A technology overview of thermal management of integrated motor drives – Electrical Machines

This paper provides a technology overview of integrated motor drives (IMDs), with a focus on thermal management of high-specific-output and high-efficiency electrical machines. The early examples of integrating electronics with electrical machines were introduced in the 1960′s. Here, both passive and active cooling techniques were employed to provide compact and robust electronics-motor systems, predominantly for automotive and aerospace applications. The latest examples of IMDs share the same generic concepts of thermal management, where dedicated or shared cooling of the individual IMD subsystems is used. However, the modern IMDs illustrate a more comprehensive integration approach, where the complete power electronics inverter and electrical machine are frequently accompanied by other subsystems, e.g. mechanical transmission, suspension, clutching, braking and others. Again, the automotive and aerospace industries have been paving the way towards high-specific-output and high-efficiency IMDs, but it is important to note that the low-power applications, e.g. consumers electronics, health and beauty goods, home appliances, garden and power tools, personal mobility vehicles and many others have been adopting the IMDs for decades now. Interestingly, some of the generic concepts first successfully introduced in low-power devices found their use in more demanding high-power applications. In general, thermal management of electrical machines in IMDs is analogous to that used in discrete motor drives (DMDs). The continuous drive towards high-specific-output and high-efficiency electrical machines have been imposing ever more demanding challenges associated with effective heat removal from the machine composite structure, with multiple localised and non-homogenous heat sources. It is important to note that balancing both generated power losses (heat), and available heat removal is essential for successful implementation of a specific machine design. The existing examples of advanced motor cooling offer a more targeted approach for removing heat directly or indirectly from the individual heat sources, e.g. direct winding oil spray cooling, forced air rotor cooling, and indirect stator-winding heat exchanger cooling, stator-winding heat guide transport. Some of the concepts originate from high-power and high-efficiency electrical machines for power generation, others are enabled by the developments in new materials and manufacturing techniques. It is evident that a more focused thermal management aiming at specific heat sources is the most effective. Here, the use of additive manufacturing, highly integrated heat exchangers, multi-functional composite materials and phase change heat transport and heat storage are some of the solutions, which have already shown a great promise for the next generation of IMDs.