Microchip E-Bike Tech Q&A - How to Prevent E-Bike Stall via Hardware Detection?

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Q: How can we control the prevention of E-Bike stalling through hardware detection?

A: Position sensor feedback + backup sensorless observer (to prevent position sensor failure).

Core Cause of Motor Stall

The actual position of the motor rotor is severely misaligned with the drive signals (such as PWM, voltage vectors) output by the controller, leading to “incorrect force direction” and ultimately causing the motor to stop rotating, sudden torque loss, or abnormal vibration. The combination of “position sensor + backup sensorless observer” essentially ensures that the motor position information is not lost or incorrect through a dual hardware-level position detection mechanism, thereby avoiding stalling from the source.

Main Methods for Speed Detection of Electric Vehicles

Sensored Control Solution

This refers to installing physical position sensors (usually Hall sensors or encoders) on the motor to directly detect changes in the rotor position, thereby calculating the speed.

Sensorless Control Solution

This method relies on hardware measurement and avoids issues such as unstable low-speed operation or difficulty in starting that may occur with pure algorithmic estimation.

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Common Sensor Types (Hardware Forms)

The mainstream position sensors in electric vehicles are resolvers or absolute encoders (e.g., magnetic encoders, optical encoders). Both are directly linked to the motor rotor through hardware circuits and output physical position signals:

  • Resolver: Features high and low temperature resistance as well as vibration/shock resistance (suitable for the harsh operating conditions of electric vehicles). Through electromagnetic coupling between stator coils and rotor coils, it outputs sine/cosine analog signals related to the rotor angle. The controller converts the analog signals into digital angle values via a resolution circuit.
  • Absolute Encoder: Directly outputs digital angle signals (e.g., CAN, SPI communication) without the need for “resolution”, offering faster response speed and high precision. However, it has higher requirements for dust and oil resistance in the installation environment.

Backup Sensorless Observer (Emergency Detection Path When Sensor Fails)

Although position sensors are reliable, they still face hardware failure risks (such as sensor coil burnout, signal line open circuit, or resolution circuit failure). Once the sensor fails, the main detection path is interrupted. Without a backup mechanism, the controller will directly lose control and stall due to “no position information”.

At this point, the backup sensorless observer, as a hardware-level emergency solution, obtains the rotor position through indirect calculation to replace the failed sensor, ensuring uninterrupted position information and preventing stalling.

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