• Energy Research

This work carries out a comparison of non-isolated topologies for power electronic converters applied to Hybrid Energy Storage Systems. At the considered application, several options for three-port circuits are evaluated when interfacing a DC link with two distinct electrical energy storage units. This work demonstrates how the proposed structure, referred to as Series-Parallel Connection, performs as a simple, compact and reliable approach, based on a modification of the H-bridge configuration. The main advantage of this solution is that an effective large voltage gain at one of the ports is attained by means of a simple topology, preventing the use of multilevel or galvanic-isolated power stages. The resulting structure is thoroughly compared against the most significant direct alternatives. The analysis carried out on the switching and conduction losses in the power switches of the target solution states the design constraints at which this solution shows a performance improvement. The experimental validations carried out on a 10 kW prototype demonstrate the feasibility of the proposed scheme, stating its benefits as well as its main limitations. As a conclusion, the Series-Parallel Connection shows a better performance in terms of efficiency, reliability and controllability in the target application of compensating grid or load variations in Non-Isolated Hybrid Storage Systems, with large mismatch in the storage device voltage ratings.

This work was supported in part by the Predoctoral Grant Programs Severo Ochoa and in part by the FPU for the Formation in Research and University Teaching of Principado De Asturias PCTI-FICYT under Grant ID PA-17-PF-BP16133 and Spain MECD under Grant ID FPU16/06829, in part by the Research, Technological Development and Innovation Program Oriented to the Society Challenges of the Spanish Ministry of Economy and Competitiveness under Grant MCIU-18-RTC-2017-6338-3 and Grant MCI-20-PID2019-111051RB-I00, in part by the European Union Through ERFD Structural Funds (FEDER) and in part by the H2020 Research and Innovation Programme under Grant 864459 (UE-19-TALENT-864459), and in part by the Cegasa Energía.

This paper proposes a novel solution for transient frequency compensation in weak 3-phase Microgrids (MGs) based on a Luenberger observer and a transient frequency detector. Unlike in conventional grids, the low inertia of the generators coupled to a MG could make their rotor speeds to be affected by load changes, varying the grid frequency and compromising the grid quality and stability. This problem has been approached in the literature by the Virtual Inertia (VI) concept. However, the existing solutions are affected by the decoupling of the grid frequency reference and the frequency estimation bandwidth. The proposed paper addresses these problems by the use of a transient frequency drift estimator based on a transient detector and a Luenberger type observer that provides a nearly-zero lag frequency estimation. The proposed alternative is analytically compared with the existing techniques and validated through simulation and exhaustive experimental results in an islanded MG. The developed method enables a 1Hz reduction in the transient frequency deviation when compared with the existing alternatives and improves the system stability. PCTI-FICYT under grants ID BP13-138, BP14- 135 and BP16-133 Research, Technological Development and Innovation Program Oriented to the Society Challenges of the Spanish Ministry of Economy and Competitiveness under grants ENE2013-44245-R and ENE2016-77919-R. European Union through ERFD Structural Funds (FEDER).

In this work, an in-depth investigation was performed on the properties of the half-bridge current-source (HBCS) bidirectional direct current (DC)-to-DC converter, used to interface two DC-link voltage sources with a high-voltage-rating mismatch. The intended implementation is particularly suitable for the interfacing of a supercapacitor (SC) module and a battery stack in a hybrid storage system (HSS) for automotive applications. It is demonstrated that the use of a synchronous rectification (SR) modulation scheme benefits both the power-stage performance (in terms of efficiency and reliability) and the control-stage performance (in terms of simplicity and versatility). Furthermore, an average model of the converter, valid for every operating condition, is derived and utilized as a tool for the design of the control system. This model includes the effects of parasitic elements (mainly the leakage inductance of the transformer) and of the converter snubbers. A 3 kW prototype of the converter was used for experimental validation of the converter modeling, design, and performance. Finally, a discussion on the control strategy of the converter operation is included.

Research, Technological Development and Innovation Program Oriented to the Society Challenges of the Spanish Ministry of Economy and Competitiveness [MCIN/AEI/10.13039/501100011033, MCI-20-PID2019-111051RB-I00]; European Union through ERFD Structural Funds (FEDER) through H2020 Research and Innovation programme [864459 (UE-19-TALENT-864459)]

This work was partially supported by the Spanish Ministry of Innovation and Science under Grant MCINN-23-PID2022-139479OB-C22 funded by MCIN/AEI/10.13039/501100011033/FEDER, UE; Grant MCINN-22-TED2021-129796BC21 funded by MCIN/AEI/10.13039/501100011033; the Principality of Asturias, Spain, FICYT, Spain, FEDER, Spain funds under Grant SV-PA-21-AYUD/2021/57546; and by the predoctoral grants program FPI for research training of Spain MCIU under a grant ID PRE2020-093328.

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.