Three-phase Dual Active Bridge Research Articles

Iron Losses in a Medium-Frequency Transformer Operated in a High-Power DC–DC Converter

The three-phase dual-active bridge is a dc-dc converter, which is highly suitable for high-power applications. Among others, this is due to the medium-frequency transformer in the ac link, which provides galvanic isolation. The transformer is operated with a square-shaped voltage waveform. The flux density in the transformer core is piecewise linear. However, for the sake of simplicity, the magnetic flux is often assumed sinusoidal. Thereby, the actual iron losses generated in the core material are misinterpreted. This paper discusses the difference between the exact piecewise linear and the sinusoidal course in terms of iron losses. Silicon steel with a thickness of 0.18 mm is measured at a frequency of 1000 Hz, comparing the sinusoidal excitation with the actual one. The measurements are validated using the improved generalized Steinmetz equation. Finally, the transformer core losses are evaluated when the dc-dc converter is operated under load. The results are confirmed through measurement.

Enhanced Modulation Strategy for a Three-Phase Dual Active Bridge—Boosting Efficiency of an Electric Vehicle Converter

Three-phase dual active bridge (3p-DAB) dc-to-dc converters are typically avoided in low-power applications especially for wide voltage and power ranges. Even so, the 3p-DAB do offer a means to reduce filter costs and volume. The aim of this study is to propose the triangular and trapezoidal modulation for the 3p-DAB to address the problem of poor partial load efficiency. The proposed modulation schemes were compared with two conventional DAB concepts. It was found that the efficiency of the 3p-DAB increased substantially. Moreover, the 3p-DAB showed a considerably lower filter volume than that of the single-phase dual active bridge converter (1p-DAB). In conclusion, a modulation strategy combining the two proposed modulation schemes with the phase-shift modulation is ideal, because they boost efficiency and take most benefit from the inherent low filter volume. Ultimately, the three-phase dual active bridge may offer a promising solution to miniaturize galvanically isolated dc-to-dc converters for electric vehicles.

Dynamic and Balanced Control of Three-Phase High-Power Dual-Active Bridge DC–DC Converters in DC-Grid Applications

The three-phase dual-active bridge (DAB) is a dc–dc converter, which provides galvanic isolation, inherent soft-switching capability, and small filter size. In this study, the dynamic behavior of three-phase DAB is analyzed and a dynamic control strategy is developed. Furthermore, a compensation technique is implemented to compensate unbalanced transformer phase currents. The latter is often caused by asymmetric leakage inductances. State space averaging and first harmonic approximation models, both for the steady state and transient analysis, are developed to describe the dynamic behavior of the three-phase DAB. The accuracy of the models is compared with a detailed circuit simulation and the benefits of each model are identified. When the transferred power of the DAB changes fast, the transformer currents can become unbalanced, leading to oscillations in the output current. A unique control method is presented, which allows settling of the transformer currents within one-third of the switching period. Additionally, the transformer currents stay symmetrical and oscillations are avoided. Based on this fast current control, an outer voltage controller is designed. The comparison of the control system using the fast current control and the conventional quasi-steady-state control demonstrates the potential advantages of the new approach under dynamic conditions. In practice, it is difficult to achieve completely symmetrical short-circuit impedances in a high-power medium-voltage transformer. Asymmetric leakage inductances, however, result in unbalanced phase currents and higher dc current ripple in a three-phase DAB. The new control scheme that is developed here can be extended to compensate any unbalances in the transformer. This approach enables effectively the balancing of the three-phase currents. The new control schemes are experimentally verified.

Improvement of Light-Load Efficiency of Three-Phase Dual Active Bridge Isolated Bidirectional DC/DC Converter by Employing Y-Δ Transformation

Improvement of Light-Load Efficiency of Three-Phase Dual Active Bridge Isolated Bidirectional DC/DC Converter by Employing Y-Δ Transformation

A Three-phase Dual Active Bridge Bidirectional ZVS DC/DC Converter

This paper discusses the detailed operations of a three-phase dual active bridge bidirectional zero-voltage switching (ZVS) DC/DC converter (TPDAB) which transfers a bidirectional power flow between a 12V net and a high voltage DC net. The converter is controlled by phase-shift-modulation (PSM) with a fixed duty cycle D=1/3. It features isolation, smoother drawing and injecting current from the 12V net, smaller capacitances, smaller switch current stress, ZVS over a wide range, high efficiency and a large power handling capability. The mathematic model is analyzed. The soft-switching principle is described and its ZVS criterias are derived. The simulation and experimental results are provided to verify the theoretical analysis.

Comparative analysis of single-and Three-Phase Dual Active Bridge Bidirectional DC-DC Converters

Many modern power conversion systems require a bidirectional energy transfer capability as a central part of their system operation. Preferably, such systems should use a single high efficiency power electronic conversion system to reduce size, weight and cost. For higher power bidirectional conversion, the common topology proposed is a dual active bridge structure, where two DC-AC converters are coupled back-to-back through an AC inductor/transformer. Either single-phase or three-phase converters have been proposed for such a system, but to date no clear-cut basis for selecting between these two alternatives has been established. This paper presents a comparative evaluation of single-and three-phase back-to-back converters for use in a bidirectional power transfer applications. The paper considers these two alternatives from the perspective of operating performance and losses, and provides a basis for selecting between the two topologies in any particular operating context.

High-Power Bi-Directional DC/DC Converter Topology for Future Automobiles

This paper presents a 2 kW three-phase Dual Active Bridge converter (DAB3) which converts power between 42 V and 300 V and which is easily scalable up to 20 kW. The DAB3 has been selected for this application based on detailed simulations comparing different suitable topologies. The circuits investigated in this paper can operate in a soft-switching manner enabling a reduction in device switching losses and therewith an increase in switching frequency. Candidate topologies under a close investigation are the single-phase dual active bridge (DAB1) and the three phase dual active bridge (DAB3). Key-features are the galvanic isolation, reduced cooling costs, and the capability of transferring energy over a wide voltage range. This paper presents the converter breadboard design, the controller design and measurements.