Choose Sensor-Based or Sensorless Approach for Position Sensing
The need for position information is a fundamental requirement for many types of motor control. For example:
In FOC of PMSM, we transform three-phase currents from the stationary frame to two orthogonal DC quantities (Id, Iq) in a rotating frame aligned with the rotor's magnetic field. This transformation requires precise knowledge of the rotor's electrical angular position (θe).
In trapezoidal (six-step) control for BLDC motors, the controller needs to know when to switch to the next step in the sequence (that is, which two phases to energize and in which direction) to maintain continuous rotation. This switching must be synchronized with the rotor's position.
The choice between a sensor-based and a sensorless approach is a critical design decision for any electronically commutated motor.
| Position Sensing Method | Component | Require open-loop start? | Starting method | Require motor parameters? | Tuning complexity | Applicable speed range |
|---|---|---|---|---|---|---|
| Sensor-based | Quadrature Encoder | Yes (only for the first time to find an index pulse position) | I-F control-based startup for loaded or unloaded motor Voltage/Frequency (V/f) control for unloaded motor | No | Low | Zero speed to very high speeds |
| Hall Sensor | No | The controller reads the initial position from the Hall sensors and begins commutation directly from a standstill. | No | Very Low | Low to medium speeds | |
| Resolver | No | Provides an absolute position at startup, allowing the controller to begin commutation from a standstill. | No | Moderate | Zero speed to very high speeds | |
| Sensorless | Flux Observer | Yes | I-F control-based startup for loaded or unloaded motor Voltage/Frequency (V/f) control for unloaded motor | Yes | High | Above min speed till base speed (10% - 100% of base speed) |
| Sliding Mode Observer | Yes | I-F control-based startup for loaded or unloaded motor Voltage/Frequency (V/f) control for unloaded motor | Yes | High | Above min speed till base speed (10% - 100% of base speed) | |
| Extended EMF | Yes | I-F control-based startup or PHFO for loaded or unloaded motor V/F for unloaded motor | Yes | High | Above min speed till base speed (10% - above base speed) | |
Pulsating High-Frequency Observer (Requires Saliency) | No | Yes | Very High | Zero speed to low-to-medium speeds |
