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At low speed, the traditional high frequency signal injection (HFSI) control strategy will lead to large torque ripple, and affect the estimation accuracy of the position/speed related to sensorless control algorithm, and finally lead to the problem of the system stability. Based on the characteristics of sevenphase Permanent Magnet Synchronous Machine (PMSM), this paper proposes a new sensorless control strategy in full speed range. In the zero/low speed range, HFSI method is applied to the 5th harmonic subspace, which reduce the torque ripple of the machine.. In the medium/high speed range, the sliding mode observer (SMO) is used in the 1st harmonic subspace to estimate the speed and position of the machine. The influences between the two methods are effectively reduced when exchanging from zero/low speed to medium/high speed range. Moreover, the estimated position and speed is more accurate and the torque ripple is smaller with the proposed sensorless control strategy. Finally, the effectiveness of the proposed strategy is verified by simulation results.

This paper presents a sensorless control strategy for seven-phase non-sinusoidal permanent magnet synchronous machine (NSPMSM) with high frequency signal injection (HFSI) method in 5th harmonic subspace. Seven-phase nonsinusoidal machine benefits high torque density due to the use of third harmonic components. Firstly, two torque generation strategy in different harmonic subspaces with the minimum injected rms value and amplitude of current is deduced in this paper. Secondly, in order to reinforce the reliabilities of multiphase machine, the HFSI sensorless control is employed. Comparing with traditional HFSI method, the proposed control strategy is achieved in 5th harmonic subspace, which can avoid the torque ripple caused by the injected signal. Finally, according to simulations results the two torque distribution method is validated and compared and the effectiveness of the HFSI method is verified.