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Simulation of the BMW i3 Traction Motor

Motors & Generators with MotorSolve

The automotive industry is producing more and more new Hybrid Electrical Vehicles (HEV) and pure Electric Vehicles (EV). It is therefore fitting to examine some of these designs in more detail. In this application page we have assembled data from the Oak Ridge National Laboratory (ORNL) and from BMW to develop a MotorSolve model of the 2016 BMW i3 traction motor.

The BMW i3 traction motor is a 12 pole/72 slot motor with an IPM rotor. It is rated at 125 kW. The rotor was designed to have a high saliency ratio; correspondingly the reluctance torque component was high as a consequence. It was also designed to have a very sinusoidal back EMF which is rare in motor designs.

Cross-sectional view of the BMW i3 Motor


Motor Data

The motor data was obtained from published materials from either the ORNL or BMW. The geometric information to put the model together was furnished by the ORNL. DXF files were created separately for the Rotor and Stator, and then imported directly into MotorSolve. The material and winding information was also provided by the ORNL. Measured values for the performance of the motor were obtained from the ORNL and BMW for the comparisons presented.

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Back EMF Waveform

The Back-EMF waveform for this motor is very sinusoidal. BMW states that it was one of its primary specifications for this motor. The following Back-EMF waveform was created by MotorSolve.

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Back EMF Harmonics

To see how sinusoidal the waveform is we can look at the harmonics of the waveform. In this case it is clear that the higher order harmonics are many times smaller than the fundamental of the waveform.

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Measured Torque and Output Power Versus Speed

The torque and output power curves which are a function of speed are highly important for traction motors. These curves were published by BMW.

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Torque and Output Power - Comparison with Measured

MotorSolve produces performance curves for the Torque and Output Power as a function of Speed. The comparison between measured and simulation results is quite good.

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Efficiency Maps - Measured

Efficiency Maps are often used by motor designers to determine the preformance of an electric motor under various drive cycles. This is the efficiency map published by BMW.

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Efficiency Maps - Simulated

MotorSolve generated the following Efficiency Map for comparison.

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