A Torque Reference Limiter to Avoid Unstable Region of High-Frequency Signal Injection-Based Sensorless Control

A pulsating high-frequency (HF) signal injection-based sensorless control enables the zero/low-frequency sensorless control. The rotor position is estimated from the induced HF current based on the machine’s saliency. So, the control performance may be degraded if the saliency characteristics change due to the magnetic flux-linkage saturation effect. Especially, rotor position estimation may fail due to the loss of saliency, making the sensorless control unstable. This paper analyzes the unstable region of the sensorless control and shows the examination result of the unstable region of permanent-magnet synchronous machines (PMSMs) where the saliency disappears. In addition, a torque reference limiter to avoid the unstable region of sensorless control is proposed in this paper. The unstable region of the sensorless control can be identified using the dynamic inductance, where the inductance is calculated from the measured current and the magnetic flux-linkage saturation model. The proposed torque reference limiter restricts the operating point to avoid the unstable region. The proposed method was verified with an 11 kW IPMSM, and the results proved that the sensorless control fault could be avoided with the proposed method.