Improved Multiport Converter Topologies and Operations
Creators: Gunawardena Loku Hettige, Pasan N
Publisher: name: University of Alberta Library
Year: 2024

<p>Recently, multiport converters (MPC) have gained attention due to their ability to integrate several sources and loads into a single converter. MPCs enjoy some unique good features over the conventional two-port converter configurations, such as higher utilization of power devices, compact realization, better synergy on various power forms, reduced power conversion stages, and low device count and realization of higher efficiency while lowering the cost of the whole system. The above merits make the research of MPCs quite popular in recent decades covering renewable energy integration,<br>
electric vehicles, distribution level AC/DC bus interfacing, wireless power transfer, and so on. Although state-of-the-art studies have conducted research on new MPC topologies, their design, and analysis for different applications, there are<br>
still some challenges associated with MPCs that remain open for further exploration and improvement. In this thesis work, which contains three phases of research, some of these challenges are further investigated and some methodologies are proposed to improve their operation and performance.</p>

<p>In the first phase of research, a more specific topology-level investigation is conducted for MPCs proposed for renewable energy applications. This research starts with proposing, analyzing, and experimental validation of a new MPC topology addressing some of the limitations of the existing converters. The proposed new MPC has advantages over some existing MPCs proposed for the same purpose, particularly the ability to operate ports simultaneously, galvanic isolation between sources and loads, and bi-directional power transferring capability. In addition, the component sharing among different power flow paths is an inherent feature of MPCs, which gives rise to problems such as transformer magnetizing inductance saturation and complicating the power flow calculations. Thus, this thesis proposes an alternate method for mitigating the transformer magnetizing inductance saturation using a variant topology of the proposed new MPC.</p>

<p>The second phase of this research focuses on MPC’s control level investigation. The power-sharing performance and fast-dynamic response of the MPCs are not thoroughly investigated in the existing literature. To that end, triple active bridge (TAB) dc-dc MPC is studied as a famous and widely used MPC for renewable energy applications. Then, a flexible power-sharing control strategy with a fast-dynamic response<br>
for the TAB dc-dc MPC is proposed in this thesis. Particularly, with the proposed control strategy, the power-sharing among the three ports of the TAB dc-dc MPC can be achieved smoothly and ultra-fast dynamic performance is ensured with the step load change, input voltage disturbances, and sudden variations of the shared power among the ports.</p>

<p>As the third and final phase of this thesis, a systematic method to design and analyze MPCs is investigated. Leveraging the experience and the insight gained from the specific topology level and control level investigations of MPCs in the first two<br>
phases of this research, it is understood, that the topological derivation and design of MPCs are heavily based on case-by-case analysis and the practical experience of the researcher. Still, a general methodology facilitating the modeling, analysis, and operation design of new MPCs is absent. Therefore, a general synthesizing approach for designing novel MPC topologies is proposed in this work based on graph theory-based duality principles.</p>

<p>Overall, this thesis proposes potential methodologies for improving the topologies and operations of MPCs in three aspects - the circuit topology structure level, converter<br>
control level, and theoretical approach of the MPC design level. Therefore, it is hoped that the presented content of this thesis will help see the MPCs and MPC research from a different perspective and further bolster their significance.</p>