Method of Heat Reduction for Vehicle Traction Motor Inverter Locked at Standstill on a Climbing Slope

Operation in the stalled condition represents a stressful special case in the operation of a traction motor drive inverter. When high torque is generated continuously in stall, as for example on a slope, heat builds up in one of the switching devices of one or more phases of the inverter. Research was conducted to develop a method of control that would reduce the heat generated in the switching devices. When the vehicle is stationary on a slope, there is a range of torque for which a vehicle remains stationary, ranging from the minimum torque required to prevent rolling down slope, to the maximum required to overcome static friction and begin propulsion upslope. Focusing on this characteristic, the control was employed so that the traction motor torque command is set to be a minimum in this range, while the torque command has a linear relationship with the accelerator command in other ranges. In addition, without changing the torque of the motor, a control technique is applied to reduce heating of the switching devices at the phase where temperature becomes maximum. These techniques together have enabled the maximum temperature of the switching device to be reduced by 21.1 °C.