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This paper exhibits a novel technique to obtain an encoderless speed control of a permanent magnet synchronous motor (PMSM) in the case of a loss of one phase. The importance of this work is that it presents solutions in order to maintain the operation of the system in various conditions. This will increase the reliability of the whole drive system to meet the safety issues required in some applications. To achieve that, a fault-tolerant inverter modulated through a 3-dimension space vector pulse width modulation technique (3D-SVPWM) is used. Besides that, an algorithm to obtain the exact position of the saturation saliency in the case of a loss of one phase is introduced to achieve a closed-loop field-oriented encoderless speed control and to further enhance the reliability of the whole drive system. This algorithm is based on measuring the transient stator current responses of the motor due to the insulated-gate bipolar transistors (IGBTs) switching actions. Then according to the operating condition (normal or a loss of one phase), the saliency position signals are constructed from the dynamic current responses. Simulation results are provided to demonstrate the effectiveness of the saliency tracking technique under normal and under a loss of one phase conditions. Moreover, the results verify the maximum reliability for the whole drive system that is achieved in this work through a continuous operation of the drive system under a loss of one phase condition and under encoderless speed control.

In this paper a sliding-mode torque and flux control is designed for encoderless synchronous reluctance motor drive. The sliding-mode plus PI controllers are designed in the stator-flux field oriented reference frame which is able to track the mentioned reference signals with a minimum pulsations in the state condition. In addition, with these controllers a fast dynamic response is also achieved for the drive system. The proposed control scheme is robust subject to parameters variation except to stator resistance. To solve this problem a simple estimator is used for on-line detecting of this parameter. Moreover, the rotor position and speed are estimated by on-line obtaining of the stator-flux-space vector. The effectiveness and capability of the proposed control approach is verified by both the simulation and experimental results., {"references":["T. A. Lipo, ÔÇÿSynchronous Reluctance Machines- A viable alternative for\nac drives-, Electric Machines and Power Systems, 1991, vol. 19, pp. 659-671.","H.F. Hofmann, S.R. Sanders, and A. EL-Antably, \"Stator-flux-oriented\nvector control of synchronous reluctance Machines with maximized efficiency\", IEEE Trans. On Ind. Elect., vol. 51, Issue 5, Oct. 2004, pp.\n1066-1072.","P. Guglielmi, M. Pastorelli, A. Vagati,\" Impact of cross-saturation in\nsensorless control of transverse-laminated synchronous reluctance\nmotors\", IEEE Trans. On Ind. Elect., vol. 53, Issue 2, 2006, pp. 429-439.","R. Morales Caporal and M. Pacas, \"Encoderless Predictive DTC for\nSynRM at Very Low and Zero Speed\", IEEE Trans. Ind. Elect., vol. 55,\nNo. 12, Dec. 2008, pp. 4408-4416.","T. H. Liu and H. H. Hsu, \"Adaptive Controller Design for a Synchronous Reluctance Motor Drive System with Direct Torque\nControl\", IET Electric Power Appl., Vol.1, No.5, 2007, pp. 815-824","R. Morales Caporal and M. Pacas, \"A Predictive Torque Control for the\nSynchronous Reluctance Machine taking into account the magnetic cross\nsaturation\", IEEE Trans. Ind. Elect., vol. 54, No. 2, 2007, pp. 1161-1167.","H. D. Lee, S. J. Kang and S. K. Sul, \"Efficiency-Optimized Direct\nTorque Control of Synchronous Reluctance Motor Using Feedback\nLinearization\", IEEE Trans. on Ind. Elect., vol. 46, No. 1, pp 192-198,\n1999es and Power Systems, vol. 19, 1991, pp. 659-671.","I. Takahashi and N. Noguchi, \"A New Quick Response and High\nEfficiency Control Strategy of an Induction Motor\", IEEE Trans. Ind.\nAppl., Vol. 22, 1986, pp. 820-827.","D. Casadi, F. P rofumo, G. Serra and A. Tani, \" FOC and DTC: Two\nVariable Schemes for Induction Motors Torque Control\", IEEE Trans.\nPower Elec., Vol. 17, No. 5, Sept. 2002, pp. 779-787.\n[10] R. Marino, and P. Tomei, ÔÇÿNonlinear Control Design-, Prentice Hall, Inc,1995.\n[11] J.Y. Hung, W. Gao, and Hung, J.C., \"Variable structure control: a\nsurvey\", IEEE Trans. Ind. Elect., Issue 1, vol. 40, Feb. 1993, pp. 2-22.\n[12] Z. Xu and M. F. Rahman, \"Direct Torque and Flux Regulation of an\nIPM Synchronous Motor Drive Using Variable Structure Control\nApproach\", IEEE Trans. On Power Elect., vol. 22, No.6 , Nov. 2007, pp. 2487-2498.\n[13] C. Lascu, I. Boldea and F. Blaabjerg, \" very Low Speed Variable\nStructure Control of Sensorless Induction Machine Drives without\nSignal Injection\", IEEE Trans. Ind. Appl., vol. 41, No. 2, Mar./Apr. 2005, pp. 591-598.\n[14] D. Casadei, G. Serra, and A. Tani, \"Implementation of a direct torque\ncontrol algorithm for induction motors based on discrete space vector\nmodulation,\" IEEE Trans. Power Elec., vol. 15, July 2000, pp. 769-777.\n[15] C. Lascu, I. Boldea, and F. Blaabjerg, \"A modified direct torque control\nfor induction motor sensorless drive,\" IEEE Trans. Ind. Appl., vol. 36,\nJan./Feb. 2000, pp. 122-130.\n[16] L Tang, and M. F Rahman, \" Investigation of an Improved Flux\nEstimator of a Direct Torque Controlled Interior Permanent Magnet\nSynchronous Machine Drive\", 35th Annual IEEE Power Electronics\nSpecialists Conf., Aachen, Germany, 2004, pp. 451-457.\n[17] S. Mir, M.E Elbuluk, and D.S Zinger, \"PI and Fuzzy Estimators for Tuning the Stator Resistance in Indirect Torque Control of Induction Machines\", IEEE Tran. On Power Elect., vol. 13, No. 2, March 1998, pp. 279-287."]}