PhD defence of Christopher Ramos – Development of an Intermediate Bus Converter for Evolving Power Grid Systems

Abstract

We are envisioning future power grid systems with much higher penetration of distributed energy sources such as solar photovoltaic arrays, wind turbines and battery energy storage systems which are essentially DC sources. Together with the proliferation of electric vehicles, rapid charging station and DC loads such as data centers, DC-based grid interfaces have also been given consideration. In this thesis, an intermediate bus converter for utilization in DC grid architectures that aid the main AC power network is developed. The conceptualized power electronic interface is a cascaded converter system resulting from the combination of isolated full-bridge converter and active bipolar Cockroft-Walton voltage multiplier. First, preliminary investigations were performed to properly define the objectives and scope of the research. The study then involved device-level, converter-level and grid-level aspects of the converter design. In the device-level research phase, the next generation Silicon-carbide power devices were studied for being a key component of the proposed converter. In the converter-level research phase, the converter is configured for bidirectional capability and a design procedure is generated for calculating the main power component values. In addition, reduced-order modelling is performed to generate the system transfer functions for control. Lastly, for the grid-level research phase, the converter is integrated into the renewable energy system. Case studies for the converter with inverter-based resource operating in grid-following and grid-forming mode are formulated to highlight the advantages of the proposed system over the conventional solution. For solar PV systems, it is shown that with the integration of the proposed converter, it is possible to extract more power from the arrays, which translates to better active power regulation. The study showed that a niche application where the proposed solution becomes attractive is in direct conversion from low voltage to medium voltage levels, eliminating the need for line-frequency transformers.