Series-connected Cells Research Articles

Single dc‐source‐based seven‐level boost inverter for electric vehicle application

This study offers an effective circuit arrangement of a multilevel inverter that can increase the number of output voltage levels with a lesser number of device count. A single dc-source-based seven-level inverter (LI) with boosting capability is proposed in this study. The proposed inverter utilises eight switches, two diodes, two capacitors, one inductor and a single dc source to generate seven-level boosted output. Usage of single dc source and boosting capability makes the proposed inverter suitable for electric vehicles as less number of series-connected battery cells are required. Phase-shifted pulse-width modulation (PWM), a multi-carrier-based PWM technique is utilised to generate switching pulses for the proposed 7LI. Device count-based comparative analysis of the proposed inverter with recent topologies is done. Viability and impact of the proposed inverter are analysed through simulation and are validated through laboratory prototype.

Assessment of the Impact of Stagnation Temperatures in Receiver Prototypes of C-PVT Collectors

Concentrating Photovoltaic Thermal (C-PVT) solar collectors produce both thermal and electric power from the same area while concentrating sunlight. This paper studies a C-PVT design where strings of series-connected solar cells are encapsulated with silicone in an aluminium receiver, inside of which the heat transfer fluid flows, and presents an evaluation on structural integrity and performance, after reaching stagnation temperatures. Eight test receivers were made, in which the following properties were varied: Size of the PV cells, type of silicone used to encapsulate the cells, existence of a strain relief between the cells, size of the gap between cells, and type of cell soldering (line or point). The test receivers were placed eight times in an oven for one hour at eight different monitored temperatures. The temperature of the last round was set at 220 °C, which exceeds the highest temperature the panel design reaches. Before and after each round in the oven, the following tests were conducted to the receivers: Electroluminescence (EL) test, IV-curve tracing, diode function, and visual inspection. The test results showed that the receivers made with the transparent silicone and strain relief between cells experienced less microcracks and lower power degradation. No prototype test receiver lost more than 30% of its initial power, despite some receivers displaying a large number of cell cracks. The transparent and more elastic silicone is better at protecting the solar cells from the mechanical stress of thermal expansion than the compared silicone alternative, which was stiffer. As expected, larger cells are more prone to develop microcracks after exposure to thermal stress. Additionally, existing microcracks tend to grow in size relatively fast under thermal stress. EL imaging taken during our experiment leads us to conclude that it is far more likely for existing cracks to expand than for new cracks to appear.

Transient Temperature Distributions on Lithium-Ion Polymer SLI Battery

Lithium-ion polymer batteries currently are the most popular vehicle onboard electric energy storage systems ranging from the 12 V/24 V starting, lighting, and ignition (SLI) battery to the high-voltage traction battery pack in hybrid and electric vehicles. The operating temperature has a significant impact on the performance, safety, and cycle lifetime of lithium-ion batteries. It is essential to quantify the heat generation and temperature distribution of a battery cell, module, and pack during different operating conditions. In this paper, the transient temperature distributions across a battery module consisting of four series-connected lithium-ion polymer battery cells are measured under various charging and discharging currents. A battery thermal model, correlated with the experimental data, is built in the module-level in the ANSYS/Fluent platform. This validated module thermal model is then extended to a pack thermal model which contains four parallel-connected modules. The temperature distributions on the battery pack model are simulated under 40 A, 60 A, and 80 A constant discharge currents. An air-cool thermal management system is integrated with the battery pack model to ensure the operating temperature and temperature gradient within the optimal range. This paper could provide thermal management design guideline for the lithium-ion polymer battery pack.

Antimony sulfide selenide prototype photovoltaic modules surpassing 4% conversion efficiency under the sun – A technological outlook

We discuss the performance under the sun, at intensity 1000 W/m2, of prototype photovoltaic modules of antimony sulfide selenide thin films, Sb2S1.06Se1.94, with optical bandgap, 1.35 eV. At 26 °C, a module of seven series-connected cells of total active area 6.97 cm2 has conversion efficiency (η) of 4.38% with open-circuit voltage (Voc), 3.13 V; short circuit current (Isc), 21.2 mA and maximum power (Pm) of 30.5 mW. Under steady state operation at 58 °C, η is 3.54%; Voc, 2.58 V; Isc, 21.73 mA and Pm 24.6 mW. Four such prototype modules connected in series of total area 26.8 cm2 give at 26 °C, η of 4.4%; Voc, 12.54 V, Isc, 21.66 mA and Pm 118 mW. At 58 °C, these values drop to η, 3.24%; Voc, 10.46 V; Isc, 20.02 mA and Pm 87 mW. We prepared these modules on commercial SnO2:F (FTO) with cell structure FTO/CdS(90 nm)/Sb2S1.06Se1.94(210 nm)/C-Ag, where the electrodes of area approximately one cm2 each are of colloidal graphite and silver paints. We deposited CdS film from chemical bath and Sb2S1.06Se1.94 film, by thermal evaporation of Sb2S3, Sb2Se3, and SbCl3. This report contains basic properties and technological outlook for this absorber.

Investigation of coupling characteristics of series-connected phase-change memory cells varied in programmable volume

The coupling characteristics of two externally series-connected mushroom-type phase-change memory (PCM) cells varied in diameter of heater plug were investigated to assess the feasibility of the stacked PCM structure. The results indicated that the pair of the series-connected cells can accomplish triple-level storage with favorable features of direct overwrite capability and large programming margin. The mushroom-type cell was also demonstrated to be suitable for the concept of the stacked PCM structure due to its great tolerance to over-programming. The stacked PCM structure is considered as a potential approach for accomplishing the multilevel storage of PCM.

Analysis and Design Considerations of Efficiency Enhanced Hierarchical Battery Equalizer Based on Bipolar CCM Buck–Boost Units

Compared with the conventional hard switching battery equalizers, hierarchical battery equalizer based on the bipolar continuous-conduction mode buck-boost units could effectively reduce the switching loss and improve the conversion efficiency. This paper mainly addresses the key technical challenges associated with the optimal design of this battery equalizer. The inductor current is controlled to enter into the negative region. Thus, the mosfet body diode provides a freewheeling path for the inductor current during the dead band. This ensures zero-voltage switching turn-on of both power mosfets in each buck-boost unit without auxiliary snubbers. Therefore, the switching losses are significantly reduced. Meanwhile, the integral of the inductor negative current is precisely controlled to minimize the circulating current. This guarantees both minimized conduction losses and suitable equalization speed. Furthermore, an equalization algorithm, which compensates the battery internal resistance induced state-of-charge error, is proposed to improve the equalization accuracy. The operating principles and design considerations are analyzed in detail. An experimental prototype to balance four series-connected lithium-ion battery cells is implemented. The experimental results validate the design of the equalizer and demonstrate obvious efficiency enhancement over the conventional method.

A Lithium-Ion Battery Balancing Circuit Based on Synchronous Rectification

In this paper, a battery balancing circuit is proposed for the series-connected lithium-ion battery cells based on the principle of synchronous rectification. The proposed balancing circuit, also referred to as an equalizer, mainly includes a buck–boost converter (BBC), a multiport half-bridge converter (MHBC), and a driving circuit. The MHBC is coupled with a multiwinding transformer. Compared with the conventional congeneric methods, the number of transformer windings is almost reduced by half, leading to a more compact size and lower cost. Moreover, the secondary <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s of the MHBC are synchronously driven by the primary half-bridge converter (HBC) without the need of additional isolated <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> gate drivers and power supplies, dramatically reducing the circuit cost and complexity. In addition, the proposed equalizer can realize the module-to-multi-cell (M2MC) equalization under severe imbalance conditions to improve the balancing speed, and work at the any-cell-to-any-cell (AC2AC) self-balancing mode under slight imbalance conditions to improve the balancing efficiency and effectiveness, which achieves a good trade-off between balancing speed and effectiveness. The expressions of the equalization current and efficiency are derived and verified by experimental results. The proposed equalizer is experimentally evaluated for a string with 12 series-connected lithium-ion cells.

A hybrid model predictive and fuzzy logic based control method for state of power estimation of series-connected Lithium-ion batteries in HEVs

Abstract Accurate estimation of the State of Power (SoP) can ensure safe and efficient operation of Lithium-ion batteries in Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs). The cell-to-cell variation within a battery pack is a major challenge towards accurate estimation of the SoP, particularly when the cells get aged. This paper presents a hybrid model predictive and fuzzy logic based control system to accurately estimate the SoP for series-connected Lithium-ion cells. The estimation strategy consists of two steps; the power capability for a single new cell is first reckoned under the light of the model predictive control algorithm. The second step is devoted to designation of a model-less fuzzy logic based control system to compensate for the concurrent aging state and State of Charge (SoC) differences among the cells. Accordingly, the present approach only utilizes the actual values of current and cell voltages together with the Electric Circuit Model (ECM) parameters of the new cell, which are identified off-line. Moreover, it benefits from a closed-loop framework which ends in an accurate and reliable SoP estimation. An experimental setup consisting of fresh and aged LiFePO4 cell samples is designed and the extracted data are utilized to verify the proposed estimation method in a feed-forward simulation model for a HEV. The results indicate that the proposed method can estimate the pack SoP accurately while the safe operation for the cells is guaranteed.

A Series Resonant Energy Storage Cell Voltage Balancing Circuit

A novel cell voltage equalizer using a series LC resonant converter is proposed for series-connected energy storage devices, namely, battery or super (or ultra)-capacitor cells. The proposed circuit is an active voltage equalization circuit for energy storage devices that is low cost, small in size, and equalizes the voltages quickly. Compared to the state-of-the-art solutions, the proposed series LC resonant circuit eliminates the complexity of multiwinding transformers, and it can balance series-connected energy storage devices in a short time by transporting energy successively between the cells having highest voltage difference. The detailed circuit operation and theoretical analysis are provided. Simulation and experimental results are presented to demonstrate the voltage equalization process from an initial voltage difference of 527 mV to a final difference of 10 mV in 900 s for three series-connected supercapacitor cells.

Bidirectional active charge equaliser for series‐connected cells

In this study, a new bidirectional charge equaliser for series-connected cells is proposed to equalise the charge of N series-connected cells in static and dynamic states, i.e. while charging, discharging and when charger/load is disconnected. The proposed topology consists of three parts: a multiplexer, H-bridge and transformer. The multiplexer section connects the target cell to the transformer. The transformer acts as temporary energy storage and the H-bridge section sets the polarity of the voltage on the primary of the transformer. In charging/static mode, the energy transfers from charger/string to the low-charged cell and in discharging mode energy transfers from the cell with the highest charge to the load. In fact, energy transfer is in the same direction as the circuit operation, in this way, the speeds of charge and discharge of series cells are increased. Also due to the existence of only one small transformer and totem-pole arrangement of bidirectional switches, which halved the switch drivers, the cost and size of the circuit is reduced. A prototype of the proposed circuit to balance the charge of four series lithium–ion battery cells is designed and implemented. The experimental results confirm the correct operation of the circuit in all three states.

Transformerless Bidirectional PWM Converter Integrating Voltage Multiplier-Based Cell Voltage Equalizer for Series-Connected Electric Double-Layer Capacitors

In the traditional energy storage systems consisting of series-connected energy storage cells such as electric double-layer capacitors (EDLCs), not only a bidirectional pulsewidth modulation (PWM) converter but also a cell voltage equalizer is required. The system is prone to complexity as two converters (i.e., the bidirectional converter and cell voltage equalizer) are separately necessary. This paper proposes the transformerless bidirectional PWM converter integrating the voltage multiplier-based cell voltage equalizer. An inductor in a conventional bidirectional PWM converter is replaced with series-connected inductors in the proposed converter in order to generate square-wave voltage with an arbitrary amplitude, by which the voltage multiplier is driven. The charge–discharge cycling test for nine EDLCs connected in series was performed using the proposed integrated converter from a voltage-imbalanced condition. The voltage imbalance was gradually eliminated during charge–discharge cycling, demonstrating the integrated functions.

Analytical Expressions for the Efficiency Limits of Radiatively Coupled Tandem Solar Cells

The limiting efficiency for series-connected multijunction solar cells is usually calculated from the assumption that the individual junctions are optically isolated. Here, we develop an analytical formalism to predict efficiencies attainable in the presence of luminescent coupling, i.e., if the individual junctions in a series-connected multijunction stack are coupled optically, so that luminescence from one junction can be absorbed by the lower bandgap junction below. The formalism deals with nonradiative recombination through the definition of the luminescence extraction efficiency. Using our general formalism, we find that the limiting efficiency of a tandem cell becomes much less dependent on exact bandgap combination when luminescent coupling is considered and proceed to consider two technologically important examples of current-mismatched tandem solar cells. We find that a series-connected GaAs on a silicon tandem cell can be more efficient than the underlying silicon cell alone, if the luminescence extraction efficiency of the GaAs junction is sufficient. An analysis of luminescent coupling in a perovskite on a silicon tandem cell shows that the efficiency penalty for a perovskite bandgap below the optimum value can be mitigated if the luminescence extraction efficiency is high. We suggest that material quality and stability might be more important considerations for perovskite on silicon tandems than engineering the bandgap to achieve precise current matching.

Experimental Characterisation of Photovoltaic Modules with Cells Connected in Different Configurations to Address Nonuniform Illumination Effect

Most concentrating systems that are being used for photovoltaic (PV) applications do not illuminate the PV module uniformly which results in power output reduction. This study investigated the electrical performance of three PV modules with cells connected in different configurations to address nonuniform illumination effect. PV module 1 is the standard module consisting of 11 solar cells connected in series whereas PV module 2 is a proposed design with 11 cells in three groups and each group consists of different cells in series connections. PV module 3 is also a new design with 11 cells in two groups and each group consists of different cells connected in series. The new PV modules were designed in such a way that the effect of nonuniform illumination should affect a group of cells but not the entire PV module, leading to high power output. The PV modules were tested under three different intensities: uniform, low nonuniform, and high nonuniform illumination. When the PV modules were tested at uniform illumination, the total maximum power output of PV module 1 was higher than that of PV module 2 and PV module 3 by about 7%. However, when the PV modules were tested at low nonuniform illumination, the total maximum power output of PV module 2 was higher than that of PV module 1 and PV module 3 by about 4% and 7%, respectively. This difference increased to about 12% for PV module 3 and 17% for PV module 1 when the modules were tested at high nonuniform illumination. Therefore, the best PV module design in addressing nonuniform illumination effect in solar collectors is PV module 2. In practical situation this implies that manufacturers of PV modules should consider designing modules with groups of cells in series connection instead of all cells being connected in series.

A high voltage multi level arbitrary waveform generator for insulation testing

Due to the extensive applications of power electronic devices in power grids, many insulation components will be stressed by high voltage PWM, multilevel or even more complex waveforms. In this paper, a high voltage generator able to produce various waveforms is developed. The generator is based on cascade connected multilevel modular converter (MMC) topology, including 20 half bridge MMC cells with the capability of 21 output voltage levels. Half of the series-connected MMC cells are charged positively, while the other half are charged negatively. Each positive and negative half bridge MMC cell is connected alternately to optimize the insulation design. The power supply of the driving circuit for each MMC cell is provided by an individual fly-back converter fed by the cell capacitor to realize a compact design. On the basis of simulations, a multilevel arbitrary waveform generator prototype was constructed, with the maximum peak-to-peak voltage of ∼ 28 kV. A capacitor switching strategy is utilized to solve the voltage-imbalance problem resulted from the difference of the element parameters and other reasons. Finally, it was tested on a typical insulation with a simulated defect.

Impact of Buffer Layer Process and Na on Shunt Paths of Monolithic Series-connected CIGSSe Thin Film Solar Cells

The illuminated current-voltage characteristics of Cu(In,Ga)(S,Se)2 (CIGSSe) thin film solar cells fabricated using two different buffer layer processes: chemical bath deposition (CBD) and atomic layer deposition (ALD) were investigated. The CIGSSe solar cell with the ALD buffer showed comparable conversion efficiency to the CIGSSe solar cell with CBD buffer but lower shunt resistance even though it showed lower point shunt defect density as measured in electroluminescence. The shunt paths were investigated in detail by capturing the high-resolution dark lock-in thermography images, resolving the shunt resistance contributions of the scribing patterns (P1, P3), and depth profiling of the constituent elements. It was found that the concentration of Na from the soda-lime glass substrate played a key role in controlling the shunt paths. In the ALD process, Na segregated at the surface of CIGSSe and contributed to the increase in the shunt current through P1 and P3, resulting in a reduction in the fill factor of the CIGSSe solar cells.

Asymmetric supercapacitor based on reduced graphene oxide/MnO2 and polypyrrole deposited on carbon foam derived from melamine sponge

Carbon sponges enclosing carbon fibers are prepared by carbonizing the melamine sponges with bunches of carbon fibers sewn in, and used as the substrate and current collector to fabricate asymmetric supercapacitors. MnO2/rGO/CS-CFs as the positive electrode and the PPy/CS-CFs as the negative electrode have been prepared and characterized, and in LiCl/polyvinyl alcohol gel electrolyte, the positive and negative electrodes are used to fabricate the asymmetric supercapacitors. The cells exhibit an operating voltage window of 1.4 V and high specific capacitance of 106.1 F g−1 based on the active materials and high cyclic stability (83.7% capacitance retention after 10000 cycles). The asymmetric supercapacitors in parallel and series connection show good electrical relationships, and two cells in series connection can turn on a light emission device after being charged, indicating the potential practical application.

Novel heterojunction bipolar transistor architectures for the practical implementation of high-efficiency three-terminal solar cells

Practical device architectures are proposed here for the implementation of three-terminal heterojunction bipolar transistor solar cells (3T-HBTSCs). These photovoltaic devices, which have a potential efficiency similar to that of multijunction cells, exhibit reduced spectral sensitivity compared with monolithically and series-connected tandem solar cells. In addition, the simplified n-p-n (or p-n-p) structure does not require the use of tunnel junctions. In this framework, four architectures are proposed and discussed in this paper: 1) one in which the top cell is based on silicon and the bottom cell is based on a heterojunction between silicon and III-V nanomaterials; 2) one in which the top cell is made of amorphous silicon and the bottom cell is made of an amorphous silicon-silicon heterojunction; 3) one based on the use of III-V semiconductors aimed at space applications; and 4) one in which the top cell is based on a perovskite material and the bottom cell is made of a perovskite-silicon heterostructure.

Switched-Capacitor-Based Single-Source Cascaded H-Bridge Multilevel Inverter Featuring Boosting Ability

Cascaded multilevel inverter (CMI) is one of the most popular multilevel inverter topologies. This topology is synthesized with some series-connected identical H-bridge cells. CMI requires several isolated dc sources which brings about some difficulties when dealing with this type of inverter. This paper addresses the problem by proposing a switched-capacitor (SC)-based CMI. The proposed topology, which is referred to as switched-capacitor single-source CMI (SCSS-CMI), makes use of some capacitors instead of the dc sources. Hence, it requires only one dc source to charge the employed capacitors. Usually, the capacitor charging process in a SC cell is companied by some current spikes which extremely harm the charging switch and the capacitor. The capacitors in SCSS-CMI are charged through a simple auxiliary circuit which eradicates the mentioned current spikes and provides zero-current switching condition for the charging switch. A computer-aid simulated model along with a laboratory-built prototype is adopted to assess the performances of SCSS-CMI, under different conditions.

&gt;10% solar-to-hydrogen efficiency unassisted water splitting on ALD-protected silicon heterojunction solar cells

We demonstrate unassisted water splitting with &gt;10% solar-to-hydrogen conversion efficiency using series-connected silicon heterojunction solar cells protected by ALD TiO2 in a novel, integrated device architecture.

Research on Influencing Factors for Consistency Performance of Lithium Ion Batteries

The capacity, energy, internal resistance and open -circuit voltage are key indicators to represent the performance of lithium ion batteries. The battery rate characteristic refers to the battery charge and discharge performance; the higher rate battery can withstand higher discharge current. This paper researched the influencing factors for consistency performance of Lithium ion batteries which were tested at 1/3C, 1.5C and 2C charge and discharge. The result shows that the charge and discharge voltage of the series-connected cell group is different slightly, and the basic electric performance (capacity, internal resistance) is not affected basically when the charge rate is less than 1C, the temperature rises slightly when charging the series-connected cell group when the charge rate is larger (higher than 1C), and proposes a method for select the appropriate battery charge and discharge rate, to eliminate the adverse batteries and ensure the good performance of batteries.