I. Introduction
High voltage power modules are widely used in flexible dc transmission, high-voltage direct energy storage, solid-state transformers, electric transportation drives, and other electric power conversion applications. Compared with low-voltage power electronic devices, the use of high-voltage power modules can reduce the number of cascaded power units, significantly increase power density, provide key support for reducing carbon emissions, improve system flexibility, and solve energy shortages [1], [2], [3]. The use of wide bandgap (WBG) power semiconductors has greatly improved the performance of high-voltage power modules, and the research on matching packaging technology is crucial to maximizing the advantages of WBG semiconductors in high-voltage power modules. Due to the presence of body parasitic diodes or external parallel diodes, the package insulation (encapsulating insulation and substrate insulation) of high-voltage power modules such as SiC MOSFET and IGBT mainly withstands unipolar square wave voltages [4], [5]. The encapsulating material such as silicone elastomer encloses the substrate and power chips to form a typical “triple point” as shown in Fig. 1. Due to the extremely uneven geometric structure, the electric field and temperature are generally high at the triple point positions. The electric field and temperature at other positions decrease as they are away from the triple point, hence forming a “double gradient” distribution of the electric field and temperature in the power module package [6], [7]. Since the triple point positions are where the high temperature and electric field are located, space charge injection and accumulation should be investigated.
Structure of a typical wired-bonded power module.