Design and testing of a liquid cooled brushless DC traction motor

The authors describe how, in addressing the requirements of a hybrid electric vehicle system to compete with a medium family saloon of today, the system must be able to manage power levels in the order of 60-75 kW. Brushless permanent magnet motors are chosen as they potentially offer the highest efficiencies over the speed range of operation. The use of progressively applied field-weakening enables extension of the motor speed range above the base speed constraint imposed by the power converter link voltage by up to three times, the resulting operating envelope encompassing that of a mechanical continuously variable transmission. The authors describe how the design of the traction motor is governed by two main criteria: the maximum continuous torque required by the vehicle and the maximum speed that the vehicle has to achieve. Here, the design and testing of a liquid cooled brushless DC traction motor for such an application are detailed by the authors