In the paper is presented a comparison of three method of back electromotive force estimation. Presented structures: the observers and the simulator, are utilized to estimate the back electromotive force for speed range below single revolution per second. Theirs instantaneous values are used then to calculate the shaft position of the permanent magnets synchronous motor. Performance of such structures is very important in a case of position estimation at the low speed range. These methods are based on the following structures for back electromotive force estimation: observer for model of the electrical part of the motor, the observer with modified correction function, and estimation based on the simplified model. Obtained in this way the instantaneous values of the back electromotive force, depending on the method of obtaining them, are characterized by different quality and accuracy of the estimated shaft position. Estimated and measured values are compared and discussed.
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