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Voltages of series-connected batteries gradually become imbalanced due to nonuniformity in terms of not only battery characteristics but also self-discharge rate that is significantly dependent on temperature. In large-scale energy storage systems, a large temperature gradient is very likely because of its huge geometry, and therefore, equalizers capable of relatively large equalization currents would be necessary to eliminate voltage imbalance originating from uneven temperature distribution. A two-switch string-to-battery voltage equalizer using a half-bridge converter with multistacked current doublers (MSCDs) is proposed for series-connected batteries in this paper. The proposed equalizer is capable of providing relatively large equalization currents without increasing ripple currents thanks to the interleaved operation of the MSCDs. Fundamental operational analysis for a discontinuous conduction mode, in which currents in the equalizer can be limited to desired levels without feedback control, is performed. The experimental results of equalization tests performed for four supercapacitor modules and lithium-ion batteries connected in series demonstrated the equalization performance of the proposed equalizer. [ABSTRACT FROM AUTHOR]

High step-down voltage conversion is necessary to bridge the voltage gap between main power converters and low-voltage auxiliary electronics in power conversion systems. Switched capacitor converters (SCCs) are an attractive candidate as a high step-down converter, but their poor voltage regulation capability may limit their applications. Pulsewidth modulation (PWM) SCCs with adjustable high step-down voltage conversion are proposed in this paper. The proposed PWM SCCs can be derived from traditional SCCs by replacing an energy transfer capacitor with a switched-capacitor-inductor (SCL) cell that comprises inductors, capacitors, and diodes to realize PWM-controllable voltage conversion. The voltage step-down ratio of the proposed PWM SCCs is not only PWM controllable but also adjustable with structures of SCCs and SCL cells. Two representative PWM SCCs were taken as examples to perform the operational analysis. The prototypes of both representative PWM SCCs were built and tested to demonstrate the proposed concept. [ABSTRACT FROM AUTHOR]

To prevent partial-shading issues in photovoltaic (PV) systems, various kinds of voltage equalizers that virtually unify characteristics of shaded and unshaded modules have been proposed. Although PV string utilization can be dramatically improved, PV systems tend to be complex and costly because, in addition to the main converter for string control, voltage equalizers are separately necessary. This paper proposes the single-switch single-magnetic pulse width modulation (PWM) converter integrating the voltage equalizer using the series-resonant voltage multiplier (SRVM) for standalone PV systems. By utilizing a square wave voltage generated across a filter inductor in a PWM buck converter for driving the SRVM, the main PWM converter and voltage equalizer can be integrated into a single unit with reducing the total switch and magnetic component counts, achieving not only system-level but also circuit-level simplifications. The experimental test using the prototype for three PV modules connected in series was performed emulating a partial-shading condition. The integrated converter effectively precluded the partial-shading issues and significantly improved the power available at a load, demonstrating its efficacy. [ABSTRACT FROM AUTHOR]

Power systems for exploration rovers tend to be complex as three separate converters are necessary; in addition to a main dc–dc converter and cell equalizer for rechargeable energy storage cells, an equalizer for photovoltaic (PV) modules is desirably equipped in order to preclude negative impacts of partial shading. This paper proposes the pulse width modulation (PWM) converter integrating voltage equalizers for PV modules and energy storage cells. The proposed integrated converter comprises a switched capacitor converter, PWM buck converter, and series-resonant voltage multiplier that perform PV equalization, power conversion from the PV modules to the load, and cell equalization, respectively. Three converters can be integrated into a single unit with reducing the total switch counts, achieving not only system-level but also circuit-level simplifications. The derivation procedure of the integrated converter is explained, followed by the operation analysis. Experimental tests were performed using series-connected supercapacitor (SC) modules and solar array simulators to emulate a partial shading condition. With the integrated converter, the extractable maximum power from the PV modules significantly increased while voltage imbalance of SC modules was adequately eliminated, demonstrating the integrated performance of the proposed converter. [ABSTRACT FROM AUTHOR]

Lithium-ion capacitors (LICs) are a hybrid energy storage device combining the energy storage mechanisms of lithium-ion batteries (LIBs) and electric double-layer capacitors (EDLCs), and are considered attractive not only in high-power applications but also as an alternative to rechargeable batteries due to their inherent long cycle life and relatively high energy density. The cycle life testing was performed for commercial-off-the-shelf (COTS) LIC cells procured from three different manufactures, and the cycle life prediction model developed for EDLCs in the previous work was applied to LICs. Based on the resultant capacitance retention trends, the activation energies of degradation ratios were calculated using an Arrhenius equation, whereupon aging acceleration factors were determined. The calculated acceleration factors varied depending on manufacturers, suggesting that a proper aging acceleration factor should be determined for each manufacture cell based on cycle life testing rather than simply applying a rule of thumb which had been accepted for LIBs and EDLCs. The resulting and predicted capacitance retention trends correlated well, verifying that the cycle life prediction model established for EDLCs in the previous work would also be usable for LICs as an alternative to rechargeable batteries. [ABSTRACT FROM PUBLISHER]

Various kinds of differential power processing converters and voltage equalizers have been proposed for series-connected photovoltaic (PV) modules to prevent negative influences of partial shading, such as significant reduction in power generation and the occurrence of multiple maximum power points (MPPs), including local and global MPPs, that hinders and confuses MPP tracking algorithms to operate properly. However, since conventional topologies are based on multiple individual dc–dc converters, the required switch count increases proportionally to the number of modules connected in series, increasing the complexity. A two-switch voltage equalizer using an LLC resonant inverter and voltage multiplier is proposed in this paper. The circuitry can be dramatically simplified compared with conventional topologies due to the two-switch configuration. Detailed operation analyses for the LLC resonant inverter and voltage multiplier are separately performed. Experimental equalization tests emulating partially shaded conditions were performed for four PV modules connected in series. With the proposed voltage equalizer, local MPPs successfully disappeared, and extractable maximum power increased compared with those without equalization, demonstrating the effectiveness and performance of the proposed voltage equalizer. [ABSTRACT FROM PUBLISHER]

Series connections of energy storage cells, such as lithium-ion cells and electric double-layer capacitors (EDLCs), require cell-voltage equalizers to ensure years of operation. Conventional equalizers require multiple switches, magnetic components, and/or secondary windings of a multiwinding transformer in proportion to the number of series connections, which usually makes them complex, expensive, bulky, and less extendable with increasing series connections. A double-switch seriesresonant equalizer using a voltage multiplier is proposed in this paper. The double-switch operation without a multiwinding transformer achieves simplified circuitry and good modularity at reduced size and cost, compared to conventional equalizers. Operational analyses were separately performed for the following two functional parts of the proposed equalizer: a series-resonant inverter and a voltage multiplier. The mathematical analyses derived a dcequivalent circuit of the proposed equalizer, with which simulation analyses of even an hour's duration can be completed in an instant. Simulation analyses were separately performed for both the original and equivalent circuits. The simulation results of the derived circuit correlated well with those of the original circuit, thus verifying the derived dc-equivalent circuit. A 5-W prototype of the proposed equalizer was built for eight cells connected in series and an experimental equalization was performed for seriesconnected EDLCs from an initially voltage-imbalanced condition. The voltage imbalance was gradually eliminated over time, and the standard deviation in the cell voltages decreased to approximately 5 mV at the end of the experiment, thus demonstrating the equalization performance of the proposed equalizer. [ABSTRACT FROM AUTHOR]

Cell voltage equalization is inevitable to ensure years of safe operation of series-connected energy storage cells, such as lithium-ion batteries and supercapacitors (SCs). Although various kinds of cell voltage equalizers have been proposed, most equalizer topologies require multiple switches and/or a multiwinding transformer, resulting in complex circuitry and poor modularity. In this paper, a single-switch single-transformer equalizer using a forward–flyback resonant inverter (FFRI) with a voltage multiplier is proposed. The required switch count of the proposed equalizer is the minimum without impairing modularity due to the single-switch circuitry with no need for a multiwinding transformer. An experimental equalization test performed for eight SCs connected in series successfully demonstrated the equalization performance of the proposed equalizer. The FFRI can be extended as a “resonant input cell,” and by combining one of resonant input cells and a voltage multiplier, a single-switch resonant equalization charger that is basically a charger with an equalization function is also derived. An experimental charging test using the resonant equalization charger was also performed, and its equalization-charging performance was demonstrated. [ABSTRACT FROM AUTHOR]

A double-switch cell voltage equalizer using a parallel-resonant-inverter (PRI) or series-parallel-resonant inverter (SPRI) and voltage multiplier is proposed for series-connected supercapacitors (SCs), such as electric double-layer capacitors (EDLCs) and lithium-ion capacitors. The double-switch operation without the need for a multiwinding transformer offers simpler circuitry as well as better modularity than conventional equalizers requiring multiple switches and/or a multiwinding transformer. Furthermore, the inherent constant current characteristic of the PRI/SPRI at a fixed frequency, not only removes the need for feedback control to limit currents under desired levels but the proposed equalizer can also operate safely, even when some cell voltage is 0 V. Detailed operation analyses were separately performed for the voltage multiplier and PRI/SPRI, and a dc equivalent circuit for the proposed equalizer was mathematically derived. A 10-W prototype for 12 cells connected in series was built, and an experimental equalization test was performed for EDLCs from an initially voltage imbalanced condition. Voltage imbalance of the series-connected EDLCs was successfully eliminated by the equalizer, demonstrating the equalization performance of the proposed equalizer. [ABSTRACT FROM AUTHOR]

When electric double-layer capacitors (EDLCs) are connected in series, a cell voltage imbalance occurs due to nonuniform cell properties. Cell voltage imbalance should be minimized to prolong cycle lives and maximize the available energy of cells. In this study, we propose a series-parallel reconfigurable cell voltage equalizer that is considered suitable for energy storage systems using EDLCs instead of traditional secondary batteries as the main energy storage sources. The proposed equalizer requires only EDLCs and switches as its main circuit elements, and it utilizes EDLCs not only for energy storage but also for equalization. An equivalent circuit model using equivalent resistors that can be regarded as an index of equalization speed is developed. Current distribution and cell voltage imbalancing during operation are quantitatively generalized. Experimental charge-discharge tests were performed on the EDLC modules to demonstrate the performance of the cell voltage equalizer. All the cells in the modules could be charged/discharged uniformly even when a degradation-mimicking cell was intentionally included in the module. The resultant cell voltage imbalances and current distributions were in good agreement with those predicted by mathematical analyses. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(4): 38-50, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21287 [ABSTRACT FROM AUTHOR]

The exploration of energization and radiation in geospace (ERG) satellite, nicknamed “Arase,” is the second satellite in a series of small scientific satellites created by the Institute of Space and Astronautical Science of the Japan Aerospace Exploration Agency. It was launched on December 20, 2016, by the Epsilon launch vehicle. The purpose of the ERG project is to investigate how high-energy (over MeV) electrons in the radiation belts surrounding Earth are generated and lost by monitoring the interactions between plasma waves and electrically charged particles. To measure these physical processes in situ, the ERG satellite traverses the heart of the radiation belts. The orbit of the ERG is highly elliptical and varies due to the perturbation force: the apogee altitude is approximately 32,200-32,300 km, and the perigee altitude is 340-440 km. In this study, we introduce the scientific background for this project and four major challenges that need to be addressed to effectively carry out this scientific mission with a small satellite: (1) dealing with harsh environmental conditions in orbit and electromagnetic compatibility issues, (2) spin attitude stabilization and avoiding excitation of the libration by flexible structures, (3) attaining an appropriate balance between the mission requirements and the limited resources of the small satellite, and (4) the adaptation and use of a flexible standardized bus. In this context, we describe the development process and the flight operations for the satellite, which is currently working as designed and obtaining excellent data in its mission. [ABSTRACT FROM AUTHOR]