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Control of electric motors*

Summary: PWM, Hall sensors/encoders, speed/torque control.

1) Why a controller is essential

  • BLDC/PMSM motors require a controller (inverter) to create AC phases from 48–51.2 V DC, synchronised with the rotor position.
  • The controller regulates the current (thus the torque), speed, applies ramps, protects (overvoltage/undervoltage/overcurrent/temperature), and exposes data (current, speed, temperature) useful for supervision/robotisation.

2) Control principles (simplified)

  • PWM (Pulse Width Modulation): adjusts the average voltage applied to the phases; limits the current.
  • Six-step / trapezoidal: sector commutation from Hall sensors (or sensorless back-EMF). Simple, economical.
  • FOC (Field Oriented Control): vector control (d,q axes) for consistent torque and better efficiency under variable load; requires Hall/encoder or estimation.
  • Loops: speed (PID) and/or torque (current). Configuration: gains, limits, ramps.

3) Sensors and feedback modes

  • Hall sensors: 3 sensors, sector info; sufficient for moderate speed and stable torque.
  • Encoder (sin/cos, absolute): fine position/speed; useful for precise control, synchronisation, robotics.
  • Sensorless (back-EMF): possible but less robust at very low speed/high torque.

5) Commissioning (minimal checklist)

  1. Check polarity and DC protections (fuse near +, isolator).
  2. Connect phases and sensors (Hall/encoder) according to manufacturer's pinout.
  3. Configure: pack voltage, currents (cont/peak), temperature limits, sensor type, rotation direction, ramps.
  4. Test unloaded: gradual ramp-up, check telemetry (current, speed, T°) and absence of faults.
  5. Test under light load: monitor motor/controller heating, abnormal noise, torque.

6) CAN Bus: practical basics

  • Topology: linear bus, 120 Ω termination resistors at each end; no long stubs.
  • Cable: twisted pair, shielding recommended; lengths according to speed (e.g. 250 kbps → ~250 m).
  • Addressing/ID: define unique IDs; speed consistent with length; check errors (bit/ACK).
  • Protocol: CiA 402 (DS402) for speed/torque/position modes; provide a master node (PLC/MCU) and safety logic (estop, watchdog).

7) Safety and good practices

  • PPE; avoid short circuits; respect tightening torques; IP compliant.
  • Controller: dissipate heat (thermal contact to chassis + paste), avoid enclosed areas without ventilation, consider derating.
  • Power cabling: reduced lengths, suitable sections, robust ground return, power/logic separation.
  • Signal cabling: twist, shield, clean reference ground; avoid loops; ensure good grounding for Hall/encoder.
  • Regeneration: if regenerative braking, provide discharge resistor or strategy to avoid overloading the battery.

8) Quick diagnosis

  • Read the controller fault codes (overvoltage/undervoltage/overcurrent/temperature/sensor).
  • Check telemetry: current, pack voltage, temperatures, speed; compare to expectations.
  • Oscilloscope/DC clamp if needed: check current ripples, noise, voltage drops.
  • Common issues: phase/sensor inversion (knocking), overheating (insufficient dissipation), CAN interference (poor termination/shielding), loose connections.

Quick checklist

  • Controller compatible with 48–51.2 V voltage and max charge margins
  • Suitable cont/peak currents; planned dissipation; IP compliant
  • Sensors configured (Hall/encoder) and rotation direction validated
  • CAN Bus wired (120 Ω terminations, shielding, IDs)


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*: The technical information presented in this article is provided for guidance only. It does not replace the official manuals of the manufacturers. Before any installation, handling or use, please consult the product documentation and follow the safety instructions. Torque.works cannot be held responsible for inappropriate use or incorrect interpretation of the information provided.