This paper explores the use of a variable inductor as an energy transfer reactive element in a Dual-Active-Bridge (DAB) converter. By using a controlled variable inductor, the optimal switching region in the operation of the phase-shift DAB can be extended, and thus high efficiencies can be achieved over wide-load ranges. Moreover, the combination of the variable inductance with the phase shift as two independent control parameters allows for the linearization of the DAB converter transfer function, which gives significant merit to the implementation of the control function. And finally, it is feasible to reduce the magnetic core size, due to the controlled saturation of the device. To study those proposed improvements, a circuitbased model is developed to simulate the converter system. Furthermore, a prototype is constructed for the DAB converter including a controlled variable inductor and preliminary experimental results are presented which validate the studies carried out.

This paper proposes and develops a circuit-based model aiming to simulate variable magnetic power elements in power electronic converters. The derived model represents the magnetic element by a reluctance-based equivalent circuit. The model takes into consideration device core losses, with the main emphasis given to hysteresis losses, which are modeled using the Jiles-Atherton model. The core loss model is further validated on different ferromagnetic materials to prove its range of applicability. The winding losses of the magnetic device are also taken into consideration, which are obtained using Dowell empirical formulas. In addition, the frequency dependence of the device losses is also considered. The proposed modeling procedure has been applied to study and characterize a double E-core variable power inductor structure in a 1 kW SiC full bridge DC-DC converter. The procedure has been verified by comparing the simulation results to the experimental measurements, confirming the validity and accuracy of the full circuit-based model.

Abstract-This paper is focused on establishing a procedure for measuring the efficiency dependency on the switching frequency for a solid state transformer (SST), being one of the ports connected to an energy storage device (Lithium-Ion battery). Multiple contributions for measuring the efficiency/losses for different power converter structures for energy storage applications can be found in the literature. However, there are few references which consider the effects of the high frequency model of the battery in the complete system performance. This research will obtain a parametric high frequency model of the battery cells, based on a vector fitting method in frequency domain. This model will be used for the estimation of the overall system losses. It will be demonstrated that the contribution of the battery losses, as well as its behavior as a function of the switching frequency, can significantly affect the selection of the converter's switching frequency.

In this paper, a full model to simulate variable magnetic elements in power electronic converters is developed. The derived model is based on the reluctance equivalent circuit of magnetic systems. Specifically, the model considers core losses, determined through Jiles-Atherton hysteresis model, and Eddy current losses obtained using Dowell empirical formulas. The frequency dependence of the device losses is also considered. The model is compared to experimental measurements in order to verify its validity and accuracy, and then it is applied to study and characterize the double E-core variable inductor structure.

This work presents a fault ride-through control scheme for a non-isolated power topology used in a hybrid energy storage system designed for DC microgrids. The hybrid system is formed by a lithium-ion battery bank and a supercapacitor module, both coordinated to achieve a high-energy and high-power combined storage system. This hybrid system is connected to a DC bus that manages the power flow of the microgrid. The power topology under consideration is based on the buck-boost bidirectional converter, and it is controlled through a bespoke modulation scheme to obtain low losses at nominal operation. The operation of the proposed control scheme during a DC bus short-circuit failure is shown, as well as a modification to the standard control to achieve fault ride-through capability once the fault is over. The proposed control provides a protection to the energy storage systems and the converter itself during the DC bus short-circuit fault. The operation of the converter is developed theoretically, and it has been verified through both simulations and experimental validation on a built prototype.

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Abstract-This work explores the Series-Parallel Connection of a Low Voltage SupercapacitorModule to obtain a Hybrid Energy Storage System for grid support applications. The Hybrid System is formed by the Supercapacitor Module itself, intended to ensure fast performance upon peak power requirements, together with a battery that provides the energy requirements. In the full system, the front end converter and the load interfacing converter share a common DC link. The battery is connected to the DC link by means of a Full-Bridge CurrentSource bidirectional DC-DC converter. The Supercapacitor Module is connected to the system using a Series-Parallel Configuration, which overcomes the main problems that arise with the most common topologies found in the literature. The full operation of the system has been demonstrated theoretically and by simulations. A demonstration of such connection is shown experimentally, in a converter operating at reduced power levels, in order to validate the feasibility of the system. Conclusions show how this scheme can be used in Hybrid Storage Systems.