Thermal capability of electric vehicle PMSM with different slot areas via thermal network analysis

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In this paper, the effect that a varied stator slot size has on the efficiency and thermal capability of a permanent magnet synchronous machine for an electric vehicle, is evaluated and quantified. A machine with four differently sized slot areas was electromagnetically evaluated with finite element analysis, and thermally with a lumped parameter network model. By decreasing the slot size while keeping other dimensions fixed, the core losses reduce due to the wider magnetic path, whereas the winding losses increase. Additionally, a higher maximum torque is reached due to reduced saturation. Results are compared in the machine’s torque-speed operating area regarding machine-part and total losses, continuous torque and transient overload capability, as well as during 19 low, middle and high-speed drive cycles regarding energy losses and peak winding temperature. The largest slot showed the lowest winding losses and thus the highest thermally limited torque capability. In contrast, the energy losses with the largest slot were the highest in 13 of the drive cycles, and the lowest in 11 of them with the smallest slot due to its lower part load (i.e. core) losses. The smallest slot would also result in the lowest material cost since it has the least copper. • Larger PMSM stator slot gives higher continuous torque than a smaller with same rotor and current. • Smaller PMSM stator slot gives higher peak torque than a larger with same rotor and peak current. • Smaller PMSM stator slot gives lower total losses than a larger during many official drive cycles.