This paper deals with an amplitude-adjusting method for signal injection in position sensorless control of interior permanent magnet synchronous motor (IPMSM) drives. Signal injection is necessary for position estimation at standstill and low speeds. Response signals to the injected signals have position information because of the saliency of the IPMSMs. The position information appears in inductances depending on the rotor positions; therefore, time derivative of motor currents has to be measured directly or indirectly. The position estimation method discussed in this paper is based on an extended electromotive force (EEMF) model. Although the EEMF model is mainly used in middleand high-speed regions of IPMSM drives, it can be applied to all speed regions by combining it with signal injection methods. We adopt a signal injection method to stabilize the estimation and reduce the effects of disturbances. Then, the amplitude of the signal currents is adjusted to maintain a sufficiently high amplitude of EEMF against disturbances. Signal setting becomes easier because the lower limit of EEMF can be adjusted against the degree of disturbances.

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This paper presents a novel pattern matching based position sensorless control method for IPMSMs. A target IPMSM for the proposed method is designed such that it has high power and torque density, while also being significantly influenced by magnetic saturation. As previously reported in papers [1, 2], for IPMSMs, heavy magnetic saturation affects the spatial distribution of phase inductances according to rotor positions. Most position sensorless controls at low speeds typically depend on the assumption that phase inductances have sinusoidal spatial distribution according to rotor positions. Therefore, it is difficult to apply conventional methods to IPMSMs with heavy magnetic saturation. In the proposed method, rotor position is estimated by pattern matching using feature values, so that the phase inductances have unique and reproducible value according to rotor positions. While template data sets are required for the proposed method, the assumption for sinusoidal phase inductances is not. In this paper, the effect of magnetic saturation for position estimation based on conventional methods is discussed in Section 1 and 2. Then, details of the proposed method are shown in Section 3. In Section 4, results of experiments carried out in steady state and transient state are presented. The effectiveness of the proposed method is verified through the experiments.

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