Noise-Free Sensorless Control of Robotic PMSMs Based on Variable Structure Speed Observer with Embedded Single-Waveform Injection Over Full-Speed Range

For the full-speed sensorless control of permanent magnet synchronous motors (PMSM) used in robotic joints, conventional methods adopt a combined strategy of zero-low-speed and medium-high-speed control methods. This requires switching between methods during motor operation, which reduces the reliability and stability, making it unable to be used in robotic joint motors. In this paper, a novel full-speed range sensorless control method is proposed. The method consists of two ranges: the zero-speed and the operation range. In the zero-speed range, a high-frequency square wave injection (HFSI) method with only 20 square-wave pulses (SWPs) is employed, resulting in a short injection duration, which ensures low noise. Leveraging the bidirectional convergence property of the linear time-invariant enhanced phase-locked loop (LTI-EPLL), the initial position and NS polarity can be determined without additional signal injection, ensuring smooth startup and rotor standstill. In the operation range, based on the eletrical properties of the PMSM, a sliding-mode speed observer (SMSO) is constructed to directly estimate the speed, and the position is obtained via integration. Thus, full-speed range operation is achieved without the need to switch between methods during operation range. Finally, the feasibility of this method is validated in MATLAB/Simulink.