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.

Overview of Dual-Active-Bridge Isolated Bidirectional DC–DC Converter for High-Frequency-Link Power-Conversion System

DC–DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc–dc converters, this paper aims to comprehensively review and classify various step-up dc–dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc–dc converters are presented and summarized with comparative study of different voltage-boosting techniques.

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Step-Up DC–DC Converters: A Comprehensive Review of Voltage-Boosting Techniques, Topologies, and Applications

Isolated dc–dc converters with galvanic isolation are commonly used in electric vehicle (EV) battery chargers. These converters interface between a dc voltage link, which is usually the output of a power factor correction stage, and an energy storage unit. CLLC and dual active bridge (DAB) dc–dc converters can achieve high power density, high-energy efficiency, wide gain range, galvanic isolation, and bidirectional power flow, and therefore, have potential applications as dc–dc converters for bidirectional EV charging systems. In this paper, full-bridge CLLC, half-bridge CLLC, full-bridge DAB, and half-bridge DAB dc–dc converters are evaluated and compared for their suitability for EV chargers. All the converters are designed with optimal soft-switching features. The operating principles, design methodologies, and design considerations are presented. Prototypes of the converters with power rating of 1 kW are designed and developed. The prototypes interface a 500 V dc link and a 200–420 V load, which is common for EV applications. The performances of the circuits are analyzed and a comprehensive comparison is conducted.

Comprehensive Analyses and Comparison of 1 kW Isolated DC–DC Converters for Bidirectional EV Charging Systems

This paper presents a comprehensive analysis of the current-stress optimization and soft-switching operation of the isolated bidirectional dual active bridge (DAB) dc–dc converter with the unified triple-phase-shift (UTPS) control. On this basis, the current-stress-optimized modulation scheme is proposed for DAB, which leads to the minimum current stress with the required transmission power and voltage conversion ratio in the whole load range. Moreover, the full soft-switching operation is achieved for the converter simultaneously. Distinct from the previous modulation schemes, the proposed optimized modulation scheme is deduced from a unified analysis of TPS where all effective switching modes are investigated. A novel algorithm based on the Karush–Kuhn–Tucker (KKT) conditions is originally proposed to derive closed-form solutions for the global optimal control parameters. This paper also presents a typical closed-loop control strategy for DAB with TPS control and detailed descriptions about the closed-loop operation. A laboratory prototype is applied, and the experimental results validate that the current-stress optimization and efficiency improvement are realized by applying the optimized modulation scheme. The experimental results also verify the effectiveness of the closed-loop control strategy for DAB with TPS control.

Unified Triple-Phase-Shift Control to Minimize Current Stress and Achieve Full Soft-Switching of Isolated Bidirectional DC–DC Converter

To reduce current stress and improve efficiency of dual active bridge (DAB) dc–dc converters, various control schemes have been proposed in recent decades. Most control schemes for directly minimizing power losses from power loss modeling analysis and optimization aspect of the adopted converter are too difficult and complicated to implement in real-time digital microcontrollers. Thus, this paper focuses on a simple solution to reduce current stress and improve the efficiency of the adopted DAB converter. However, traditional current-stress-optimized (CSO) schemes have some drawbacks, such as inductance dependency and an additional load-current sensor. In this paper, a simple CSO scheme with a unified phase-shift (UPS) control, which can be equivalent to the existing conventional phase-shift controls, is proposed for DAB dc–dc converters to realize current stress optimization. The simple CSO scheme can overcome those drawbacks of traditional CSO schemes, gain the minimum current stress, and improve efficiency. Then, a comparison of single-phase-shift (SPS) control, simple CSO scheme with dual-phase-shift (CSO-DPS) control, simple CSO scheme with extended-phase-shift (CSO-EPS) control, and simple CSO scheme with UPS (CSO-UPS) control is analyzed in detail. Finally, experimental results verify the excellent performance of the proposed CSO-UPS control scheme and the correctness of theoretical analysis.

Minimum-Current-Stress Scheme of Dual Active Bridge DC–DC Converter With Unified Phase-Shift Control

As the development of isolated bidirectional full-bridge dc-dc converter (IBDC), the dead-time effect has become an apparent issue. This paper presents a comprehensive theoretical analysis and experimental verification of dead-time effect in the IBDC. Besides the internal power transfer and phase drift phenomena mentioned in previous works, there are also many other novel phenomena caused by the dead time, such as voltage polarity reversal and voltage sag phenomena, etc. The paper gives a detailed switching characterization of the IBDC with dead-time effect in all operation states. On this basis, the transmission power characterization is analyzed comprehensively. Compared to the traditional theoretical model, the transmission power model with dead-time effect is not a strictly monotone increasing function, the relation curve is not symmetric around the median axis, and the zero point is not achieved at zero phase-shift ratio. In addition, in different operation states, the characterization is also different. Finally, experimental results verify the theoretical analysis.

Dead-Time Effect of the High-Frequency Isolated Bidirectional Full-Bridge DC–DC Converter: Comprehensive Theoretical Analysis and Experimental Verification

This paper reviews recent advances of key components in isolated bidirectional dc-dc converter (IBDC) and discusses potential of IBDC based on advanced components. The concept of safe operation area of IBDC is proposed and clearly defined, which is determined by the intersection of the effective operation areas of transmission power, current stress, and current root mean square. By analyzing efficiency and power density characteristic, this paper points out that the efficiency optimization of IBDC needs to give way to the power density optimization. On this basis, a novel synthetic discrete optimization design methodology of IBDC based on advanced components for battery energy storage system (BESS) is proposed. Finally, an experimental prototype is implemented, and some design suggestions for hardware optimization are provided. The experimental results verify the effectiveness of the designed BESS and show that the practical applications of next-generation high-frequency conversion system are expected with the appearance and application of advanced components.

A Synthetic Discrete Design Methodology of High-Frequency Isolated Bidirectional DC/DC Converter for Grid-Connected Battery Energy Storage System Using Advanced Components

In this paper, the application performance characteristics of high-frequency isolated bidirectional DC-DC converter (IBDC) based on SiC-DMOS and SiC-SBD samples provided by ROHM SEMICONDUCTOR Inc. are analyzed. The paper gave the basic design procedure of SiC-based converter, and established the mathematical model of power losses by analyzing the switching characteristic of the converter. On this basis, the power loss and efficiency characteristics of the SiC-based converter were analyzed and the related experimental results were presented. Theoretical analysis and experimental results show that the SiC-based converter has better performance than the Si-based converter; it will have a wide application prospect in the future smart electricity network.

Characterization and application of next-generation SiC power devices for high-frequency isolated bidirectional DC-DC converter

This article presents a new pole-changing (PC) doubly salient permanent magnet (DSPM) motor. According to the general air-gap field modulation theory (GAFMT), the permanent magnet excitation field can be modulated by the stator and rotor teeth to a series of harmonics with different pole-pair numbers and different slot pitch angles. Thus, when the armature winding is connected and reconnected according to the different excitation field harmonics, the PC operation can be realized to obtain a high torque density at the low-speed region and a widened speed regulation range with a simple motor structure. According to the GAFMT, the operating principle of the proposed motor is introduced, and the winding connection is discussed. Then, to verify the validity, the electromagnetic performance of the proposed motor is analyzed by the finite element analysis. Finally, a prototype is built and tested.

Yandong Sun

Papers

Overview of Dual-Active-Bridge Isolated Bidirectional DC–DC Converter for High-Frequency-Link Power-Conversion System

Dead-Time Effect of the High-Frequency Isolated Bidirectional Full-Bridge DC–DC Converter: Comprehensive Theoretical Analysis and Experimental Verification

A Synthetic Discrete Design Methodology of High-Frequency Isolated Bidirectional DC/DC Converter for Grid-Connected Battery Energy Storage System Using Advanced Components

Characterization and application of next-generation SiC power devices for high-frequency isolated bidirectional DC-DC converter

A Pole-Changing Doubly Salient Permanent Magnet Motor