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A study on systematic errors concerning rotor position estimation of PMSM based on back EMF voltage observation

Many published methods of rotor position estimation of permanent magnet synchronous machines (PMSM) for medium to high speed are based on the estimation of the back electromotive force (EMF) voltage. From a practical point of view and the demand of minimum complexity, a simple idealized motor model is used many times. Due to this simplification and to a change of coordinates, an observation error of the back EMF voltage occurs, which has, as a consequence, an effect on the estimated rotor position. This study describes an intelligent method of sensorless speed control of PMSM for the whole speed range, which is especially appropriate for pump- and fan-applications. A quite simple method of back EMF voltage observation was found and integrated into the control strategy. Furthermore, the mentioned systematic errors and their effects on the accuracy of the estimated rotor position are analyzed systematically and documented carefully. Theoretical results are verified by simulations and measurement results.