Dual Active Bridge DC-DC Converter Research Articles

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.

Discrete Extended-Phase-Shift Control for Dual-Active-Bridge DC–DC Converter With Fast Dynamic Response

In this paper, a discrete extended-phase-shift (DEPS) control scheme is proposed to improve dynamic response of dual-active-bridge (DAB) dc-dc converter. The proposed DEPS control adjusts the transmission power of the DAB dc-dc converter by generating high and low power control pulses, which are preset to have discrete phase-shift ratios, rather than employing PWM control. Thus, it is simple and easy to implement in digital-signal processor or field-programmable gate array. Moreover, without error amplifier and corresponding compensation circuit, its dynamic response is fast and robust. Parameter design method considering the effect of equivalent resistance of the DAB dc-dc converter and dc-bias current elimination is also presented. Theoretical analyses, energy-balance-based iteration modeling and control performance of DEPS controlled DAB dc-dc converter are given, and they are verified by experiments on a 96V-48V, 50kHz (100kHz), 288 W DAB dc-dc converter.

High Efficiency Isolated 5-Level Dual Active DC–DC Converter Using Wide Band Gap Devices

In this paper a bidirectional isolated dc-dc converter is proposed for application in shipboard power systems. In this topology, an active 5-level T-type converter is used on the primary and secondary sides of a high-frequency transformer. The operation of the proposed converter is optimized based on minimizing power losses. For the optimization, the transformer core loss, reactive power, and rms current are considered. Wide band gap devices are used for minimization of semiconductor switching losses. A control method based on the Fourier series and decomposition theorem is proposed. The proposed converter features higher efficiency, fault tolerant capability and smaller filter size compared to the common dual active bridge dc-dc converters. To reduce voltage overshoot, a laminated dc-link is designed and a two-level turn-off method is used for operating frequencies around 75 kHz. Finally, the step-up and step-down operations of the proposed structure are verified through experiments.

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.

Experimental analysis of phase shift modulation methods effects on EMI in dual active bridge DC-DC converter

Dual active bridge DC-DC converters (DAB) are one of the bidirectional converters and mainly used in electric vehicles and micro grids. With the increasing number of electric vehicles in use, and the increasing amount of batteries in these vehicles and rapidly spanning micro grids, the importance of DAB converters has increased and they are expected to be smaller in size and operate at higher power levels. The reduction in size has increased the importance of power density and efficiency, which are two significant parameters of DAB circuits. One of the methods to increase efficiency and power density is to increase the switching frequency. However, with the increase at the switching frequency, electromagnetic interference (EMI) in the DAB circuit also increases.In this manuscript, the change in the EMI values emitted by conduction, according to the phase shift modulation methods at DAB converters are evaluated. Also the effect of type of MOSFETs on conducted EMI is examined. Prototypes of the DAB converters by using Si and SiC MOSFETs with power rating of 1 kW are designed and developed. Switching frequency of converter is 25 kHz and leakage inductance is determined 81uH and 75uH. Si based circuit is operated with %88.5 efficiency. SiC based circuit is also operated with %88 efficiency. The designed circuits are operated using the phase shift modulations SPS and DPS. Conducted emission noise emitted by these circuits are analyzed by dividing them into common mode and difference mode noises. It has been observed that the EMI value when using SPS method is 15–20 dBµV lower than the EMI when using DPS method. The relationship between the measured noises and the efficiency of the circuits was observed.

Fault-Tolerant Dual Active Isolated DC-DC Converter

In this paper a fault-tolerant isolated dc-dc converter is proposed for shipboard power applications. In this topology, an active 5-level T-type converter is used on the primary and secondary sides of a high-frequency transformer. The operation of the proposed converter is optimized based on minimizing the losses. A fault-tolerant analysis is carried out for this converter and post-fault switching methods are proposed for each faulty condition. The proposed converter features better fault tolerance options and higher efficiency compared to the common dual active bridge dc-dc converters. Finally, the operation of the proposed structure in the normal and faulty conditions are verified through experiments.

Design and Control of Two-Stage DC-AC Solid-State Transformer for Remote Area and Microgrid Applications

The critical challenges with integrating renewable energy into the grid are smooth power flow control, isolation between the high-voltage and low-voltage networks, voltage regulation, harmonic isolation, and power quality regulation. This paper considers the design and construction of a two-stage DC-AC solid-state transformer based on wide bandgap (WBG) semiconductor technologies, an optimized medium-frequency transformer, and PI and dq controllers for supplying urban area electric drive systems and microgrid applications. The designed SST consists of a dual active bridge (DAB) DC-DC converter followed by a DC-AC three-phase inverter. Each stage of the SST was simulated with independent controllers. The proposed system was initially developed in MATLAB/Simulink and a laboratory prototype was constructed to verify the results experimentally. Resistive and inductive load were used to test the load disturbance to evaluate the voltage regulation performance. This work has comprehensively provided the performance of a double stage (DC-DC and DC-AC converter) by taking into consideration input voltage, load disturbance, and voltage tracking both in simulation and experiment. The dual active bridge with its controller is able to maintain the desired output reference voltage with minimal voltage ripples under input voltage fluctuations and load variations. Similarly, the three-phase DC-AC converter’s controller exhibits better performance in tracking the desired reference voltage and producing well-regulated AC voltage with low harmonic distortion.

Dual-Terminal Voltage Feedforward Based Direct Power Control Scheme and Stability Analysis of Dual Active Bridge Converter in DC Microgrid Systems

The dual active bridge (DAB) dc-dc converter plays an important role in energy exchange between DC microgrids integrated with energy storage systems. To directly control the power flow between the adjacent DC microgrids rapidly and accurately, a dual-terminal voltage feedforward based direct power control scheme (DVF-DPC) with single-phase-shift control is proposed for the DAB dc-dc converter. The strategy makes the converter realize rapid and precise output power regulation under the following conditions, including the start-up process, load step-change, the desired output power step-change, and voltage fluctuations. An accurate discrete-time model is applied to analyze the system's dynamic characteristics, and a discrete-time small-signal model of the system is established to design the controller's parameters. In addition, a comprehensive and systematic analysis of all the possible unstable phenomena for adjacent DC microgrids is conducted based on the discrete-time model. Accordingly, the underlying mechanisms are revealed by analyzing the relationships among the state variables, the Floquet multipliers, and system parameters. Hence, the stability-oriented parameter design method is given which can provide guidance in practice. The theoretical analysis is verified in both the time domain and frequency domain. Finally, by comparing the DVF-DPC method with the traditional PI feedback control, the superiority of the proposed strategy is verified through theoretical analysis and experimental results, which demonstrates its application prospect in the field of electric energy dispatch control of the DC power supply network.

Performance Characterization of T-Type Multilevel Dual Active Bridge DC-DC Converter

Conventionally, single phase shift control technique is used for controlling dual active bridge (DAB) performance, which works efficiently at unity voltage conversion ratio and full load. However, when there is mismatch between primary voltage and reflected secondary voltage on primary side at light load, its efficiency reduces because of increased current stress and reactive power. Moreover, due to single control variable, its power flow controllability is confined. In this paper, analysis, implementation and performance characterization of isolated bi-directional T-type multilevel dual active bridge DC-DC converter topology is presented. It has five level voltages on both the primary and secondary side of high frequency transformer, which reduces the current stress and reactive power over wide operating range. It also has five control variables which gives extra edge for enhancing power flow controllability. Comparative analysis reveals that the proposed converter has high efficiency over wide operating range, due to reduced reactive power and current stress. Performance of the proposed T- type multilevel dual active bridge DC-DC converter topology has been verified via simulation and experimental prototype developed in the laboratory.

A Load Adaptive Hybrid DPS Control for DAB to Secure Minimum Current Stress and Full ZVS Operation Over Wide Load and Voltage Conversion Ratio

Wide variations in voltage conversion ratio and loading are the most important parameters to consider when designing off-board EV chargers to achieve high power density and efficiency. Dual phase shift (DPS) modulation provides a better way for dual active bridge (DAB) DC-DC converter operation when load side parameter variation is utmost important. To accomplish this, conventional DPS control is modified to ensure zero voltage switching (ZVS) across the entire load range despite wide variations in voltage conversion ratio. The designed control provides ZVS of all FETs as compared to the conventional DPS control over full loading range. For this, magnetizing inductance of HF isolation transformer is utilized and designed to shape the secondary side current for getting ZVS for both active legs. The light loading performance of the converter is improved with the bidirectional conduction angle control. The hybrid utilization of DPS control is incorporated with minimum peak current stress considerations. A Karush-Kuhn-Tucker (KKT) method based on Lagrange's multipliers is used for mathematical derivation of optimized solution of both control parameters. Performance of designed control is verified using experimental results for wide variation in battery terminal voltage. For validation, a 1250 W laboratory prototype is developed. A comparison of ZVS regions among the conventional and designed modulation technique, shows the effectiveness under wide voltage and loading scenarios.

Comparison and Validation of Five Modulation Strategies for a Dual Active Bridge Converter

This paper addresses the comparison and validation of different modulations for an isolated dc-dc dual active bridge converter (DAB), namely, Duty-Cycle Modulation, Single Phase Shift (SPS), Dual Phase Shift (DPS), Extended Phase Shift (EPS) and Triple Phase Shift (TPS). Given the DAB’s applicability in a wide variety of power electronics branches, several control strategies are being studied to improve its efficiency, by mitigating circulating currents and reactive power. Regardless of the chosen architecture, appropriate modulations must be adopted, assessing which one presents the better cost-benefit ratio. This simulation-based analysis aims to investigate the DAB performance when controlled by the above-mentioned modulations and operating with a nominal power of 3.6 kW. Thus, simulation results show that only SPS, DPS, and TPS are considered suitable, while Duty-Cycle Modulation has time limitations during power transfer and EPS is more appropriate for dynamic power applications.

A Virtual Direct Current Control Method of LCL-DAB DC-DC Converters for Fast Transient Response and No Backflow Power

The LCL-type dual active bridge (LCL-DAB) DC-DC converter is a promising part for DC micro-grids due to its high voltage gain and low bridge current, but the issues of backflow power elimination and transient response optimization deserve attention in its operation. In this article, a virtual direct current control (VDCC) method of the LCL-DAB converter for fast transient response and no backflow power is proposed, which can eliminate the backflow power and improve the transient response against the input voltage and load disturbances. With dual-phase-shift (DPS) modulation scheme, the voltage-current characteristics are first analyzed using the phasor method. The small-signal mathematic model of the LCL-DAB converter is then established. The power characteristic is derived so the design regions of no backflow power can be graphed. On this basis, an appropriate outer phase shift ratio can be estimated to ensure a wide range of no backflow power operation. Moreover, a virtual voltage is generated to compensate in the control loop, thus the transient response against disturbances of the LCL-DAB converter can be improved under no backflow power. Simulation and prototype experimental results are presented to verify the feasibility of the proposed VDCC method.

Research on optimum extended phase-shift control with minimum peak-to-peak current of DAB converter applied to small DC power grid

The Dual Active Bridge (DAB) DC-DC converter has the ability of bidirectional power transmission and the modulation scheme that is easy to implement, which can ensure the efficient transmission of energy in the system. Therefore, it is often used in various scenarios of small DC grid, such as energy storage, photovoltaic system, electric vehicle charging and so on. The main methods to improve the efficiency of dual active bridge include reducing the effective value of current and widening the soft switching area. Based on the above idea, an optimized extended phase-shift (EPS) modulation strategy is proposed in this paper. The modulation strategy achieves the goal of reducing the effective value of the current through the constraint optimization of the corresponding variables, and then improves the efficiency of the converter. In this paper, the working principles of several typical modulation strategies are introduced in detail, and then the power characteristics and soft-switching characteristics of the new method and other commonly used modulation schemes are analyzed and compared. Finally, the effectiveness of the optimization method for extended phase-shift modulation strategy is verified by the dual active bridge experimental prototype.

Comparative Study of Control Methods for Bidirectional Isolated Dual Active Bridge DC-DC Converter

Comparative Study of Control Methods for Bidirectional Isolated Dual Active Bridge DC-DC Converter

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.

Model predictive current control for dual-active-bridge dc-dc converter with single-phase shift modulation

This paper proposes a model predictive current control for the dual-active bridge (DAB) dc-dc converter with single-phase shift modulation. The DAB dc-dc converter model is established using the averaging method. To eliminate the steady-state error caused by model uncertainties, the integral of feedback error is combined with the state error to form the augmented system for the control design. Moreover, the controller gain can be systematically tuned by only one tuning scalar variable, making the proposed controller easy to implement. Furthermore, an offline optimization problem is used for computing the controller gain, so real-time computation burden is significantly reduced, enabling the use of low-cost DSP controller. Overshoot-free and fast convergence performance of output current can be achieved using the proposed method in simulations and Typhoon HIL emulator.

A New Fault-Tolerant Scheme for Switch Failures in Dual Active Bridge DC-DC Converter

The dual active bridge (DAB) dc-dc converter is widely investigated for applications such as solid-state transformers (SSTs), battery energy storage systems, and electric vehicle (EV) chargers. Failures in active devices of the DAB can cause reduced terminal voltages or uncontrollable currents eventually leading to converter disconnection. The above-mentioned consequences cannot be corrected by disabling the complementary switches of the faulty leg or reconfiguring the full-bridge (FB) DAB to a half-bridge (HB) DAB topology. In this article, a new fault-tolerant (FT) approach is proposed that works for both short-circuit (SC) or open-circuit (OC) failures in the active devices of the DAB dc-dc converter. Parallel combination of a fault-tolerant capacitor and a fast acting fuse, known as fault-tolerant unit, is connected in series with the primary as well as secondary of the transformer. Once the fault is detected, the output voltage is boosted to its pre-fault value through the incorporation of fault-tolerant capacitors along with variation in control parameters, ensuring the continuity of operation. The proposed post-fault reconfiguration scheme is validated experimentally using a 1 kW, 250 V DAB prototype.

Generalized Average Modeling of a Dual Active Bridge DC-DC Converter with Triple-Phase-Shift Modulation

This paper shows an elaboration of an equivalent electrical circuit of a Dual Active Bridge (DAB) and its application as a versatile tool for steady-states analysis in wide range of operating conditions. This work analyses the converter which is controlled with a coherently defined Triple Phase-Shift (TPS) modulation which allows appropriate switching functions to be written, thus enabling the circuit’s state-space equations to be derived. Due to this approach, a Fourier series expansion may be easily applied to utilize Generalized Averaged Modeling (GAM)—a convenient method for modeling resonant and quasi-resonant power converters. Moreover, this paper shows the utilization of the GAM model higher harmonics’ complex magnitudes to calculate the steady-state power characteristics for bidirectional operation; additionally, a method for a particular state variable waveform signal reconstruction is presented. All the discussed model properites are validated with a 1.5 kW 100 kHz SiC-based DAB prototype.

Three Winding Coupled Inductor-Based Dual Active Bridge DC-DC Converter With Full Load Range ZVS Under Wide Voltage Range

In this article, a three winding coupled inductor-based dual active bridge (TWCI DAB) dc-dc converter is proposed. Similar to the current-fed DAB converter, the proposed TWCI DAB has small input current ripple and wide input voltage range. In addition, the zero-voltage switching (ZVS) of all switches in the full load range under wide input voltage variation can be realized. With the magnetic integration structure, the size of the total magnetics can be reduced, and the efficiency is also increased compared with the discrete magnetic case. To better analyze the working principle of the three winding coupled inductor, a general analysis method based on magnetic reluctance model is first introduced to obtain the expressions of high frequency current. Furthermore, ZVS analysis and inductor design to obtain low inductor root mean square (rms) current and full load range ZVS based on the ZVS conditions, maximum power transfer and rms current are presented. Finally, the validity of the proposed topology and design are verified by experimental results from a 1-kW laboratory prototype.

Design and Development of Bidirectional DC-DC Dual Active Bridge Converter for Energy Storage Systems

The ever-increasing demand for renewable energy resources as compared to conventional means of energy generation has resulted in a growing demand for more efficient power storage systems and applications. However, this necessitates the use of different converters that must be employed to achieve efficient voltage conversions right from the generation stage to the point power is stored in the battery banks. To achieve efficient conversions of the voltage levels, Bidirectional DC-DC Dual-Active-Bridge (DAB) converters can be employed. Accordingly, this research work involves use of a closed-loop PI controller for controlling the outputs of a DC-DC converter and compensating for the load disturbances. The Simulink-derived results indicate the input & output characteristics of the converter to achieve the design of a controller that is capable of providing significant tracking reference command without undergoing steady-state error, thereby offering a fast transient response. Hence, by maximizing the performance of the converter, the controller resolves the issues identified in the output current. The system was also implemented on a 400W laboratory experimental model with a view to additionally validate its performance effectiveness. As a whole, a DAB system was successfully designed, simulated, implemented and analyzed for employing in various energy storage applications