Single-stage power conversion with high frequency transformer isolation has gained interest as a key enabler in improving the efficiency and power density of electrical systems. Traditionally, the power conversion from one voltage level to multiple voltage levels is performed using discrete modules of AC-DC and/or DC-DC converters that meet the isolation requirements. Due to low level of integration in terms of high frequency magnetic link and driving power electronic converters, such solutions suffer from large volume/weight and low efficiencies. Regardless, such multiple input/output converter architectures are extensively used in a wide range of applications, including electric vehicles, DC smart homes, data centers and personal computers. While these architectures are realized using a combination of interconnected discrete power converters, this Ph.D. dissertation presents a multi-port energy router which is capable of integrating multiple systems with different voltage levels, resulting in substantial improvements in power density and efficiency. The proposed energy router employs multi-active-bridge (MAB) converter derived topologies as the fundamental building blocks to create an electrically and magnetically integrated, scalable, single-stage, power electronic converter which can be extended to n-ports. Several key challenges that have impeded the use of MAB converters are investigated in detail.

The estimation of the optimal modulation parameters of an MAB converter is vital for achieving desired converter performance. The accurate modeling of the high frequency ac-link plays a major role in determining modulation parameters due to sophisticated magnetic coupling relationships. As the first contribution of this dissertation, a full-order n x n impedance matrix-based model which captures all the coupling information of the magnetic link is used to obtain desired power flow, minimize conduction losses, and analyze zero-voltage-switching (ZVS) conditions of the MAB converter topology. A frequency domain model of the MAB converter is developed which uses the impedance matrix to solve for port currents. Subsequently, the proposed model is used to formulate a constrained numerical optimization routine to find the optimal modulation parameters, which minimizes the conduction and switching losses. The inductance matrix of the high-frequency ac-link is further used in conjunction with the frequency domain model to analyze the port ZVS conditions by investigating the port equivalent inductive energy in the high frequency ac-link.

The broad range of operating points (port loading conditions and voltage levels) in an MAB converter presents a complex problem in the design of efficient and power-dense magnetic components. As such, it is not feasible to use traditional optimization approaches developed for two-winding transformers, due to the presence of a high number of design parameters, modulation variables, and the effect of the port loading conditions on the dynamic AC resistance and core losses. As the second contribution, comprehensive planar PCB-based magnetics are developed using a multi-objective design and optimization framework to realize a highly efficient and compact planar magnetic link for the MAB converter. As a key component of this framework, accurate and scalable analytical models for conduction and core loss estimation are developed, which capture loss mechanisms distinctive to multi-winding transformers. Using the proposed loss models, the design framework integrates multi-objective optimization methods for all magnetic components in the high-frequency link, namely, the multi-winding transformer and the series branch inductors. The proposed approach determines the optimal combination of magnetic core geometries, turns ratios, number of turns, branch inductances, and winding interleaving configuration, with the objectives of minimizing the operating point weighted-efficiency drop and the magnetic volume. Finally, a Pareto-optimal magnetic link design is selected. The proposed concepts of obtaining optimal modulation parameters and the design of high frequency planar magnetic link are validated using comprehensive circuit and finite-element-analysis (FEA) simulations. The experimental verification is performed on a Gallium Nitride based 4-port 1-kW DC-DC MAB converter with its ports rated at 420V, 48V, 24V, 12V.

With the modeling, design and optimization methodologies obtained from the above two works, a new family of MAB derived converter topologies with AC ports is proposed as the third contribution of this dissertation. Particularly, the single-stage power conversion between DC and three-phase AC is investigated. The operating principles of the proposed topologies are discussed in detail along with systematic modeling and optimal modulation methods by using the concepts developed above for DC-DC MAB converters. The circuit operation is also investigated in terms of ZVS. To validate the topology configurations and the modulation methods, comprehensive Simulink simulation models are developed. Compared to traditional two-stage converter systems comprised of DC-DC and DC-AC stages, the proposed topologies provide multiple benefits in terms of single-stage power conversion, ZVS, high-efficiency and galvanic isolation.