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A rotor initial position estimation method for sensorless control of SPMSM

High frequency (HF) sinusoidal voltage injection is a common method to estimate the initial rotor position of permanent magnet synchronous machines (PMSM). When a HF sinusoidal voltage is injected into d-axis, the saturation of magnetic field in d-axis can lead to HF current response including harmonics. This paper makes a detailed analysis on the harmonic current response. Based on the analysis, a novel method of magnetic polarity detection is proposed. Conventionally, a positive and a negative pulse voltage are injected into d-axis after the primary estimation to detect the magnetic polarity, while the novel method can detect the magnetic polarity with no extra signal injection. Compared with the conventional way, the proposed method has some advantages as follows: 1) No extra signal injection which simplifies the estimating process; 2) No comparison of the current response which lowers the requirement of sensor's precision. Simulations and experiments both verify the proposed method.