Search

Battery energy storage system based on the modular multilevel converter (MMC-BESS) is able to realize the decentralized management of battery packs, which is suitable for the retired battery utilization to improve the efficiency of battery recycling. With multiple submodules (SM), the corresponding SM fault ride-through method is mandatory to improve operational reliability. This paper proposes a redistributed pulsewidth modulation method for MMC-BESS to ride-through the SM fault through employing the simple logic operation, which could avoid the unexpected carrier shift under various modulation indexes induced by the SM fault or grid voltage rise. MATLAB simulations and experimental results are presented to verify the performance of the proposed method. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) systems having rechargeable batteries are prone to be complex and costly because multiple converters are necessary to individually regulate a load, PV panel, and battery. This paper proposes novel nonisolated multiport converters (MPCs) integrating a bidirectional pulsewidth modulation (PWM) converter and phase-shift-switched capacitor converter (PS-SCC) for standalone PV systems. A PWM converter and PS-SCC are integrated by reducing the total switch count, realizing the simplified system and circuit. In the proposed MPCs, two control freedoms of duty cycle and phase shift angle are manipulated to individually regulate the load, PV panel, and/or battery. The detailed operation analysis was performed to mathematically derive gain characteristics and zero voltage switching operation boundaries. For the battery discharging mode, in which the PV panel is not available and the MPC behaves as a single-input–single-output converter with two control freedoms available, the optimized control scheme achieving the lowest rms current is also proposed to maximize power conversion efficiencies. Various kinds of experimental verification tests using a 200-W prototype were performed to verify the theoretical analysis and to demonstrate the performance of the proposed MPC. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper presents a novel design for a test platform to determine the state of health (SOH) of lithium-ion batteries (LIBs). The SOH is a key parameter of a battery energy storage system and its estimation remains a challenging issue. The batteries that have been tested are 18,650 Li-ion cells as they are the most commonly used batteries on the market. The test platform design is detailed from the building of the charging and discharging circuitry to the software. Data acquired from the testing circuitry are stored and displayed in LabVIEW to obtain the charging and discharging curves. The resulting graphs are compared to the outcome predicted by the battery datasheets, to verify that the platform delivers coherent values. The SOH of the battery is then calculated using a Coulomb counting method in LabVIEW. The batteries will be discharged through various types of resistive circuits, and the differences in the resulting curves will be discussed. A single battery cell will also be tested over 30 cycles and the decrease in the SOH will be clearly identified. [ABSTRACT FROM AUTHOR]

This paper proposes a new single-phase dc/ac converter topology with soft-switching operation. The proposed converter achieves soft-switching by using DCM (discontinuous current mode) operation and a common turn-off snubber capacitor connected to the dc terminals of a full-bridge configuration. One additional semiconductor switch is used to disconnect the snubber capacitor from the dc side, and allows the snubber capacitor to be discharged. The DCM operation realizes zero-current turn-on and the snubber capacitor achieves zero-voltage turn-off. The proposed converter can be applied to a grid-connected converter for domestic renewable energy and energy storage, including Photovoltaic and battery energy storage devices. This paper describes operation principles, control and modulation techniques as a grid-connecting converter. Experimental verification including loss analysis with a 1-kW pilot device is provided. [ABSTRACT FROM AUTHOR]

In this paper, a family of bidirectional dual-input dc/dc converters is proposed to combine a photovoltaic system and battery energy storage system. This family of converters utilizes a full-bridge, or half-bridge current-source circuit, as the primary side, and a quasi-switched-capacitor circuit as the secondary side. Depending on the power level of the primary side and voltage level of the battery, different topologies can be selected. Compared to other bidirectional multiple-input dc/dc converters with galvanic isolation, this family of converters requires less switches and passive components, reduces voltage stress on switches, and realizes soft switching for all switches. The operation principle of the converter is presented, and a power sharing strategy between two input sources is proposed. A 2-kW full-bridge circuit prototype is built in the lab, based on Gallium Nitride (GaN) switching devices. Simulation and experimental results are also presented to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, a novel dual-battery energy storage system (DBESS) is proposed to firmly dispatch the intermittent wind power onto the grid with a lower system operation cost. Thanks to the DBESS, a wind farm can commit to integrate constant power in each dispatching time interval. In the proposed DBESS, the battery energy storage system (BESS) that takes the charged role is active when the dispatch power is lower than the wind power, and another is enabled if the dispatch power is higher than the wind power. These roles of the BESSs switch when one BESS is either fully charged or deeply discharged. To extend the BESS lifetime, the dispatch power is optimized to ensure both BESSs are operating under full charge–discharge cycles, so the system's operating cost is reduced significantly by using the proposed DBESS. In addition, short-term power dispatch control is considered to deal with wind power forecasting errors. In order to evaluate the proposed optimized system, we performed several numerical studies using a 3-MW wind turbine generator with real wind power data. Moreover, a wind-battery power test bed is implemented in the laboratory to validate the feasibility of the proposed DBESS. [ABSTRACT FROM PUBLISHER]

This paper describes a diode-clamped three-level inverter-based battery/supercapacitor direct integration scheme for renewable energy systems. The study is carried out for three different cases. In the first case, one of the two dc-link capacitors of the inverter is replaced by a battery bank and the other by a supercapacitor bank. In the second case, dc-link capacitors are replaced by two battery banks. In the third case, ordinary dc-link capacitors are replaced by two supercapacitor banks. The first system is supposed to mitigate both long-term and short-term power fluctuations while the last two systems are intended for smoothening long-term and short-term power fluctuations, respectively. These topologies eliminate the need for interfacing dc-dc converters and thus considerably improve the overall system efficiency. The major issue in aforementioned systems is the unavoidable imbalance in dc-link voltages. An analysis on the effects of unbalance and a space vector modulation method, which can produce undistorted current even in the presence of such unbalances, are presented in this paper. Furthermore, small vector selection-based power sharing and state of charge balancing techniques are proposed. Experimental results, obtained from a laboratory prototype, are presented to verify the efficacy of the proposed modulation and control techniques. [ABSTRACT FROM AUTHOR]

This paper presents a boost-multilevel inverter design with integrated battery energy storage system for standalone application. The inverter consists of modular switched-battery cells and a full-bridge. It is multifunctional and has two modes of operation: 1) the charging mode, which charges the battery bank and 2) the inverter mode, which supplies ac power to the load. This inverter topology requires significantly less power switches compared to conventional topology such as cascaded H-bridge multilevel inverter, leading to reduced size/cost and improved reliability. To selectively eliminate low-order harmonics and control the desired fundamental component, nonlinear system equations are represented in fitness function through the manipulation of modulation index and the genetic algorithm (GA) is employed to find the optimum switching angles. A seven-level inverter prototype is implemented and experimental results are provided to verify the feasibility of the proposed inverter design. [ABSTRACT FROM AUTHOR]

This paper provides a theoretical and experimental discussion about the performance, availability, and flexibility of a battery energy storage system (BESS) using a modular multilevel cascaded converter based on single-star bridge cells (MMCC-SSBC). The SSBC-based BESS produces three-phase multilevel voltage waveforms, and eliminates both harmonic filters and a complicated zig-zag transformer from the ac side. The circuit modularity of the SSBC enables the usage of multiple individual low-voltage battery modules. Along with control strategy based on zero-sequence-voltage injection, this modularity enhances the availability and flexibility of the BESS. A three-phase laboratory downscaled system rated at 140 V, 10 kW, and 21 kW·h is designed, constructed, and tested to verify the operating principles and performance. The tested BESS produces a current total harmonic distortion (THD) of 3.0% even when it operates with different active-power commands for individual bridge cells. In addition, zero-voltage ride-through capability is verified for the severest single-phase, two-phase, and three-phase voltage sags. Mathematical analysis and experimental verification validate the downscaled system and performance, making the BESS prospective. [ABSTRACT FROM PUBLISHER]