Enhanced thermal management by direct water spray of high-voltage, high power devices in a three-phase, 18-hp AC motor drive demonstration

The combination of high power dissipation (e.g., >500 W) and high power densities required of power conversion devices, such as those utilized within variable-speed motor drives, necessitates thermal management systems with ever-increasing capabilities. Although device power densities on the order of 100 W/cm² are relatively common in applications today, technology roadmaps project power densities in excess of 1 kW/cm² within a few years. Unfortunately, conventional thermal management designs based on solid-state conduction become unworkable at such power densities. In the present DARPA-funded investigation we have approached this problem through implementation of direct low-pressure water spray-cooling of both switch and diode surfaces within a variable-speed motor drive. Problems that were addressed include the packaging of a nozzle array design in a high-power module (>650 W dissipation) that operates with high standoff voltages (V_rms∼325 VAC). Electrical isolation of the devices was achieved by a Parylene coating. An effective thermal resistance of ∼0.007 C/W was achieved through direct water spray-cooling of the electronic devices. In the presentation, we will compare the calculated and measured spray-cooling thermal resistances to those of more conventional thermal management schemes.