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In this article, a quasi-two-stage buck-DAB (QBDAB) converter is proposed for improving the performance of the conventional dual active bridge (DAB) solution under a wide voltage range. For the proposed QBDAB converter, the DAB can always work under voltage matching conditions for wide voltage range applications, and the gain is adjusted through the added front-end circuit. The front-end circuit is similar to a buck converter, while only part of the transmission power flows through the circuit, which could also reduce the burden of achieving ZVS of the front-end circuit. Therefore, compared with the traditional two-stage buck-DAB converter solution, the related loss for the buck circuit can be reduced. The working principle, power transfer characteristics, and full load range ZVS design are analyzed deeply in this article. A detailed comparison of the QBDAB and other related combined buck+DAB topologies is also presented. Finally, the effectiveness of the proposed QBDAB is verified through experimental results from a 1kW prototype. [ABSTRACT FROM AUTHOR]

The LLC resonant converter and dual-active-bridge (DAB) converter are attractive topologies to be used in bidirectional power applications for their respective advantages. In this letter, a dual-mode bidirectional LLC-DAB converter based on a modulated coupled inductor is proposed to combine the LLC and DAB converter into a single converter. By only modulating the PWM signals, the LC tank of the converter in two operation modes can be changed without adding any other additional diodes or switches. Meanwhile, by utilizing the modulated coupled inductor, the inductance of the LC tank will be different for two operation modes. The small leakage inductance is suitable for resonance with resonant capacitor in the LLC mode. And the large inductance is adopted to transfer the power in the DAB mode. Therefore, the LC tank parameters for two operation modes can be designed separately. The principle of the proposed dual-mode converter based on the modulated coupled inductor is investigated. After that, the parameters design consideration of the converter is given. Finally, a 2000-W prototype is built to verify the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

Due to the mismatched line resistance in the modular online uninterruptible power supply (UPS) systems, accurate active power and harmonic power sharing is an arduous work. To tackle this issue, this article proposes a distributed dynamic event-triggered control for the power sharing to accurately compensate the effect of mismatch among the line resistances. Benefiting from the proposed control strategy, the UPS modules adaptively regulate the virtual resistance at the fundamental and harmonic frequencies, and hence, the accurate active power and harmonic power sharing are achieved. In addition, the suggested technique allows the UPS modules to exchange information at only the event-triggered times, which greatly reduces the number of communication among the neighboring units. Furthermore, the system's stability is analyzed using a Lyapunov function. Finally, experimental case studies are provided to evaluate the performance of the proposed control strategy, showing its effectiveness in achieving the accurate power sharing, and plug-and-play capability. [ABSTRACT FROM AUTHOR]

Federated learning (FL) has recently become one of the hottest focuses in wireless edge networks with the ever-increasing computing capability of user equipment (UE). In FL, UEs train local machine learning models and transmit them to an aggregator, where a global model is formed and then sent back to UEs. In wireless networks, local training and model transmission can be unsuccessful due to constrained computing resources, wireless channel impairments, bandwidth limitations, etc., which degrades FL performance in model accuracy and/or training time. Moreover, we need to quantify the benefits and cost of deploying edge intelligence, as model training and transmission consume certain amount of resources. Therefore, it is imperative to deeply understand the relationship between FL performance and multiple-dimensional resources. In this paper, we construct an analytical model to investigate the relationship between the FL model accuracy and consumed resources in FL empowered wireless edge networks. Based on the analytical model, we explicitly quantify the model accuracy, available computing resources and communication resources. Numerical results validate the effectiveness of our theoretical modeling and analysis, and demonstrate the trade-off between the communication and computing resources for achieving a certain model accuracy. [ABSTRACT FROM AUTHOR]

The magnetic elements are the important parts of the dc–dc converters, which is the constriction to improve the power density of the systems. In this letter, a magnetic integration structure is proposed to integrate the magnetizing and leakage inductance for split transformer with standard UI cores, which are mass-produced. Compared with the EI/EE-core structure to achieve magnetic integration, the magnetic field is theoretically evenly distributed in a UI core, and the center leg is removed because of the flux cancelation during the derivation process of the proposed magnetic structure. In this magnetic integration structure, the magnetizing inductance and the leakage inductance can be controlled accurately by designing the numbers of printed circuit board (PCB) windings and the air gap length of the UI core. The derivation process of the proposed magnetic integration and mathematical analysis is studied. The step-by-step design process is investigated, and a design example is given. A 250 kHz, 800 W, 360/380 V LLC prototype is built to verify the feasibility of the proposed magnetic integration method. [ABSTRACT FROM AUTHOR]

Virtual synchronous generator (VSG) control introduces active power oscillation especially under the condition of multi-VSG. This article proposes a decentralized mutual damping control method that suppresses power oscillation in the multi-VSG grid. The idea is that as the local frequency is greater than the frequency of the VSG other than itself, the input energy of the local VSG is reduced, and thus dωi/dt increases. On the contrary, when the local frequency is less than others, the input energy is increased, and thus dωi/dt decreases. In this way, all frequencies get close to each other in the dynamic process with the method. The idea is verified by the stability analysis. Participation factor analysis and sensitivity analysis are presented to guide parameter design. Finally, the effectiveness of the decentralized mutual damping method is verified through the simulation results and experimental results. [ABSTRACT FROM AUTHOR]

This article reveals the power and frequency oscillation mechanism of the islanded cascaded-type virtual synchronous generators (VSGs), and proposes a decentralized mutual damping suppression method. In the proposed scheme, the mutual damping term is constructed via the decentralized manner with transmission line current. It contributes to increasing damping and accelerating the frequency convergence of cascaded-type VSGs in the dynamic process. As a result, the power and frequency oscillations are restrained, and the system dynamic performance is improved. Further, the system stability based on the Lyapunov energy function method is proved. Finally, the effectiveness of the proposed decentralized mutual damping control is verified by simulations and experimental results. [ABSTRACT FROM AUTHOR]

Frequency-domain modeling is an effective technique in the dynamic analysis of power electronic converters-based power systems. In this paper, a unified single-input single-output (SISO) loop gain modeling for the three-phase grid-tied voltage source converters (VSCs) under both symmetric and asymmetric AC grids is presented, which facilitates the physical measurement and stability analysis. Based on the linear-time-periodic (LTP) modeling technique, the harmonic admittance model of the three-phase grid-tied VSC is developed in the stationary (αβ)-frame, which accurately captures the coupling dynamics. This model can be transformed into other existing models through coordinate transformations. According to the idea of mathematical induction, a two-by-two recursive admittance matrix (RAM) model is derived, which is easy to include frequency coupling components of arbitrary order. It is illustrated that the VSC admittance is coupled with the grid admittance due to the frequency coupling effect (FCE). Furthermore, the RAM is converted to its equivalent SISO models following the concept of loop gain. The system stability is thus assessed by the SISO stability criteria (e.g., Nyquist stability criterion). In addition, the loop gain allows the traditional SISO perturbation and measurement scheme to be used for detecting the stability margin information. Finally, simulation results verify the feasibility and correctness of the theoretical analysis presented above. [ABSTRACT FROM AUTHOR]

When multiple virtual synchronous generators (VSGs) operate in parallel, severe power oscillation may be suffered. To deal with this issue, this article offers an adaptive virtual impedance method applied to a multi-VSG grid. The core idea is to change the output active power by adaptive virtual impedance. When the angular frequency of the local controller is greater than the angular frequency of the neighbors’ controllers, the output active power of local VSG falls, and thus dωi/dt rises. Then, as the angular frequency is lower than neighbors’, the output active power rises, and dωi/dt falls. As a result of this, the method facilitates the consistency of response curves of all angular frequencies. Besides, the stability of the offered algorithm is demonstrated. A final proof of the efficacy of the proposed control method is shown by simulation and hardware-in-loop results. [ABSTRACT FROM AUTHOR]