This paper presents signal conditions taking motor efficiency into account for position sensorless control of interior permanent magnet synchronous motors (IPMSMs). Signal injection is necessary for position estimation based on an extended electromotive force (EEMF) model at standstill and low speeds. We have proposed a maximum torque control reference frame and the EEMF model suitable for signal injection, and we executed sensorless control in the entire driving area. However, its effects on motor efficiency have not been evaluated in the previous study. Therefore, in this paper, we optimize the amplitude, phase, and frequency of signal current. Moreover, we applied a signal current amplitude adjusting method. This method makes the signal current amplitude minimum based on the EEMF. As a result, we can maintain constant efficiency including copper loss and other losses of the motor, regardless of the signal frequency. The signal frequency can be freely selected in terms of the motor efficiency, so that the proposed method can improve the flexibility to design the injection signals for the position sensorless control of the IPMSMs.
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