sensorless

Sensorless refers to techniques that infer quantities usually measured by sensors using information available from the system, rather than direct measurements. In control engineering, sensorless control aims to estimate variables such as rotor position, speed, or torque without physical position sensors, relying on mathematical models and observed signals.

In electric motor drives, sensorless control is common for brushless DC motors (BLDC), permanent-magnet synchronous motors (PMSM), and other motor types. Estimation is achieved with observers or estimators based on voltages and currents, including back-EMF methods, Kalman filters, sliding mode observers, and model-based observers. Back-EMF methods exploit the relationship between induced voltages and rotor position and typically require some rotor speed; high-frequency signal injection can aid starting and low-speed operation.

Advantages of sensorless control include reduced hardware cost, improved reliability by removing mechanical sensors, and a smaller drive package. Disadvantages include reduced observability at standstill or very low speed, sensitivity to motor parameter drift and temperature, and higher computational requirements for real-time estimation. Performance can vary with motor design and operating conditions.

Applications span electric vehicles, robotics, CNC machinery, and consumer appliances, particularly in environments where sensors are undesirable due to cost, space, or durability concerns. Ongoing research addresses robust starting at zero speed, estimation under parameter variations, and fault detection, as well as extending sensorless techniques to a wider range of machines and operating regimes.