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With some advantages, such as electric isolation, high efficiency, and fast dynamic response, the input-series output-parallel (ISOP) dual-active-bridge (DAB) dc–dc converter has been regarded as one of the most promising candidates for connecting the medium voltage terminal and the low voltage terminal. For the ISOP DAB dc–dc converter, the existing control strategies are mainly focusing on the equivalent power sharing control, but the fast-dynamic response is not included and the decoupling between the regulation of input voltage and the adjustment of output voltage is not eliminated significantly. In this article, the average model of this ISOP DAB dc–dc converter is presented first, which can be employed to analyze the power distributions of this modular topology clearly. Then, an input-oriented power sharing control scheme with fast-dynamic response is proposed for ensuring both the power sharing ability and the fast-dynamic performance of the ISOP DAB dc–dc converter in this article. Compared with the existing methods, this proposed scheme can also significantly reduce the coupling between the power sharing control and the output voltage regulation. In addition, an inductance-estimating method is proposed for ensuring the power sharing performance of the ISOP DAB dc–dc converter. Finally, the experimental results are provided to verify the effectiveness of the proposed input-oriented power sharing control with fast-dynamic response for the ISOP DAB dc–dc converter system. [ABSTRACT FROM AUTHOR]

Benefitting from some significant advantages, the dual active bridge (DAB) dc–dc converter has become one of the most promising candidates for dc–dc power conversion. In recent years, some strategies have been proposed to boost the dynamic performance of DAB dc–dc converter under the disturbance of input voltage and load condition. According to the relationship between the compensation part and the model-based part, these existing schemes can be divided into two structures including the parallel structure and series structure. In the parallel control structure, the compensation part is added to the model-based part. In contrast, the compensation part is multiplied with the model-based part in the series control structure. By adopting proper feedback control, both control structures can provide excellent dynamic performance for DAB dc–dc converter easily. Hence, the modified parallel-structure fast-dynamic control scheme and the modified series-structure fast-dynamic control scheme are both proposed in this article. Then, using these two proposed schemes as examples, the merits and the demerits of both structures are analyzed, and the corresponding compensation methods are also presented. Moreover, a general PI design principle of the model-based control scheme for the DAB dc–dc converter is provided, which is different from the traditional concept for designing the PI parameters. In addition, the control delay of these two proposed schemes is analyzed, and a compensation method is also proposed. Finally, simulation results and experimental results are obtained to verify the analysis in this article and the excellent performance of the proposed methods. [ABSTRACT FROM AUTHOR]

The dual-active-bridge (DAB) dc–dc converter is a promising candidate for the isolated dc–dc power transferred applications, such as in the dc distribution system, the solid-state transformer, and the energy storage system. In these applications, the fast-dynamic response is usually a core requirement, especially under load changes. To improve the dynamic performance of the DAB dc–dc converter, this article proposes a simple load-current-estimating (LCE) scheme with delay compensation for fast dynamic performance. Based on the current flowing model of the DAB dc–dc converter, the LCE strategy is proposed with single-phase-shift modulation method. Moreover, the inherent switching-period delay phenomenon of the LCE scheme is analyzed. Therefore, the corresponding delay compensation method is proposed for further boosting dynamic responses, and the dynamic limitation of the LCE scheme may be obtained for DAB dc–dc converter. Then, for the proposed LCE scheme, a damping coefficient is introduced to restrict the potential instability caused by the measurement noise, and the fast-dynamic response will be influenced a little when the load resistor is changed. In addition, the extended rule for the optimized triple-phase-shift modulation method is discussed. Finally, the simulation result and the experimental result both validate the fast-dynamic performance of this proposed LCE strategy without or with delay compensation. [ABSTRACT FROM AUTHOR]

Along with the development of the renewable energy, such as the photovoltaics and the wind turbine, the energy storage system (ESS) is becoming as a critical part for the renewable-based microgrids. In this article, dual-active-bridge (DAB) dc–dc converter with bidirectional power flowing ability, wide soft-switching range, and ultrafast dynamic characteristic is adopted for integrating multiple energy storage units (ESUs) for balancing the power flowing between the renewable energy and the loads in a islanded dc microgrids. For the multiple DAB-based ESS, a communication-free power management strategy is proposed in this article to maintain the dc-link voltage for the islanded dc microgrid, and high robustness of the dc-link voltage can be ensured when the output voltage of energy storage equipment, the load condition, and the power sharing performance of the ESS are changed. The proposed strategy also ensures seamless ESU plug-in or plug-out operations. Finally, the small-scale simulation model and experimental platform are both employed to verify the effectiveness of the proposed communication-free power management scheme. [ABSTRACT FROM AUTHOR]

To boost the dynamic performance of the full-bridge (FB) dc–dc converter, some model-based controls have been recently proposed in the literature. However, in terms of dynamic performance, these methods have failed to reveal the potential of this converter since the inherent relationship among the duty ratio, the input voltage, the output voltage, and the load resistor is not adopted in the controller, and the dynamic performances are still relayed on the fuzzy adjustment based on the disturbances of output voltage as the single-voltage-loop control method. In this article, based on this inherent characteristic of the FB dc–dc converter, an accurate transferred current modulation method is presented first. Based on this modulation method, a simple direct current control (DCC) scheme is proposed for a fast dynamic response with the feedback values of input voltage and load current. Moreover, the model uncertainties such as the power losses and control delay may influence the control performance. Therefore, a compensation operation is also presented to reduce the impact caused by these uncertainties to ensure the dynamic performance of the proposed strategy. In addition, since the circuit parameters including the leakage inductance and the output capacitor should be employed to implement the proposed DCC strategy with compensation operation, inaccurate circuit parameters may influence the performance of these proposed strategies. Therefore, the circuit-parameter estimation methods for these two circuit parameters are also proposed to ensure the dynamic performance of the FB dc–dc converter. Finally, the simulation and experiment results have verified the correctness and effectiveness of the proposed DCC strategy. [ABSTRACT FROM AUTHOR]

The centralized output-parallel dual-active-bridge (OP-DAB) dc–dc system is a promising candidate for achieving isolated dc–dc energy conversion with large current and power rating. To implement the flexible power sharing performance of the OP-DAB dc–dc converter, a simple tunable power sharing (TPS) strategy is proposed with the single-phase-shift method in this article. Based on the TPS strategy, the excellent dynamic performance under disturbances of input voltage for each module and load resistor can be provided. However, inaccurate circuit-parameter information always damages the power sharing performance among different DAB converters. Therefore, the comprehensive circuit-parameter estimating schemes proposed for different conditions of the OP-DAB dc–dc system including the start-up process, the working process and plugging-in a new DAB dc–dc converter, respectively. Moreover, the hot swap (plug-in and plug-out) control methods of the DAB converter without large influence on output voltage is also discussed in detail. Experimental results are obtained to verify the analysis in this article and the excellent performance of the proposed methods. [ABSTRACT FROM AUTHOR]

The nonresonant single-phase dual-active-bridge (NSDAB) dc–dc converter has been increasingly adopted for isolated dc–dc power conversion systems. Over the past few years, significant research has been carried out to address the technical challenges associated with modulations and controls of the NSDAB dc–dc converter. The aim of this paper is to review and compare these recent state-of-the-art modulation and control strategies. First, the modulation strategies for the NSDAB dc–dc converter are analyzed. All possible phase-shift patterns are demonstrated, and the correlation analysis of the typical phases-shift modulation methods for the NSDAB dc–dc converter is presented. Then, an overview of steady-state efficiency-optimization strategies is discussed for the NSDAB dc–dc converter. Moreover, a review of optimized techniques for dynamic responses is also provided. For both the efficiency and dynamic optimizations, thorough comparisons and recommendations are provided in this paper. Finally, to improve both steady-state and transient performances, a combination approach to optimize both the efficiency and dynamics for an NSDAB dc–dc converter based on the reviewed methods is presented in this paper. [ABSTRACT FROM AUTHOR]

To connect the low voltage energy storage source equipment and the medium voltage dc (MVdc) bus, the output-series dual-active-bridge (OS-DAB) dc–dc converter system with independent or common input terminals becomes a promising option. For the OS-DAB dc–dc converter system, this letter proposes a simple tunable power sharing control (TPSC) strategy to maintain the voltage of MVdc bus, manage power sharing ratio for each energy storage system. The proposed strategy allows energy storage equipment hot swap as well as converter system black start. Experimental results verify the analysis in this letter and the excellent performance of proposed TPSC strategy. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive optimization control scheme to improve efficiency and dynamic response of dual-active-bridge (DAB) dc–dc converters. Unified-phase-shift (UPS) control is widely used to increase the efficiency of DAB dc–dc converters by minimizing the peak current, but dynamic performance of the converters needs to be further enhanced. In this paper, to gain superior dynamic performance of DAB dc–dc converters, an equivalent power-balancing (PB) model is employed, which is capable of predicting dynamic behavior of converter output voltages due to input voltage fluctuation and load disturbance. And then, combining the UPS control and the PB control, a comprehensive UPS and PB (UPS-PB) scheme is proposed to improve the efficiency and dynamic performance simultaneously. This work also includes the detailed inductance parameter sensitivity of the proposed UPS-PB scheme and a zonal voltage control strategy to further improve dynamic responses of the output voltage under the start-up process or a large step change of the output voltage reference. Moreover, the variant of UPS-PB scheme for constant power load is analyzed in the experimental part. Finally, experimental results have verified the excellent performance of the proposed UPS-PB scheme and correctness of theoretical analysis in this work. [ABSTRACT FROM AUTHOR]

One of the essential requirements for high-performance dual active bridge (DAB) dc–dc converters as the controlled dc voltage sources is to obtain the constant output voltage rapidly and accurately under all working conditions. In order to reach fast dynamic response, combing direct power control with feedforward control strategy, this paper proposes a virtual direct power control (VDPC) scheme with single-phase-shift control for DAB dc–dc converters to face with these following extreme conditions, such as start-up, load step-change, no-load, the input voltage fluctuation, and the desired output voltage step-change. The proposed VDPC scheme of DAB dc–dc converters can achieve no overshoot and fast transient response for the output voltage in load or input voltage disturbances and start-up stage. Dynamic response of the output voltage control has been also improved when the desired value steps up and down. Finally, four control schemes consisting of traditional voltage loop control, load current feed-forward control, model-based phase-shift control, and the proposed VDPC schemes are compared and tested in a scale-down DAB dc–dc converter experimental prototype. Experimental results verify the above excellent performance of the proposed VDPC scheme and the effectiveness of theoretical analysis. [ABSTRACT FROM AUTHOR]

To reduce current stress and improve efficiency of dual active bridge (DAB) dc–dc converters, various control schemes have been proposed in recent decades. Most control schemes for directly minimizing power losses from power loss modeling analysis and optimization aspect of the adopted converter are too difficult and complicated to implement in real-time digital microcontrollers. Thus, this paper focuses on a simple solution to reduce current stress and improve the efficiency of the adopted DAB converter. However, traditional current-stress-optimized (CSO) schemes have some drawbacks, such as inductance dependency and an additional load-current sensor. In this paper, a simple CSO scheme with a unified phase-shift (UPS) control, which can be equivalent to the existing conventional phase-shift controls, is proposed for DAB dc–dc converters to realize current stress optimization. The simple CSO scheme can overcome those drawbacks of traditional CSO schemes, gain the minimum current stress, and improve efficiency. Then, a comparison of single-phase-shift (SPS) control, simple CSO scheme with dual-phase-shift (CSO-DPS) control, simple CSO scheme with extended-phase-shift (CSO-EPS) control, and simple CSO scheme with UPS (CSO-UPS) control is analyzed in detail. Finally, experimental results verify the excellent performance of the proposed CSO-UPS control scheme and the correctness of theoretical analysis. [ABSTRACT FROM AUTHOR]

The current-fed isolated dc/dc converters are suitable solutions for applications requiring low high-frequency current ripple and convenient current control, such as fuel cells and Li-ion batteries. The existing current-fed isolated dc/dc converters are combined with a current-fed bridge-type terminal and a voltage-fed bridge-type terminal, which can only partially obtain the merits of the current-fed terminals. In this article, a dual-current-fed dual-active-bridge dc/dc converter is proposed with the inductor connection on both terminals. Hence, low high-frequency current ripple and convenient current control can be realized on both sides. Besides, it can also realize the voltage spike suppression without snubber circuits and has the inherent soft-switching operation and voltage boost function. Then, the operation principle, design process, and loss analysis of the proposed converter are presented in detail. The experimental results based on a proof-of-concept laboratory prototype are given to verify the steady-state and dynamic performance of the proposed converter. [ABSTRACT FROM AUTHOR]

High dynamic performance is an essential requirement for the dual-active-bridge (DAB) dc/dc converters. As dc voltage sources, they should maintain the desired output voltage instantly under all working conditions. However, the previous literature mainly focus on the dynamic control of the voltage-fed DAB converters, and the existing control schemes for the current-fed DAB converters achieve limited dynamic performance. Aiming at improving the dynamic performance, a direct actual-power control (DAPC) scheme based on virtual impedance estimation (VIE) is proposed for the current-fed DAB converters in this article. The proposed DAPC scheme is based on a parallel structure instead of the series structure of existing control schemes, and it realizes fast dynamic control through combining actual power control with the VIE method. The proposed DAPC scheme can obtain the fastest transient response for the output voltage without voltage overshoot in transient conditions, such as load step change, input voltage fluctuation, and the desired output voltage step change. Besides, a leakage inductor precharging method is integrated into the DAPC scheme to avoid the current mismatching. Finally, the proposed DAPC schemes are compared with two existing control schemes and tested in a scale-down experimental prototype. Experimental results verify the effectiveness of the proposed DAPC scheme. [ABSTRACT FROM AUTHOR]

With the development of power system electronization, distributed new energy generation-based DC microgrid system has become a hot spot of the current research. Aiming to implement the collection, transformation and transmission of the new energy sources, the dual active bridge (DAB) converter has become a key energy conversion device. Aiming to promote the transmitted efficiency for such DAB converter, a deep reinforcement learning (DRL) optimization scheme with the triple-phase-shift (TPS) is proposed. Specifically, the deep deterministic policy gradient (DDPG) algorithm is used for solving optimal solutions with the minimum power losses. Then, the trained DDPG agent is used as a fast surrogate predictor, which giving the suitable control decisions under whole operation conditions. The main control objective is to minimize the power losses for getting the target maximum efficiency. Besides, the soft switching constrains are added to the DDPG algorithm. Based on this, the proposed optimized method can be used for different operation conditions with excellent performance. The operation principles, the loss analyses, and the training consideration and evaluation of the DDPG algorithm are given. Finally, simulation and experimental results using a 200 W hardware prototype are displayed and compared to prove to effectiveness of theoretical analysis. [ABSTRACT FROM AUTHOR]

The problem of leakage-inductor parameter in paralleled current-fed isolated dc/dc system has not been solved. Aiming at solving that problem, a leakage-inductor parameter compensation method is proposed without an additional sensor. It provides tunable reflected voltage for parameter difference individually and compensation loops for parameter uncertainty. Thus, the circulating current and the current stress are minimized, and the voltage spike is avoided. The experimental results are given to validate the effectiveness of the method. [ABSTRACT FROM AUTHOR]