Bidirectional Dual Active Bridge Research Articles

Natural Power Factor Correction and Soft Switching Design for a Single-Stage Bidirectional Dual Active Bridge AC–DC Converter

Natural Power Factor Correction and Soft Switching Design for a Single-Stage Bidirectional Dual Active Bridge AC–DC Converter

Improving the Efficiency of an Isolated Bidirectional Dual Active Bridge DC–DC Converter Using Variable Frequency

This article presents a control method for an isolated bidirectional dual active bridge DC–DC converter (IBDC) where single phase shift (SPS) and variable frequency (VF) modulations are combined simultaneously with the purpose of improving the efficiency of the converter applied to the bidirectional charging of electric vehicles batteries. A complete power characterization of the dual active bridge (DAB) converter is carried out. The combined control achieves lossless turn-on and turn-off on the primary bridge for a wide range of output powers. A comparative study of power losses between the traditional SPS control and the combined method proposed here was also carried out. A prototype with an output power of 10 kW was built based on Silicon Carbide (SiC) Metal Oxide Semiconductor Field-Effect Transistors (MOSFET), with which a peak efficiency close to 99% was obtained, thus verifying the viability of the method.

Linearized Minimum Current Stress Modulation Scheme of Single-Phase Bidirectional DAB AC–DC Converters

In this paper, the detailed steps for the derivation of linearized minimum current stress (LMCS) modulation scheme for single-phase bidirectional and isolated dual active bridge (DAB) ac-dc converters is presented. In order to reduce the current stress of the converter, a Lagrange multiplier method (LMM) scheme is designed to obtain the control coordinates constraint on the minimum value of the current stress. Compared with the conventional minimum current stress (MCS) control scheme, the proposed scheme realizes the linearization of power control, which significantly reduces the complexity of the controller algorithm. Moreover, the synchronous inverter control applied to the back-stage full-bridge is designed. Thus, the single stage power conversion is realized and the converter topology is electrolytic capacitorless, which promote the improvement of system reliability and power density. The impact of the ZVS scheme is analyzed in detail, and the adaptive-ZVS scheme for less system loss is selected. Finally, experimental results confirm the validity and feasibility of the proposed control scheme.

The Generalization of Bidirectional Dual Active Bridge DC/DC Converter Modulation Schemes: State-of-the-Art Analysis under Triple Phase Shift Control

The main objective of this paper is to provide a thorough analysis of currently used modulation control schemes for single-phase bidirectional dual active bridge DC/DC converters. In this article, it will be shown that single phase shift, extended phase shift and dual phase shift modulation schemes are special cases of the triple phase shift (TPS) modulation scheme. The article aims to highlight six TPS switching modes and their complements with operational constraints. Unlike previous studies that regarded TPS as a complex scheme, this paper simplifies the analysis of each mode and aims to standardize the understanding of TPS modulation for dual active bridge (DAB) converters. Power equations, range of power transferred and zero-voltage switching (ZVS) are derived for all the modes under TPS without assuming fundamental component analysis. Additionally, a generic optimization algorithm is developed to show the advantages of TPS modulation, and thus, the analysis in this paper offers a valuable insight for single-phase DAB converter designers in identifying a wide range of optimization algorithms to achieve higher efficiency under TPS modulation. This analysis contributes to the advancement of bidirectional DAB converter technology and facilitates its application in various power electronic systems.

Isolated Cascaded DAB DC-DC Converter to Boost Medium DC Voltage to HVDC

The offshore wind farms typically use ac system to collect power from each generator, with the voltage increased by means of high, heavy step-up transformers. DC collection grids have also recently been taken into consideration as solution to simplify and minimize the offshore windfarm platforms. DC collection grids offer an additional method to reduce complexity of offshore windfarms. However, to increase the DC voltage for HVDC transmission requires the development of high-power and high voltage converters, which presents a technical challenge. This research makes use of an isolated cascaded dual active bridge (DAB) DC-DC converter to boost medium DC voltage to HVDC. Isolated Cascaded DAB DC-DC Converters are connected in series on the output side and in parallel on the input side to obtain a high transformation ratio and high power. The bidirectional DAB DC-DC converters cab be designed with power densities in the variability of tens to hundreds of kilowatts, depending on the components used and the switching frequency at which the converters function most effectively. The input parallel output series (IPOS) topology, 225 kV HVDC can be generated from a 5 kV MVDC input by cascading DAB DC-DC up to 30 stages. This converter family is useful due to its scalability and flexibility, since the power and voltage ratings can be increased while still using the same cells. MATLAB Simulink simulations are performed and verified the elementary operating characteristics of the system.

High frequency isolated bidirectional dual active bridge DC-DC converters and its application to distributed energy systems: an overview

Among the DC-DC converters, an isolated bidirectional dual active bridge converter is a core circuit for high-frequency power converters in distributed energy system applications. These high-frequency power conversion systems attract academia and industry due to various advantages, such as high-power density, less weight, reduced noise, high efficiency, low cost and high reliability. First, the importance of power electronic converters in modern-day life is introduced. Second, a topological overview of voltage-fed and current-fed isolated bidirectional dual active bridge converters is presented with their importance in integrating hybrid power sources. Third, switching modes of isolated bidirectional DC-DC converters are also presented with a degree of freedom of control. Forth, performance evaluation of voltage-fed and current-fed isolated bidirectional converters has been presented with an example. Their suitability in integrating fuel cells and photovoltaics with energy storage systems in low to medium-power applications is presented.

Stability Analysis of Bidirectional Dual Active Bridge Converter With Input and Output LC Filters Applying Power-Feedback Control

This article analyzes the dynamic characteristics of a dual active bridge (DAB) converter with input/output LC filters connected and power-feedback control applied, and then discusses an impedance stability criterion about both side LC filters and the converter. Power control is suitable as a control method for grid-connected converters because of its affinity with the energy management system, which is being introduced as a new way to operate power systems in recent years. In order to provide stable power supply, it is necessary to ensure the stability of the converter, and information on dynamic characteristics is essential for the design and development of converters. Since there are no previous papers found yet where the impedance stability criterion is applied when LC filters are connected to both ends of a bidirectional DAB converter, this article discusses the procedures and key points to be considered to apply the criterion. Based on the analysis, the design guidelines of the system will be discussed.

Adaptive online auto-tuning using Particle Swarm optimized PI controller with time-variant approach for high accuracy and speed in Dual Active Bridge converter

<abstract> <p>Electric vehicles (EVs) are an emerging technology that contribute to reducing air pollution. This paper presents the development of a 200 kW DC charger for the vehicle-to-grid (V2G) application. The bidirectional dual active bridge (DAB) converter was the preferred fit for a high-power DC-DC conversion due its attractive features such as high power density and bidirectional power flow. A particle swarm optimization (PSO) algorithm was used to online auto-tune the optimal proportional gain (<italic>K<sub>P</sub></italic>) and integral gain (<italic>K<sub>I</sub></italic>) value with minimized error voltage. Then, knowing that the controller with fixed gains have limitation in its response during dynamic change, the PSO was improved to allow re-tuning and update the new <italic>K<sub>P</sub></italic> and <italic>K<sub>I</sub></italic> upon step changes or disturbances through a time-variant approach. The proposed controller, online auto-tuned PI using PSO with re-tuning (OPSO-PI-RT) and one-time (OPSO-PI-OT) execution were compared under desired output voltage step changes and load step changes in terms of steady-state error and dynamic performance. The OPSO-PI-RT method was a superior controller with 98.16% accuracy and faster controller with 85.28 s<sup>-1</sup> average speed compared to OPSO-PI-OT using controller hardware-in-the-loop (CHIL) approach.</p> </abstract>

A Robust Voltage Control of DAB Converter With Super-Twisting Sliding Mode Approach

This article presents a supertwisting sliding mode control (ST-SMC) for the isolated dc-dc bi-directional dual active bridge (DAB) power converter for enhanced output voltage regulation. The sliding mode control (SMC) is well-known for its robustness and improved dynamic performance for a nonlinear system. However, it includes the drawback of chattering and degradation of tracking performance. Here, the suggested ST-SMC scheme incorporates the advantages of a sliding mode controller and subsequently eliminates the problem of chattering. The average model of DAB under single phase-shift modulation is considered for controller design, which simplifies the design process. Thus, improved dc-link voltage stability and high robustness for accurate reference voltage tracking are obtained. Further, the proposed scheme provides a robust control for parameter uncertainties as well as the steady-state output voltage contains less ripple when compared to the classical SMC and proportional-integral controller. The experimental results for a 2 kW DAB converter are provided to validate the effectiveness and the robustness of the proposed strategy.

A Comprehensive loss analysis of SiC-based DAB DC-DC converter for electric vehicle application

This paper presents loss analysis of SiC MOSFET based bidirectional DAB (Dual Active Bridge) DC-DC converter for EV application. This converter benefits the efficiency of the EV vehicle by reducing power loss and voltage drop across the converter. The DAB uses WBG (Wide-Bandgap) semiconductor devices such as SiC MOSFET to optimize the efficiency and extend soft-switching over whole operating range. The SiC MOSFET switching devices rated at 1200 V with different drain- source on-state resistance Rds(on) of 21 mΩ/32 mΩ is considered. Therefore, a reliable converter rated at 10 kW which works under normal operating condition at high-switching frequency of 100 kHz. The switching and conduction losses are taken under two different junction temperature such as 25 °C and 100 °C with various operating load current between 10 A to 40 A. Based on an analysis of SiC MOSFET based DAB attains 98.8% efficiency. The simulation results are taken as voltage and current waveforms at various points of converter are reported. This SiC based DAB converter would be used in next generation of V2G (Vehicle-to-Grid) and G2V (Grid-to-Vehicle) technology.

High Efficiency Bidirectional Dual Active Bridge (DAB) Converter Adopting Boost-Up Function for Increasing Output Power

In this article, we proposed a bidirectional dual active bridge (DAB) converter adopting a boost-up function. The proposed converter can be implemented by adding only one capacitor to the high voltage side without additional active components. By utilizing the boost-up function, the proposed converter can achieve higher output power than the conventional DAB converter under the same leakage inductance condition. In comparison with the resonant converter in addressing the output power limitation, the proposed converter can reduce the switching and conduction losses due to the low turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> and circulating currents, and complex control is not required to drive the synchronous rectifier. Furthermore, the direction of the output power can be easily changed with a simple control circuit. Experimental results from the proposed converter with a 3 kW rated power, 28-V low-side voltage, and 600-V high-side voltage are demonstrated to verify the proposed works.

Power Electronics Converters for the Internet of Energy: A Review

This paper presents a comprehensive review of multi-port power electronics converters used for application in AC, DC, or hybrid distribution systems in an Internet of Energy scenario. In particular, multi-port solid-state transformer (SST) topologies have been addressed and classified according to their isolation capabilities and their conversion stages configurations. Non-conventional configurations have been considered. A comparison of the most relevant features and design specifications between popular topologies has been provided through a comprehensive and effective table. Potential benefits of SSTs in distribution applications have been highlighted even with reference to a network active nodes usage. This review also highlights standards and technical regulations in force for connecting SSTs to the electrical distribution system. Finally, two case studies of multi-port topologies have been presented and discussed. The first one is an isolated multi-port bidirectional dual active bridge DC-DC converter useful in fast-charging applications. The second case of study deals with a three-port AC-AC multi-level power converter in H-Bridge configuration able to replicate a network active node and capable of routing and controlling energy under different operating conditions.

A Detailed Full-Order Discrete-Time Modeling and Stability Prediction of the Single-Phase Dual Active Bridge DC-DC Converter

The standard methodology to obtain the model of a power electronic converter is achieved by averaging the state-space dynamics of the converter’s state variables. But the average of the transformer current is null over a switching cycle in the resonant dc-dc converter. Therefore, the conventional method is not suitable for resonant converters, including the phase-shifted bidirectional dual active bridge (PSBDAB) converter. The two-time scale discrete-type models can resolve the problem associated with the standard state-space averaging methodology. The time-scale segregates the dynamics of the PSBDAB converter into fast and slow state variables, which can be modeled separately and eases the analysis of the PSBDAB converter. The effect of the core-loss of the inductor, dead-time of the semiconductor devices, output filter capacitor’s equivalent series resistance, semiconductor on-resistance, and the transformer copper loss components are included in the model to improve its steady-state and dynamics characteristics. Moreover, the stability analysis using a bifurcation diagram is carried out for the digitally controlled closed-loop of the system. Furthermore, the critical gain for the stable region with variations in the circuit parameters like load resistance, circuit equivalent inductance, and voltage demand is extensively studied. The modeling and stability analysis is validated in the simulation and experimental setup. The results verify that the proposed method accurately predicts the stable region with variations in the system circuit parameters. Thus this study provides a guide to select and tune the controller parameter to ensure the converter operates within the boundaries of the stable region.

Distributed generation in low-voltage DC systems by wind energy in the Baja California Peninsula, Mexico

Mexico's national electric grid comprises ten regional systems, with one isolated in the south of the Baja California Peninsula. In addition, providing electricity access remains a challenge in the country. Therefore, distributed renewable energy solutions are relevant to satisfy the electricity demand and promote grid development. Distributed renewable energy access (DREA) based on a wind energy conversion system integrated into low-voltage direct current (LVDC) networks is presented. The DREA is analysed and simulated under wind speed conditions measured and recorded for one year at Baja California Sur. A representative variability is applied to five type-4 wind turbines based on wind speed turbulence intensity analysis. The generated power is transferred through a bidirectional dual active bridge converter, controlled by a novel small-signal model using a single closed-loop proportional-integral control, owing to its modularity, power density, and ability to transfer power from LVDC to high-voltage direct current. The effectiveness and robustness of the proposed DREA are assessed via a complete mathematical model, corroborated by the simulation results in MATLAB-Simulink®, and validated by experimental results using the real-time simulator Opal-RT Technologies® and laboratory prototyping. The results indicate a DC-link voltage compensation and integration of a power capacity of 150 kW in the LVDC networks with an efficiency of 94%.

A Dual Active Bridge Converter With Multiphase Boost Interfaces for Single-Stage Bidirectional DC–AC Conversion

A novel bidirectional dual active bridge based dc-ac converter is proposed in this article. The converter has multiphase boost interfaces at both the dc and ac ports. The interleaved operation of the multiphase units cancels the ripple currents and eliminates the input filter requirement. The dc to ac conversion is carried out in a single stage using only eight switches. The converter utilizes the low-frequency and high-frequency components in the inverter output to achieve both power conversion and power transfer across the high-frequency transformer simultaneously. A thorough analysis of the converter is carried out for the proper design of the components. Based on the results, a detailed design method is discussed. A multiresonant controller based phase-shift control is suggested to eliminate the low-frequency ripple in the input dc current. Finally, the effectiveness of the proposed converter is validated using results obtained from a 3-kW hardware prototype.

Modular electric vehicle battery charger with bidirectional power flow

Prospects for the use of rechargeable battery electric vehicles as regulators of the network or backup power supplies in accordance with the concepts of V2G (Vehicle to Grid) and G2V (Grid to Vehicle) are described. The requirements for bidirectional power converters are defined: a wide range of input voltage parameters, correction of the input current power factor, maximum power take-off from renewable energy sources, high energy efficiency. The chosen topology of the bidirectional dual active bridge converter, which supports soft switching of transistors at zero voltage and the proposed modular approach to the construction of converters, has a number of advantages: provide any voltage or current, reduce ripple, high efficiency, high reliability, due to the ability to include backup modules that can be replaced by the main in case of failure, reduction of the size of reactive elements and the ability to operate each cell on other frequencies. The most effective type of cell combination for the main task is developed - input parallel and output parallel connection are allows sharing input and output current between the modules. The dependence of the ripple coefficient on each cell is defined. The calculation of one cell of converters, namely the calculation of high-frequency transformer, transistors, and smoothing LC-filter is presented and the comparative analysis of technical indicators in one-cell and multi-cell converters is carried out. Modeling in Matlab Simulink software environment, evaluation of the effect of using a modular converter when working with DC and AC sources, comparison of ripple coefficients in converters with a different number of a cell at a constant value of the parameters of the LC-filter, and selected filter parameters at which one coefficient of pulsations is applied. The simulation results showed that the coefficients of the ripple are decreasing depending on the number of cells of the transducer in accordance with the dependence obtained by analytical calculations. Thus, the results are confirming the correctness of the calculations and prove the efficiency of the use of modular transformation topology.

Explicit discrete modelling of bidirectional dual active bridge dc–dc converter using multi‐time scale mixed system model

Dual active bridge (DAB) is one of the most popular high power isolated bidirectional dc–dc converter. It offers high power density, a low number of passive components, high efficiency. It is essential to model the converter so that it can be used in applications such as solid-state transformer, micro-grids, and dc distribution systems. Moreover, modelling a system is used to design inductor, select the switches, and controller design. The advantage of the discrete-time models is that they explicitly describe state trajectories in all sub-intervals of converter operation, meaning they are capable of providing exact solutions for ac state variables. This study proposes time scaling mixed system model of the DAB. The proposed method provides explicit solutions of the large and small signal, which can be used to study the steady-state and transient nature of the converter. The experimental results validate the proposed model with high accuracy in the open and closed-loop operation.

A Novel Interleaved Parallel Bidirectional Dual-Active-Bridge DC–DC Converter With Coupled Inductor for More-Electric Aircraft

Although conventional dual-active-bridge (DAB) dc–dc converters have been applied in more-electric aircraft, the maximum transmission power of conventional DAB converters is still limited by its structure. In order to increase the maximum transmission power, this article proposes a novel interleaved parallel bidirectional DAB converter. Two bidirectional buck/boost converters are applied in low-voltage side of the proposed converter. So the voltage of transformer primary side would not be limited by the voltage of low-voltage bus and can be controlled by the duty cycle according to the modulation strategies. In this article, three phase-shift control methods are used for the proposed topology. From the analysis of operation modes and power characteristics of the proposed topology, compared with the single phase-shift (SPS), the extended phase shift can reduce the reactive power and current stress. The pulsewidth modulation (PWM) plus single phase-shift (PWMSPS) can achieve more than twice of the maximum transmission power of conventional DAB converter. Finally, test results verify the theoretical analysis and the validity of the proposed converter.

Novel Phase-Shift Method for Fast Power Reversal With Transient Zero Voltage Switching in a Bidirectional Dual Active Bridge DC–DC Converter

The transient performance during power reversal in a bidirectional dual active bridge (DAB) dc-dc converter usually suffers from the issues of current deviation, hard switching, and other induced problems. In this article, a novel phase-shift method for fast power reversal in a DAB converter is proposed, which can achieve transient zero voltage switching (ZVS) without dc current bias, and therefore, shows advanced transient performance. The detailed algorithms and the effective phase-shift ranges based on different voltage conversion ratios are elaborated. An error analysis of the performance of dc bias elimination is provided to evaluate probable errors within allowed tolerances. Extensive and comparative experimental results are provided to support the validity of the proposed phase-shift method. It is shown that smooth, fast, and reliable power reversal can be effectively achieved with the novel method, and there is no need to add snubbers into the circuit by virtue of transient ZVS.

Soft Start-Up Control Strategy for Dual Active Bridge Converter with a Supercapacitor

Renewable energy needs are steadily on the rise. Bidirectional DC/DC converters are essential in charging and discharging various storage batteries, such as PV/ESS (photovoltaic/energy storage system). A dual active bridge (DAB) converter, in particular, transfers power in both directions by phase shift using a soiled state transformer (SST). To reduce switching inrush current in batteries under high voltages, a soft start-up is demonstrated during the initial switching operation. When a supercapacitor (SC) is used as a battery, the reverse power caused by the inrush current appears under high voltage at the DC-link side. This causes serious electrical damage to the PV/ESS’ boost converter and inverter. To suppress peak overshoot voltage and stabilize soft start-up transients, we propose a three-step soft start-up controller and algorithm for bidirectional DAB converter implementation at virtual ESS and UPS. The step-by-step control strategy by OLDC (open loop duty control), OLPSC (open loop phase shift control), and OLFC (open loop frequency control) provides a stable soft start-up operation. In the initial stage of the OLDC, the duty ratio is gradually increased by the PWM (Pulse width modulation) signal. In the middle stage, a phase difference is seen as per the voltage of the SC. The OLPSC is performed to reduce the phase difference. In the final stage, the OLFC is performed to smoothly control the small phase difference. The overshoot or inrush current is drastically suppressed toward the DC-link and SC module. Consequently, we demonstrate a proposed controller and algorithm with prototype 5 kW DAB converter.