Motor 'identity' - a motor model for torque analysis and control

Abstract

Production of smooth and maximum torque are two main goals for achieving good performance in torque control of Permanent-Magnet Synchronous Motors (PMSMs). Various proposals have been advanced to solve these two problems [1, 2, 3]. In all these publications motor parameters such as inductances and resistances are used in lumped parameter models and used with the proposed control strategy to attempt to achieve good torque performance. This paper presents a new approach for modelling the motor for torque analysis and control. This method is unconventional in that no parametric model of the motor is required, instead a new concept of 'motor identity' is introduced and used. This 'identity' is defined as the per-phase torque profile of the motor and it can be represented in a matrix form - called the 'identity matrix'. This characterizes the motor and this matrix can be used for torque analysis and control. This concept is also applicable to all synchronous machines but a PMSM is used here for the illustration of this concept. An analysis is also presented for deriving optimal drive currents by using the motor identity. A method to extract the motor identity experimentally is also given in this paper.