Very low speed PMSM sensorless control based on signal injection

1 Introduction
In recent years, speed sensorless vector control of permanent magnet synchronous motor (PMSM) has become a research hotspot. At present, PMSM speed sensorless vector control has achieved good control performance in the medium and high speed range, but has not yet achieved good control in the ultra-low speed range (<1Hz). This is because PMSM speed sensorless vector control requires the use of back electromotive force, which is very small at ultra-low speed and is greatly affected by changes in motor parameters, resulting in reduced control performance and inability to achieve speed sensorless vector control at ultra-low speed and zero speed.
In order to achieve PMSM speed sensorless control at ultra-low speed, researchers have proposed various control methods. Among them, the most studied is the high-frequency signal injection method, which uses the current response generated by the injected high-frequency stator voltage signal to estimate the rotor position [1]-[7]. These methods based on high-frequency signal injection all utilize the non-ideal characteristics of PMSM, such as electromagnetic salient poles and saturation effects. Therefore, these methods are suitable for internal permanent magnet synchronous motors (IPMSM) with rotor salient poles, but have little control effect on surface permanent magnet synchronous motors (SPMSM).
This paper introduces a low-frequency signal injection method [8] and builds a simulation model to realize the speed sensorless control of SPMSM in the extremely low speed section and zero speed area. This method injects a low-frequency d-axis stator current signal and uses the generated back-EMF response to estimate the motor speed. It only uses the fundamental wave model of PMSM and does not rely on various non-ideal characteristics. Therefore, it is suitable for SPMSM control. This paper conducts a large number of simulations and analyzes the simulation results. It not only proves the effectiveness of this method, but also puts forward issues and directions that need further research.
2 PMSM mathematical model