This article investigates the design and performance of isolated DC-DC converters operating at switching frequencies in the MHz range, with a focus on achieving zero-voltage switching (ZVS) conditions. A comparative evaluation of resonant converter topologies-conventional LLC, conventional CLLC, and asymmetrical CLLC-is conducted, alongside an analysis of air-core and ferrite-core transformers in terms of efficiency, losses, thermal behavior, and practical limitations. First, the study reviews various solutions, including dual active bridge, LLC, CLLC, and asymmetrical CLLC, suitable for high-frequency operation, and discusses the ZVS conditions required for each topology. Second, the ZVS conditions for the considered solutions are analyzed in detail. Third, transformer core options are compared, focusing on losses and volume tradeoffs between commercially available ferrite cores and custom-designed air-core transformers for MHz frequency operation. Finally, experimental validation is performed to assess the performance of air-core and ferrite-core transformers in LLC, CLLC, and asymmetrical CLLC configurations under 1 MHz switching frequency, 3.5-4.5 kW power range, and 350 V input voltage conditions. The results address power losses, thermal management, practical limitations, and potential solutions while evaluating ZVS soft-switching performance. This study provides practical design considerations for high-frequency resonant converters, addressing both performance and feasibility for MHz-range and high-power (kW) applications.

The rapid scaling of accelerated computing is pushing rack power well beyond 1 MW, making conventional 48 V distribution increasingly inefficient due to busbar and connector currents. High-voltage DC (HVDC) distribution (e.g., 800 V) enables lower distribution losses and motivates server boards that interface directly to an HVDC bus. This paper addresses two enabling building blocks on the server board: (i) safe hotswap and eFuse functionality with controlled pre-charging and telemetry, and (ii) high-power-density conversion from 800 V to intermediate-bus voltages. For hot-swap, a 1200 V-rated SiC JFET cascode is evaluated in linear mode and demonstrated to pre-charge 300 mu F from 0 V to 800 V in approximately 1.5 s while staying within the device SOA limits. For power conversion, an unregulated LLC-DCX approach is investigated. An 800 V-to-50 V input-series-output-parallel (ISOP) half-bridge converter using GaN switches on the primary and secondary side and a matrix transformer reaches 98.1% efficiency at full load and a peak efficiency above 98.4(%). A direct 800 V-to-12 V converter prototype achieves 97% at 6 kW and 98.2% peak efficiency.

Wide voltage gain range dc-dc converters are vital in applications like photovoltaic and energy storage systems. Over the past decade, extensive research has focused on developing efficient converter topologies capable of accommodating a wide voltage gain range, including wide input or output voltage ranges. This paper systematically categorizes these converters into two main groups based on their approach to extending the voltage gain range (≥1:3). The first group includes topology morphing control (TMC) based dc-dc converters, which dynamically modify the converter topology through reconfiguration at either the input or output side, or by adjusting transformer turns ratio or resonant tank components. The second category comprises isolated buck-boost converters (IBBC), boost half-bridge converters (BHBC), resonant converters, and multi-phase converters. These converters achieve wide voltage gain ranges through structural modifications or control strategies. Additionally, each group is divided into subgroups that highlight their operating principles, features, and limitations. The paper also discusses challenges, including efficiency optimization and control complexity, in achieving wide voltage gain ranges. This paper serves as a valuable resource for researchers and engineers developing high-performance isolated dc-dc converters for applications requiring a wide voltage gain range. The findings provide insights into current challenges and future research opportunities, thereby supporting the development of innovative and efficient converter topologies for wide voltage gain applications.

This paper introduces a universal, bidirectional onboard charging architecture for electric vehicles, designed to support high-efficiency operation across a wide range of ac and dc grid configurations. The system is capable of interfacing with single-phase and three-phase ac sources, as well as two-wire and three-wire dc supplies, without requiring any hardware reconfiguration—offering true plug-and-play flexibility for global charging infrastructure. The converter employs GaN-based power devices to enable high-frequency operation, with the rectifier stage switching at 100 kHz and the isolated dc-dc stage operating at 1 MHz. This high-frequency design significantly reduces the size of the magnetic components, particularly the isolation transformer, resulting in a compact and thermally efficient system. To address core losses and magnetic saturation at high ripple currents, air-core transformers are used in the dc-dc stage, enhancing both performance and reliability. The system also incorporates soft-switching techniques to reduce switching losses and maintain high overall efficiency. A bidirectional power flow capability enables both grid-to-vehicle (G2V) and vehicle-to-grid (V2G) operation. A hardware prototype rated at 11 kW was developed and experimentally validated, demonstrating reliable operation up to 800 V battery voltage, with an efficiency exceeding 95% and a power density of 7 kW/L.

The practical deployment of resonant dual-active-bridge (DAB) DC–AC converters is often constrained by the implementation cost associated with complex modulation and modeling, which creates a trade-off between conversion efficiency and real-time implementation. This article proposes a simplified, real-time optimal modulation strategy based on variable-frequency extended phase-shift modulation (VFEPS) that is analytically solvable and readily implementable in real time, while simultaneously lowering conduction and switching losses. Unlike traditional single-phase-shift (SPS) modulation, which suffers from high circulating currents, or RMS-current minimization (RMSM) strategies, which have restricted zero-voltage switching (ZVS) ranges, the proposed strategy dynamically tracks soft-switching boundaries and strategically permits controlled backflow power. This enables the joint optimization of phase-shift angles and switching frequency, thereby ensuring robust soft-switching performance across the entire AC cycle, especially near the AC zero-crossing region. The algorithm is closed-form and non-iterative, making it suitable for low-cost microcontrollers and enabling seamless transitions between different modulation modes through continuous control trajectories. Experimental validation was conducted on a 500-W prototype using monolithic bidirectional GaN (BDS GaN) switches, demonstrating the effectiveness and superior efficiency of the proposed control scheme.

This work presents a concept of a universal, bidirectional onboard charging structure for electric vehicles, designed for the ability to be connected to any type of residential ac and dc grids with minimized redundancy. Offering true plug-and-play flexibility for global charging infrastructure, the electric vehicle equipped with a universal onboard charger can be charged from single-phase and three-phase ac sources, as well as two-wire and three-wire dc supplies. The bidirectional power flow capability enables both vehicle-to-grid (V2G) and grid-to-vehicle (G2V) operation. Several possible solutions are proposed and compared. The hardware setup rated up to 11 kW was designed and experimentally validated, demonstrating all claimed features.

This work introduces a quasi-single-stage 48 V, 350 A VRM voltage regulator module (VRM). A single module combines a four-phase half-bridge current doubler (HB-CD) and a single-phase non-isolated buck converter. The former performs the direct conversion from the 48 V, while the latter from an intermediate bus voltage (IBV) of 5 V. Phase coupling is realized thanks to TLVR, which the buck converter actively supplies to drive the output, achieving zero DC-bias flux in the HB-CD integrated magnetic (ZB-TLVR). Optionally, buck power stages can be further coupled by a conventional, second level TLVR (Cascaded TLVR). A system demonstrator for 48 V/0.8 V has been built. With multifrequency, cascaded ZB-TLVR operation, the converter is capable of fast transient response in an overall efficient (90% peak, up to 84.7% TDC) solution.

In modern power distribution systems, the conversion from a 48V bus to the point-of-load (POL) voltage is commonly implemented in two stages. Intermediate bus converters (IBCs) often employ resonant LLC topologies that typically step the bus voltage down to approximately 12V. In these converters, the transformer size is largely dictated by the output voltage, and zero-voltage switching (ZVS) is achieved through the transformer’s magnetizing inductance. Conversely, resonant switched capacitor converter (SCC) derivatives generally operate with zero-current switching (ZCS), which limits switching frequency flexibility and increases sensitivity to component tolerances.This work presents a novel unregulated Fractional Switched Capacitor (FSC) converter, derived from Dickson-based topologies, capable of delivering flexible non-integer conversion ratios (e.g., 3.25:1, 3.5:1) while maintaining ZVS across all MOSFETs. The proposed FSC integrates an autotransformer, removing the need for additional inductors to provide both ZVS and resonant operation, thereby enhancing power density. A 1kW prototype, derived from a 3:1 Dickson configuration, is presented in this work. It achieves a compact footprint (23.5mm×19mm) and a peak efficiency exceeding 98.5%. Experimental results confirm symmetrical ZVS operation and robust performance, even in the presence of component tolerances and under non-optimal switching frequency conditions.

This article presents an optimization strategy for enhancing the efficiency and power density of a GaN-based dc-dc converter, tailored for different applications with a wide input voltage range regulation. The optimization employs air-core inductors and implements a variable switching frequency modulation method to enable zero voltage switching turn-on for GaN transistors, facilitating greater flexibility in frequency adjustment and improved thermal management. Additionally, a specialized thermal model is introduced for the interleaved Buck-Boost GaN transistor-based dc-dc converter, accounting for the presence of a natural convection heatsink. In the conclusion, theoretical discussions transition to practical implementation through the testing of a laboratory prototype. This prototype achieves high efficiency (around 99%), along with power densities of >17.5 kW/L and 6 kW/kg when equipped with a natural convection (without airflow) heatsink. It features a wide input voltage range (110-450 V), a constant output voltage of 350 V, variable switching frequency (18-304 kHz) and supports up to 9 kW output power.

The introduction of 400 V CoolSiC (TM) MOSFET technology bridges the voltage range gap between 200 V medium-voltage MOSFETs and 600 V super-junction MOSFETs. This technology is characterized by low switching losses and low on-state resistance, making it suitable for innovative 3-level topologies. The technology concept is presented and important device properties are discussed. The combination of the novel 400 V SiC MOSFET device technology with a multi-level topology enables a 12 kW AC/DC single-phase power supply to meet the growing power demands of data centres and provides high power density (100 W/in(3)) and efficiency (eta > 97.5%). To keep the load transients of AI chips away from the AC line, a novel control concept involving a power-pulsation buffer circuit is introduced, which acts as an active filter and also provides full control of re-rush currents after line-cycle drop-outs.

This paper presents a control strategy for Electric Vehicle (EV) battery charging that combines a soft-switched isolated dc-dc converter with a three-phase unfolding-based Power Factor Correction (PFC) topology and reduced number of inductors. The proposed system introduces a finite cycle-based model predictive control method, which regulates current by optimally allocating discrete switching cycles across multiple energy paths. For instance, operating at a 25 kHz sampling rate with 40 switching cycles per interval (enabling a 1 MHz switching frequency), the controller achieves 2.5% resolution in power delivery while maintaining sinusoidal grid currents and a high power factor. Unlike conventional designs that require three inductors and separate PFC stages, the proposed architecture uses only two inductors and shifts the PFC function to the high-frequency dc-dc stage, significantly enhancing power density and reducing system complexity. A soft-switching modulation strategy ensures that all GaN-based switches operate under zero voltage switching conditions at high switching frequencies (hundreds of kHz to several MHz), effectively minimizing switching losses. Simulation results show a total harmonic distortion below 3% and confirm the proposed system's ability to deliver high efficiency, compact design, and precise regulation across a wide output range making it well-suited for next-generation EV chargers.

AI applications in data centers are quickly advancing, leading to a surge in the development of new hardware accelerators for Machine Learning (ML), Deep Learning (DL), and High-Performance Computing (HPC). These new devices have high power demands, thereby assigning data centers a critical role in global power consumption. Updated regulations and technological improvements, including on efficiency, will be crucial to moderate the surge in energy consumption from data centers. The power conversion chain is crucial for maximizing overall system efficiency. This paper introduces an innovative power conversion architecture that employs a multi-stage approach to ensure high efficiency and a rapid transient response, thereby enhancing Power Density and Power Delivery Network (PDN) performance.

Nonisolated three-phase ac/dc electric vehicle (EV) chargers show improved efficiency and power density compared with their counterparts with a galvanic isolation stage, but residual current devices (RCDs) are mandatory to ensure electrical safety. However, RCDs are prone to nuisance tripping caused by low-frequency (LF) common-mode (CM) leakage currents through the ground, which therefore must be suppressed. Therefore, first, modulation schemes that do not result in LF CM voltages (i.e., do not use third-harmonic voltage injection) that could drive LF CM currents through parasitic capacitors from the dc output to ground must be used. Second, closed-loop ground current control (GCC) ensures near-zero LF CM leakage currents even with a direct connection of the charger dc output midpoint to protective earth (PE). Considering a voltage DC-link power-factor-correction (PFC) rectifier system that consists of a boost-type three-level T-type (Vienna) ac/dc-stage and a dc/dc-stage with two stacked buck converters, this article proposes a new modulation scheme for buck-mode operation at low dc output voltages: the dc/dc-stage then shapes the DC-link voltage such that only one of the ac/dc-stage's three bridge-legs operates with high-frequency (HF) switching [1/3-pulse-width modulation (PWM)] at any given time, and, different from previous methods, does not require third-harmonic injection to do so. Furthermore, a synergetic GCC is proposed, which operates the two converter stages in the loss-optimum mode for any output dc voltage (buck-mode and boost-mode) and regulates the LF CM ground current to near zero. The proposed concepts are verified using a 10-kW hardware demonstrator with a wide output voltage range (200-800V) and a direct connection of the dc output midpoint to PE, considering terra-terra (TT) and terra-neutral (TN) grid grounding systems, whereby the proposed GCC results in LF CM leakage currents below 7mA, i.e., far below typical RCD trip limits (30mA). The test voltages obtained with the human-body impedance model from UL 2202 are below 120mV, i.e., below 50% of even the most stringent limit of 250mV of the standard.

This paper presents a current-fed isolated buckboost converter with active clamping for a wide input voltage range, such as PV applications in dc microgrids. The currentfed configuration at the primary side minimizes input current ripple, thereby enhancing system stability. Through topology morphing control (TMC), the converter operates in five distinct modes, thereby extending both the voltage gain and the ZVS range. Additionally, the active clamp circuit limits the peak voltage across the switches and absorbs the voltage spikes, allowing the use of MOSFETs with relatively low VDS and RDS(on) ratings. The operation principle and working modes of the converter are briefly explained. A 350 W prototype with an input voltage range of 10 to 60 V was built and experimentally tested, demonstrating high efficiency and a wide gain range.

This paper presents a 12kW AC/DC single-phase power supply to meet the growing power demands of data centers driven by training very large AI models. The combination of novel 400V SiC MOSFET device technology and multi-level topology are essential in achieving the desired power density (100 W/in(exp 3)) and efficiency target (h > 97.5%). The introduction of 400V SiC MOSFET technology bridges the gap between 200 and 600V super-junction MOSFETs and is characterized by low switching losses and low on-state resistance. In order to keep the load transients of AI chips away from the AC line, a novel control concept involving a power-pulsation buffer circuit is introduced, which acts as an active filter and also provides full control of re-rush currents after line-cycle drop-outs.

In this paper, a universal bidirectional ac/dc-dc power electronic converter is introduced to enable power transfer between input and output in both directions. This converter is particularly suited for onboard battery charging systems, offering vehicle-to-grid and grid-to-vehicle functionality. The proposed system serves as a versatile and universal interface for connecting ac or dc grids and facilitating efficient power transfer. The system supports three-phase and single-phase ac, as well as two-wire and three-wire dc sources, without altering input wiring. Enhanced safety is provided through input-output isolation, and the use of active diodes at higher frequencies improves overall efficiency compared to traditional passive diodes. An 11 kW prototype was developed to validate the proposed converter. It operated successfully at up to 800 V battery voltage, with 100 kHz and 700 kHz switching frequencies for the rectifier and dc-dc stages. Proper functionality was demonstrated in both single-phase and threephase inverter modes under 5 kW testing.

The isolated buck-boost current-fed (CF) series resonant converter with active clamping integrates low input current ripple, resonant soft-switching, and voltage spike suppression, thereby enhancing power conversion efficiency. While CF converters inherently operate in boost mode, achieving buck operation is crucial for applications that require a wide voltage gain range. To address this, various constant-frequency buck modulation methods have been proposed to regulate the step-down operation of CF-SRCs. This paper examines three buck control methods for an active-clamped CF series resonant converter: conventional Phase Shift Modulation (PSM), Hybrid Phase Shift Modulation (HPSM), and Single-Switch (1Sw) Buck Modulation. A comparative evaluation is conducted through theoretical analysis and experimental validation on a 350 W prototype, assessing efficiency, switching behavior, and voltage gain characteristics. The results confirm that 1Sw buck modulations achieve peak efficiencies while also highlighting key trade-offs in conduction losses and switching stress across the different modulation methods.

The rapid growth of AI applications in data centers has led to a surge in the development of new hardware accelerators, resulting in increased power demands and energy consumption. To ensure this trend remains feasible and sustainable, it is crucial to focus on enhancing efficiency, especially within the energy conversion chain. The key enablers for achieving this objective include the precise integration of topology and magnetic structure, as well as the implementation of advanced 3D designs to enhance two critical parameters: efficiency and current density. This paper introduces a compact ultra-low profile Current Multiplier module, exploiting the advantages offered by the Hybrid Switched Capacitor (HSC) topology. Experimental results show the effectiveness of the topology achieving Electrical Current Design (EDC) density of 2.2 A/mm2.

Power semiconductors are key enablers for highly efficient power conversion to address our global societal challenges. Silicon-based power devices have dominated the field for the past four decades with thyristors, power MOSFETs, diodes, and IGBTs. However, these devices are slowly but surely reaching the material limits of silicon, namely its maximum electric field strength due to the small bandgap. Wide-bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) allow the silicon limit to be overcome with a tenfold increase in the critical electric field. We present the main SiC and GaN device concepts and their technological implementations. We compare their performance with best-in-class silicon devices for the most important power electronics topologies. Finally, we will show the benefits of these new devices for some real-world use cases, such as a 10-kW photovoltaic inverter with a record efficiency of 99.4%.

Fast charging of electric vehicles (EVs) requires isolated AC/DC converters with a wide output voltage range of 200V to 1000V. Combining a three-level Vienna Rectifier (VR) with four isolated Dual-Active-Bridge DC/DC Converter (DABC) modules and latest-generation 600V GaN technology enables very high switching frequencies of 560 kHz for the VR and up to 330 kHz for the DABCs. Hence, in this paper an ultra-compact realization of a 10 kW EV charger module with a power density of 9 kW/dm 3 (about 150 W/in 3 ), not including the coldplate, is presented. In this context, a simplified DABC modulation method and straightforward yet accurate (confirmed by experiments) loss models for the DABCs and the VR are introduced, which facilitate a thorough investigation of the optimum synergetic operation of the two stages: For the considered converter, changing the VR operating mode from conventional 3/3-PWM (where the two stages operate rather independently and hence all three VR bridge-legs operate with PWM) to 1/3-PWM (where the DABCs shape the voltage of the shared intermediate DC-link such that always only one of the VR’s three bridge-legs must operate with PWM) results in an advantageous efficiency improvement of up to about 2% over a large part of the output voltage and power range, and in a peak efficiency of more than 97%. Further, the synergetic operation of the two-stage system (VR and DABCs) is experimentally verified for the first time, confirming the modeling results and the efficiency advantage of 1/3-PWM (i.e., 95.4% vs. 95.1% at the rated load of 10 kW and with 500V output voltage). Conducted EMI pre-compliance measurements indicate that the change of the operating strategy from 3/3-PWM to 1/3-PWM only requires minor changes of the EMI filter design.