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T-type primary bridge-based resonant converters employed in unfolding-based single-stage ac–dc conversion systems commonly adopt a leading-edge aligned modulation strategy, as it facilitates zero-voltage switching (ZVS) throughout the grid cycle. However, the application of this modulation strategy can result in partial ZVS of the common-source mosfets within the T-type bridge. In this letter, we investigate the underlying reasoning of such partial ZVS, quantify the severity of the problem, and propose a mitigation solution. Specifically, an optimized leading-edge aligned modulation strategy is introduced, incorporating an intentional staggered time delay for the turn-off of the common-source mosfets during the leading edge. The proposed modulation strategy is validated through hardware testing on a 20-kW unfolding-based ac–dc conversion system. 

Unfolder-based quasi-single-stage ac-dc power converter has been widely used for high-power electric vehicle (EV) charging systems for its high efficiency and power density. However, the resonance between the grid inductance (impedance) and the capacitors on the soft-dc-link of the converter impacts the system stability and significantly limits the system control bandwidth and dynamic response performance. A quasi-single-stage ac-dc converter with unfolder plus T-bridge series resonant converter (T-SRC) is studied in this work. The small-signal modeling and plant transfer function derivation of the T-SRC is presented in this paper. A damping filter design using the extra element theorem (EET) is then proposed to achieve high- bandwidth and stable operation of the quasi-single-stage ac-dc converter. Simulation and hardware results from an 18 kW module for high-power EV charging are provided to validate the proposed modeling and damping filter design. 

As transportation electrification keeps accelerating across a wide range of vehicle classes from light-duty cars to heavy-duty trucks, the need for high-power electric vehicle (EV) charging equipment continues to grow rapidly. Even though the advancements in power electronics are enabling higher efficiency for EV chargers, thermal management continues to be a significant challenge in high-power charger development Liquid cooling with cold plates is commonly used for dissipating the heat generated by semiconductor devices m high-power chargers To design an effective and optimized thermal management system, accurate thermal modeling and analysis are critical, especially m the preliminary design phases. Complex fluid dynamics (CFD) software such as Ansys has been widely used for thermal modeling and analysis in the literature; however, using CFD analysis tools can be expensive, time-consuming, and computationally intense. To address the technical needs for a rapid, accurate preliminary thermal analysis tool, this paper presents a novel and accurate thermal modeling and analysis approach for high- power EV chargers with liquid cooling and Silicon Carbide (SiC) MOSFETs mounted on cold plates. The proposed modeling and analysis approach utilizes a lumped element model for each of the many pieces within the system to mathematically represent the physical system and form thermal networks. The effectiveness, accuracy, and light computational load of the proposed approach have been validated through experimental results conducted on a 21 kW power converter module hardware from a 1 MW EV wireless charge developed by the team for Class 8 semi-trucks. 

To optimize the utilization of a T-type bridge structure in resonant converters, one must thoroughly examine the soft-switching criteria specific to the T-type configuration. This work proposes an energy-based method to determine the softs-witching requirements of a T-type bridge during its various switching transitions. The study estimates the minimum required zero voltage switching (ZVS) current while considering the nonlinearity and voltage dependence associated with the output capacitance of MOSFETs. Moreover, this paper demonstrates that existing studies on ZVS analysis for T-type bridge-based resonant dc-dc converters, which rely only on capacitive energy considerations, significantly underestimate the necessary ZVS current values, with errors as high as 50%. Simulation and hardware results on a T-type primary bridge circuit validate the accuracy of the proposed minimum ZVS current calculation. Hardware tests are conducted on a T-type bridge in a 20 kW electric vehicle charger. 

Unfolding-based single-stage ac-dc converters offer benefits in terms of efficiency and power density due to the low-frequency operation of the Unfolder, resulting in negligible switching losses. However, the operation of the Unfolder results in time-varying dc voltages at the input of the subsequent dc-dc converter, complicating its soft-switching analysis. The complication is further enhanced due to the nonlinear nature of the output capacitance ( Coss ) of MOSFETs employed in the dc-dc converter. Furthermore, unlike two-stage topologies with a constant dc-link voltage, as seen in high-frequency grid-tied converters, grid voltage fluctuations also impact the dc input voltages of the dc-dc converter in unfolding-based systems. This work comprehensively analyzes the soft-switching phenomenon in the T-type primary bridge-based dc-dc converter used in unfolding-based topologies, considering all the aforementioned challenges. An energy-based methodology is proposed to determine the minimum zero-voltage switching (ZVS) current and ZVS time during various switching transitions of the T-type bridge. It is shown that the existing literature on the ZVS analysis of the T-type bridge-based resonant dc-dc converter, relying solely on capacitive energy considerations, substantially underestimates the required ZVS current values, with errors reaching up to 50%. The proposed analysis is verified through both simulation and hardware testing. The hardware testing is conducted on a 20-kW 3- ϕ unfolding-based ac-dc converter designed for high-power electric vehicle battery charging applications. The ZVS analysis is verified at various grid angles with the proposed analysis ensuring a complete ZVS operation of the ac-dc system throughout the grid cycle.