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.
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.
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.
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.
Renewable energy sources such as fuel cells and photovoltaics (PV) modules are widely installed in recent years. Due to these sources' characteristics such as low port voltage, ...current-harmonic-sensitive, and weak short-circuit withstanding capability, their interface converters usually require high voltage gains, low high-frequency (HF) current harmonics, and short-circuit protection. At present, the existing step-up isolated dc-dc converters are usually combined with two capacitor-connected terminals or one capacitor-connected terminal plus one inductor-connected terminal, failing to obtain the low HF current harmonics and convenient direct current control (DCC) on both ports. Hence, a dual-inductor-connected (DIC) isolated dc-dc converter is proposed in this article with the inductor connection on both ports. Then, low HF current harmonics and convenient DCC capability can be realized simultaneously through the connected inductors. Meanwhile, the proposed converter can also achieve voltage spike suppression and soft-switching operation without snubber circuits, and its inherent voltage boost function makes it suitable for high voltage-gain applications. Subsequently, the modulation scheme, topology characters, and control scheme are elaborated in this article. The experimental results based on a scale-down laboratory prototype are presented to verify the steady-state and transient-state performance of the proposed converter.
A soft-switched current-fed dual-input isolated dc-dc converter topology is proposed in this article. This converter integrates two low-voltage dc sources with similar transferred characteristics ...such as two PV panels or two batteries into a dc bus using a simple circuit topology and a minimum number of active and passive components. The energy transfer between the input and output ports is controlled by modulating the pulse-width of the control signals. Moreover, the soft-switching operations are discussed, and the smooth connection between the input-side inductor and the transformer leakage inductance is achieved. Furthermore, the operation of the converter in reverse power flow direction is presented to demonstrate the bidirectional operational capability of the converter. Finally, different operation modes of the proposed dual-input converter are verified by the experimental results obtained from a 250 W hardware prototype.
Multi-port power converters are widely used in managing multiple energy sources and loads. To that end, a dual-input single-output dc-dc converter is proposed in this article. The converter ...integrates two low-voltage dc sources into a dc bus. Pulse width modulation is used to control the transfer energy from the input ports to the output port. The soft-switching operation in the primary side switches is achieved with the help of the secondary side modulation and the discontinuous conduction mode (DCM) operation of the primary inductors. Moreover, the DCM operation helps avoid the high-frequency transformer saturation even when the two input voltages have different magnitudes. Detailed analysis of the proposed dc-dc converter is presented in this article. The steady-state operation, the dynamic performance at the output load variation and input voltage disturbances, and maximum power point operation of the converter are validated through the simulation and experimental results obtained from a 200 W hardware prototype.
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.
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.
Combining buck, boost, or buck-boost stages, the dual-active-bridge (DAB)-based two-stage dc-dc converter is regarded as a promising solution for high-power electric vehicle (EV) charging, where wide ...voltage range is required. However, the design of the control system becomes more complicated because of the power coupling between the two stages. Therefore, a natural transient-behavior-based control theory is proposed for simplifying the control system of the DAB-based two-stage dc-dc converter. Expect for the EV charging, this control theory can also be used for this two-stage converter connected to other high inertia loads, where the terminal voltage is changed slowly. Under the proposed method, the DAB stage is controlled as a step-change current source. Besides, the duty ratio of the buck, boost, or buck-boost stages, which can be directly calculated by the input and output voltage, is employed to match the middle dc-link voltage and the input voltage for DAB stage. Then the dynamic response for the input current of the buck, boost, or buck-boost stages is relied on their own natural transient behavior. Crucially, based on the transient analysis, the settling time of the buck, boost, or buck-boost stage can be determined for the step change, and the control period only needs to be larger than this settling time. Moreover, since the steady state can be obtained for each control period, a reliable control performance can be obtained without general stability analysis. Finally, experiment results are provided to verify the effectiveness of the proposed theory.
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