Electromagnetic compatibility (EMC) remains a serious challenge in the design of high-density power supplies. Advancements in power semiconductors have enabled higher switching frequencies and greater system integration. However, the combination of fast switching and compact layout exacerbates the effects of parasitic near-field couplings within the power supply. These couplings create unintended paths for electromagnetic interference (EMI) propagation, which are layout-dependent and difficult to measure or quantify analytically. As a result, designers often rely on iterative trial-and-error methods to comply with EMC standards. This article introduces a framework to accurately predict the differential-mode (DM) noise of frontend converters, including the effects of magnetic couplings between components in the power factor correction and EMI filter stages. A lumped element DM noise model is presented, and each magnetic coupling value is quantified with 3-D finite-element analysis. The model is then simplified, and a novel experimental approach is introduced to validate the impact of individual magnetic couplings. Finally, this framework is used to evaluate various EMI mitigation techniques, demonstrating up to 30 dB reduction in DM noise.

The PCB winding-based transformer is renowned for its low profile, easy manufacturability, and cost-effectiveness. However, it encounters challenges in high-power applications due to substantial winding loss caused by the proximity effect in high-frequency currents. On the other hand, Litz wire is designed to handle high-frequency currents efficiently through its twisting and interweaving structure, making it suitable for high-power applications. Yet, constructing the Litz wire pattern within PCB winding poses a significant challenge due to its complex structure. This paper introduces a novel design and optimization method, presenting a Litz wire version of PCB for Solid-State Transformers. The construction of the Litz wire version of PCB is detailed, and the principle of the flux cancellation effect inside it is analyzed. A comprehensive optimization process is proposed for the design of a PCB Litz wire-based Solid-State Transformer. Results demonstrate that, compared to traditional PCB winding, PCB Litz wire achieves a 30% reduction in winding loss, significantly improves current distribution, and enhances thermal performance. To validate the concept's effectiveness, a prototype of a 1.6/1.05kV, 192kHz, 30-kW CLLC converter is built, demonstrating an impressive 99.0% efficiency with 6.8 kW/L power density.

A solid-state transformer (SST) offers direct medium voltage to low voltage conversion, resulting in higher system efficiency and a smaller footprint compared to traditional transformers. Among the popular SST architectures, a two-stage system comprising a cascade H-bridge (CHB) as the first stage and a resonant converter as the second stage has gained prominence. However, the CHB circuit introduces power ripple at twice the line frequency, leading to poor power density due to the necessity of large bus capacitors for power regulation. To address this issue, a partial fluctuation power control method is proposed that allows a portion of the power ripple to flow through the resonant converter, thus reducing the size of the bus capacitors. Additionally, a loss evaluation is presented to calculate the losses related to fluctuation power, and a magnetic component optimization methodology is conducted to achieve an optimal tradeoff between loss and size for the resonant converter. The effectiveness of the proposed control method is demonstrated through a 15 kW 180 kHz CLLC converter module, achieving a peak efficiency of 98.8% and a power density of 3.1 kW/L. Furthermore, the bus capacitor size is reduced to 60% without compromising overall losses when compared to conventional regulated resonant converters.

A solid-state transformer can directly convert medium voltage to low voltage (e.g., 400 V) with minimized power-conversion stages. The transformer in the dc–dc module not only provides medium-voltage insulation but also significantly affects the power density of the module. In this article, an innovative compact transformer structure is proposed to handle medium-voltage insulation using an insulation coordination with epoxy, bobbin, shielding layer, and stress-control layer. A brand-new bobbin design and related fabrication process ensures a partial-discharge-free insulation. Besides the traditional core loss and winding loss, high-frequency-related core loss and shielding loss are modeled in detail for the accurate loss evaluation. A simple and comprehensive multiparameter, multiobjective optimization process is proposed to achieve the size and loss tradeoff. The transformer prototype passes the related insulation tests, following the standard IEEE Std. C57.12.01. Finally, the design is demonstrated on a 15 kW, 200 kHz CLLC converter with 98.9% peak efficiency and 3.8 kW/L power density.

To date, $LLC$ resonant converters have been deployed in many applications for improved efficiency, density, and reliability. With the introduction of wide-bandgap devices coupled with the soft switching feature, the switching frequency can be extended beyond megahertz. With the significant increase in operating frequency, complicated magnetic components can be broken down into a cellular structure, each with a few number of turns. They can be easily implemented using four to six layers of printed circuit board windings. Moreover, integrating the cellular cores using flux cancellation can further improve the power density. The proposed integrated magnetics can be automated in the manufacturing process. With the recently developed high-frequency core material, phenomena referred to as the dimensional effects on core loss are observed. The dimensional effects are discussed in the literature when using an unusually large core structure; however, at high excitation frequencies, it can be observed more frequently, particularly with integrated magnetic components. In this article, we give an overview of the dimensional effects on core loss, namely flux crowding, dimensional resonance, and eddy loss, with the latest being a dominant factor in the 1-MHz transformer loss. We also introduce a practical method for the characterization of the dimensional effects to help engineers better design their high-frequency converter. This includes measuring the ferrite material characteristics and evaluating the dimensional effects using finite-element analysis. Finally, a case study of 1-MHz 400-to-48 V converter design is presented, showing superiority in both power density and efficiency metrics compared to other reported literature from the same category. This shows the importance of including the dimensional effects and, specifically, the core eddy loss in the design procedure.

As the 48 V data center power architecture becomes an alternative to the traditional 12 V architecture, it is essential and critical to design a more energy-efficient and power-dense solution for 48 V to point-of-load (PoL) power conversion. In this paper, a single-stage 48 V/1.8 V coupled-transformer voltage regulator (CTVR) is proposed for high-performance microprocessors in data center applications. The proposed solution utilizes a novel coupled transformer structure. The magnetizing inductors of the transformers work as output inductors, which are indirect-coupled through transformer structures. Finally, a hardware prototype is built, demonstrating 0.45 W/mm 2 and 1.13 W/mm 2 power area density under continuous and peak output power, respectively.

CLLC resonant converter can achieve zero voltage switching (ZVS) turn-on and low current turn-off for the primary side, both zero current switching (ZCS) and ZVS for the secondary side switches, which makes it a great candidate for today's high-frequency, high-efficiency applications. However, for high power applications like electrical vehicle (EV) charger, photovoltaic (PV) power station, energy storage, and railway auxiliary power supply applications, the wide input and/or output voltage range is usually a challenge for resonant converters. Besides, the influence of the secondary-side devices' junction caps to commutation is no longer negligible, but rarely analyzed in literature. In this paper, a control strategy of CLLC converter to boost the output voltage is reviewed. The design of magnetic component, an integrated transformer, is introduced. The process of conventional commutation strategy is analyzed for the cases where the secondary side junction caps are comparable to the primary side ones. Then another commutation strategy is compared, which could reduce the circulating energy by half. Finally, a 100 kHz 30 kW SiC based CLLC converter prototype verifies the proposed design and achieves a peak efficiency higher than 99%.

The LLC converter is the most efficient topology in server and telecom applications. Furthermore, three interleaved LLC converters have been shown to yield efficiency advantages at power levels of several kilowatts. The magnetic components of a multiphase LLC , on the other hand, are complex, laborious, and difficult to build cost-effectively. To solve these issues, a high-frequency GaN-based three-phase LLC converter is used in this research. With GaN working at 500 kHz, all magnetic components, including six inductors and six transformers, can be housed in a single structure, while all magnetic windings are accommodated in a four-layer PCB with 3 oz. of copper. Furthermore, electromagnetic interference can be improved by virtue of three-phase by 20 dB and an additional two layers are added to gain an additional 20–30 dB reduction from a low frequency up to 30 MHz. The proposed construction is simple and economically mass-producible. A 6 kW 400V/48V 3-phase prototype is implemented, with a peak efficiency of over 99% and a power density of 1000 W/in3 (61 kW/L)

Litz wire is known for its ability to minimize winding losses in high-frequency applications. However, its implementation in PCB winding poses significant challenges. This paper presents a novel PCB Litz wire concept aimed at minimizing winding loss in high-frequency applications, specifically in the design of a solid-state transformer using PCB-winding-based technology. The proposed PCB Litz wire is designed in a circular winding configuration with curved strands, optimizing its performance. The construction method and the turn-to-turn connection are demonstrated. Factors affecting the resistance of the PCB Litz wire, including the number of strands, their width, and section, are discussed. The results show that compared to traditional PCB winding, the PCB Litz wire achieves a 30% reduction in winding loss and significantly improves current distribution, leading to enhanced thermal performance. To validate the concept's effectiveness, a prototype of a 1.6/1.05kV, 190kHz, 30-kW CLLC converter is built, demonstrating an impressive 98.8% efficiency.

Modular multilevel converter is deemed the solution for high-voltage high-power applications. The introduction of capacitor to each arm leads to complicated power flow and thus complicated control scheme. Without a proper control, this often results in large circulating energy. The state plane analysis identified the two types of circulating energies, one related to the power difference between input and output, and the other related to the internal power swapping. Due to their orthogonal nature, a coordinate transformation is proposed, which leads to a decoupled equivalent circuit model. The proposed model suggests two control laws, aiming at eliminating both types of circulating energy.

The two nonlinear components in a PWM converter are power switches and PWM modulator. In a voltage-mode control, they were modeled separately due to the sufficient low-pass filtering from both power stage and feedback compensator. In more advanced controls such as peak current-mode, constant on-time, or $\mathrm{v}^{2}$ controls, more state variables are fed-back into the control loop with less or no filtering in order to achieve a better dynamic performance. Consequently, power stage and feedback control must be considered as one entity to properly account for contribution from harmonics. J. Li derived the corresponding models based on describing function method, and the mathematical model was then approximated with an equivalent-circuit form by Y. Yan. However, the perspective of the current feedback was lost since power stage and feedback were lumped together. Moreover, the average-model based power stage cannot address the contribution from harmonics. This paper proposes an equivalent circuit model that preserves the current feedback information, and is accurate at half switching frequency at all terminals due to the improved power stage model.

This essay synthesizes critical contract theory and radical democratic theory to contest U.S. authoritarianism and U.S. neoliberalism. Theoretically, I argue that radical democratic theory needs critical contract theory to expose the gendered and raced infrastructure of U.S. liberal democracy, while critical contract theory needs radical democratic theory to reframe race and gender dominance in terms of popular struggle. Historically, I argue that U.S. "fraternal whiteness" or "white democracy" is a deep inegalitarian infrastructure of U.S. liberal democracy. The implication is that recent U.S. turns toward neoliberalism and authoritarianism are more updates on white democracy than departures from liberal democracy. In this theoretical and historical context, I argue that effective left strategies - socialist and other anti-capitalist ones not excepted - must work from the premise that fraternal whiteness coheres the U.S. neoliberal-U.S. authoritarian alliance. I conclude with suggestions on how the U.S. left could use gendered and raced "wedges" to split the U.S. authoritarian neoliberal bloc.

Since there are less control means than state variables to be controlled, the modular multilevel converter is an overly-constrained system. The minimum circulating energy was unknown, and the control implementation to address this challenge was vague. In Part I, two types of circulating energy with orthogonal nature are identified though state-space analysis: one related to instantaneous input and output power unbalance, and the other related to internal power swapping. The corresponding decoupled equivalent circuit based on the proposed coordinate transformation was presented, which leads to two control laws aiming at eliminating each type of circulating energy. In Part II, the convoluted multi-state-variable is clearly explained using the proposed equivalent circuit model. The two control laws and the state planes are utilized to evaluate the effectiveness of the existing control methods.

In this article, balance technique is applied into two-channel interleaved three-phase ac–dc converters with critical conduction mode based soft switching modulation. By adding additional inductors and coupling them with the original ones, the realization of the balance becomes possible with proper design; thus reducing the common-mode (CM) EMI noise. The balance condition is derived, and the impact of balance technique on the circuit operation especially on the switching frequency variation is quantified in order to provide the design guideline. Based on the application of balance technique, instead of the commonly used litz-wire-based inductors, PCB winding coupled inductors are adopted and designed to effectively achieve the reduction of CM EMI noise. The design methodology and process are presented, and the design tradeoff is made between the inductor loss and the inductor footprint. Finally, the effect of CM EMI noise reduction and the system efficiency with balance techniques and PCB winding magnetics are tested on a 25-kW silicon-carbide-based soft-switching three-phase ac–dc converter prototype.

Recently, resonant DC-DC converters have been deployed in many fields such as information and communications technology (ICT) and with electric vehicles (EVs) due to their improved efficiency, density, and reliability. With the introduction of wide-bandgap (WBG) devices coupled with the soft-switching feature, switching frequencies can be extended beyond mega-hertz. However, the design of the magnetic components (trans-former and inductor) becomes more challenging to accommodate for high efficiency, high power density, and lower cost. This paper leverages the printed circuit board (PCB) to integrate a matrix of four transformers plus a resonant inductor in a novel five-leg magnetic core structure. The proposed design allows controllable leakage inductance for the matrix transformer within the footprint of the original matrix transformer, which offers excellent power density for the magnetics. The proposed structure is used to implement a regulated CLL resonant con-verter. The magnetic concept is demonstrated on 3kW 400V/48V CLL converter addresses for the data center applications. The converter achieves a power density of 550W/in 3 and a peak efficiency of 97.3%.

Presents the recipients of MMTS 2021 Best Industry and Best Student Paper awards.

This article presents a control scheme for an omnidirectional wireless power transfer system. A system architecture is proposed to implement the current amplitude control. To focus power transfer towards targeted loads, a smart detection algorithm for identifying the positioning and orientation of receiver devices based on the input power information is presented. The system efficiency is further improved by a maximum efficiency point tracking function. A novel power flow control with a load combination strategy to charge multiple loads simultaneously is explained. Finally, the proposed control scheme is successfully applied to an example 6.78 MHz omnidirectional wireless charging bowl system. The experimental results confirm the accuracy of the load detection algorithm and validate the power flow control strategy.

A design and control method are introduced in this paper to improve the overall efficiency of an LLC converter for railway applications, with high power and wide gain range requirements. Multi operation modes are combined together. Magnetizing inductance is designed to minimize device loss under unity gain operation. Boost mode operation provides an ability to boost gain much higher than frequency modulation could, and release the constrain of resonant tank design with respect to the peak gain requirement. The 30kW prototype circuit verifies the proposed design and control method.

As portable devices become smaller and thinner, an integrated voltage regulator (IVR) can save space and improve the efficiency of the whole system dramatically, thereby becoming a promising solution to power microprocessors. However, its high-frequency magnetic design is quite challenging and usually becomes the bottleneck. In previous work, a novel, two-phase coupled inductor structure with unsymmetrical through-core conductor distribution was demonstrated as a good candidate due to its small loss, footprint, and low profile. In this paper, the unique coupling mechanism of this specific structure is revealed, based on an equivalent circuit model to fully explore its benefits. Then, a four-phase integrated inductor is proposed to further improve inductor performance by utilizing flux cancellation. To realize a fully integrated three-dimensional IVR, PCB-embedded inductor samples are fabricated and tested experimentally. Compared with other state-of-art solutions, the proposed inductor structure integrates four inductors into one magnetic core with much smaller dc resistance and large inductance density.

With the advancements in wide-bandgap power devices, the solid state transformer (SST) becomes attractive to industry due to its merits of high efficiency and power density, modularity, and scalability. However, the complexity and cost remain obstacles to widespread adoption. This article presents a unidirectional SST with a cascaded three-level bridgeless power factor correction rectifier stage and a series-half-bridge (SHB) LLC dc–dc stage, which is simpler and more cost effective than its bidirectional counterpart. The quasi-two-level (Q2L) modulation method is proposed for the three-level bridgeless PFC rectifier. In contrast with the three-level modulation, the Q2L modulation almost eliminates the neutral-point (NP) voltage ripple at line frequency, resulting in much less dc-link capacitor volume. Further, the only safe switching sequence to implement the Q2L modulation is identified and analyzed. The NP voltage shall be balanced by the SHB LLC dc–dc stage for proper operation of the system. A phase-shift-based three-level operation mode is proposed for the SHB LLC converter to balance the NP voltage. The proposed methods are experimentally verified on a 10 kW silicon carbide-based three-level converter cell and a single-phase multicell SST prototype.