Design and Implementation of a Novel 11kW GaN-Based Bi-directional Partial Power DC-DC Converter for Battery Storage Integration in Bipolar DC Grids

This thesis presents the design, optimization, implementation, and experimental validation of a novel bidirectional, non-isolated buck-boost DC-DC converter employing gallium nitride (GaN) semiconductor switches. Developed in collaboration with DC Opportunities R&D B.V., the converter integrates battery energy storage systems (BESS) into bipolar DC grids and utilizes the partial power processing (PPP) concept to enhance system efficiency and power density. The project aims to achieve a high-power-density converter (11kW) with exceptional efficiency through passive cooling techniques. GaN’s high-speed switching capabilities are leveraged alongside full-range zero-voltage switching (ZVS) conditions to minimize switching losses. A comprehensive methodology is adopted, combining theoretical analysis, simulations, and prototype development. Key focus areas include modelling the novel converter topology, deriving ZVS conditions to minimize switching losses, and developing and optimizing frequency control strategy to maintain ZVS across the entire operating range of the converter. Additionally, closed-loop control system and droop control strategies are developed, and electrical and thermal performance analyses are conducted under various load conditions. The thermal performance of GaN HEMTs is also assessed to validate their suitability for passive cooling applications. This research contributes practical droop control strategies for load sharing and grid stability in bipolar DC grids, provides insights into GaN-based power conversion with ZVS, and delivers a validated prototype.