Pump Characteristic Based Optimization of a Direct Water Cooling System for a lOkW/500kHz

ethz.ch AbstractA high power density IOkW/SOOkHz three-phase PWM rectifier (Vienna Rectifier) is under development. Due to preliminary measurements and numerical simulations the total efficiency is assumed to be 95% at full load, resulting in power losses of up to 150W in each multi-chip power module re alizing a bridge leg of the rectifier. In order to keep the power density of the system high direct water cooling is employed where water is in direct contact with the module base plate. Based on the measured characteristic of the water pump (pressure drop dependent on water flow) the geometry of different water channe l strucrures below the module base plate is systematically optimized based on analytical expressions which are formulated based on the well-established theory of fluid dynamics. The design optimization is constrained by the desire to keep the geometry of the water channels in a range that allows simple and low-cost manufacruring. The aim is to find a channel strucrure resulting in a minimum thermal resistance of the power module for a given pump characteristic. In this paper a very simple slot channel is investigated. The dependency of the thermal resistance on the cooling system is calculated in dependency on the height of the slot channel, and an optimized channel height is found under the side condition of simple manufacturabi lity . Discussing the shortcomings of the simple slot strucrure, a novel metallic inlay structure is introduc ed and optimized resulting in a reduction of the thermal resistance of the direct water cooling scheme as compared to the slot channel system. All theoretical considerations are verified via experimental meas urements. The general optimization scheme introduced in this paper can easily be adapted to other cooling problems.