Low Terminal Voltage Research Articles

A 3X and X/3 voltage conversion‐based bidirectional CuK converter for supercapacitor‐assisted electric vehicles

AbstractIn this paper, a high‐gain bidirectional DC–DC converter is presented for electric vehicles where low terminal voltage source like a supercapacitor is used along with the battery. The supercapacitor provides or absorbs large amount power during acceleration and deacceleration and extends the life of main energy source, that is, battery. The supercapacitor terminal voltage varies considerably during charging and discharging activities; hence, a bidirectional DC–DC converter with a high‐voltage conversion ratio must be used to connect the lower supercapacitor voltage to the higher DC‐link voltage. Such application requires steep voltage conversion ratio along with continuous gain‐based bidirectional DC–DC converters. In this study, a typical CuK converter is employed to produce a voltage gain of 3X and X/3 with the ability to transmit power in both directions. The suggested bidirectional converter has a continuous current on both the low‐ and high‐voltage sides, which reduces the requirement for filter capacitance and increases the lifespan of the supercapacitor and DC‐link capacitor. Further, inherent inrush current safety is provided by the proposed converter as the inclusion of an inductor in the path of capacitor charging or discharging. Both in the charging and discharging phases, a detailed steady‐state analysis of the proposed circuit was performed. Moreover, a deep discharge analysis of the supercapacitor and its implication on the performance of the converter is also investigated.

Flyback converter employed non-dissipative cell equalization in electric vehicle lithium-ion batteries

The effective and dependable usage of rechargeable batteries has emerged as a central topic for automobile manufacturers in the wake of the rise of electric vehicle technology. When it comes to rechargeable batteries with high specific energy and specific power, lithium-ion battery technology is the most well-known. The low terminal voltage battery cells in the lithium-ion battery pack are linked in series to provide the necessary voltage for the electric vehicle system. The low charge cell in the string limits the usable capacity of the battery pack, though. Disturbances in the battery pack's charge are due to variations in manufacturing quality and to the unique operating circumstances of each individual cell. These inconsistencies cause a decline in usable capacity, a quickening of cell deterioration, and, most significantly, substantial safety issues including overcharging. The cell balancing controller is a critical component of the battery management system in all electric vehicle and hence performs a crucial function in extending battery life and ensuring the battery's safety. This paper presents a hardware-in-the-loop simulation of a RCD buffer included fly-back converter-based active cell equaliser for lithium-ion batteries in electric vehicles. With the equaliser, all the series-connected cells may be brought to a more even State of Charge. All of the MOSFETs employed in the proposed approach are selected for their low conduction loss. The suggested equaliser is able to produce equalization without the need for a switch driving circuit or sophisticated control method, allowing it to function automatically. The system's overall price is reduced, and the balanced circuit's complexity is considerably reduced. In-depth discussions on circuit configuration, operating principle, modeling, and design consideration are presented. Finally, both Matlab simulation results and Hardware-in-loop based experimental findings are offered to back up the claims that the suggested cell equaliser is both practical and effective.

ANALISA PERUBAHAN PEMBEBANAN TERHADAP ARUS EXITASI UNIT 1 PADA PT PLN (PERSERO) SEKTOR PEMBANGKITAN TELUK SIRIH

Changes in the load of a generator are always changing according to the needs of community demand. On the generator side of the Teluk Sirih PLTU using charcoal brush media as a reinforcing field. Where excitation plays an important role providing DC current to the generator rotor to create an intersection of electromotive forces. Changes in generator load that are always changing can have an impact on damage to equipment such as generators, and excitation. Where on December 6, 2017 the excitation current reads low at 473.7 amperes directly proportional to the armature current of 1404.2 amperes, the resulting power will also be low at 13200000 watts and a frequency of 49.9 Hz, creating a magnetic flux of 0.125 Weber that is larger or feels heavy so that the generator rotation is low at 2999 rpm and vice versa. Therefore the role of excitation takes over in order to provide greater current so that the field strength is maintained stable. Increasing the excitation current (If) results in a greater induced electromotive force (Ea). This increase in Ea also impacts the terminal voltage (Vt), causing it to vary. This relationship demonstrates that higher excitation current leads to an increase in terminal voltage, which is essential for maintaining voltage stability. To stabilize the low terminal voltage resulting from load changes, it is necessary to amplify the field gain current. This can be achieved by increasing the excitation current on the synchronous generator rotor. Understanding the characteristics of the excitation system allows for minimizing and avoiding damage to the generator caused by both overexcitation and underexcitation, ensuring the maintenance of a stable terminal voltage.

Thin, Flexible, and High-Performance Solid-State Polymer Electrolyte Membranes for Li–O2 Batteries

A solid-state lithium–oxygen battery (SSLOB) has become more attractive as a next-generation energy storage device, with the expectation of long-term safe and wide applications with superior energy density. However, the development of a thin and flexible solid-state electrolyte having good interfacial and chemical stability toward lithium metal and/or oxygen has been a big challenge. Accordingly, a solid-state composite electrolyte membrane has been prepared by impregnating polyethylene glycol (PEG) and succinonitrile plastic crystals (SNPCs) along with lithium bromide redox mediator into a porous polytetrafluoroethylene (PTFE) substrate for application in a SSLOB. The prepared thin electrolyte membrane (23 μm) displays a high ionic conductivity of 1.03 mS cm–1, a tensile strength of 46.5 MPa, and elongation at a break of 100% with excellent flexibility. It also exhibits a wide electrochemical stability window (∼4.9 V) and low interfacial resistance of 80 Ω cm2. The SSLOB cell assembled with the synthesized XPEG/SNPC@PTFE electrolyte membrane shows excellent electrochemical stability during 277 cycles, maintaining a 1000 mAh g–1 discharge capacity. The low terminal voltage difference between the charge and discharge processes of these polymer electrolyte membranes (∼0.65 V) compared to those of liquid or other polymer electrolytes (∼1.4 V) is also an advantageous characteristic for their application in high-performance SSLOBs.

Ultraporous, Ultrasmall MgMn2O4 Spinel Cathode for a Room-Temperature Magnesium Rechargeable Battery.

Magnesium rechargeable batteries (MRBs) promise to be the next post lithium-ion batteries that can help meet the increasing demand for high-energy, cost-effective, high-safety energy storage devices. Early prototype MRBs that use molybdenum-sulfide cathodes have low terminal voltages, requiring the development of oxide-based cathodes capable of overcoming the sulfide's low Mg2+ conductivity. Here, we fabricate an ultraporous (>500 m2 g-1) and ultrasmall (<2.5 nm) cubic spinel MgMn2O4 (MMO) by a freeze-dry assisted room-temperature alcohol reduction process. While the as-fabricated MMO exhibits a discharge capacity of 160 mAh g-1, the removal of its surface hydroxy groups by heat-treatment activates it without structural change, improving its discharge capacity to 270 mAh g-1─the theoretical capacity at room temperature. These results are made possible by the ultraporous, ultrasmall particles that stabilize the metastable cubic spinel phase, promoting both the Mg2+ insertion/deintercalation in the MMO and the reversible transformation between the cubic spinel and cubic rock-salt phases.

Transformerless Grid Connected Control of Wind Turbine Based on H-MMC

A high-power wind turbine has low rotational speed and a relatively low terminal voltage level. Thus, the wind energy conversion system (WECS) is commonly connected to the grid by an isolated boost transformer, which increases costs and room greatly. In this article, the hexagonal modular multilevel converter (H-MMC) is applied so that the high-power wind turbine can be directly connected to the medium-voltage ac grid. It has the advantages of transformerless grid connection and low ripples of capacitor voltages. As the bridge arm voltage of H-MMC contains both the low-frequency component induced by a wind turbine and the power frequency component induced by the grid, the voltage ripples of submodules (SMs) are reduced. Due to the large differences in the voltage level between the wind turbine and the grid, the low-amplitude-modulation voltage of the wind turbine side is easily obliterated by the high-amplitude-modulation voltage of the grid side, which will cause distortion of the bridge arm current. Therefore, auxiliary SMs with variable reference voltage are adopted to improve the tracking accuracy. The MATLAB/Simulink simulation and the RT-LAB hardware-in-the-loop experimental results verify the feasibility of the proposed topology and the effectiveness of the control strategy.

A novel high‐gain bidirectional DC–DC converter for EV onboard charger applications

AbstractIn electric vehicle (EV) onboard applications, the bidirectional DC‐DC converter is proposed in this paper to interface low terminal voltage battery with DC bus of the motor. The proposed bidirectional DC–DC converter is configured based on a ladder switching network of inductors and a capacitor. Due to this configuration, the proposed converter has a simple structure, and it can archive high voltage gain with fewer components. A detailed comparative analysis is presented to verify the uniqueness and superiority of the proposed topology. Furthermore, the detailed steady‐state analysis and working principles are presented in this paper. Finally, the 300‐W prototype is built, and the experimental results are presented to verify the performance and feasibility of the proposed bidirectional converter.

Comparison of methods for the detection of 10Be with AMS and a new approach based on a silicon nitride foil stack

Natural 10Be (t1/2 = 1.387 ± 0.012 Ma) is produced by cosmic rays and is present on Earth's surface only at ultratrace concentrations (typically 104 to 1010 atoms/g). Its cosmogenic origin makes it an important tracer for many applications in Earth and environmental sciences. An improved accelerator mass spectrometry (AMS) method has been developed at the Vienna Environmental Research Accelerator (VERA) at the University of Vienna to detect the long-lived radionuclide 10Be and separate it from its isobar 10B. Recently installed and projected AMS facilities mainly apply a degrader foil followed by an electrostatic or magnetic separator to remove 10B from the ion beam. This provides the highest suppression of 10B, but suffers from significant transmission losses of 10Be ions. The new technique described here achieves comparable 10B suppression with a passive absorber, consisting of a stack of silicon nitride foils. Compared to a gas absorber, the smaller energy straggling in foils allows separation at lower energies. For a tandem accelerator operated at 3 MV, the charge state 2 + instead of 3 + can be used, with a stripping yield as high as 55%. This way, a high overall efficiency is gained. The setup is simple to operate, and provides good precision and accuracy. We compare this new approach with other methods used at VERA and at other AMS facilities. The foil stack setup was fully characterized with artificial samples from chemically and isotopically well-defined reagents, and is now routinely applied to real samples in various research projects at VERA. The new method is straightforward to be implemented, and was already adopted at another AMS facility with higher terminal voltage, the potential use at tandem accelerators with lower terminal voltage is under exploration.

Net power positive maximum power point tracking energy harvesting system for microbial fuel cell

Microbial fuel cells (MFCs) have been investigated as a promising renewable energy source, although harvesting energy from MFCs is not a simple task because of their low terminal voltage and output power. For an energy harvesting system (EHS) for MFC, controlling the MFC's operating point to track the maximum power point (MPP) is essential to maximize the harvested energy, but it requires a complex control system that consumes significant amount of energy. Although this control power is a critical factor because of its substantial impact on overall efficiency, it has been largely neglected. Furthermore, the transient of MFC reactor has not been taken into consideration enough for MPPT algorithms even though it could significantly affect the operation of such algorithms. In this paper, a net power positive EHS for MFC is proposed, which has a microcontroller that tracks the MPP using a novel power estimation method considering the dynamics of MFC reactor. The proposed EHS uses only a fraction of the harvested MFC power and was able to operate at a steady-state MPP without any external power. The experimental results show that the overall efficiency of the proposed system at MPP is 59.4% with a microcontroller power consumption of 8.67 μW.

Improved transmission of electrostatic accelerator in a wide range of terminal voltages by controlling the focal strength of entrance acceleration tube

Abstract Tandem electrostatic accelerators often require the flexibility to operate at a variety of terminal voltages to accommodate various user requirements. However, the ion beam transmission will only be optimal for a limited range of terminal voltages. This paper describes the operational performance of a novel focusing system that expands the range of terminal voltages for optimal transmission. This is accomplished by controlling the gradient of the entrance of the low-energy tube, providing an additional focusing element. In this specific case it is achieved by applying up to 150 kV to the fifth electrode of the first unit of the accelerator tube. Numerical simulations and beam transmission tests have been performed to confirm the effectiveness of the lens. An analytical expression has been derived describing its focal properties. These tests demonstrate that the entrance lens control eliminates the need to short out sections of the tube for operation at low terminal voltage.

Design of a Bidirectional Energy Storage System for a Vanadium Redox Flow Battery in a Microgrid with SOC Estimation

This paper used a Vanadium Redox flow Battery (VRB) as the storage battery and designed a two-stage topology of a VRB energy storage system in which a phase-shifted full bridge dc-dc converter and three-phase inverter were used, considering the low terminal voltage of the VRB. Following this, a model of the VRB was simplified, according to the operational characteristics of the VRB in this designed topology of a VRB energy storage system (ESS). By using the simplified equivalent model of the VRB, the control parameters of the ESS were designed. For effectively estimating the state of charge (SOC) of the VRB, a traditional method for providing the SOC estimation was simplified, and a simple and effective SOC estimation method was proposed in this paper. Finally, to illustrate the proper design of the VRB ESS and the proposed SOC estimation method, a corresponding simulation was designed by Simulink. The test results have demonstrated that this proposed SOC estimation method is feasible and effective for indicating the SOC of a VRB and the proper design of this VRB ESS is very reasonable for VRB applications.

A novel beam focus control at the entrance to the ANU 14UD accelerator

Tandem electrostatic accelerators often require the flexibility to operate at variety of terminal voltages to cater for various user needs. However beam transmission will only be optimal for a limited range of terminal voltages. This paper describes a focussing system that greatly expands the range of terminal voltages for optimal transmission. This is achieved by controlling the gradient of the entrance of the low-energy tube providing an additional controllable focusing element. Up to 150 kV is applied to the fifth electrode of the first unit of the accelerator tube giving control of the tube entrance lens strength. Beam tests to confirm the efficacy of the lens have been performed. These tests demonstrate that the entrance lens control eliminates the need to short out sections of the tube for low terminal voltage operation.

A Wide Bandwidth Electronic Load

Electronic load (E-load) is commonly used to test power supplies. In order to test computer power supplies, the E-load must possess an ideal controlled current source property which draws a desired load current even in the case of a very low terminal voltage of the source under test (SUT). It also needs to have superior dynamic performance to simulate high-slew-rate load transients. This paper proposes the design of a switching-converter-based E-load with very large operational bandwidth. The overall architecture of the E-load consists of a low-bandwidth converter, which functions under steady state, and a high-bandwidth auxiliary circuit that is only active during transient state. The converter circuit is realized using a novel switched-boost topology, and the auxiliary circuit is realized using a MOSFET operating at the edge of saturation and linear region. The proposed topology is capable of sinking a specific amount of load current even with a very low SUT terminal voltage. Simulation and experimental validations are provided to verify the proposed concepts. A prototype has been built to test the proposed architecture. The operational input voltage (SUT voltage) ranges of the prototype are between 0.5 and 6 V. The load current range is between 0.75 and 7 A. The results validate the excellent dynamic characteristics of the proposed architecture.

Optimal PAM Control for a Buck Boost DC-DC Converter with a Wide-Speed-Range of Operation for a PMSM

A pulse width modulation-voltage source inverter (PWM-VSI) is used for variable speed permanent magnet synchronous motor (PMSM) drives. The PWM-VSI fed PMSM has two major disadvantages. Firstly, the PWM-VSI DC-link voltage limits the magnitude of the PMSM terminal voltage. As a result, the motor speed is restricted. Secondly, in a low speed range, the PWM-VSI modulation index declines. This is caused by a high DC-link voltage and a low terminal voltage ratio. As a result, the distortion of the voltage command and the stator current are increased. This paper proposes an optimal pulse amplitude modulation (PAM) control which can adjust the inverter DC-link voltage by using a buck-boost DC-DC converter. At a low speed range, the proposed system can reduce the distortion of the voltage command, which improves the stator current waveform. Also, the allowable speed range is extended. In order to verify the proposed method, experimental results are provided to confirm the simulation results.

New concepts of 10Be AMS at low energies

Isotopic ratios of 10Be/9Be with a background sensitivity of 2×10−14 can now be measured with the 0.6MV Tandem accelerator of PSI/ETH Zurich using BeF2 instead of BeO as sample material and injecting BeF− to suppress the boron detector count rate. A new, high-resolution gas ionization detector with a thin silicon nitride entrance window and special preamplifier design are essential in order to achieve this sensitivity. A particle transmission of 50% is possible for charge state 1+. Due to the maximum count rate that can be accepted by the detector the BeF− currents are limited to a few hundred nA.Measurements of 10Be in rainwater samples performed under these conditions at the low terminal voltage of 0.6MV with the new compact AMS system show good agreement with results using the conventional 10Be measurement setup on the 6MV facility. Thus, this type of small scale equipment can now also be applied for 10Be AMS as long as 10Be/9Be ratios are sufficiently high and measurement time is not a limiting factor.Instead, using BeO and the degrader foil technique with a silicon nitride membrane the boron count rate can also be suppressed sufficiently but the 10Be/9Be background level is limited to 10−13 by scattered 9Be and the overall transmission is less than 5%.

Comparison of boron halide, decaborane and B implants in Si from Molecular Dynamics simulations

Ultra shallow junctions (depths <0.1 μm) are required for future generations of silicon devices. This requires either very low energy ion implantation (<1 keV for B for the shallowest of implants) or the use of heavier implanted species (either elemental or molecular). Many commercial implanters have problems operating at such low terminal voltages. For many years molecular ions, in particular BF 2 +, have been used to transport low velocity boron at higher energies, enabling the use of conventional implanters in the production of shallow junctions. However, with ever shrinking scales the energies required even for BF 2 are becoming too low. The investigation here is to look at the alternative heavier halides and decaborane as possible alternatives to allow continued use of conventional ion implanters. We use a molecular dynamics simulation to see if we can find any evidence of non-linear behaviour from the use of such molecular species for implantation, thereby making the modelling and simulation of such implants more complex than more conventional implantation. The simulation results presented suggest that there is no evidence of non-linear behaviour and all the standard parameters of implantation – ion ranges and displacements of silicon atoms – change in a well predicted manner.

Accelerator mass spectrometry analyses of environmental radionuclides: sensitivity, precision and standardisation

Accelerator Mass Spectrometry (AMS) is the analytical technique of choice for the detection of long-lived radionuclides which cannot be practically analysed with decay counting or conventional mass spectrometry. AMS allows an isotopic sensitivity as low as one part in 1015 for 14C (5.73 ka), 10Be (1.6 Ma), 26Al (720 ka), 36Cl (301 ka), 41Ca (104 ka), 129I (16 Ma) and other long-lived radionuclides occurring in nature at ultra-trace levels. These radionuclides can be used as tracers and chronometers in many disciplines: geology, archaeology, astrophysics, biomedicine and materials science. Low-level decay counting techniques have been developed in the last 40–50 years to detect the concentration of cosmogenic, radiogenic and anthropogenic radionuclides in a variety of specimens. Radioactivity measurements for long-lived radionuclides are made difficult by low counting rates and in some cases the need for complicated radiochemistry procedures and efficient detectors of soft β-particles and low energy x-rays. The sensitivity of AMS is unaffected by the half-life of the isotope being measured, since the atoms not the radiations that result from their decay, are counted directly. Hence, the efficiency of AMS in the detection of long-lived radionuclides is 106–109 times higher than decay counting and the size of the sample required for analysis is reduced accordingly. For example, 14C is being analysed in samples containing as little as 20 μg carbon. There is also a world-wide effort to use AMS for the analysis of rare nuclides of heavy mass, such as actinides, with important applications in safeguards and nuclear waste disposal. Finally, AMS microprobes are being developed for the in-situ analysis of stable isotopes in geological samples, semiconductors and other materials. Unfortunately, the use of AMS is limited by the expensive accelerator technology required, but there are several attempts to develop compact AMS spectrometers at low (⩽0.5 MV) terminal voltages. Recent advances in AMS will be reviewed with highlights from the scientific programs at Lucas Heights and other AMS centres.

AMS of 14C at low energies

At the ETH/PSI AMS facility 14C test measurements have been performed at low terminal voltages of 0.5 and 1 MV in order to study the feasibility of AMS with very small accelerators. These experiments have demonstrated that molecules (13CH and 12CH2) in charge states 1+ and 2+ can be destroyed in an Ar gas stripper reducing their intensities by at least ten orders of magnitude at a stripper thickness of about 1 μg/cm2. It could be shown that particle identification and separation of 12CH2 and 14N from 14C is possible with a ΔE-E gas counter for an energy of 3 MeV (using charge state 2+ at 1 MV terminal voltage). A Si detector combined with a time-of-flight system was used for the experiments at 1 MeV. At both energies background has been found at levels below 10−13. This is certainly sufficient for biomedical applications. For 14C dating, further background reduction is required.

The correlation of low frequency optical noise spectrum and electrical noise spectrum in a laser diode, with experimental results

The models presented by Fronen and Vandamme [ IEEE J. Quantum Electron. 24, 724 (1988)] seem to be able to explain qualitatively the low frequency optical noise spectrum S p( ω) (included 1 f noise and G-R noise), and the dependence S p-P m. However the correlative form between low frequency optical noise spectrum and terminal voltage noise spectrum has not been clearly shown. In this paper, the low frequency optical noise spectrum of a laser diode has been calculated by considering both the fluctuation of carriers in active layer, the spontaneous emission of photons and the fluctuation of gains, then the correlative form between optical noise and electrical noise has been characterized. The new experiment results demonstrated that the stronger correlation exists between low frequency optical noise and electrical noise.

Steady state analysis and performance characteristics of a three-phase induction generator self excited with a single capacitor

Steady-state analysis and performance characteristics of a three-phase isolated star or delta connected induction generator self-excited with a single capacitor are discussed. Analytical expressions are derived to determine the no-load capacitance required to maintain self-excitation. The performance characteristics of a self-excited induction generator are affected by the terminal capacitance, C, machine speed, nu , and the load parameters. Generally, the value of C has a stronger influence on the performance characteristics and should be selected such that the terminal voltage, V/sub t/, is near its rated value while keeping C close to its lower limiting value. The accuracy of the method was experimentally verified, and good agreement is obtained between the two sets of results. The performance characteristics of star and delta connected induction generators are compared. In the mode of operation discussed, the voltages and currents are unbalanced with relatively high losses and rather low efficiency. Among the two configurations discussed, the delta connected generator offers a higher current and lower terminal voltage and a wider range of excitation capacitance. >