Sensored or Sensorless BLDC Motor Controller?

To drive a brushless (BLDC) motor, the controller must know where the rotor is at every moment. That information either comes from a sensor in the motor or is estimated by the controller from the voltage the motor generates. That is the question behind “sensorless BLDC controller” searches: is a sensor necessary?

Hall Sensors

Three Hall sensors in the motor report rotor position in six steps. They are simple and reliable, and because they know the position from zero speed, starting under load is no problem. Resolution is limited, but usually enough for vehicle traction.

Encoders

An encoder gives much finer position and speed information from the shaft. It is preferred for AGVs, AMRs and machines that need smooth low-speed torque, precise speed control and positioning.

Resolvers

A resolver is a magnetic position sensor with no electronics inside. Because it withstands high temperature, vibration and shock, it stands out in heavy-duty and defence applications.

Sensorless Control

In sensorless control the controller calculates rotor position from the back-EMF the spinning motor generates. Sensor and cabling costs disappear, and it works well for fans and pumps that start without load. But a stationary motor generates no back-EMF, so starting under heavy load — especially on a ramp — is difficult. For traction and positioning, sensored control is the safer choice.

Which Should You Choose?

• Fans, pumps, applications that start unloaded → sensorless control may be enough.
• Vehicle traction, starting under load → Hall sensors or an encoder.
• Precise speed and position control → encoder.
• High temperature, vibration, harsh field use → resolver.

Feedback on the TULPAR Series

All models in our BLDC motor controller series TULPAR support encoder and Hall feedback; a resolver is optional on TULPAR 300, TULPAR 275 and TULPAR 100. We explain how feedback affects the control method in what is FOC.