Dual Active Bridge Topology Research Articles

Maximum-Power-Per-Ampere Variable Frequency Modulation for Dual Active Bridge Converters in Battery-Balancing Application

Varying the operating frequency helps dual-active bridge topologies increase the system efficiency since the soft-switching is regained at low-load condition. This article proposes a conduction-loss-based variable frequency modulation (VFM) that decouples the phase-shift from the frequency control that conventional VFM applies. The power losses for the shared-bus battery-balancing topology are elaborated as switching frequency varies. The results show that increasing the operating frequency within the reasonable boundaries can benefit not only the switching loss but also the conduction losses. The switching loss is nearly constant, whereas the conduction losses decrease significantly. A factor of output power and transformer current, namely power-per-ampere, is derived as a function of operating conditions and phase-shift independent of switching frequency. The operating setpoints are selected to minimize the factor using both online and offline optimizations. The proposed control strategy outperforms constant frequency modulation by up to 30% below 30% rated power. Furthermore, compared with conventional VFM, the proposed method improves the efficiency of the system under test by 1.5% below 50% normalized power, with significantly less computational resources needed.

Analytical Modeling and Control of Dual Active Bridge Converter Considering All Phase-Shifts

In the field of power electronics-based electrical power conversion, the Dual Active Bridge (DAB) topology has become very popular in recent years due to its characteristics (e.g., bidirectional operation and galvanic isolation), which are particularly suitable to applications such as interface to renewable energy sources, battery storage systems and in smart grids. Although this converter type has been extensively investigated, its analysis and control still pose many challenges, due to the multiple control variables that affect the complex behavior of the converter. This paper presents a theoretical model of the single-phase DAB converter. The proposed model is very general, i.e., it can consider any modulation technique and operating condition. In particular, the converter is seen as composed by four legs, each capable of generating voltage on the inductor, and by the two output legs, which can steer the resulting inductor current to the load. Three variables are considered as the control inputs, i.e., the phase-shifts with respect to one leg. This approach results in a very simple yet accurate closed-form algorithm for obtaining the inductor current waveform. Moreover, a novel analytical model is proposed for calculating the average output current, based on the phase-shift values, independently of the output voltage. It is also shown that average output current can be varied cycle-by-cycle, with no further dynamics. In fact, average output current is not affected by the initial value of inductor current or by DC offset (which may arise during transients). The proposed models can be exploited at several stages of development of a DAB: during the design stage, for fast iteration, when selecting its operating points and when designing the control. In fact, based on the analytical results, a novel control loop is proposed, which adopts a “fictitious” (i.e., open-loop) inner current regulation loop, which can be applied to any modulation scheme (e.g., Single Phase-Shift, Triple Phase-Shift, etc.). The main advantage of this control scheme is that the simple dynamics of the output voltage versus the average output current can be decoupled from the complicated relationship between the phase-shifts and the output current. Moreover, a Finite Control Set (FCS) method is proposed, which selects the optimal operating points for each operating condition and control request, ensuring full Zero-Voltage Switching (ZVS) in all cases. The analytical results obtained and control methods proposed are verified through simulations and extensive experimental tests.

Development of a Medium Voltage, High Power, High Frequency Four-Port Solid State Transformer

The power and voltage levels of renewable energy resources is growing with the evolution of the power electronics and switching module technologies. For that, the need for the development of a compact and highly efficient solid-state transformer is becoming a critical task in-order to integrate the current AC grid with the new renewable energy systems. The objective of this paper is to present the design, implementation, and testing of a compact multi-port solid-state transformer for microgrid integration applications. The proposed system has a four-port transformer and four converters connected to the ports. The transformer has four windings integrated on a single common core. Thus, it can integrate different renewable energy resources and energy storage systems. Each port has a rated power of 25kW, and the switching frequency is pushed to 50kHz. The ports are chosen to represent a realistic industrial microgrid model consisting of grid, energy storage system, photovoltaic system, and load. The grid port is designed to operate at 4.16kVAC corresponding to 7.2kV DC bus voltage, while the other three ports operate at 500VDC. Moreover, the grid, energy storage and photovoltaic ports are active ports with dual active bridge topologies, while the load port is a passive port with full bridge rectifier one. The proposed design is first validated with simulation results, and then the proposed transformer is implemented and tested. Experimental results show that the designed system is suitable for 4.16kVAC medium voltage grid integration.

Dual Active Bridge Based Reduced Stage Multiport DC/AC Converter for PV-Battery Systems

Standalone power systems are significant for electrifying the remote areas where extending the grid connectivity is not feasible, either economically or logistically. Solar Photovoltaic (PV) systems with battery backup are among the most popular candidates to serve as an energy source in standalone systems. This article presents a novel multiport converter (MPC) for PV-battery systems powering standalone loads. The proposed converter is a reduced stage power converter based on current fed dual active bridge (CF-DAB) topology. CF-DAB offers galvanic isolation and a high voltage ratio without sacrificing efficiency. Switching losses are further reduced by a modified modulation scheme that reduces the average switching frequency of some of the switches. The proposed converter performs the functions of tracking maximum power point of the solar panel and regulating the load voltage while using fewer power conversion stages. This is done by sharing components among the various stages performing maximum power point tracking, voltage boosting, and dc/ac conversion. A small-signal model of the proposed MPC required for its closed-loop control is also proposed, which can also be utilized for other CF-DAB-based converters. A lab prototype of the proposed MPC has been fabricated and its operation has been validated under various static and dynamic conditions.

DAB Converter With Q Capability for BESS/EV Applications to Allow V2H/V2G Services

This paper presents a dual active bridge (DAB) converter with reactive power control capability (Q-capability) for a battery energy storage system (BESS) or an electric vehicle (EV) to deliver vehicle-to-home (V2H) and vehicle-to-grid (V2G) services. The DAB topology is preferable for EV charging systems due to its galvanic isolation and bidirectional power flow capabilities. However, this topology increases reactive current peak and loses zero voltage switching (ZVS) operation at light loads if it is not controlled with improved modulation strategies and proper Q control. This paper proposes a mixed modulation method and a reactive power optimization (RPO) algorithm based on power system load flow concepts. Due to the complexities associated with the analytical solution using time domain analysis, this paper develops detailed universal expressions of a DAB converter using the harmonic analysis method. Analytical identification of ZVS boundaries and DSP implementation of the RPO algorithm become easier with these universal expressions. Multiple modes analysis for different operational states is no longer required. Simulation results have been shown for different modulation strategies of the DAB converters. The theoretical analysis of modulation strategies, RPO algorithm and ZVS operation are validated by experimental results on a DAB prototype. Results show that the proposed control strategy reduces the reactive power and provide ZVS operation over a wide ranges of voltages.

Predictive Control Applied to a Single-Stage, Single-Phase Bidirectional AC-DC Converter

This work aims to implement the control system of a single-phase, multi-port AC-DC converter with high-frequency isolation based on the dual active bridge (DAB) topology associated with the three-state switching cell (3SSC) applied to a distributed generation system. The converter has one ac port and two dc ports, this being a multi-input, multi-output (MIMO) system in which there is a coupling between the input and output variables. The generalized predictive control (GPC) is chosen to regulate the dc-link voltages. GPC is a well-consolidated approach in the literature, which can deal with MIMO coupled systems while presenting friendly-tuning rules. The current loop employs a traditional proportional plus resonant (P+R) controller because it has a single-input, single output (SISO) characteristic, as advanced controllers are unnecessary. Experiments are performed on a 1-kW prototype to validate the performance of the developed controller and show its advantages compared with traditional control strategies.

Cascaded Voltage and Current Control for a Dual Active Bridge Converter with Current Filters

The paper describes the cascaded voltage and current control for a bidirectional DC/DC converter in Dual Active Bridge (DAB) topology. The typical DAB converter circuit was extended by additional current filters, which allow it to operate in application fields with high requirements on current ripples. The core concept of the presented solution is usage of the modified Single Phase Shift (SPS) modulation, which allows to compensate for the DC-bias current occurring in dynamic states and provides a settling time of half switching cycle during transients. Its features were utilized to build a simplified dynamic model of the converter. The linear Proportional-Integral (PI) controllers are used in both voltage and current control loops. Based on the developed dynamic models, the tuning rules for both controllers were derived. In both cases, a number of the tuned parameters were reduced from two to one (which can present a great practical value for application engineers). The proposed solutions are validated based on a laboratory prototype. An important part of the experiments was devoted to non-linear effects occurring near the current limitation boundary of the system. The paper ends with a brief discussion regarding the future research directions.

Modeling and Analysis of DC Microgrids as Stochastic Hybrid Systems

This article proposes a method of predicting the influence of random load behavior on the dynamics of dc microgrids and distribution systems. This is accomplished by combining stochastic load models and deterministic microgrid models. Together, these elements constitute a stochastic hybrid system. The resulting model enables straightforward calculation of dynamic state moments, which are used to assess the probability of desirable operating conditions. Specific consideration is given to systems based on the dual active bridge (DAB) topology. Bounds are derived for the probability of zero voltage switching (ZVS) in DAB converters. A simple example is presented to demonstrate how these bounds may be used to improve ZVS performance as an optimization problem. Predictions of state moment dynamics and ZVS probability assessments are verified through comparisons to Monte Carlo simulations.

Comparison of DAB and LLC DC–DC Converters in High-Step-Down Fixed-Conversion-Ratio (DCX) Applications

This article compares the dual active bridge (DAB) and LLC converter topologies when utilized in a high-step-down fixed-conversion-ratio application, such as the dc-dc stage in laptop and LED TV adapters. Multiple candidate topologies for this application are compared, motivating the selection of the DAB and the LLC for further investigation. The two converters are first compared using first-order insights, and then using a detailed analytical design methodology focused on zero-voltage switching. Fundamental tradeoffs between conduction and switching losses are analyzed, predicting that the DAB converter should achieve higher efficiency at heavy loads due to lower conduction losses, while the LLC converter should achieve higher efficiency at lighter loads due to lower switching losses. To validate these predictions, design examples are developed for a 1-MHz 400-20 V 330-W application, and experimental prototypes for both converters are built based on these designs. Measured results match well with the predictions. The DAB prototype achieves a peak efficiency of 94.9% at full load, corresponding to a 27% reduction in losses compared to the LLC prototype.

Improved dynamic response strategy with dual phase‐shift control for dual‐active‐bridge DC–DC converter

In this study, an improved dynamic response strategy with dual phase-shift (IDR-DPS) for dual-active-bridge (DAB) DC–DC converter is proposed to improve system performance and eliminate DC bias caused by power mutation. Firstly, a unique combination of independent variables about inner and outer phase shift duty ratios is calculated at a given reference power through combining the minimum current stress calculation method with DPS control, which makes DAB run efficiently. On this basis, a DC bias elimination method is proposed to eliminate DC bias current in half a switching period through modifying inner duty ratios during transient process and drive DAB to reach new steady state quickly. Finally, a DAB topology platform is built to perform experiments of proposed IDR-DPS strategy and traditional direct control, the effectiveness of the proposed strategy is verified by comparative experiments.

An Interleaved Boost and Dual Active Bridge-Based Single-Stage Three-Port DC–DC–AC Converter With Sine PWM Modulation

In this article, a new three-port converter is proposed that interfaces two dc voltage sources of different magnitudes and an output ac port in a single stage. The proposed converter is primarily based on the dual active bridge topology where the secondary bridge is composed of four quadrant bidirectional switches, which allows it to be directly connected to an ac port. The primary bridge can also be used as an interleaved bidirectional boost converter by connecting two inductors across the transformer primary, which forms an additional input DC port. The power flow between the dc ports to the ac port is based on dual phase-shift modulation where a phase shift is introduced between the two legs of the primary bridge switches and another phase shift between the primary and secondary bridges. This enables the standard sine pulsewidth modulation to be used for synthesizing ac output. For the power flow mode between the two dc ports alone, a parallel boost modulation is proposed that improves the system efficiency by removing any circulating current introduced by traditional interleaving. The proposed converter achieves fully soft switched three-port power conversion with a reduced number of active devices compared to the existing topologies. The modulation scheme is also much simpler and requires no optimization or complex control. A PowerSim-based simulation program is used for validating the proposed converter. A 200-W prototype is built to experimentally verify the theoretical analysis of the proposed converter.

Non-inverting and Non-isolated Magnetically Coupled Buck–Boost Bidirectional DC–DC Converter

A new non-isolated dc–dc converter with non-inverting output and buck–boost operation, named magnetically coupled buck–boost bidirectional (MCB3) converter, is presented in this article. The MCB3 passive components arrangement connects the input and output ports getting an equivalent behavior to that of the dual active bridge (DAB) converter, but in a non-isolated topology. This equivalency allows applying Triple Phase Shift (TPS) modulation to MCB3. TPS is known to minimize conduction losses and to achieve soft switching at any load in the DAB converter. Throughout the article, the features of the DAB converter are used as a reference to show the main features of the proposed converter. Moreover, other modulation strategies based on TPS modulation are used in MCB3 to operate within the minimum losses path. The multiple operation modes found on the MCB3 under TPS modulation are identified, classified, and used to find the operating points that minimize the switching and conduction losses over the power range. The analysis is shown for the boost mode that is the worst case design. MCB3 and DAB topologies are designed and simulated for the same specification to validate the theoretical study. Finally, experimental measurements on 460-W prototypes for both topologies corroborate the equivalent operation and the main features of the MCB3.

Medium-frequency power transformer using GOES for a three-phase dual active bridge

Medium-frequency transformers are used in high power electronic dc/dc converters. In case of the three-phase dual active bridge topology (DAB3), a six-step voltage is applied to the transformer. In this study, a 200 kVA three phase power transformer prototype is using 0.18 mm thick high permeability Grain Oriented Electrical Steel (GOES) at B = 1.5 T and f = 1000 Hz. The prototype has been designed and built in link with a transformer manufacturer. In this paper, a complete test bench is set up to validate GOES as a suitable material for medium-frequency transformers. The efficiency of the components is evaluated at different operating points.

Active Rectification For the Optimal Command of Bidirectional Resonant Wireless Power Transfer Robust to Severe Circuit Parameters Deviations

In this article, a method resorting to active rectification for the optimal control of a bidirectional resonant wireless power transfer system is proposed. Benefiting from a dual active bridge topology and without requiring any additional dc-dc converter, the real and the imaginary parts of the equivalent load impedance are modulated simultaneously and independently, for achieving optimal operating conditions despite circuit parameters deviations. Based on a first harmonic analysis, the methodology and its beneficial impacts against variations in the windings mutual inductance or against mistuned resonant capacitor are presented and illustrated. By an argued discussion, the proposed method extent is enlarged to changes in any circuit parameters. Time-domain simulations of the converters topology and command demonstrates the method effectiveness by achieving the system maximum efficiency. Controllability restrictions preventing the compensation of the most severe parameters variations are highlighted. Associated with the limited voltage producible by conventional full-bridge converters, the latter restrictions are surmounted with success by considering Z-source topologies for the front-end and back-end converters.

Enhanced DAB for Efficiency Preservation Using Adjustable-Tap High-Frequency Transformer

Efficient dc-dc power-conversion with wide-span voltage-regulation is crucial to a sustainable and robust power electronics system. Dual-active-bridge (DAB) offers straight-forward regulation and its transformer enables voltage step-up/down required for many applications, such as battery chargers and bus converters for dc distribution systems. However, losing soft-switching at light loads or when operating at voltage gains far from the turns ratio severely degrades the efficiency of DAB, especially at high switching frequencies. In this article, we demonstrate an enhanced DAB (E-DAB) topology which employs an adjustable-tap transformer to extend the soft-switching over wider voltage gains and increase the power-transfer capability. By a proper tap adjustment and with single phase-shift modulation, the proposed gallium nitride (GaN)-based converter achieved a peak efficiency of 97.4% with an overall efficiency greater than a conventional DAB for voltage gains of up to 2.8 times higher. Employing a quasi-planar matrix transformer with integrated leakage inductance at 300 kHz allowed for an extremely high power density of 10 kW/l (7.5 kW/l with cooling). The tapped transformer did not incur extra losses to the topology. The gain versus power-transfer characteristic for soft-switching operation was derived for the E-DAB and its improvement in efficiency was experimentally verified over a wide power range.

Online PSO-tuned phase shift angle controller for dual active bridge DC–DC converter

The deep concern towards efficient and green energy has brought to the development of intermediate energy storage system. Electric vehicles (EVs), for example, is an application where the energy storage devices are vital. In EV, the bidirectional DC–DC converter is high in demand due to its nature EV of having two or more separate DC sources. A recent technology called the dual active bridge (DAB) converter has quickly become popular in DC–DC converter thanks to its inherent galvanic isolation via a high-frequency transformer. Furthermore, DAB topology allows for high-efficiency conversion and soft switching adaption. This paper presents the optimization of the phase shift angle controller of DAB using Particle Swarm Optimization (PSO). From the preliminary study, it was found out that the optimization performs well until there are abrupt changes in the system. The system is not able to respond to the reference voltage step change as the traditional one-time execution PSO have local optima entrapped in react to the changes. The paper proposes a reset function to allow PSO to identify that its current optimized value is not optimal anymore. This drives PSO to look for a new optimal value to improve DAB’s overall dynamic performance. Simulation of the modified PSO is done on a 200 kW DAB system with 20 kHz switching frequency is developed in MATLAB/Simulink environment. Simulation has been carried out with the objective to minimize the steady-state error as well as to improve the dynamic performance of the DAB. The DAB performance with the proposed solution is evaluated in terms of steady-state error and transient response by testing the system under various reference voltage and step-change input voltage. The self-excited re-exploration PSO also have been presented as to respond to the reference voltage step change as the basic PSO have local optima entrapped in react to the changes. In order to validate the simulation results, a hardware-in-the-loop (HIL) experimental circuit is built in Typhoon HIL-402 to verify the dynamic response and the steady state performance of the system.

An Overview and Comprehensive Comparative Evaluation of Current-Fed-Isolated-Bidirectional DC/DC Converter

Renewable energy generations have been attracting sustained attentions in academic and industry. Current-fed-isolated-bidirectional dc/dc converters (CF-IBDCs) are widely adopted in low-voltage high-current applications such as solar photovoltaic fuel cell with energy storage. This paper gives an overview and a comprehensive comparative evaluation of CF-IBDCs. The active clamped, dual half-bridge, L-L type dual active bridge, resonant-type, naturally clamped, and other type topologies of CF-IBDCs are investigated, analyzed, and compared regarding their circuit topological structures, operation characteristics, modulation methods, and soft-switching technologies. In addition, component cost models and loss models of converters are deduced and presented. On this basis, quantitative and comprehensive performance comparison of seven typical CF-IBDC topologies selected from each type is conducted in terms of costs, losses, weight, volume, and power density for the given system specifications and design constraints. Finally, the application range of different CF-IBDCs and future trend are presented to encourage further development.

Operation of Current-fed Dual Active Bridge DC-DC Converters for Microgrid

Dual Active Bridge (DAB) is an isolated bidirectional DC-DC converter, which comprises two full bridge converters linked through a high frequency transformer. It has low stresses and permits high frequency performance because of the soft-switching. All the switches in the converter achieves the turn ON & OFF during Zero Voltage Switching (ZVS) and Zero Current Switching (ZCS) to minimize switching loss. Generally, DAB is classified as two types, namely, voltage-fed and current-fed variants. At light load conditions, soft-switching is not realized in case of voltage-fed DAB topologies. The application of current-fed DAB converters is to reduce the losses at the time of switching under light load conditions and improves the efficiency. This paper describes the various topologies of voltage-fed and current-fed DAB used for different applications in microgrid and fuel cell energy generation system by using the simulation. The performance of voltage-fed and current-fed DAB with snubber-less converters are also demonstrated and their effectiveness are validated.

Frozen Leg Operation of a Three-Phase Dual Active Bridge Converter

Three-phase dual active bridge (DAB) topology is a potential alternative for high-power applications when a compact and efficient converter with a bidirectional power transfer capability is desired. In a constructed prototype, high-power SiC modules with dedicated drivers are utilized to achieve high-efficiency and compact size. Each module has two interconnected switches with anti-parallel diodes resembling a converter leg. It is observed that the driver halts the module operation as a result of protective actions such as overcurrent, gate undervoltage, or gate overvoltage. In this frozen leg mode, the module operates as a leg with two diodes until an external hardware signal resets the driver. The converter continues operation but with a reduced performance. Analysis, simulation, and verification of a three-phase DAB converter under a frozen leg operation are considered in this paper. The converter with a frozen leg has two different behaviors at light loads and heavy loads. Consequently, two different analysis methods are developed to solve converter operation in different load conditions. Results show that the power transfer capability is reduced, but this fault mode is nondestructive.

A Structurally Reconfigurable Resonant Dual-Active-Bridge Converter and Modulation Method to Achieve Full-Range Soft-Switching and Enhanced Light-Load Efficiency

This paper proposes a reconfigurable dual-active-bridge (DAB) converter that is capable of switching between two converter structures for enhancing its performances at different output power levels. For 50%–100% load, the converter operates in full-bridge mode and achieves soft-switching in all switches independently of the input-to-output voltage ratio. Below 50% load, the converter is reconfigured to operate in half-bridge mode for reduced circulating current and improved light-load efficiency while maintaining the desired soft-switching characteristic of full-bridge mode. The achievement of soft-switching is aided by the use of a tuned $LCL$ resonant tank, which enables an accurate prediction of the phases of tank currents with respect to tank voltages, and therefore simplifies the realization of soft-switching. The effects of dead time are discussed and expressions for guiding the selection of appropriate dead time for ensuring soft-switching in practical implementation are derived. The proposed converter and the modulation scheme are experimentally verified with a 1.6-kW converter prototype, which demonstrates their merits in comparison with a nonreconfigurable, full-bridge DAB topology and conventional modulation schemes.