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This paper addresses the problem of the variation of stator resistance, which significantly degrades the performance of a direct torque controlled (DTC) interior permanent magnet (IMP) synchronous motor. The problem is manifested by errors in the estimated flux linkage vector and in the electromagnetic torque, which causes unstable operation of the DTC drive. The extent of the problem associated with variation of stator resistance on the performance of the DTC controller of an interior permanent magnet synchronous motor drive is first presented, followed by a technique for the estimation and compensation of the effect of stator resistance variation. A method of stator resistance estimation using proportional-integral (PI) estimator has been investigated in this paper. Modeling and experimental results presented clearly demonstrate the effectiveness of the estimator in tracking the stator resistance and in compensating for the effects of its variation.