sensorlosen

Sensorless control, or sensorless drive, is a method used in electric motor drives to estimate rotor position and speed without physical position sensors. Information is derived from electrical signals such as stator voltages and currents and the motor’s back-EMF, combined with a dynamic model of the machine. This approach is commonly applied to brushless DC (BLDC) motors and permanent magnet synchronous motors (PMSM).

Techniques include back-EMF based estimation, which uses the measured back-EMF to deduce rotor angle at moderate to high speeds, and model-based observers (for example, Luenberger or sliding-mode observers) or Kalman filters that reconstruct rotor position from a selected set of measurements. At low speed or standstill, back-EMF is weak, so methods such as high-frequency current injection, rotor resistance estimation, or other estimators are used to reveal rotor position.

Sensorless control is frequently integrated with field-oriented control (FOC) or direct torque control (DTC) to achieve torque and flux control without rotor sensors. The approach reduces hardware cost and increases reliability by removing sensors, while being advantageous in harsh environments. However, it faces challenges at zero or very low speed, during rapid load changes, and under parameter variations (stator resistance, inductance, magnet strength). Robust performance depends on accurate motor modeling and estimation algorithms.

Applications span electric vehicles, robotics, home appliances, CNC machinery and industrial drives, where cost reduction and reliability are critical.