6.5 kV Silicon Carbide Half-Bridge Power Switch Module for Energy Storage System Applications

As renewable resources such as wind and solar start to penetrate the electrical infrastructure, the transient nature of these resources requires energy storage systems to buffer the fluctuations in output. Power conversion systems in the 100 to 200 kW regime are sought to address needs on the industrial user, community and mobile level, however the cost and size of the equipment must come down to meet municipality budgets and space limitations. Currently, the cost of power conversion is limited by the abilities of Si switches to operate at higher voltages and faster frequencies. The impact of a medium voltage switch could greatly shrink the weight and cost of power converters by reducing cable size, transformer size, and eliminating forced convection cooling systems all together. In addition to utility scale energy storage, the switch module will have an ancillary benefit in heavy hybrid vehicle drive trains where operating at higher DC link voltages improve conversion efficiency and reduce weight. United Silicon Carbide, Inc. (USCi) proposes to address the need for medium voltage switches by developing a unique 6.5 kV Silicon Carbide (SiC) Normally Off JFET based Half-Bridge power switch module. The proposed module will provide a significantly smaller, more efficient and lower cost solution for DC converters/inverters and will enable higher DC-Link voltages, up to 5 kV, for utility scale smart grid and energy management applications. By utilizing an approach that does not rely on Metal-Oxide-Semiconductor (MOS) technology, the proposed module can run at much higher junction temperatures, (Tj & gt;250C), thereby reducing cooling requirements dramatically and increasing reliability. The proposed module targets a high operation frequency of ~ 20-30 kHz which enables the use of much smaller transformers and magnetics. The proposed SiC Half-Bridge switch module is based on normally-off vertical JFETs utilizing a patented device structure that is expected to overcome the following limitations of the competing technologies: Silicon power switches are plagued by excessive cooling requirements due to high switching and conduction losses, MOS based SiC switches, such as MOSFETs and IGBTs, suffer from long-term reliability concerns when operating at high junction temperature and high electric field and Bipolar switches, such as BJTs, GTOs, and IGBTs, have much lower switching speeds, and suffer from a forward voltage drift problem due to defect propagation. The proposal will outline USCis approach to realize a prototype (TRL 5) half-bridge module where the epitaxial growth, device and driver fabrication will be performed at USCis wafer fab in Princeton, NJ. Phase I will focus on the device, driver and module designs, proof of 6.5 kV packaging fundamentals as well as the epitaxial growth. Phase II will involve device processing, module assembly and half-bridge module proof of performance. In addition, USCi will obtain critical application requirements by consulting with Princeton Power Systems, also located in Princeton and offer state-of-the-art commercial power conversion technology for energy storage systems.