The Last Frontier of Sensorless FOC Falls

Breaking the Final Barrier of Sensorless FOC: Stable Zero-Speed Torque Control
The Last Frontier of Sensorless FOC is About to Fall

Over the past decade, I have personally witnessed and participated in the evolution of motor control technology – from impossibility to disruptive innovation to practical implementation. We’ve progressed through key milestones: open-loop forced starting with sensorless observers, zero-speed closed-loop control, and now achieving stable zero-speed torque maintenance. This represents nearly ten years of technological iteration.

The journey from believing rotor position/speed estimation was fundamentally impossible without back-EMF or flux linkage, to overturning these assumptions through practical innovation, has been truly enlightening. This experience proves that true technological advancement comes not from recycled knowledge peddled in training courses, but from relentless practical verification and refinement that becomes core competence while pushing industry technology forward.

Demonstration of Stable Zero-Speed Torque in Sensorless FOC:
Test platform: 72MHz Cortex-M0 MCU
Motor: SPMSM (24V, 60W, 3000RPM)
Configuration: Max phase current limited to 1A to highlight torque stability during stall/reversal

Algorithm Characteristics:
A.No HFI (High-Frequency Injection) required
B.During stall: zero speed, fixed angle, constant three-phase current
C.Single observer for full speed range
D.Speed closed-loop operation

Why Zero-Speed Torque Was Considered Impossible:
The core challenge lies in the disappearance of back-EMF at standstill – the “eyes” of traditional observers. Without this signal:
a.Position estimators become “blind”
b.Incorrect initial position estimation causes:
c.Violent vibration
d.Loss of synchronization
e.Failed starts

Industry Solutions (and Their Limitations):
1.HFI injection (adds noise/cost)
2.Advanced IPD (Initial Position Detection)
3.Hybrid observer switching strategies

Conclusion:
The breakthrough in zero-speed torque stability marks a new era for sensorless FOC:
1.Ultra-reliable startup
2.Silent, precise control
3.Perfect cost-performance balance

This isn’t just an engineering milestone – it represents humanity’s growing mastery of electromagnetic forces. When motors can deliver precise, powerful torque from complete standstill without sensors, we’ll have reached the pinnacle of sensorless FOC technology.

The revolution is coming – and we’ll all witness it.