Driving-scenario oriented design of an axial-flux permanent-magnet synchronous motor for a pedal electric cycle

This paper proposes a driving-scenario oriented design of an axial-flux permanent-magnet synchronous motor for a pedal electric cycle (Pedelec). Traditional motors are usually designed according to a torque and speed (TN) curve with two operation zones - constant torque and constant power, without being closely related to a driving scenario. The proposed design method defines the TN curve with three operation zones - constant torque, maximum DC current and maximum voltage, which are specified by a driving scenario, the modulation method of motor drive and basic torque and voltage equations of motors. This target TN curve provides admissible ranges for the back electromotive force constant and phase resistance of the motor to be designed. A systematic design procedure is introduced by a quasi-three-dimensional (3D) magnetic circuit model, a multi-objective optimisation process for sizing the motor and a finite element analysis for verifying and refining the design. The resulting TN curve of the proposed Pedelec motor is proved to be very close to the target TN curve that is prescribed by the driving scenario, and motor and drive parameters.