Study on cooling system for SR motors by pumpless forced convection boiling equipment with liquid dielectric coolant

A forced convection boiling system with liquid dielectric coolant is proposed as a new cooling system for SR motors (switched reluctance motors) for electric vehicles. In a previous study, the superiority of cooling by liquid dielectric coolant was confirmed compared to conventional cooling by epoxy resin. We have improved the cooling method using this liquid dielectric coolant and devised a method to cool the coils by forced convection boiling of the liquid dielectric coolant inside the motor. The liquid dielectric coolant is divided into a "heating room" that is directly heated by coils and a "cooling room" that is cooled by external cooling water, and the liquid dielectric coolant is circulated in the two rooms. This system is named the "Boiling Immersion Cooling System". However, if boiling cannot be controlled, the coils are exposed from the liquid surface and the cooling capacity is lost. In this experiment, this cooling system was verified by experiment. In addition, to reduce the cost of performance estimation and model improvement, a thermo-fluid analysis method was established to reproduce the boiling phenomenon of liquid dielectric coolant in the simulation. Thermo-fluid analysis and experiments confirmed that thermal runaway due to coil exposure does not occur even when the heat generated by the coil is assumed to be 19 kW at the motor's steady-state output.