Control of a BLPM machine using an integrated torque sensor in place of a rotor position sensor

Closed-loop torque and speed control of the brushless permanent magnet (BLPM) machine requires rotor positional information to control the associated power electronic inverter. Rotor position information is acquired by position sensors or position sensorless schemes. These position sensors increase the cost and size of the BLPM drive systems and make it prone to mechanical failure due to the sensitive nature of typical rotor position sensing devices. Many researchers are investigating position sensorless schemes to address these points, however most position sensorless techniques behave poorly at stand-still and low speeds (0-300rpm); they also behave poorly due to the fact that they estimate load torque which can be difficult in undefined load applications due to control parameter changes. This paper proposes a novel idea to achieve closed-loop control of a BLPM machine by using measured shaft torque feedback from an integrated, low-cost, torque surface acoustic torque (SAW) transducer.