Design and development of high step-up single-switch DC/DC converters for micro-inverter applications

Abstract

Concerns about climate change have accelerated the shift towards renewable energy sources (RESs). Distributed energy systems, especially solar photovoltaic (PV), batteries and fuel cells (FC), are now key players in sustainable power generation. Hence, these sources require efficient high-step-up DC–DC converters to interface low-voltage inputs with high-voltage DC buses. However, traditional converters such as boost and buck-boost require extreme duty cycles to achieve high voltage gains. For instance, achieving a gain ratio of 8 to 10 requires a duty cycle of 0.87 to 0.9. Under these operating conditions, the switch and diode currents increase approximately by a factor of (1/(1-δ)), which significantly increases conduction losses and growth in diode reverse-recovery losses due to higher diode current and switching stress.

To overcome these limitations, this thesis proposes and experimentally validates three novel non-isolated quadratic boost derived DC/DC converter topologies: QBĆUK, QBC-SEPIC and 3QBC_(SL/VL), which systematically address the fundamental limitations of conventional QBCs. Rather than providing modifications of a single design, these designs are intentionally developed as a family of structurally distinct architectures, each optimised for a specific design objective: 1) QBĆUK converter prioritises switch voltage stress reduction while maintaining continuous input and output currents. 2) QBC-SEPIC converter provides dual-output capability and limits switch voltage stress to approximately half of the output voltage. 3) 3QBC_(SL/VL) converter is designed to achieve ultra-high voltage gain without requiring extreme duty cycles or coupled inductors. All three converters offer continuous input current with low ripple making them suitable for solar maximum power point tracking (MPPT) applications. Meanwhile, all of them also employ a single switch and share a common ground which simplifies control and design.

Thesis is embargoed until 31 July 2028.

Date of Award	Jul 2026
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Royal Embassy of Saudi Arabia Cultural Bureau in London
Supervisor	Ahmad Elkhateb (Supervisor) & David Laverty (Supervisor)