Ceramic heat pipe cooling system for high-power magnetic components
The structure and working principle of ceramic heat pipes are similar to those of metal heat pipes (such as copper water heat pipes). However, the pipes of ceramic heat pipes are sintered from high thermal conductivity, non porous ceramic materials, and the liquid absorbing core is fired from porous ceramics, which are filled with working fluid inside. When heat is applied to one end of the pipeline (evaporator), the fluid inside the pipeline will evaporate, and then the steam will flow to the other end of the pipeline (condenser), which is usually in contact with the radiator or cooling medium. When steam releases heat to the cooler end, it condenses into a liquid and returns to the evaporator section through capillary action in porous ceramic materials. Repeat this cycle to effectively transfer heat from the hot end of the pipeline to the cold end.
The earliest ceramic heat pipe can be traced back to 1975. Early ceramic heat pipes were made of silicon carbide (SiC) and used sodium as the working fluid. The chemical vapor deposition of tungsten (W) layer attached to the inner surface of the tube can prevent the interaction between sodium and ceramic wall materials. The functions of these pipes have been experimentally verified at temperatures as high as 1100 ° C and are used for high-temperature applications, but they are expensive to manufacture .
High frequency transformers used in charging stations, charging boxes, and other applications are mainly composed of magnetic cores, windings, and insulation materials for fixed windings. Usually, magnetic cores are made of magnetic materials such as ferrite to meet performance indicators such as frequency response and magnetic core loss. High frequency transformers generate a large amount of heat due to resistance Joule heat and eddy current losses, and their pursuit of smaller volume hinders effective ventilation and heat dissipation. Therefore, it is necessary to design an effective heat dissipation system for the transformer body and PCB circuit board to prevent device overheating and ensure reliable operation. This can be achieved through various methods, such as forced air cooling, liquid cooling, or mixed cooling schemes.
In the selection of the cooling system for electric vehicle charging stations (charging boxes), a mixed cooling method of heat pipe combined with liquid cooling plates can be used to help power devices such as MOSFETs and magnetic devices (such as inductors and transformers) dissipate heat quickly. The first solution is to force air circulation inside the charger housing, while transferring heat to the liquid cooling plate through an aluminum fin radiator and heat pipe assembly. The second solution is to encapsulate the magnetic components and heat pipes together with thermal conductive epoxy resin, and transfer heat to the liquid cooling plate through the heat pipe components
Research has shown that the heat pipe and magnetic components of the second scheme can fully exchange heat, transferring heat to the liquid cooled plate with very low thermal resistance. However, the first solution has lower cooling performance than the heat pipe sealing solution due to the inability of the aluminum fin radiator to fully contact the magnetic components.
However, there is a considerable amount of eddy current loss in metal heat sinks in current cooling schemes, such as aluminum finned heat sinks and copper heat pipes. These eddy current losses caused by magnetic components have adverse effects on the performance and reliability of chargers. Ceramics are an electrical insulation material that prevents the generation of current and therefore does not generate eddy currents, effectively eliminating eddy current losses. They are particularly suitable for cooling high-frequency magnetic components, such as high-frequency inductors and transformers.
Ceramic heat pipes provide a cooling solution that is resistant to high temperatures, long-lasting, and low loss for high-frequency magnetic electronic devices. However, it also faces high cost issues due to complex manufacturing processes and immature supply chains. At present, the demand for DC fast charging is rapidly increasing, and the heat dissipation challenge of high-power and high-frequency magnetic components in electric vehicle charging applications is intensifying. This will inevitably highlight the insufficient magnetic loss of metal radiators, and the advantage of ceramic heat pipes in eliminating eddy current losses will be amplified. Therefore, the insulation two-phase passive heat dissipation technology represented by ceramic heat pipes is expected to open up new prospects in the field of thermal management of high-power power electronic equipment in electric vehicles.
