Increasing Electric Machine Power Density With a New End-winding Cooling System
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One of the key challenges for the electric vehicle industry is to develop high-power-density electric motors. Achieving higher power density requires efficient heat removal from inside the motor. For high performance electric motors, water-jacket cooling systems are usually used to remove heat coming from the windings and the laminations. However, this limits the maximum power density as the coolant is far away from the slots. Moreover, this radial heat transfer through the lamitations causes the end-windings to be the main hot-spot of the motor. Today, several solutions have been developed to have a direct cooling of these end-windings and further increase the power density of the motor. The first solution are fan blades placed on top of the rotor. This solution based on forced air convection only is limited by a low maximum heat transfer coefficient (HTC). The next method which has gained interest in the automotive industry is oil spray or jet impingement directly onto the end-windings. This provides much higher HTC. However, the coolant in contact with end-windings must be dielectric (oil is typically used) which results in an additional cooling loop for the vehicle. The last one is high thermal conductivity potting material which enhance the heat transfer from the end-winding to the housing. However, this solution still faces limitation in terms of mass production feasibility. Thus, this thesis proposed the investigation of a new type of cooling system based on end-winding channels. This new solution allows for high HTC using the same cooling loop as for the water-jacket. Besides, the design of these channels has been thought for an easy integration in the end-windings with the goal of mass production capability.