Sensorless control of an axial flux motor using square-wave injection for low switching frequencies

A new sensorless control approach is introduced for a yokeless and segmented armature axial flux-switching sandwiched permanent-magnet motor with a 12-slot/19-pole configuration (12S/19P YASA-AFFSSPM), specifically designed to enhance rotor position estimation at low speeds under low switching frequency conditions. The approach employs a square wave voltage injection technique, which is particularly suited for applications like rail transit systems, where low switching frequencies are common. To improve performance, a dual-frequency control architecture is implemented, combining voltage injection and error signal processing in the modulation cycle while simultaneously tracking rotor position and speed in the control cycle. This methodology extends the effectiveness of the control system at low switching frequencies and resolves phase error and dynamic performance issues typically caused by filter-based approaches. Additionally, the influence of extended PWM delays on rotor position estimation is analysed, and a compensation algorithm is introduced to mitigate these delays. Experimental validation confirms the proposed strategy’s capability for accurate rotor position estimation and speed tracking, even under the influence of PWM delays, while ensuring consistent dynamic performance.