Dr. Lizana-Fuentes, Ricardo

Energy storage systems (ESSs) allow improving the stability and efficiency of the electrical grids with a high penetration of renewable energy sources. Moreover, the use of Hybrid ESSs (HESSs) enables storage solutions with both high-energy and high-power densities, by combining different storage technologies such as diverse battery chemistries, ultracapacitors, or hydrogen fuel cells to name a few. In this article, an HESS-based multioutput multilevel (MOM) converter is presented. The proposed topology enables decoupled control of each ac converter voltage output. The internal switching states further allow the use of different storage units and high-quality multilevel voltage in each ac output. The mathematical model of the proposed topology and the defined operation region of the system, besides a model-predictive control strategy, are developed. Finally, simulation and experimental results validate the performance of the proposed topology.

Hybrid Energy Storage Systems (HESSs) have gathered considerable interest due to their potential to achieve high energy and power density by integrating different storage technologies, such as batteries and capacitors, to name a few. Among the various topologies explored for HESSs, the multi-output multilevel converter stands out as a promising option, offering decoupled operation of the AC ports while maintaining an internal balance among the diverse storage units. In this paper, the operation and restrictions of a HESS based on a multi-output multilevel converter with a carrier-based modulation scheme are presented. The study provides compelling evidence of the correct operation of the proposed modulation scheme and highlights its advantages, including simplicity and stability.

The increasing power levels handled by electric vehicle (EV) dc fast chargers will impose additional challenges to the switching devices in order to cope with the efficiency requirements. A cost-effective alternative to achieve highly efficient power conversion is through the partial-power conversion concept. This article validates the advantages of a step-down Type II partial-power converter (PPC), based on the phase-shifted full-bridge converter, for EV fast chargers. By exploiting the reduced voltage range of an EV battery pack along with the reduced power ratio for a Type II PPC, an extremely efficient charging process can be achieved. The concept is validated with the development of a 7-kW demonstrator, and hence, realistic efficiency measurements are obtained. Results indicate the effectiveness of charging a battery by merely handling 13.32% of the power provided to it, with a peak efficiency of 99.11%.

Electrification has been a key component of technological progress and economic development since the industrial revolution. It has improved living conditions, spurred innovation, and increased efficiency across all sectors of our economy and all aspects of our lives. During the coming decades, electrification is expected to reach further and deeper into the transportation, building, and industry sectors, mainly motivated by the energy transition to a zero-carbonemission-based economy to mitigate climate change.

This article provides a detailed analysis of the power electronics solutions enabling bipolar dc grids. The bipolar dc grid concept has proven to be more efficient, flexible, and higher in quality than the conventional unipolar one. However, despite its many features, these systems still have to overcome their issues with asymmetrical loading to avoid voltage imbalances, besides meeting regulatory and safety requirements that are still under development. Advances in power electronics and the large-scale deployment of dc consumer appliances have put this growing architecture in the spotlight, as it has drawn the attention of different research groups recently. The following provides an insightful discussion regarding the topologies that enable these architectures and their regulatory requirements, besides their features and level of development. In addition, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

This article proposes a novel bipolar-type dc system suitable for both distribution and transmission systems based on modular multilevel series/parallel converters (MMSPCs). The system features decoupled operations of each pole of the bipolar system, being able to operate in both asymmetrical and regenerative modes. This enables two independent dc systems by using a single grid-tied converter. The MMSPC is based on a three-switch cell configuration and enables a simple balancing mechanism in combination with a wide range of output voltage frequencies. The simple balancing mechanism is the key to enable the dc operation and lead to simpler scalability for different voltage levels. Theoretical studies and experimental results are provided to verify and characterize the proposed system.

Split-battery converters based on cascaded H-bridges (CHBs) are gaining popularity due to their excellent physical modularity. During operation, however, the batteries experience substantial current ripple. Conventional ripple-current reduction methods rely on bulky passive components or complicated control. This article presents modulation and common-mode voltage injection methods for cascaded double-H-bridge converters (CHB 2). The control methods directly mitigate the source of the ripple current—the fluctuating arm power—by exploiting the parallel interconnection across the CHB 2 arms. In the lab setup, the proposed solution approximately halves the battery current ripple compared to the CHB counterpart. Finally, this article studies component sizing and limitations of the proposed solution.

Cascaded H-bridge (CHB) converters are receiving growing attention in battery energy storage systems (BESS) due to their modularity and flexibility. However, direct generation of ac output in CHB-BESSs incurs large second-order current ripple in the batteries, which causes additional loss and might accelerate battery aging. Existing methods for ripple-current suppression usually require bulky passive components due to the high energy content of the ripple components. This paper presents a class of current injection methods for delta-configured CHB-BESSs. The injected currents flow through the CHB arms and transfer the original second-order oscillating power to the fourth or the sixth order, or even to an arbitrarily high-order frequency. As such, the battery current ripple appears at much higher frequencies with lower oscillating energy and can be easily filtered by small passive components. In the laboratory setup, the proposed methods reduced the battery root-mean-square current ripple to less than 10% of the dc component with negligible distortion in the loads. The proposed methods and the filter implementations show good tolerance to load frequencies and to the control error of the injected currents.

Modules with series and parallel connectivity add new features and operation modes to modular multilevel converters (MMCs). Compared to full- and half-bridges, the series/parallel modules allow sensorless module balancing and reduce conduction loss with the same semiconductor area. However, in high-voltage applications with limited switching rates, the sensorless operation of the series/parallel modules suffers from large charge-balancing currents. This paper introduces a series/parallel module variant with a small port inductor. The port inductor suppresses the charge-balancing current despite low switching rates. We also propose a carrier-based modulation framework and show the importance of the carrier assignment in terms of efficiency and balancing. The proposed module and the modulation method are verified on a lab setup with module switching rates down to 200 Hz. The module voltages are kept within a narrow band with the charge-balancing currents below 5% of the arm current. The experimental results show practicality and advantages of the new series/parallel modules in high-voltage MMC applications.

This paper presents a modular multilevel series/parallel converter (MMSPC) with intermodule switched-inductor power transfer. The switched-inductor voltage conversion feature allows controllable and efficient transfer of energy between modules with nonnegligible voltage difference, providing both step-down and step-up functionalities. Thus, this converter can accurately control and rapidly adjust the voltage of each module to generate an ac output voltage waveform with a controllable number of levels, increasing the quality of the output. Moreover, the intrinsic dc-dc conversion feature can generate a dc controllable output voltage and enable new applications. In this text, we specifically demonstrate how the flexibility of obtaining both ac and dc output with the same setup renders the topology promising for battery energy storage systems and dc microgrid applications. Experimental results validate the topology and concept of an MMSPC with intrinsic switched-inductor conversion.