Sensorless position estimation for slotless surface mounted permanent magnet synchronous motors in full speed range

This paper presents a scheme for rotor position estimation from standstill to nominal speed for slotless surface mounted permanent magnet synchronous motors, which do not contain structural anisotropy. At standstill and very low speed, the position is estimated by signal injection, while the rotor polarity is identified by a special process based on the estimation of the back electromotive force (back-emf) generated by small rotor motion. At high speed, the position is estimated by using a linear back-emf observer. Different observer gains are used at different speed ranges, such that the position estimate is reliable even at low speed. The combination of these two methods enables sensorless motor control in the full speed range including standstill. Experiments demonstrate the accuracy of the proposed estimation scheme.