Research On Phase Change Cooling Technology In Power Devices

With the development of HVDC and electric vehicles,power electronic devices have been widely used in various fields.With the increasing demand for capacity,the water cooling system usually used inside the converter valve has the disadvantages of poor cooling water insulation,low heat exchange efficiency,complex system,and high difficulty in operation and maintenance,making the current water cooling system a replacement.The main problem facing the safe and stable operation of the flow valve system is an urgent need for more efficient cooling technology to compensate for the deionized water cooling technology.Many compounds have the characteristics of high insulation and high latent heat of phase change,which can be used as phase change medium.Phase change cooling uses these compounds as cooling medium.The medium absorbs a lot of heat during the phase change process,and the heat exchange efficiency is higher.Compared with deionized water cooling,the system is simpler,more reliable,operating temperature,strong overload capacity,etc.This dissertation focuses on applying phase change cooling technology to power electronic devices,designing and building phase change cooling systems suitable for IGBT and thyristor devices,and exploring phase changes from the perspective of computational fluid dynamics(CFD)simulation calculations and experiments.Applicability and advantages of the cooling system.Based on the principle of phase change heat,a simulation heat source is used to simulate the thermal characteristics of power devices,and a phase change cooling performance test platform applied to power devices is built.The design uses 9 analog heat sources and 10 radiator plates attached to the wall type phase change cooling structure,composed of analog heat sources,radiators,risers,condensers,downcomers,chillers and other components to form a structural system;K-type thermocouple,Pt100 thermal resistance,pressure sensor,and flow meter constitute the measurement system.The finite element CFD method is used to simulate and calculate the cooling unit in the phase change cooling system.The model is a simplified cooling unit structure consisting of a heat sink and two simulated heat sources.According to the calculation requirements,without paying attention to the phase interface,the mixture method is selected as the method of analyzing the phase change fluid,and the boundary conditions are reasonably simplified.Based on the establishment of the simulation model,the cooling capacity of the two types of heat sink structures in the selection design is explored.The ribbed heat sink has better cooling performance and provides a new method for future verification and improvement of the heat sink structure.Comparing the simulation results of phase change cooling with the simulation results of single-phase water cooling,it is verified that the phase change cooling technology makes the temperature distribution more uniform and has advantages in cooling performance.In terms of testing,a testing process was designed around the phase change cooling platform.In order to explore the effects of different influencing factors on phase change cooling,the cooling water temperature and the flow rate of the working fluid were respectively controlled,and the cooling performance was tested under the conditions of simulated heat source powers of 2 kW,4 kW and 6 kW.A total of 18 working conditions were tested.Both factors prove that in the drastic change direction of the phase change process,the phase change cooling technology will make the temperature rise change more gradual.Based on the same platform,the cooling performance of single-phase water cooling was tested,and the difference in cooling performance between phase change cooling and single-phase water cooling was compared,which proved that phase change cooling has performance advantages,and th e greater the heating power,the more obvious advantages are reflected.The comparison shows that the results are basically the same.In order to verify the accuracy of the CFD simulation results,the simulation results are compared with the test results.The simulation and test results can be consistent in the temperature change trend,and the temperature value error does not exceed 10%,which basically meets the needs of the project.