A Comparative Study Of Pedestal PPI And Stakpak PPI

The continuous development of flexible High Voltage Direct Current(HVDC)transmission system poses more requirements to the applied IGBT devices.Press Pack IGBTs(PPI)are valued for their development demand of high voltage,high current and high power in the areas like flexible HVDC transmission system.At present,two types of Press Pack IGBTs,pedestal structure represented by WESTCODE and TOSHIBA as well as Stakpak structure represented by ABB,have been successfully applied to the flexible HVDC transmission projects.China’s research on Press Pack IGBTs started late.At present,there are not many studies on the pressure and temperature distribution and fatigue life of Press Pack IGBTs.Due to ABB’s patent blockade for spring structure,the packaging forms of all other manufacturers are Pedestal structure,most of the existing researches have focused on the Pedestal PPI.There has been no in-depth research on Stakpak PPI.Only ABB has released some descriptions of its products.The spring is very different from the Pedestal structure,and its internal pressure and temperature distribution characteristics as well as fatigue life are still unclear.A comparative study of the pressure,temperature and fatigue characteristics of these two different structures can further clarify the advantages and disadvantages of the two structures,which is helpful to the optimization of device structure design and have important practical significance and research necessity.Based on the finite element method,two finite element simulation models of Stakpak PPI and Pedestal PPI are established in this paper.Their internal pressure and temperature distribution and fatigue life are compared and analyzed for different working conditions of the device’s steady state(non-operation normal pressurized and normal working state),power cycle transient and fatigue.The simulation results show that the pressure distribution of the two types of Press Pack IGBTs under steady state is relatively uniform under normal pressure.Due to the existence of the spring structure,the pressure distribution of the Stakpak PPI under normal working conditions is more uniform.Under the power cycling condition,the Pedestal PPI allows double-sided heat dissipation and is better than the Stakpak PPI’s single-sided heat dissipation.Therefore,the Pedestal PPI has a lower junction temperature,while the Stakpak PPI has more uniform internal pressure distribution and longer overall fatigue life.Finally,based on the simulation results,this paper proposes possible solutions to the structural optimization of the Press Pack IGBTs.