Speed control for a Pseudo Direct Drive permanent magnet machine with one position sensor on low-speed rotor

The paper describes a novel approach to operate a Pseudo Direct Drive (PDD) permanent magnet (PM) machine with a single sensor on the low-speed rotor. Due to the magnetic coupling between its two rotors, the PDD machine exhibits torsional oscillation when a conventional drive is employed. While full state feedback control can effectively supress the torsional oscillation, its implementation requires two position/speed sensors: one on the high-speed rotor for electronic commutation, and the other on the low-speed rotor for speed/position control of the payload. This not only increases the drive system cost, but the need for fitting a position/speed sensor on the high-speed rotor imposes great constraints on the PDD mechanical design. A novel technique has been developed in order to control the PDD machine using a single sensor mounted on the low-speed rotor while the position and speed of the high-speed rotor needed for electronic commutation and state feedback control is estimated with an observer. The commutation signal is generated with a specially designed hardware to mimic a hardware resolver.