Brushless Direct Current motor (BLDC) is widely used for Ebike applications. However, even with BLDC motors widely used in electric vehicle, there is still room for improvement in terms of torque density of the machine. The magnetic flux generated by permanent magnets at the rotor section is fixed and can’t be increased.
Designing a machine requires understanding the operation of the machine that acquired for several situations.Tractive study is very important as we are able to analyze and predict the actual speed of the machine in the vehicle in real world environment that have many types of road conditions.There are 6 conditions faced by the electric vehicle especially electric bike which are early start, normal speed, acceleration, high speed, deceleration and stop position. Illustration #1 shows the diagram of operating conditions faced by the machine.
The net loading of the machine must be increased in order for the magnetic flux intensity of the motor to improve. The coil winding method affect the magnetic loading which contributes the magnetic flux generated by the coil in the stator slot. There are two types of armature coil winding that can be implemented which are concentrated winding and distributed winding like in Illustration #2.
Concentrated coil winding make the conductors winded up together with several conductor in series in order to form multi turn coil whereby distributed coil winding arranged the conductors in several slots under single pole across the air gap periphery. Arranging the coil winding in series making all of the coil turns generated the same magnetic field across the same area of the slot in the machine. Thus, the total EMF generated by the concentrated coil winding is the summation of EMF all coil sides which generate higher magnetic flux. Plus, it produce low power losses which improve the efficiency of the motor due to reduce Joule losses. For distributed coil windings, the conductors are placed in several slots under single pole in order to obtain smooth sinusoidal EMF wave form. The waveform of distributed coil winding generate smooth sinusoidal waveform which shows the similarity waveform of the three phase power supply. This happen because the harmonic EMF and permanent magnet eddy current loss that caused by the machine was reduced. Thus, the magnetic flux of each FEM coil waveform was generated smoother than concentrated winding.
Another design was inspired from in wheel motor applied to the machine which contributes the concept of non-contact magnetic planetary gear with the permanent magnet outer rotor BLDC machine.The output of this model shows that mutual magnetic coupling between outer rotor with planet gear improve magnetic flux intensity by making both of them as individual part of the machine. Therefore, the magnetic flux generated by both of individual part will increase the performance of the machine. Other than that, this model will able to achieve various speed with constant speed.Therefore, the performance of the motor can also be increased by designing a motor with double layer outer rotor PM that applying the same concept but different design.