Relative Speed Compensation for Sensorless Control of Magnetic Screw Motor Based on an Improved Pulsating Current Injection Method

The magnetic screw motor (MSM) drive systems often require both a rotary encoder and a linear encoder for their precise positioning, which makes the design of such systems very challenging and costly. This paper proposes a novel position sensorless control strategy. First, an improved pulsating current injection (IPCI) sensorless control is proposed to replace the rotary encoder. This method associates the amplitude of the injection signal with the q -axis current by introducing a transformation matrix. In the proposed method, the amplitude of the injection signal increases with the load/speed variation, which enhances the rotary speed estimation accuracy in transients. Meanwhile, when the motor operates in a steady state, the amplitude of the injection signal is maintained in a low range, which reduces the audible noise. Second, the linear encoder is eliminated using a relative speed compensation based on a lookup table (LUT) method. The relative speed under different linear speeds can be obtained and tabulated from several experimental tests. The presented experimental results verify the proposed method and its performance.