SENSORLESS VELOCITY CONTROL OF PERMANENT-MAGNET SYNCHRONOUS MOTORS

A sensorless velocity controller for the permanent-magnet synchronous motor is designed using discrete-time reduced order models. A nonlinea r observer estimates rotor position and velocity from stator current m easurements, thus eliminating the need for shaft-mounted sensors. The observer is based on least-squares optimization, and exploits a piecew ise-bilinear representation of the back-emf (speed voltage) function. By smoothly switching from an observer-based closed-loop control to an open-loop control at low velocity, observer ill-conditioning is avoid ed and reliable operation is achieved under all operating conditions. The new scheme delivers performance comparable to sensor-based closed- loop control, yet requires only a moderate amount of on-line computati on. Experimental results provide evidence of the viability and perform ance of the new scheme.