Thermal management in traction applications as a constraint optimal control problem

In traction applications, electrical drivetrain components are subjected to unpredictable load and temperature variations depending on the driving cycle and ambient conditions. As performance and power density requirements are getting increasingly stringent, the power electronic devices and electromagnetic actuators are stressed heavily due to temperature cycling effects and face the risk of overheating, compromising lifetime and reliability. To protect the drivetrain from thermally induced failure, a model-based thermal management strategy is proposed in this paper. Critical component temperatures are calculated online with a combined loss and thermal model and are limited progressively by applying constraints to loss-influencing operating variables. Starting from the requested torque, the dq-current setpoint calculation is formulated as a constraint optimization problem in order to protect all drivetrain components while maximizing overall efficiency over the entire torque-speed operating range, including field weakening at elevated speed. Unlike conventional approaches, which are often ad-hoc or based on de-rating, the proposed strategy allows the drivetrain to operate safely at maximum performance limits, without unnecessarily degrading performance.