Loss minimizing gear shifting algorithm based on optimal current sets for IPMSM

Two speed gear is preferable in the commercial EVs such as EV trucks and EV bus, since they require a high starting torque and high speed driving, too. In this work, two speed gear with 12.5:1 and 5:1 is considered. The wheel torque is mapped to different points in the torque-speed plane of the motor depending on the reduction ratio. To determine the efficiency, it is necessary to calculate the losses for the two cases. To be fair, optimal current set (i
_d
, i
_q
) should be found for each case before calculating the loss, since the copper and inverter losses depend heavily on the current magnitude. The operation points are found by the MTPA method, or at the intersection between the torque and voltage limit curve. Ferrari's method is utilized to solve the fourth order equation resulted from the intersection. After comparing the losses for different gear ratios, the wheel torque-speed plane is separated, and from which an optimal gear shifting algorithm is developed. Simulation was performed by using NEDC. The results show that the proposed gear shift algorithm is superior to a fixed gear in minimizing the loss.