppressing the pulsating torque. Finally, the efficiency of the presented methods will be studied in section V by simulation and experimentation. II. MODEL OF SPIM UNDER OPEN PHASE FAULT The basic equations of SPIM under balanced operating conditions are expressed in [2]. Here, because of the space restrictions, we give only the model under fault conditions. To do this, we begin by the following stator and rotor voltage equations: [ ] [ ][ ] [ ][ ] [ ][ ] ) . . ( . r sr s ss s s s I L I L dt d I R V + + = (1-a) [ ] [ ][ ] [ ][ ] [ ][ ] ) . . ( . s rs r rr r r r I L I L dt d I R V + + = (1-b) In which the current and voltage vectors are: [ ][ ] [ ][ ] [ ][ ] [ ][ ] T r r r r r r r T r T s s s s s s T s s s s s s i i i i i i I V i i i i i I v v v v v V 6 5 4 3 2 1 6 5 4 3 2 6 5 4 3 2 0 0 0 0 0 0 = = = = (1-c) O 1 2 3 4 5 6 Vs1 Vs2 Vs3 Vs4 Vs5 Vs6 Vr1 Vr2 Vs3 Vr4 Vr5 Vr6 γ 1363 1-4244-0136-4/06/$20.00 '2006 IEEE