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

With the number of electric vehicles (EVs) on the rise, there is a need for an adequate charging infrastructure to serve these vehicles. The emerging extreme fast-charging (XFC) technology has the potential to provide a refueling experience similar to that of gasoline vehicles. In this article, we review the state-of-the-art EV charging infrastructure and focus on the XFC technology, which will be necessary to support the current and future EV refueling needs. We present the design considerations of the XFC stations and review the typical power electronics converter topologies suitable to deliver XFC. We consider the benefits of using the solid-state transformers (SSTs) in the XFC stations to replace the conventional line-frequency transformers and further provide a comprehensive review of the medium-voltage SST designs for the XFC application.

Extreme Fast Charging of Electric Vehicles: A Technology Overview

Bidirectional DC-DC power converters are increasingly employed in diverse applications whereby power flow in both forward and reverse directions are required. These include but not limited to energy storage systems, uninterruptable power supplies, electric vehicles, and renewable energy systems, to name a few. This paper aims to review these converters from the point of view of topology as well as control schemes. From the point of view of topology, these converters are divided into two main categories, namely non-isolated and isolated configurations. Each category is divided into eight groups along with their respective schematics and a table of summary. Furthermore, the common control schemes and switching strategies for these converters are also reviewed. Some of the control schemes are typically applied to all DC-DC power converters such as PID, sliding mode, fuzzy, model predictive, digital control, etc. In this context, it should be noted that some switching strategies were designed specifically for isolated bidirectional DC-DC converters in order to improve their performance such as single phase shift, dual phase shift, triple phase shift, etc. The features of each topology and control scheme along with their typical applications are discussed, in order to provide a ground of comparison for realizing new configurations or finding the appropriate converter for the specific application.

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Topologies and Control Schemes of Bidirectional DC–DC Power Converters: An Overview

This paper proposes an analytical procedure for computation of all pairs of valid switching angles used in pattern generation in five-level H-bridge cascaded inverters. The proposed procedure eliminates harmonic components from inverter output voltage and, for each harmonic, returns the exact boundaries of all valid modulation index intervals. Due to its simple mathematical formulation, it can be easily implemented in real time using a digital signal processor or a field-programmable gate array. In this paper, after a detailed description of the method, simulation and experimental results demonstrate the high quality of achievable results.

Analytical Method for Pattern Generation in Five-Level Cascaded H-Bridge Inverter Using Selective Harmonic Elimination

With the rapid development of power electronics technology, microgrid (MG) concept has been widely accepted in the field of electrical engineering. Due to the advantages of direct current (DC) distribution systems such as reduced losses and easy integration with energy storage resources, DC MGs have drawn increasing attentions nowadays. With the increase of distributed generation, a DC MG consisting of multiple sources is a hot research topic. The challenge in such a multi-source DC MG is to provide voltage support and good power sharing performance. As the control strategy plays an important role in ensuring MG’s power quality and efficiency, a comprehensive review of the state-of-art control approaches in DC MGs is necessary. This paper provides an overview of the primary and secondary control methods under the hierarchical control architecture for DC MGs. Specifically, inner loop and droop control approaches in primary control are reviewed. Centralized, distributed, and decentralized approach based secondary control is discussed in details. Key findings and future trends are also presented at last.

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Primary and secondary control in DC microgrids: a review

Input-series-output-parallel dc–dc converters are suited for high-input voltage and low output voltage applications. This letter presents a decentralized inverse-droop control for this configuration. Each module is self-contained and no central controller is needed; thus, improving the system modularity, reliability, and flexibility. With the proposed inverse-droop control, the output voltage reference rises as the load becomes heavy. Even though the input voltages are not used in the inverse-droop loop, the power sharing including input voltage sharing and output current sharing can still be well achieved. Besides, the output voltage regulation characteristic is not affected by the variation of input voltage. The operation principle is introduced, and stability of the strategy is also revealed based on small signal modeling. Finally, the experiment is conducted to verify the effectiveness of the control strategy.

Decentralized Inverse-Droop Control for Input-Series–Output-Parallel DC–DC Converters

A bidirectional high-frequency isolated ac–dc converter for utility direct interfaced electric vehicle charger with vehicle-to-grid (V2G) capability is presented in this paper. This type of charger can achieve the direct utility interface with medium voltage input. It is composed of multilevel cascaded H-bridge ac–dc converter as the first stage and modular current-fed dual active bridge dc–dc converters as the second stage. For the cascaded H-bridge converter, a unified control to balance the cascaded H-bridge dc voltages is proposed for both charging and discharging modes. For the second dc–dc isolation stage, the current-fed dual active bridge converter is used in facing of the wide conversion gain in battery charging application and also to reduce the charging current ripple. Meanwhile, to improve the system flexibility and reliability, decentralized control is utilized for individual current-fed dual active bridge converters in view of the battery charging profile. The proposed method along with the presented topology can achieve voltage balance in spite of the power flow direction, simplification of the controller for the dc–dc modules and can also bear unbalanced power flow. The simulation and experimental results have been presented to show the effectiveness of the proposed control.

Utility Direct Interfaced Charger/Discharger Employing Unified Voltage Balance Control for Cascaded H-Bridge Units and Decentralized Control for CF-DAB Modules

This paper proposes a voltage match (VM) control for hybrid-bridge-based dual active bridge (DAB) converter in wide voltage conversion gain applications. With the addition of an auxiliary half-bridge circuit, the topology becomes an integration of a half-bridge and a full-bridge DAB converter. Unlike other pulse width modulation generation method for DAB converters, this converter utilizes four-level voltage at one port of the transformer to obtain matched voltage waveforms within the range of twice the minimum conversion gain. Wide conversion gain, decoupling of the two power control variables and wide zero-voltage switching (ZVS) ranges can be achieved with the proposed VM control. Full load ranges of ZVS for the six main power switches can be achieved and the two auxiliary switches can also operate in a wide ZVS range. In addition, the power control is done only using two control variables and its implementation is very simple, only needing a divider and a conventional voltage regulator. These characteristics and benefits of the proposed control are verified by experimental results from a 1-kw converter prototype.

Hybrid-Bridge-Based DAB Converter With Voltage Match Control for Wide Voltage Conversion Gain Application

The unified boundary trapezoidal modulation (TZM) control utilizing fixed duty cycle compensation and magnetizing current design for dual active bridge dc–dc converter is proposed in this paper. The fixed duty cycle compensation and magnetizing current design are first introduced to achieve the zero voltage switching (ZVS) of the power switches, which cannot be ensured with the conventional TZM control. As a result, all the power switches of dual active dc–dc converter can achieve ZVS and four switches can be turned off with very low current. Besides, based on the revealed power transfer characteristic, the power control variables including the duty cycles and phase-shift ratio can be unified without lookup tables or operation region division. With the proposed boundary TZM control, circulating current losses can be reduced and nonactive power is significantly suppressed according to the mathematic analysis, resulting in decrease of the conduction loss. A 1.6-kW laboratory prototype is built to verify the theoretical analysis and effectiveness of the proposed control.

Unified Boundary Trapezoidal Modulation Control Utilizing Fixed Duty Cycle Compensation and Magnetizing Current Design for Dual Active Bridge DC–DC Converter

A control strategy is proposed for the dual-transformer-based dual-active-bridge converter to achieve wide zero-voltage switching (ZVS) range for wide voltage conversion gain range application The phase-shift control is adopted for the dual-transformer-based converter with minimum power switches employing half bridge output, and a control law is proposed to achieve wide ZVS range and reduce the current-related loss With the proposed method, four switches of the converter can achieve full range of ZVS The other two switches can achieve full-range ZVS under positive power flow, while a slightly reduced ZVS region under reverse power flow Unlike the methods employing three control degrees of freedom, the proposed method only utilizes two decoupled control variables, making the controller easy to be implemented, more reliable, and independent of the converter parameters In addition, the design of turns ratios for the two transformers is also optimized based on the control law and loss analysis The effectiveness of the converter with the proposed control is verified by experimental results from a 1-kW prototype

Guo Xu

Papers

Decentralized Inverse-Droop Control for Input-Series–Output-Parallel DC–DC Converters

Utility Direct Interfaced Charger/Discharger Employing Unified Voltage Balance Control for Cascaded H-Bridge Units and Decentralized Control for CF-DAB Modules

Hybrid-Bridge-Based DAB Converter With Voltage Match Control for Wide Voltage Conversion Gain Application

Unified Boundary Trapezoidal Modulation Control Utilizing Fixed Duty Cycle Compensation and Magnetizing Current Design for Dual Active Bridge DC–DC Converter

Dual-Transformer-Based DAB Converter With Wide ZVS Range for Wide Voltage Conversion Gain Application