sensorloze

Sensorless control is a motor control method that estimates rotor position and speed without physical position sensors such as encoders or Hall-effect devices. It is widely used in brushless DC motors (BLDC) and permanent-magnet synchronous motors (PMSM) to reduce hardware costs and improve reliability, particularly in compact drives or harsh environments.

Most sensorless approaches rely on the motor’s electrical signals. Back-EMF based methods infer rotor angle from the measured phase voltages and currents when the motor is spinning and back electromotive force is present. At low speed or standstill, back-EMF is weak, so alternative strategies are employed. These include high-frequency signal injection, which adds a small, detectable disturbance to extract rotor position; and model-based observers such as Luenberger observers, extended Kalman filters (EKF), or sliding-mode observers that use a mathematical motor model to estimate position and speed. Model reference adaptive systems (MRAS) are another approach used in some applications.

Sensorless control is commonly integrated with field-oriented control (FOC) or vector control, enabling decoupled torque and flux control in PMSM and BLDC drives. It can also be used in direct torque control (DTC) schemes. Startup and low-speed operation remain challenging, and reliable estimation often requires accurate motor parameter knowledge (resistance, inductance) and careful handling of temperature effects and noise.

Advantages of sensorless control include lower cost, fewer components, improved safety in sealed or high-vibration environments, and reduced maintenance. Limitations involve degraded performance at very low speeds, potential sensitivity to parameter variations, higher computational demands, and occasional instability during transients. Ongoing research targets expanding speed ranges, improving robustness, and reducing sensitivity to motor parameter drift.