High-frequency-link (HFL) power conversion systems (PCSs) are attracting more and more attentions in academia and industry for high power density, reduced weight, and low noise without compromising ...efficiency, cost, and reliability. In HFL PCSs, dual-active-bridge (DAB) isolated bidirectional dc-dc converter (IBDC) serves as the core circuit. This paper gives an overview of DAB-IBDC for HFL PCSs. First, the research necessity and development history are introduced. Second, the research subjects about basic characterization, control strategy, soft-switching solution and variant, as well as hardware design and optimization are reviewed and analyzed. On this basis, several typical application schemes of DAB-IBDC for HPL PCSs are presented in a worldwide scope. Finally, design recommendations and future trends are presented. As the core circuit of HFL PCSs, DAB-IBDC has wide prospects. The large-scale practical application of DAB-IBDC for HFL PCSs is expected with the recent advances in solid-state semiconductors, magnetic and capacitive materials, and microelectronic technologies.
By establishing the mathematical model of the current stress of the isolated bidirectional dc-dc converter (IBDC), this paper comparatively analyzes the performances of IBDC under traditional ...single-phase-shift control and dual-phase-shift (DPS) control. On this basis, this paper proposes a current-stress-optimized switching strategy for IBDC with DPS control, and the corresponding control scheme is designed and implemented. The current-stress-optimized switching strategy can minimize the current stress, improve the system efficiency, and increase system power capability, and these performances are particularly effective for operation conditions with high voltage conversion ratio and light load. At last, experimental results verify the excellent performance of the current-stress-optimized switching strategy and correctness of the theoretical analysis.
This letter first develops a universal steady-state model to simply and accurately describe the analytical expressions for the high-frequency-link (HFL) electrical quantities of isolated ...dual-active-bridge (DAB) dc-dc converter under PWM plus phase-shift control. Second, a universal reactive power interaction among the HFL electrical quantities is present; using this interaction, the circulating current characteristic of DAB can be described accurately by HFL power factor. On this basis, a practical HFL fundamental-optimal strategy is proposed to decrease the circulating current and increase the efficiency. At last, experimental results verify the correctness of the universal model and the effectiveness of the fundamental-optimal strategy.
This paper proposes a modular multilevel dc-link dc solid-state transformer (MADCT) based on high-frequency dual active phase shift for HVDC grid integration. The proposed MADCT employs one arm of ...modular multilevel converter as HVDC active front-end interface and dual active bridge as high-frequency power transfer link, which brings many advantages and makes the operation of MADCT quiet different with traditional dc transformers. Compared with the traditional dc transformer schemes, the MADCT not only has good modularity and flexibility but also has good fault handling capacity. Especially, the performances of current stress, power transfer capacitor, and efficiency are improved. The topology, operation principle, voltage, current, power performances, and control and parameter design are presented and analyzed comprehensively in this paper. At last, a MADCT prototype is built and the experimental results verify the correctness and effectively of the proposed solution.
This paper proposes a practical solution of high-frequency-link (HFL) ac solid-state transformer (ACSST) based on advanced components in hybrid microgrid. In the proposed solution, all the power ...devices are SiC power devices produced commercially; all the HF magnetic components are made of iron-based nanocrystalline soft magnetic material; the high-voltage grid interface adopts multilevel cascade structure; the isolated bidirectional dc/dc converter employs dual-phase-shift control to decrease circulating current and increase efficiency; the HF isolated unit is responsible to control voltage and power balancing to avoid control coupling. The configuration, operation principle, intelligent control and management strategy, and hardware design and implement solution of the proposed HFL ACSST are analyzed. Finally, comprehensive experiments verify the validity and effectiveness of the proposed solution.
Compared to the traditional single-phase-shift control, dual-phase-shift (DPS) control can greatly improve the performance of the isolated bidirectional dual-active-bridge dc-dc converter (IBDC). ...This letter points out some wrong knowledge about transmission power of IBDC under DPS control in the earlier studies. On this basis, this letter gives the detailed theoretical and experimental analyses of the transmission power of IBDC under DPS control. And the experimental results showed agreement with theoretical analysis.
Compared to the traditional single-phase-shift control, dual-phase-shift (DPS) control can greatly improve the performance of the isolated bidirectional dc-dc converter (IBDC). This paper gives a ...detailed switching characteristic analysis of IBDC under DPS control, establishes a power loss model to predict the dissipated power for each power component, and analyzes the efficiency-optimized characteristic across the whole range. On this basis, an efficiency-optimized switching strategy is proposed and the corresponding control scheme is designed and implemented. At last, an experimental prototype was implemented to verify the feasibility of the proposed switching strategy and correctness of the theoretical analysis. The experimental results show that the proposed method can minimize the power loss and maximize the system efficiency, and these performances are particularly effective for operation conditions with high voltage conversion ratio.
This paper proposes a multilevel high-frequency-link dc transformer (MDCT) based on dual active phase-shift principle for medium-voltage dc (MVDC) power distribution application. The proposed MDCT ...employs multilevel and multiplex conversion principle, which brings many advantages and makes the operation of MDCT quite different with the traditional dc transformer (TDCT) and modular multilevel converter. Compared to the TDCT scheme, the proposed MDCT has smaller circulating current and higher power factor; it can operate as a dc breaker to cutoff the connection with the MVDC distribution grid absolutely when a short fault occurs in the distribution grid; the redundant design can be achieved when some submodules failure to improve the reliability. In the paper, the topology, operation principle, modulation method, switching characterization, voltage, and power characterization, and control strategy of MDCT are presented and analyzed comprehensively. At last, a MDCT prototype is built and the experimental results verify the correctness and effectively of the proposed solution.
Metal sulfides, such as MoS2, are widely investigated in lithium–sulfur (Li–S) batteries to suppress the shuttling of lithium polysulfides (LiPSs) due to their chemical adsorption ability and ...catalytic activity. However, their relatively low conductivity and activity limit the LiPS conversion kinetics. Herein, the Co-doped MoS2 is proposed to accelerate the catalytic conversion of LiPS as the Co doping can promote the transition from semiconducting 2H phase to metallic 1T phase and introduce the sulfur vacancies in MoS2. A one-step hydrothermal process is used to prepare such a Co-doped MoS2 with more 1T phase and rich sulfur vacancies, which enhances the electron transfer and catalytic activity, thus effectively improving the LiPS adsorption and conversion kinetics. The cathode using the three-dimensional graphene monolith loaded with Co-doped MoS2 catalyst as the sulfur host shows a high rate capability and long cycling stability. A high capacity of 941 mAh g–1 at 2 C and a low capacity fading of 0.029% per cycle at 1 C over 1000 cycles are achieved, suggesting the effectively suppressed LiPS shuttling and improved sulfur utilization. Good cyclic stability is also maintained under a high sulfur loading indicating the doping is an effective way to optimize the metal sulfide catalysts in Li–S batteries.
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