Robust HFI-Based Sensorless Control of SMPMSMs in the Presence of Large Position Estimation Errors

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Abstract
Due to the inherently low saliency of SMPMSMs, achieving stable high-load operation with HFI-based sensorless control at startup or low speeds is challenging. Moreover, even small cross-saturation inductances can cause significant errors in the estimated rotor angle. This paper proposes a physics-informed strategy that adjusts the $d$-axis reference current to ensure a minimum saliency while running FOC with the estimated angle, without explicit angle compensation. Positive $I_{d}$ injection intentionally saturates the motor, reducing inductances and creating sufficient saliency for stable HFI operation. The method defines the minimum $I_{d}$ for maximum torque operation, ensures accurate torque tracking across the full torque range, and provides an initial position detection (IPD) scheme that eliminates the need for a polarity check. Resonant controllers are incorporated to mitigate inverter nonlinearities and spatial harmonic effects, reducing speed and angle ripple. Experiments on a 400 W SMPMSM demonstrate reliable low-speed operation, startup under load, smooth transitions to a B-emf observer, and robust performance under varying torque conditions, validating the effectiveness and practical applicability of the proposed approach, which is also mathematically formulated and rigorously analyzed.

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