Design of a Gallium Nitride DC-DC MPPT Converter for Bipolar DC Microgrids

Abstract

The use of DC microgrids in combination with photovoltaic (PV) energy generation sources results in higher efficiencies by avoiding AC to DC conversion. Moreover, bipolar DC grids allow for more system flexibility and increased reliability at the cost of an additional conductor when compared to unipolar DC. However, maximum power point tracking (MPPT) converters are still required in order to optimize the power delivered to the microgrid by PV systems. The development of more efficient and cost-effective DC-DC MPPT converters will be proven vital considering the expected growth in solar PV installation as a consequence of the relentlessly increasing global energy demand.

The objective of this thesis is to design a DC-DC MPPT converter for bipolar DC microgrids based on gallium nitride (GaN) high-electron-mobility transistors (HEMTs). GaN transistors are wide-bandgap semiconductor devices that can operate at very high switching frequencies due to their superior electron mobility compared to other semiconductor materials used in electronic switching. Increasing the operational frequency of an electronic converter allows for smaller passive components, which in turn has the potential to result in system size and cost reductions. A complete electrical and thermal analysis of the performance of these components is simulated and presented in this report, and the implications of employing these devices for the selected application are evaluated. The design overview of the DC-DC MPPT converter using these GaN HEMTs is also showcased in this work, as well as the results obtained from testing the assembled DC-DC MPPT converter for bipolar DC microgrids. The main conclusions of this work aim to clarify the advantages of GaN devices in MPPT applications, as well as demonstrate a design solution to the integration of MPPT converters to DC microgrids. The project was developed in collaboration with the company DC Opportunities, and the designed converter was assembled and tested in their laboratory.