Phase Drift Phenomenon in Dual Active Bridge Converter – Analysis and Compensation

This paper proposes a dual active bridge (DAB) converter constructed with two nine-switch five-level active neutral-point-clamped (9S-5L-ANPC) bridges. The dead time effect in DAB converter with five-level active-neutral-point clamped circuit is analyzed, then an elimination method using the zero state with dual current paths is proposed in 9S-5L-ANPC circuit. On this basis, a modulation method that can effectively balance the loss distribution of power devices and balance the voltage of flying capacitor is proposed. Meanwhile, the soft switching conditions of all nine switches are derived. The performance of the proposed 9S-5L-ANPC DAB converter is verified by a 1.3 kW experimental prototype.

This paper presents the design of new highfrequency transformer isolated bidirectional dc-dc converter modules connected in module-cascaded solid state transformer (SST). A phase-shift dual active bridge (DAB) converter is employed to achieve high-frequency galvanic isolation, bidirectional power flow, and zero voltage switching (ZVS) of all switching devices, which leads to low switching losses even with high-frequency operation. Bidirectional DC-DC converter is crucial to the power transmission in SST. The proposed DAB converter consists of two three-leg bridges and a high-frequency transformer with winding shunting taps. Furthermore, the commutation inductance connected in series with the transformer in the conventional DAB converter is integrated into the transformer windings, thus, enjoying smaller volume and higher power density. By changing the number of primary winding turns, leakage inductance, which is the key parameter in the energy transfer process of DAB converter, can be adjusted on a large scale, enabling the possibility of reducing loss over wide load range. Additionally, time-sharing circuit topology and operation mode are adopted to adapt to the output power by detecting the output current as the feedback. As a result, the efficiency at both light and heavy load can be significantly improved compared with the conventional DAB converter, and, therefore, high efficiency over wide load range and high power density can be achieved. Besides, the additional bridge arm structure along with a flexible control scheme provides possible high-level fault tolerance. Finally, the simulation results on a 2-kW DAB converter module switching at 10kHz are presented to validate the theoretical analysis.

The dual active bridge (DAB) converter achieves relatively high efficiency and high power density. Therefore, it is widely used in ac–dc–ac converters to provide electrical isolation between the input and output. However, the single-phase converter inherently exhibits significant low-frequency voltage ripple in the DAB topology. Traditional control strategies focus on reducing voltage ripple and optimizing the capacitor size by transferring fluctuating power through the DAB converter. This method leads to higher magnetic component and switch currents, as well as a larger transformer size. To suppress these effects, this article proposes a constant power transmission (CPT) control for the DAB converter. The proposed CPT control dynamically adjusts the modulation width of each operating cycle by tracking the input–output voltage fluctuations in real-time through the control variables. This ensures constant power transfer in the DAB converter. Compared to traditional methods, the proposed control strategy reduces both the RMS and peak-to-peak values of the inductor current, thereby reducing the size of the converter and improving system efficiency. Simulation and experimental results confirm that the CPT control effectively reduces the peak-to-peak and RMS values of the inductor current by 40.7% and 18.8%, respectively, reduces the transformer size by 21.4%, and increases the efficiency by 1.1%.

The dual active bridge (DAB) converter is widely used in different fields, such as electric vehicles, distributed power generation system, energy networks. it also can be introduced in railway applications to implement power electronic transformers, bidirectional battery chargers etc. The DAB converter is usually designed combining with series resonant to reduce the switching off loss. Nevertheless this will make it hard to achieve the zero voltage switching on of the primary power semiconductor at light load, especially when voltage conversion ratio is far away from one. Besides, the dead-time has great effect to the soft switching implementation. The voltage polarity reversal and voltage sag phenomena etc. are caused by the dead-time effect. This paper provides a precise mathematical transmission power model considering the resonant and dead-time effect respectively. A comprehensive theoretical analysis of the dead-time effect on the series resonant DAB converter is presented. By improving the dead-time, the soft switching rang is increased and the efficiency will be improved at light load. The experimental results are provided to verify the theoretical analysis.

The dual active bridge (DAB) converter attracts more and more attentions thanks to its advantages over the other isolated dc-dc converters, such as soft-switching, immunity to parasitic inductance, less circuit components and less component stress. Rectangular (also named as phase-shifted) modulation method on DAB has been widely studied and but other two proposed modulations (trapezoidal and triangular methods) have much less applications. Due to the characteristics of the modulation principles, one of these three methods outperforms the other two in certain operating ranges from system efficiency point of view. This paper summarizes the properties of three modulation methods and optimizes the combined use of three modulations on a DAB converter (12V/360V, 1 kW and 25 kHz) in order to obtain the best system efficiencies over full converter operating range. A validated loss model is utilized as the analyzing platform, based on which the optimal operating ranges of three modulations are determined.

It is becoming a great interest to employ SiC based power devices in dual active bridge (DAB) converter as an alternative to conventional Si-IGBT, due to its higher switching frequency potential, smaller switching losses as well as the capability to operate at synchronous rectification (SR) condition. This paper introduces the device loss model of a SiC MOSFET power module based DAB converter considering the effect of synchronous rectification, and the dead-time effect is also discussed. The calculated device loss for both SiC-MOSFET and Si-IGBT are discussed. The results show that the overall device loss is reduced by 40%, where the conduction loss is reduced by 38% because of SR capability of SiC-MOSFET, and the switching loss is reduced by 48% due to the faster transient of SiC-MOSFET during dead-time. On the other hand, the device losses are not even between the primary bridge and the secondary bridge of the DAB converter, and it is more significant for SiC-MOSFET based DAB due to the effect of SR with a maximum of 20%. At last, the dead-time range is given based on the device properties.

This paper demonstrates a novel frequency domain general harmonic approximation (GHA) based steady state modeling technique of the dual active bridge (DAB) converter. This proposed model is employed to simplify the mathematical formulation of the instantaneous as well as RMS currents of the converter, critically accountable for the system switching and conduction losses. Also, all the possible phase shift control methods, including single, dual, and triple phase shift modulations are rigorously studied and investigated in order to provide a generic and detailed insight on the applicability and benefits of using them on a wide range of gain and load demand while ensuring minimized conduction losses. A 400W proof-of-concept of DAB DC-DC converter has been developed to validate and establish the proposed frequency domain model-based theoretical analysis and claims. While the converter has a fixed input DC bus voltage of 160V, the output load power is varied within a range of 50W to 400W with a large swing in output voltage level, i.e., from 90V to 150V. With the implementation of the proposed optimal triple phase shift (TPS) control at extreme gain conditions, the experimental results show a system efficiency increment of 3.5% and 2.2 % compared to the conventional single-phase shift (SPS) modulation technique at 90V, 50W and 150V, 200W outputs, respectively.

This paper presents a ripple-current compensation method for a dual active bridge (DAB) converter with a matching transformerless series DC active filter (DCAF) in a DC distribution feeder. The input and output currents of the DAB converter contain large ripples, which can negatively affect connected devices such as batteries and solar cells. A matching transformerless DCAF is connected in series between the DC source and DAB converter. The DCAF compensates for the ripple voltage and current of the DAB converter. Experimental results indicate that the proposed method lowers the ripple voltage and current of the DAB converter to 44.9% and 65.0%, respectively.

SummaryIn battery energy storage system (BESS) applications, the life of the battery depends on the quality of the charging/discharging current. However, the dual active bridge (DAB) converter, which interfaces BESS with the DC link, suffers from a backflow current in all modulation schemes, degrading the battery's performance. Hence, this paper proposes a particle swarm optimization (PSO) based universal phase shift (UPS) modulation scheme to improve the battery's life. In the proposed modulation scheme, the phase shift ratio of DAB to eliminate the backflow power is estimated using PSO. Also, it is observed that there is an improvement in the zero voltage switching (ZVS) range of the DAB. Hence, the overall efficiency of the DAB converter is increased over a wide operating region. The operating principle of the proposed modulation scheme, steady state analysis of power transmission, and backflow power are reported in this paper. The theoretical performance of the proposed modulation scheme is validated in a 2 kW experimental setup.

In this paper, the design and comparison of single and three-phase transformers in Dual Active Bridge (DAB) Converter are carried out. DAB converter topology and operating schemes are introduced. And core-type transformers design optimization methods are proposed for both single and three-phase DAB converters (DAB1 and DAB3). Based on DAB topology assumptions, single and three-phase transformers are compared in volume with various design constraints. And analysis shows that comparison result varies at different cases of flux and thermal limits. Scaled-down DAB1 and DAB3 systems have been built and temperature rises of the transformers have been tested for verification.

This article proposes a single-stage three-phase AC-DC converter composed of a SWISS converter and two Dual Active Bridge (DAB) converters connected in parallel at the output. The input current relationship between the SWISS and DAB converters is analyzed, and the optimal triple-phase-shift (TPS) control of the DAB converter is introduced to achieve the unity power factor for the entire load power. Under optimal TPS control, zero voltage switching (ZVS) and minimal current stress can be achieved. Based on the optimal working modes of TPS control, the analytical expression is derived to describe the relationship between the phase-shift angle and the input current of the DAB converter. A dual-loop control strategy is proposed to achieve good power quality and output regulation. The ranges of working modes and the control variables under different load power conditions are analyzed, demonstrating the adaptability of this strategy to a wide range of load powers. The design of the series inductor and the calculation of losses are discussed, and the loss distribution under different power conditions is presented. Finally, the proposed control strategy is applied to a 1.6 kW three-phase single-stage DAB-based SWISS converter with 200V/50Hz input line voltage and 200V output voltage. The experimental results validate the feasibility and effectiveness of the control strategy.

A key component for all-DC wind farms is the DC/DC converter. The converter must have multi-megawatt power capability, a high step-up ratio, provide galvanic isolation, and operate efficiently while being able to fit in the wind turbine nacelle. The single active bridge (SAB) and dual active bridge (DAB) converters in standalone or cascaded configuration are promising topologies that have the potential to meet these requirements. This paper reviews the operation and control of these converters, and compares their volume, weight, and efficiency for a 15 MW wind turbine with 80 kV DC connection. The results show that the standalone topologies are significantly smaller and lighter than their cascaded counterparts. However, all topologies fit inside the wind turbine nacelle. The SAB designs are the most efficient and robust, as they use diodes in the output bridge. The DAB topologies have the advantage of bidirectional power flow at the cost of additional switches and losses. The standalone DAB requires series-connected switches in the output bridge, which may difficult to implement. The cascaded topologies offer higher reliability without significantly increasing losses, making them the most attractive option for future DC wind turbines.

Dual active bridge (DAB) converters are widely used in dc microgrids due to their advantages of electrical isolation, wide voltage range operation, and bidirectional power flow. When the voltage conversion ratio is mismatched, the conventional symmetric phase shift modulation method has a narrow zero voltage switching (ZVS) range, low light-load efficiency, and uncontrollable inductor current oscillations caused by abrupt changes in variables during mode switching. In order to solve the above-mentioned problems, an extended dual side asymmetric phase shift modulation (EDAPSM) and smooth mode transition method is proposed in this article. Analytical solutions over the entire power range are derived based on the proposed approximation method. The inherent cause of variable discontinuities during mode transitions is identified, and a novel approach to achieve smooth mode switching is presented, thereby improving the efficiency of the DAB converter over a wide voltage range, particularly under light-load conditions. A 1-kW DAB prototype is constructed, and the modulation method can achieve a maximal efficiency of 98.03%. The experimental results verify the correctness and effectiveness of the method proposed in this article.

Dual active bridge converter is very attractive for bidirectional power conversion for its simple control, easy to achieve soft switching and wide power flow and operating voltage range. Triple phase shift modulation is one of the most popular choice of modulation due as it widens the soft switching range over complete power flow range. However, being a three degree of freedom scheme, finding an optimum operating point based on the phase shift and conduction angles of the active bridge which minimizes the rms current and the losses due to reactive power flow is not easily obtained. In this paper, a harmonic model is discussed which allows analytical optimization when the phase shift is considered constant. Analytical expression for the optimum operating point is derived to achieve minimized rms current, circulating current and reactive power while maintaining soft switching conditions. Theoretical analysis has been verified by Matlab simulation and experimental result provided for a 100W dual active bridge converter.

This paper proposes a new design concept of small air-gap bidirectional Wireless Power Transfer (WPT) system using Dual Active Bridge (DAB) topology. The wireless charging coils are considered as a weakly coupled transformer having relatively high leakage inductance, and thus the new design can obtain soft switching without implementing resonant capacitor or external inductor. This design has a simple construction and can enable bidirectional inductive power transfer with superior performance compared to the traditional large air-gap system. The new system can transfer high power via a compact coil structure thanks to smaller air gap. Moreover, soft-switching operation enables significant improvement in efficiency. The proposed design enables electrical vehicles and smart wheels to use batteries for supporting grid silently and seamlessly. This paper considers the application of smart wheel charger and presents an analytical design of the system using finite element analysis and circuit simulation. As a result, the design can achieve 97% efficiency at 3-kW, 85-kHz operation.