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A three-phase dual-active-bridge (3p-DAB) converter is an attractive topology for bidirectional power conversion in high-power applications. However, conduction and switching losses are two main loss mechanisms that severely affect its efficiency performance, and adoption of any single modulation scheme or topology cannot minimize these losses over a wide operating range. For this purpose, a reconfigurable topology of the 3p-DAB converter is proposed in this article that utilizes a reconfigurable and tunable resonant network to offer multiple degrees of freedom in minimizing conduction and switching losses over a wide range of operating conditions. The converter is designed such that for 40–100% of the rated output power, it operates as a tunable 3p-DAB resonant immittance converter with its output power controlled by varying switching frequency and tuning the resonant frequency of a resonant immittance network to track the switching frequency. Below 40% of the rated output power, the converter transforms to a tunable 3p-DAB series-resonant converter with its output power controlled by varying the impedance of a series-resonant network while keeping the switching frequency and phase shift constant. The combination of both operation modes jointly leads to wide-range zero circulating current and soft switching of all the switches and, hence, a wide-range high-efficiency performance, as validated by the experimental results. [ABSTRACT FROM AUTHOR]

Leakage and magnetizing inductances of a loosely coupled transformer are constantly changing due to the relative positions of the primary and secondary transformer windings in inductive power transfer systems. In order to counteract the nonnegligible inductances and extract desirable characteristics from the system, various compensation networks have been proposed to obtain unity input power factor and constant output voltage for minimum reactive power and ease of control for battery charging or other power electronic applications. However, most of the existing control methods with fixed compensation networks, which are usually designed for a specific coupling coefficient, have failed to fulfill both requirements simultaneously due to the mismatch between the resonant frequencies of the networks after the deviation of the designed coupling condition. In this article, a dynamic series/series–parallel compensation network based on a switch-controlled capacitor is proposed to rematch the series- and parallel-resonant frequencies of the network such that the magnetizing inductance can be adaptively compensated for different sizes of air gap/misalignment. By doing so, the requirements of load-independent output voltage and unity input power factor can be simultaneously fulfilled, while zero-voltage switching on the primary bridge is still maintained under different coupling conditions by a single-stage converter. An experimental prototype with the air gap ranging from 10–16 cm is built to verify the idea. [ABSTRACT FROM AUTHOR]

Switching loss and conduction loss are two main loss mechanisms in dual-active-bridge (DAB) converter and the degree to which they affect the efficiency of DAB converter depends on the chosen power modulation scheme. In general, no single modulation scheme will perform optimally under all operating conditions. In this article, a hybrid modulation scheme and a new DAB converter topology designed for its realization are presented. The DAB converter is designed to switch between two operation modes—dynamic frequency matching (DFM) for medium- to full-load condition and enhanced dual-phase-shift (EDPS) modulation for light-load condition. Under DFM modulation, a switch-controlled capacitor is used to tune the resonant frequency of an LCL immittance network such that minimum rms current is guaranteed by unity-power-factor operation under different load conditions, leading to zero backflow power, zero circulating current, and zero-voltage switching (ZVS) operation of all switches. Under EDPS modulation, zero backflow power, and ZVS operation of all switches are achieved. These advantageous features are critical to ensuring a high-efficiency operation of DAB converter. The proposed solution is experimentally verified using a 1.5-kW hardware prototype with efficiency exceeding 96% for all output power levels. [ABSTRACT FROM AUTHOR]

This paper proposes a reconfigurable dual-active-bridge (DAB) converter that is capable of switching between two converter structures for enhancing its performances at different output power levels. For 50%–100% load, the converter operates in full-bridge mode and achieves soft-switching in all switches independently of the input-to-output voltage ratio. Below 50% load, the converter is reconfigured to operate in half-bridge mode for reduced circulating current and improved light-load efficiency while maintaining the desired soft-switching characteristic of full-bridge mode. The achievement of soft-switching is aided by the use of a tuned $LCL$ resonant tank, which enables an accurate prediction of the phases of tank currents with respect to tank voltages, and therefore simplifies the realization of soft-switching. The effects of dead time are discussed and expressions for guiding the selection of appropriate dead time for ensuring soft-switching in practical implementation are derived. The proposed converter and the modulation scheme are experimentally verified with a 1.6-kW converter prototype, which demonstrates their merits in comparison with a nonreconfigurable, full-bridge DAB topology and conventional modulation schemes. [ABSTRACT FROM AUTHOR]

This paper proposes a fifth-order resonant immittance network based dual-active-bridge (DAB) converter and an optimal modulation method that will ensure high-efficiency operation of the converter under wide-range variations in voltage ratio and output power level. The proposed modulation method is based on the concept of total power loss minimization, where a loss model is developed and an optimization algorithm is formulated to compute the optimal set of internal and external phase shift parameters that will lead to the maximum efficiency for a given set of operating parameters including voltage ratio and output power level. It is found that to maintain high-efficiency operation under wide-range variations in voltage ratio and output power level, the DAB converter is required to switch between different operation modes and neither soft-switching operation nor unity-power-factor operation is able to achieve wide-range high efficiency performance when used alone. The importance of $reconfigurability$ of operation mode for achieving wide-range high efficiency performance is clearly illustrated in this paper. [ABSTRACT FROM AUTHOR]