An Improved Design of Synthetic Loading Method for a Rapid In-Wheel Motor Characterization in Different Operating Points

In-wheel motors as a crucial component of an electric vehicle need to be tested at the end of the production line, at service intervals, and during motor design validation. This paper presents an improved synthetic loading (SL) method for the rapid characterization of the in-wheel motors. The proposed method emulates mechanical loading at a specific operating point by a current harmonic injection. We introduce a novel algorithm for the current reference setting that is based on the manufacturer’s motor design data and accounts for the motor’s non-linearities. Also, the method features a trapezoidal reference instead of a sinusoidal, which lowers the instantaneous peak current of the converter and thereby increases the attainable torque-speed range. The performance of the proposed SL method is comparable to the classic back-to-back (BB) testing method, which is confirmed by the theoretical analysis, simulations, and experimental results. The difference in motor efficiency measured with the BB and the improved SL method is smaller than 1 % in most operating points. The proposed method offers considerable time and cost savings for the manufacturer – eliminating the mechanical coupling/decoupling operation – and can be applied to surface-mounted permanent magnet synchronous machines in general.