Non-linear Dead-time Error Compensation Method of Dual Active Bridge DC-DC Converter for Variable DC-bus Voltage

This paper discusses an expansion method of zero voltage switching (ZVS) operation range in a dual active bridge (DAB) dc-dc converter using a three-level neutral-point-clamped (NPC) inverter topology. A DAB converter consists of two active bridges connected through a high-frequency transformer. A drawback of a conventional DAB converter is that ZVS operation range is limited. This paper presents a novel control strategy for the proposed DAB converter using a three-level NPC inverter to expand the range of the conventional ZVS operating mode. In addition, the effectiveness of the proposed scheme for the DAB converter is verified through simulations and experiments.

This paper proposes a unified phase shift control strategy for optimized transient current response of dual active bridge (DAB) dc-dc converters. Conventional phase shift control for DAB converters may cause dc offset in the high-frequency-link inductor current during transients, which may lead to magnetic flux saturation and excessive current stress on the switching devices. The proposed phase shift method can eliminate the transient current offset during both unidirectional and bidirectional power flow changes in a unified form. Experimental results are provided to verify the theoretical analysis.

DC-DC Dual Active Bridge (DAB) converters can potentially be used as an interface between DC micro-grids and battery packs of PHEVs/EVs. This paper focuses on presenting a new method to achieve Zero Voltage Switching (ZVS) for all the switches in DAB converters. This is done by initially extracting the ZVS criteria, which corresponds to different operating conditions (bus voltage and power level). Then, a Look-Up-Table (LUT) is created that is compliant with the derived ZVS region. The LUT can be used in the control system of DAB converters to achieve ZVS for a wide range of operating conditions. Simulation and Experimental results are provided to validate the effectiveness of the proposed method.

Compared to single-phase dual active bridge (1p-DAB) DC-DC converters, three-phase dual active bridge (3p-DAB) DC-DC converters have advantages such as high single machine power, high power density, small filtering capacitance, and are more suitable for high-voltage situations. Therefore, they have good application prospects in DC transmission and industrial high-power DC-DC converters. However, under traditional single-phase shift (SPS) control, especially in the low power range, there is a large reactive current and severe soft switch loss. This article adopts an asymmetric modulation strategy for its larger reactive power, which reduces its reactive power in the low power range with more degrees of freedom and improves the efficiency of power transmission. Taking current stress as the optimization objective, the KKT algorithm is used to solve, and the corresponding analytical solution is ultimately obtained. Finally, a simulation is built by using MATLAB software to verify the feasibility of the proposed solution.

The dual active bridge (DAB) DC-DC converter is the core link of a power electronic transformer (PET). With the development of PETs toward medium- and high-voltage applications, more DAB modules are adopted. However, conventional Electromagnetic Transient (EMT) simulation for a multi-switch circuit is quite time consuming. In this paper digest, a modified constant admittance method has been developed for modeling of an isolated DAB. By reducing the expense of admittance matrix reconstruction and related iterative operation at switching instant, the simulation efficiency has been improved significantly, and the new model becomes more suitable for a real-time simulation algorithm. Meanwhile, time domain simulations are given, which show that the proposed method can keep the same accuracy as the conventional model.

The small-signal approximations which are generally used in the DC-DC converters provide the limited range of operation which is around the steady-state point. However, if the ripples are large, this approximation is generally not true for which the generalized average modelling is better to capture the effects of other harmonic components along with the DC component. Here, the author has employed the generalized averaging technique including the input and output side parameters using the feedforward and feedback control on the dual active bridge converter. The inductor current is alternating and to capture the behaviour of system parameters, the generalized average modelling is done. It is found that the input parameter will also affect the overall dynamics and using MATLAB/Simulink tool the overall analysis is validated.

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.

Aimed at the input parallel and output parallel (IPOP) dual-active bridge (DAB) dc-dc converters, this paper proposes an unbalanced-power-distribution scheme (UPDS) that considers the practical parameter deviation between DAB converters for minimizing the total backflow power. Firstly, combined with the characteristics of extended-phase-shift (EPS) control, the popular balanced-power-distribution scheme (BPDS) cannot achieve minimum backflow power due to the parameter deviation. In this regard, UPDS is established by detailed mathematical derivation, dividing the system operation into three sections. Simulation model and two-parallel DAB converters protype were built, and the results substantiated the validity of the theoretical analysis and the effectiveness of the proposed method.

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.

Recently, energy network systems with energy storage such as batteries have been focused on using for electric vehicles and power grid systems. Therefore, the Dual Active Bridge (DAB) dc-dc converter has been focused on because it has some unique advantages, such as bi-directional power transmission and high efficiency by Zero-Voltage-Switching (ZVS). However, hard switching and surge current are critical issues at light load. For the improvement of this problem, "masked-switching control (MSC)" was reported previously. However, another hard switching and surge current has confirmed at medium load by MSC. In this paper, the adaptive control method is proposed that can reduce surge current and operate ZVS at medium load. By experimental results, 1.4% of maximum power efficiency improvement at the medium load is confirmed. From the results, it can be seen that the proposed control method can achieve ZVS and realization of high power efficiency with wide load range.

Recently, the bi-directional dc-dc converter has been focused on because of the huge demand for diversification of power supply network including battery. The dual active bridge (DAB) dc-dc converter is one of the most popular circuits for bi-directional applications because of its simple structure. However, power efficiency at light load is the intrinsic problem of a bi-directional DAB DC-DC converter. In this paper, the simple solution with digital operation for the problem is proposed and experiments are performed with 1kW system. This method can reduce a switching surge without other circuits such as snubber and improve power efficiency at light load. Therefore it can reduce loss of switching surge, and improve power efficiency. From the results, 37% maximum power efficiency improvement at light load is confirmed. Furthermore, this method is capable for control in the conventional method in the heavy load range. Consequently, it is possible to reduce the switching surge and realize high power efficiency in a wide load range.

Solid State Transformer (SST) is widely used in distribution renewable energy resources. SST includes AC-DC rectifier, DC-DC Dual Active Bridge (DAB) converter and AC-DC inverter. In this paper, continuous time average model and dynamic phasor model for combined Rectifier and DAB converter (R-DAB) are developed. Control scheme for R-DAB model is proposed for dynamic phasor based model, in which rectifier and DAB are being individually controlled using PI controller. The effect of controller has been analysed with change in input grid voltage variation. Stability analysis has performed using small signal stability analysis and Lyapunov's criterion. Developed model is verified with simulation in MATLAB/Simulink. Simulation result verifies the proposed modelling technique and controller performance.

In this paper, a variable dc bus control strategy is evaluated for a bidirectional grid connected electric vehicle (EV) charger topology. The EV charger under consideration comprises of an ac-dc 3-φ active rectifier stage followed by a dc-dc dual active bridge (DAB) converter. The voltage of the common dc-link between the ac-dc stage and the dc-dc stage is regulated such that it follows the voltage variations of the battery pack. The proposed control strategy helps to minimize circulating reactive currents in the DAB converter and extends the soft-switching operating range of the same to achieve high system efficiency. An optimal design approach is presented to select the DAB converter parameters that can be used in conjunction with the variable dc bus control strategy. Experimental results on a 3.3 kW EV charger hardware prototype validate the benefits of the variable dc bus control and proposed optimal design methodology.

This paper analyzes a three-phase Dual Active Bridge (DAB) dc-dc converter with three-level phase-legs, showing a significant increase in the soft-switching region compared to two-level operation. A strategy is presented that results in a Zero Voltage Switching (ZVS) modulation scheme that relies on analytical equations, uses a small amount of switching modes, and obtains close-to-minimal rms currents.

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.