Design & Evaluation of a Hybrid Switched Capacitor Circuit with Wide-Bandgap Devices for DC Grid Applications

ABSTRACT As technologies advance, the rate at which renewable power sources, such as solar photovoltaic (PV) and wind, are being added to the power grid is increasing. Typically, PV power plants require large inverters for direct current to alternating current (DC-AC) power conversion, as well as large transformers to step up voltages to the grid voltage. Offshore wind farms and large PV power plants in remote locations often aggregate power on a DC bus in order to improve efficiency and reduce the cost of power conversion hardware within the energy complex. However, the power must still be converted to AC for integration into the grid. Research is being done to allow greater adoption of low, medium, and high voltage DC distribution, wherein DC power is used directly by loads. This has the potential for additional cost savings. To better realize this vision, however, new DC-DC converter technologies must be developed that are small, cheap and efficient at the voltages and power levels relevant to grid integrations. This project demonstrates the feasibility of a switched capacitor boost converter topology that is scalable to 10 kilovolts, and can serve as an interface between lower voltage PV arrays and medium voltage DC (MVDC) distribution lines. In particular, this approach relies on switched capacitors, wide-bandgap (WGB) devices, and high-frequency switching to achieve high power density and high gain. As part of this work, two prototypes were constructed including a benchtop-scale prototype rated for 25W at 500 Volts and a 6 kW 10 kV converter. In particular, this second converter was demonstrated in hardware to deliver 2.56 kW at 10 kV DC to a resistive load with greater than 95% efficiency, demonstrating the feasibility of this converter for grid applications