Advanced control and modulation of isolated bidirectional DC-DC converters for LVDC systems
File(s)
Author(s)
Liu, Chengwei
Type
Thesis
Abstract
The increasing penetration of DC sources, energy storage systems, and DC loads has made low-voltage DC (LVDC) systems an attractive solution for emerging applications such as data centres and electric vehicle charging infrastructure. In these systems, isolated bidirectional DC-DC converters (IBDCs) are key interfaces for power balancing and voltage regulation. However, achieving high efficiency while providing system-level support remains challenging. This thesis develops modulation and control strategies for IBDCs to improve efficiency and enhance voltage regulation and protection in LVDC systems.
A hybrid modulation is first developed for two-port CLLC-based IBDCs to achieve high efficiency in buck mode. By coordinating phase shift and switching frequency, the proposed modulation aligns the commutation of the primary and secondary bridges, achieving natural synchronous rectification and modulation optimization simultaneously. Experiments show efficiency improvements over conventional modulations, with a peak gain of 4.72 %.
The efficiency-improvement approach is then extended to modular multi-active-bridge (MMAB) converters. A hardware decoupling method is introduced, followed by an inductance-current-minimization optimization. The resulting closed-form solution is scalable to arbitrary port numbers and suitable for online implementation without look-up tables. Experiments show efficiency improvements compared with conventional modulation methods, with a peak gain of 9.48 %. Based on the decoupled MMAB converter, a decentralized control method is further developed to support plug-and-play operation through local frequency and phase shift regulation.
System-level functions of IBDCs are also investigated. A unified control scheme is developed for interlink converters in multi-voltage DC systems, enabling autonomous transitions between power-flow regulation and bus-voltage support based on the availability of voltage sources. Finally, a converter-based fault detection and location algorithm is proposed for LVDC interconnection networks without line sensors or DC circuit breakers. Simulation results demonstrate robust performance under different fault conditions and network configurations.
A hybrid modulation is first developed for two-port CLLC-based IBDCs to achieve high efficiency in buck mode. By coordinating phase shift and switching frequency, the proposed modulation aligns the commutation of the primary and secondary bridges, achieving natural synchronous rectification and modulation optimization simultaneously. Experiments show efficiency improvements over conventional modulations, with a peak gain of 4.72 %.
The efficiency-improvement approach is then extended to modular multi-active-bridge (MMAB) converters. A hardware decoupling method is introduced, followed by an inductance-current-minimization optimization. The resulting closed-form solution is scalable to arbitrary port numbers and suitable for online implementation without look-up tables. Experiments show efficiency improvements compared with conventional modulation methods, with a peak gain of 9.48 %. Based on the decoupled MMAB converter, a decentralized control method is further developed to support plug-and-play operation through local frequency and phase shift regulation.
System-level functions of IBDCs are also investigated. A unified control scheme is developed for interlink converters in multi-voltage DC systems, enabling autonomous transitions between power-flow regulation and bus-voltage support based on the availability of voltage sources. Finally, a converter-based fault detection and location algorithm is proposed for LVDC interconnection networks without line sensors or DC circuit breakers. Simulation results demonstrate robust performance under different fault conditions and network configurations.
Version
Open Access
Date Issued
2026-01-20
Date Awarded
2026-06-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Junyent-Ferré, Adrià
Rodriguez, Joan Marc
Publisher Department
Department of Electrical and Electronic Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)