A dynamic model for the investigation of twisting effect in long flux- switching PM motors in ESPs

Shaft twisting occurs along the length of electric motors rotors. The twisting depends on the shaft properties and the transmitted torque. In Electrical Submersible Pumps, due to the high ratio of length to the diameter of the motor and the high load torque, the twisting effect occurs significantly. Thus, when such a condition emerges for an electric motor, the electromagnetic torque is not uniformly produced along the motor length, since shaft twisting results in rotor position variation with respect to the stator. Therefore, the twisting and the produced electromagnetic torque of the motor are interdependent. It means that these two issues cannot be studied separately and a model must be proposed to consider them together so that the electromagnetic performance of the motor can be studied under such conditions. Despite the importance of modeling the twisting effect for the electric motor, this issue has never been investigated before. In this article, a novel dynamic model for the flux-switching permanent magnet motor is proposed by which the shaft twisting effect is simulated to study the motor performance. Eventually, the twisting effect during startup and steady-state are studied as well as the effect of shaft diameter and motor length on shaft twisting. To evaluate the model, it is compared with the verified steady-state model for the flux-switching permanent magnet motor with the twisted shaft obtained from another article, and also results obtained by finite element analysis.