Microchip E-Bike Tech Q&A - Which Components Need Monitoring to Ensure Stability?

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Q: What components need to be monitored in an E-Bike to ensure its stability?

A: Position signal feedback, output phase current, bus voltage, bus current, power transistor temperature, motor temperature, and relevant data on the battery side.

The stability control of an E-Bike essentially relies on real-time monitoring of key physical quantities to build a “perception-decision-execution” closed-loop system, ensuring that motor output, energy distribution, and safety protection are always in a controllable state.

1. Drive System Stability: Dynamic Matching Between Motor Output and Load

Position Signal Feedback

This directly reflects the real-time angle and speed of the motor rotor (e.g., the electrical angle of a permanent magnet synchronous motor) and serves as the core basis for the controller to implement FOC (Field Oriented Control).
If the position signal is lost or incorrect, the controller cannot accurately output a matching voltage vector, which will cause torque fluctuation, speed runaway (such as sudden jerking or stalling), and seriously affect driving stability.

Output Phase Current (Stator Three-Phase Current)

This element reflects in real time the actual output state of the motor and is directly related to torque (PMSM torque formula: T ∝ Iq, where Iq is the q-axis current).
Monitoring purposes:

  1. Prevent motor or power device burnout due to overcurrent;
  2. Ensure the actual current tracks the command current through current closed-loop control (PI regulation), avoiding abnormal torque output (e.g., insufficient torque during acceleration, unstable braking during deceleration).

Bus Voltage (DC Bus Voltage, e.g., Inverter Input Voltage)

Bus voltage reflects the power supply state of the DC side (battery/capacitor) and directly affects the voltage amplitude of the inverter output (the voltage range of PWM modulation is limited by the bus voltage).
If the bus voltage drops suddenly (e.g., battery depletion, poor cable contact), the motor output torque will decrease abruptly; if the voltage rises suddenly (e.g., overcharging during regenerative braking), it may cause breakdown of power devices. Real-time monitoring can trigger protections such as torque limitation and shutdown to maintain system stability.

Bus Current (DC Side Input Current)

Bus current reflects the energy input intensity of the entire drive system and is directly related to motor power consumption and battery discharge capability.
Example: Excessive bus current during sudden acceleration will cause over-discharge of the battery (affecting its service life) or trigger the overcurrent cut-off function of the battery protection board, leading to power interruption. Monitoring can limit the maximum current to balance power output and battery safety.

2. Hardware Safety Stability: Preventing Device Failure and Thermal Runaway

Power devices for E-Bikes (e.g., IGBTs, motors) are prone to damage due to overheating under high load. Temperature monitoring is the key to avoiding stability collapse caused by hardware failure:

Power Transistor Temperature (e.g., IGBT, MOSFET Chip Temperature)

Power devices have losses (switching loss, conduction loss) during conduction, which are converted into heat. Excessively high temperatures will cause device breakdown (thermal breakdown), directly leading to inverter failure and motor loss of drive.
Monitoring purpose: When the temperature approaches the threshold, the controller will actively reduce torque (by reducing switching frequency or current) to lower the device load and avoid overheating damage.

Motor Temperature (Stator Winding or Housing Temperature)

During motor operation, the winding resistance increases with temperature rise (increasing copper loss), and permanent magnets may demagnetize at high temperatures (resulting in permanent torque drop).
Monitoring purpose: Prevent performance degradation or permanent damage of the motor due to overheating. For example, trigger speed reduction protection during long-term climbing to ensure the motor operates within a safe temperature range.

3. Energy System Stability: Balance Between Battery and E-Bike Energy Flow

The battery is the energy source of an E-Bike, and its state directly affects the continuity and safety of power output. The core data to be monitored include:

  • Battery SOC (State of Charge): Refers to the remaining charge, used to avoid over-discharge (sudden voltage drop and power interruption due to low charge) or overcharging (during charging).
  • Battery SOH (State of Health): Reflects the aging degree of the battery. Aged batteries have reduced charging and discharging capabilities, so the controller needs to adjust the maximum output power according to SOH to avoid insufficient power caused by the battery’s inability to provide sufficient current.
  • Battery Cell Voltage and Temperature: Prevent overvoltage/undervoltage of a single battery cell (affecting the service life of the entire battery pack) or local overheating (triggering thermal runaway and fire risks).
  • Battery Circuit Current: Linked with the bus current to ensure that the charging/discharging current does not exceed the battery’s safety thresholds (e.g., peak discharge current, continuous current).

Summary: Multi-Component Monitoring Builds a “Stability Protection Network”

These monitored components do not exist in isolation but form synergy through the controller’s algorithms:

  • Position signal + phase current → Ensure accurate motor torque output (dynamic response stability);
  • Bus voltage + bus current + battery data → Ensure balance between energy supply and consumption (energy stability);
  • Power transistor temperature + motor temperature → Ensure hardware operates within safe thresholds (hardware stability).

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