Microchip E-Bike Tech Q&A - How Do You Prevent Thermal Runaway of an E-Bike?

Semiconductor Integrated Circuits (ICs)
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Q: In the E-Bike scheme, how do you prevent thermal runaway of an E-Bike ?

A: 1. FOC control + MTPA mode ensures that the current consumed for the same torque output is smaller, thereby reducing heat loss.
2. Provide various protection monitoring functions, including over-temperature monitoring and overload monitoring, while offering a limp home mode. This mode limits torque output when over-temperature or overload occurs, while still ensuring the basic operation capability of the motor.
3. Regenerative braking can recover energy to charge the battery, instead of using bleeder resistors to dissipate energy (which causes additional heat loss).

1. FOC Control + MTPA Mode

FOC (Field Oriented Control)

An efficient control algorithm for three-phase permanent magnet synchronous motors (PMSMs), which can precisely control the motor’s torque and magnetic field.
Compared with traditional square-wave control, FOC has higher current utilization and generates less heat under the same torque.

MTPA (Maximum Torque Per Ampere) Mode

A mode that enables the motor to consume smaller phase current while outputting the same torque.
Principle: Optimize the distribution of the motor’s d-axis current and q-axis current to maximize the utilization rate of electromagnetic energy, thereby reducing copper loss (I²R loss) and heat generation.

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2. Protection Monitoring + Limp Home Mode

Over-Temperature Monitoring

Real-time monitoring of the temperature of motor windings and controller power devices (MOSFET/IGBT). When the temperature is too high, it issues an alarm or reduces power.

Overload Monitoring

Detects when the motor is in a high-current state for a long time (e.g., climbing slopes, overloading) and intervenes in advance.

Limp Home Mode

When over-temperature or overload is detected, it does not cut off power directly; instead, it limits torque output. This not only prevents further temperature rise but also maintains the basic rideability of the vehicle.

3. Regenerative Braking Replaces Bleeder Resistors

Traditional Scheme

When going downhill or braking, the energy generated by the motor (when it operates as a generator) is dissipated by bleeder resistors and converted into heat.

Improved Scheme

Regenerative braking is used to recharge this part of the energy into the battery. This not only saves energy but also avoids generating additional heat in the controller or braking resistors.

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