Masatoshi Uno

Ibaraki University · Department of Electrical and Electronic Engineering

High step‐up boost converters with large input current capacity are necessary for low‐voltage renewable energy sources, such as photovoltaic panels and fuel cells. Interleaved converters are a suitable topology for low‐voltage, large input current applications. Conventional interleaved converters, however, face a variety of challenges, such as the...

High step-up boost converters with large input current capacity are necessary for low-voltage renewable energy sources, such as photovoltaic panels and fuel cells. Interleaved converters are a suitable topology for low-voltage, large input current applications. Conventional interleaved converters, however, face a variety of challenges, such as the...

Voltages of series-connected energy storage cells, such as electric double-layer capacitors (EDLCs) and lithium-ion batteries, need to be equalized to ensure years of safe operation. However, to this end, a voltage equalizer is necessary in addition to a charger, increasing the system complexity and cost. This paper proposes a family of transformer...

Multiport converters (MPCs) that integrate multiple converters into a single unit have been proposed to reduce the converter count in electric vehicle power systems where multiple batteries are employed. However, conventional MPCs comprising a dual active bridge (DAB) converter and an interleaved PWM converter require feedback control loops and cur...

Multiport converters (MPCs) that can regulate multiple input/output ports have been proposed to reduce a converter count in electric vehicle battery systems consisting of multiple batteries (12-V, 48-V, and high-voltage batteries). Conventional MPCs consist of an interleaved PWM converter and DAB converter, and an active current balancing control i...

Ordinary modular energy storage systems require cell- and module-level equalizers, in addition to a main bidirectional converter, increasing the system complexity and cost. This article proposes a bidirectional buck-boost converter using cascaded energy storage modules. Each module contains a cell-level equalizer with a half-bridge cell. The half-b...

Multiport converters (MPCs) that integrate multiple converters into a single unit have been proposed to reduce the converter count in electric vehicle power systems where multiple batteries are employed. However, conventional MPCs comprising a dual active bridge (DAB) converter and an interleaved PWM converter require feedback control loops and cur...

Voltages of electric double-layer capacitor (EDLC) modules vary rather wider than traditional secondary batteries. Although EDLCs should desirably be cycled in a voltage range as wide as possible to achieve a high energy utilization ratio, the wide voltage variation of EDLC modules impairs the performance of DC–DC converters. To address such issues...

Lithium-ion batteries in electric vehicles must be adequately heated at low temperatures to prevent the decrease in discharge capacity. Therefore, ac heating techniques that use the Joule heat generated by the internal resistance of batteries have been proposed. Although these techniques achieve higher heating efficiency and uniform heating, they r...

Various kinds of differential power processing (DPP) converters have been developed to improve the energy yield of partially-shaded photovoltaic (PV) panels by addressing partial shading issues, such as the reduction in power generation and the occurrence of multiple maximum power points (MPPs). Meanwhile, PV systems require fault diagnosis tools t...

Photovoltaic (PV) systems consist of multiple dc-dc converters, such as a front-end converter for a PV panel and a bidirectional converter for battery regulation. In addition, a differential power processing (DPP) converter is desirably installed to preclude partial shading issues of the significant reduction in energy yield and the occurrence of m...

To meet the increasing demand for high-power isolated converters, interleaved LLC converters are being extensively studied. However, traditional interleaved LLC converters need auxiliary circuits or bulky magnetic components to achieve current balancing among parallel-connected phases, resulting in increased circuit complexity and volume. The autom...

Partial shading on a photovoltaic (PV) panel consisting of multiple substrings is known to trigger a significant reduction in energy yield and the occurrence of multiple maximum power points (MPPs), including one global and multiple local MPPs. Uneven irradiance on curved PV panels, such as flexible panels and solar roofs of electric vehicles, also...

Interest in photovoltaic systems, which are a renewable energy technology that transforms the energy from the Sun into electricity using photovoltaics, or solar panels, is on the rise. With non-renewable energy sources such as coal and fuel recognised as finite, the importance of improving renewable sources, such as solar energy, is more and more p...

Interleaved converters are a typical solution to enhance a current capacity and to reduce current ripples of an input or output port. Conventional interleaved LLC resonant converters need additional switches and passive components with a feedback control loop for active current balancing, increasing the circuit complexity and cost. This paper propo...

Partial shading on photovoltaic (PV) strings consisting of multiple panels connected in series is known to trigger severe issues, such as reduced energy yield and the occurrence of multiple power point maxima. Various kinds of differential power processing (DPP) converters have been proposed and developed to prevent partial shading issues. Voltage...

Partial shading often appears on photovoltaic (PV) strings installed in small space probes, such as moon exploration rovers, due to their body structures, reducing the power yield of PV strings. Such partial shading issues can be precluded by differential power processing (DPP) converters. However, in addition to a main dc-dc converter, a DPP conve...

Conventional microinverter or moduleintegrated converter (MIC)-based photovoltaic (PV) systems are prone to be complex and costly because each MIC requires not only a boost converter to bridge a huge voltage gap between a PV panel and grid but also desirably a differential power processing (DPP) converter to preclude partial shading issues. This pa...

Conventional photovoltaic (PV) systems require not only a converter for string control but also preferably a voltage equalizer to preclude partial shading issues, which increases the system complexity because two separate converters are necessary. A single‐switch, single‐magnetic pulse width modulation (PWM) converter integrating a series‐resonant...

Single-cell battery power systems are a promising bus architecture for small scientific satellites. However, to bridge the huge voltage gap between a single-cell battery and power bus, bidirectional converters with a high voltage conversion ratio and a large current capability for the low-voltage side are necessary. This article proposes a bidirect...

Voltages of series-connected batteries gradually become imbalanced due to non-uniformity 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...

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. PWM SCCs...

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 contro...

Partial shading on a photovoltaic (PV) panel comprising of multiple substrings connected in series leads to major issues, such as decreased power generation and occurrence of multiple power point maxima. Various PV equalizers have been proposed to preclude partial shading issues. However, system complexity increases because of the addition of PV eq...

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 PWM con...

Differential power processing converters and voltage equalizers have been proposed and used for photovoltaic (PV) string comprising multiple modules/substrings connected in series in order to preclude negative influences of partial shading. The single-switch voltage equalizer using multi-stacked buck-boost converters can significantly reduce the ne...

In conventional energy storage systems using series-connected energy storage cells such as lithium-ion battery cells and supercapacitors (SCs), an interface bidirectional converter and cell voltage equalizer are separately required to manage charging/discharging and ensure years of safe operation. In this paper, a bidirectional PWM converter integr...

Partial shading on a photovoltaic (PV) string comprising multiple modules/substrings triggers issues such as a significant reduction in power generation and the occurrence of multiple maximum power points (MPPs), including a global and local MPPs, that encumber MPP tracking algorithms. Single-switch voltage equalizers using multi-stacked buck-boost...

Cell voltage equalizers are necessary to ensure years of operation and maximize the chargeable/dischargeable energy of series-connected supercapacitors (SCs). A two-switch voltage equalizer using a series-resonant voltage multiplier operating in frequency-multiplied discontinuous conduction mode (DCM) is proposed for series-connected SCs in this pa...

Various kinds of differential power processing (DPP) 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, tha...

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 relati...

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 multi-winding transformer, resulting in comple...

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 connec...

A pumpless reactant recirculation system that offers several major advantages over conventional pump‐ or ejector‐based recirculation systems is derived on the basis of the analogy between fluid flow and an electrical circuit. According to the electricity–fluid analogy, a fuel cell fluid system, including a cell and a reactant recirculation device,...

It is an object to provide a circuit for equalizing voltages of energy storage cells, with less number of element and simpler circuit configuration than ever before. A plurality of field-effect transistors are arranged such that each of a plurality of parallel circuits formed, in one of connection states attained by switching of the switches, by co...

A photovoltaic (PV) string comprising multiple modules/sub-modules connected in series is well known to suffer from partial shading issues, such as decreased power generation and the occurrence of multiple power-point maxima. Although various kinds of differential power processing converters and voltage equalizers that can preclude partial-shading...

A two-switch voltage equalizer using a half-bridge converter with multi-stacked current doublers (MSCDs) is proposed for series-connected batteries in this paper, for which only two switches are required, regardless of the number of batteries connected in series. The proposed equalizer is also capable of relatively large equalization currents witho...

A double-switch cell voltage equalizer using a parallel-resonant-inverter (PRI) or series-parallel-resonant inverter (SPRI) and voltage multiplier is proposed for seriesconnected supercapacitors (SCs), such as electric double-layer capacitors (EDLCs) and lithium-ion capacitors. The double-switch operation without the need for a multiwinding transfo...

Voltage equalization is essential for series-connected energy storage cells, such as lithium-ion cells and supercapacitors (SCs), because it ensures years of service life and maximizes the available energies of cells. Conventional equalizers and multi output chargers require many switches and/or a multiwinding transformer, which are not desirable i...

Although switched capacitor converters (SCCs) offer high power density and a miniature footprint, applications of SCCs have been mainly limited to unregulated converters because the voltage conversion ratio of conventional SCCs is basically not controllable. This paper proposes a PWM-SCC that provides PWM-controllable high step-down voltage convers...

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 multi-winding transformer in proportion to the number of series conne...

A novel cell equalizer using a parallel-resonant inverter (PRI) and voltage multiplier (VM) is proposed. The required number of switches and magnetic components can be dramatically reduced compared to conventional equalizers, thus achieving simplified circuitry and compactness. In addition, the proposed equalizer can work safely, even in the event...

Series connections of energy-storage modules such as electric double-layer capacitors (EDLCs) and lithium-ion batteries result in voltage imbalance because of the nonuniform properties of individual modules. Conventional voltage equalizers based on traditional DC-DC converters require numerous switches and/or transformers, and therefore their costs...

http://dx.doi.org/10.5772/52215

The feasibility of a spacecraft power system using lithium-ion capacitors (LICs) as the energy storage source is analyzed and compared to a system using lithium-ion batteries (LIBs). The mass of the LIB- and LIC-based power systems, including PV arrays, are compared at various DoD levels. The LIC-based system at deep DoD of 60–80% can be comparable...

Supercapacitors (SCs), which are mainly used in high-power applications, can be potential energy storage sources for alternative battery applications once their outstanding cycle life performance at wide temperature ranges is considered. Because the cycle life of SCs is inherently long, aging acceleration and cycle life prediction are of primary im...

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 s...

Cell voltage equalizers are necessary to ensure years of operation for series-connected supercapacitors (SCs) by eliminating cell voltage imbalance. Conventional equalizers require numerous switches and/or magnetic components, and hence the circuit complexity and size tend to increase. In this paper, a double-switch single-transformer equalizer, wh...

Conventional cell/module voltage equalizers or equalization chargers based on traditional DC-DC converters require numerous switches or transformers as the number of series connections increases; therefore, their cost and complexity tend to increase and their reliability decreases as the number of connections increases. This paper proposes a novel...

Series connections of energy-storage modules such as electric double-layer capacitors (EDLCs) and lithium-ion batteries result in voltage imbalance because of the nonuniform properties of individual modules. Conventional voltage equalizers based on traditional dc-dc converters require numerous switches and/or transformers, and therefore, their cost...

A cell voltage equalizer using a series-resonant inverter and voltage multiplier is proposed. Unlike conventional equalizers that require multiple switches and/or magnetic components, the proposed equalizer can be configured with two switches and a single magnetic component. This means the circuitry can be significantly simplified and scaled down c...

Cell equalizers are usually used for series-connected energy storage cells, such as lithium-ion cells and supercapacitors (SCs), to eliminate voltage imbalance that may cause premature deterioration and reduce the available energies of the cells. Because conventional cell equalizers are based on multiple individual bidirectional dc-dc converters, t...

A novel single-switch cell voltage equalizer using voltage multipliers for series-connected supercapacitors (SCs) is proposed. Since the proposed equalizer can operate with a single switch at a fixed duty cycle when operated in discontinuous conduction mode (DCM), the circuit complexity can be reduced significantly when compared with conventional e...

Although supercapacitors (SCs) offer many advantages over traditional secondary batteries, they have two major drawbacks—low specific energy and large voltage variations due to cycling. For SCs to be used as alternatives to batteries, a high efficiency power converter that can operate in a wide voltage range is required to maximize the use of the s...

Supercapacitors (SCs) have potential to be good alternatives to batteries in satellite power systems because they not only have a longer life but also reduce the mass of photovoltaic arrays when they are charged using a constant-power (CP) charging scheme. In this paper, we propose singles-witch CP equalization chargers using multi-stacked buck-boo...

The cell voltage imbalance of series-connected energy storage cells, such as supercapacitors (SCs) and lithium-ion cells, causes premature deterioration and a decrease in the available energies of the cells. Various equalization techniques have been developed for diminishing such imbalances. However, since the number of switches, sensors, and/or mu...

Proton exchange membrane fuel cells are operated using switching power converters that produce highfrequency ripple currents. These ripples cause high-frequency potential cycling of cells, which is believed to lead premature deterioration in the electrochemical surface area (ECA) of Pt/C catalysts. The qualitative relationship between ECA losses an...

A lithium-ion battery was developed using off-the-shelf pouch cells and launched with a small scientific satellite “REIMEI.” The cells were potted with polyurethane or epoxy resin to protect the battery from vacuum in space. Preliminary experimental test results of pouch cells potted in a soft aluminum cap suggested that the cells tended to swell i...

Cell voltage equalizers are usually used for series-connected energy storage cells, such as lithium-ion cells and supercapacitors (SCs), to eliminate cell voltage imbalance that may cause premature deterioration and reduce the available energy of the cells. Because conventional cell voltage equalizers are based on multiple individual dc-dc converte...

Since supercapacitors (SCs) have inherently long life, they can be an alternative energy storage source to traditional secondary batteries in long-life applications where the batteries are cycled with shallow depth of discharge to extend their cycle life. Cycle life performance tests were conducted under various cycling conditions in order to evalu...

This paper describes the outline and the five years' on-orbit results of the small scientific satellite REIMEI for aurora observations and demonstrations of advanced small satellite technologies. REIMEI is a small satellite with 72 kg mass, and is provided with three-axis attitude control capabilities for aurora observations. REIMEI was launched in...

Electric double-layer capacitors (EDLCs) offer several advantages over traditional batteries, such as long cycle life, high power capability, good low-temperature performance, etc. However, their major drawbacks, such as low specific energy and large voltage variation due to charge/discharge cycling, necessitate the use of high-efficiency power con...

Various types of cell voltage equalizers that exchange charges among cells have been proposed for series-connected lithium-ion cells. During equalization, cells are possibly cycled not only over a conventional period that ranges from seconds to hours but at a high frequency that is equal to the operating frequency of the equalizers as well. This pa...

When electric double-layer capacitors (EDLCs) are connected in series, cell voltage imbalance that results due to non-uniform cell properties is observed. 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 tha...

Conventional cell/module voltage equalizers or equalization chargers based on traditional dc-dc converters require numerous switches or transformers as the number of series connections increases; therefore, their cost and complexity tend to increase and their reliability decreases as the number of connections increases. This paper proposes a novel...

Power conversion electronics for photovoltaic (PV) systems are desired to operate as efficiently as possible to exploit the power generated by PV modules. This paper proposes a novel PV system in which a dc-dc converter is partially connected to series-connected PV modules. The proposed system achieves high power-conversion efficiency by reducing t...

Series-connected energy storage modules such as supercapacitors (SCs) and lithium-ion batteries cause module voltage imbalances that lead to premature deterioration of modules. Various equalization techniques have been proposed for series-connected energy storage cells/modules to alleviate such voltage imbalances. However, since the conventional to...

To minimize the wastage of supplied reactant, fuel cells need to be operated in either dead-end or recirculation modes. A fuel cell operating in a dead-end mode is not durable without periodic purging because of flooding; therefore, a little reactant is unavoidably wasted. Conventional recirculation systems employ mechanical pumps or ejectors as th...

Conventional cell equalizers based on dc-dc converters require many switches or transformers as the number of series connections increases, raising their cost and complexity and decreasing reliability. This paper proposes a novel equalization charger that consists only of a capacitor-diode network and an ac power source. A dual capacitor-diode netw...

Unreacted fuel expelled from the outlet of fuel cells should be recirculated back to the inlet if wastage of the fuel must be minimized. Conventional recirculation systems employ mechanical pumps that consume electrical power and generate vibration and noise. This paper derives the pump-less recirculation system based on the analogy between electri...

Conventional voltage equalizers or equalization chargers, which are used for series-connected energy storage cells to eliminate cell voltage imbalance, consisting of a number of switches or transformers tend to be complex with the number of series connection of the energy storage cells. A novel voltage equalization charger consisting only of capaci...

DC-DC converters are commonly used as an interface between a photovoltaic (PV) module and a load because the characteristics of PV modules vary with environmental conditions. In a conventional system, all the power extracted from the PV modules is transferred through the converter with an efficiency penalty; thus, the converter must operate as effi...

Series-connected energy storage cells require cell equalizers in order to mitigate cell voltage imbalance. Conventional cell equalizers, however, consist of a number of switches or transformers that are considered not preferable in the viewpoint of circuit complexity and reliability. This paper proposes an equalization charger that consists of a si...

Conventional cell equalizers derived from dc-dc converters consist of numerous switches, sensors, or transformers; thus, their cost and circuit complexity are high. In this paper, Cockcroft-Walton charge equalizers consisting only of capacitors, diodes, and an ac power source are presented. In addition, a novel charge equalizer that outperforms the...

One of the most commonly used cell equalizers, the shunting equalizer, exhibits interactive performance with series connected energy storage cells. Experimental charging tests were carried out on series connected supercapacitors or lithium-ion cells to investigate this interactive performance. This paper presents and analyzes the charging performan...

Proton exchange membrane fuel cell offers higher energy density than the existing battery technologies for high-energy applications, and it is a promising power source for various industries including aerospace vehicles. We have been developing and testing a non-external humidified fuel cell system for high-altitude balloons, which require simple,...

Series connection of supercapacitors (SCs) leads to cell voltage imbalance due to individual differences in cell properties. Cell voltage imbalance should be minimized to prolong cycle lives and maximize the available energies of SCs. In this paper, an equalization technique utilizing series-parallel connected SCs, which is considered to be suitabl...