CAREER: Universal SiC-Based Power Converters for Renewable Energy Systems

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Power converters are vital to renewable energy systems and key components in enabling the integration of renewable energy sources into the utility grid. However, high failure rates, large volume and weight, and the high cost of power converters can often restrict the grid penetration of clean energy. Wide-bandgap semiconductor devices, including those made of silicon carbide, are a promising solution for improving power converters, but their merits cannot be fully realized with current converter topologies. The goal of this CAREER plan is to create high power density and ultra-reliable converters by combining wide-bandgap devices with new universal converter topologies that have an ability to eliminate less reliable components commonly used in power converters, such as electrolytic capacitors, as well as bulky components like low frequency transformers. These improvements will contribute to the long-term research goal of the PI, which is to realize ultra-high-performance renewable energy systems. The PI’s long-term educational goals are to increase diversity in engineering and train the next generation of engineers who are aware of the major challenges in the power electronics field and well-prepared for addressing the future energy needs of the United States. There is an obvious need for a more diverse workforce in the energy fields. This project will create an opportunity for several graduate and undergraduate students, including students from underrepresented groups, to learn about wide-bandgap-based power converters and their applications in renewable energy systems. The proposed research is relevant to a wide range of applications, but, for the scope of this work, the PI and her team will focus on renewable energy systems and microgrid applications. Silicon carbide devices offer significant advantages at the device level, including dramatically higher switching frequency. Despite significant device-level advantages, simply substituting silicon carbide semiconductors for their silicon counterparts will not result in significant improvements to a converter. For instance, in power converters that involve transferring the power from a source to a load with unequal instantaneous values of power, such as single-phase inverters, the size of passive components is not reduced by increasing the switching frequency and use of silicon carbide devices. These converters typically employ large electrolytic capacitors, which have high failure rates. A primary component of this proposal is that it includes a total elimination of low reliability electrolytic capacitors as well as low frequency transformers in all power converters. This will be achieved by creating novel, single-stage multi-port silicon carbide-based converter topologies that accomplish power conversion between any type of source and load, including dc, single-phase ac or multi-phase ac, in one stage, thereby eliminating the need for cascaded converters and decoupling capacitors. These topologies are inspired by isolated dc-dc converters, which can use high frequency transformers instead of low frequency transformers and will be complemented with the use of soft-switching techniques. The input side and output side switches cannot be controlled independently in these converters. The main challenge is the complex control of these converters, especially when the link current/voltage ripple values are large. Therefore, conventional modulation techniques cannot be used. In this project modified modulation techniques will be developed for these converters.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.