Terminal Voltage Variation Research Articles

Distributed control for multiple hybrid energy storage systems using consensus algorithm in direct current power supply system

Multiple hybrid energy storage systems (multi-HESSs) consisting of batteries and supercapacitors (SCs) is widely used to share the requirement of system pulsating power, reducing the dependence on a single hybrid energy storage system (HESS) to improve the system reliability. The filter composed of virtual resistance droop control (VRDC) and virtual capacitance droop control (VCDC) in a HESS can achieve frequency distribution of pulsating power between a battery and SC. However, it suffers from the output voltage deviation and terminal voltage variation. Mismatched line impedances and different system parameters can cause different output voltages and inaccurate current sharing in the multi-HESSs. Meanwhile, the differences in the terminal voltages of SCs can affect the transient output capability. Therefore, this paper proposes a consensus-based distributed control strategy (CDCS) for multi-HESSs, which not only achieves global average output voltage and current sharing for batteries but also realizes restoration and consistency of SCs terminal voltage. The state variable information of adjacent converters for multi-HESSs is exchanged by the sparse communication network, and the steady-state analysis of state variables is proved. The direct current (DC) power supply system with four HESSs is established to verify the effectiveness of the proposed control strategy.

Maximizing Efficiency in Smart Adjustable DC Link Powertrains with IGBTs and SiC MOSFETs via Optimized DC-Link Voltage Control

In recent years, the push towards electrifying transportation has gained significant traction, with battery-electric vehicles (BEVs) emerging as a viable alternative. However, the widespread adoption of BEVs faces multiple challenges, such as limited driving range, making powertrain efficiency improvements crucial. One approach to improve powertrain energy efficiency is to adjust the DC-link voltage using a DC-DC converter between the battery and inverter. Here, it is necessary to address the losses introduced by the DC-DC converter. This paper presents a dynamic programming approach to optimize the DC-link voltage, taking into account the battery terminal voltage variation and its impact on the overall powertrain losses. We also examine the energy efficiency gains of IGBT-based and silicon carbide (SiC) MOSFET-based adjustable DC-link voltage powertrains during WLTC driving cycles through PLECS and Matlab/Simulink simulations. The findings indicate that both IGBT and MOSFET-based adjustable DC-link voltage powertrains can enhance the WLTC drive-cycle efficiency up to 2.51% and 3.25% compared to conventional IGBT and MOSFET-based powertrains, respectively.

A Load Adaptive Hybrid DPS Control for DAB to Secure Minimum Current Stress and Full ZVS Operation Over Wide Load and Voltage Conversion Ratio

Wide variations in voltage conversion ratio and loading are the most important parameters to consider when designing off-board EV chargers to achieve high power density and efficiency. Dual phase shift (DPS) modulation provides a better way for dual active bridge (DAB) DC-DC converter operation when load side parameter variation is utmost important. To accomplish this, conventional DPS control is modified to ensure zero voltage switching (ZVS) across the entire load range despite wide variations in voltage conversion ratio. The designed control provides ZVS of all FETs as compared to the conventional DPS control over full loading range. For this, magnetizing inductance of HF isolation transformer is utilized and designed to shape the secondary side current for getting ZVS for both active legs. The light loading performance of the converter is improved with the bidirectional conduction angle control. The hybrid utilization of DPS control is incorporated with minimum peak current stress considerations. A Karush-Kuhn-Tucker (KKT) method based on Lagrange's multipliers is used for mathematical derivation of optimized solution of both control parameters. Performance of designed control is verified using experimental results for wide variation in battery terminal voltage. For validation, a 1250 W laboratory prototype is developed. A comparison of ZVS regions among the conventional and designed modulation technique, shows the effectiveness under wide voltage and loading scenarios.

Fabrication and Test of a 1:4 Scaled HTS Coil for the Defocusing Magnet of 2 GeV FFAG Accelerator

The basic design of a 2 GeV fixed field alternating gradient (FFAG) accelerator was proposed by China Institute of Atomic Energy (CIAE) in 2019. A preliminary study of high temperature superconducting (HTS) magnet for the 2 GeV FFAG accelerator lattice scheme was carried out, considering the beam loss of high energy proton beams and energy efficiency of the main machine. In order to demonstrate the feasibility of manufacturing a spiral-shaped HTS magnet with concave edges based on ReBCO tapes, a 1:4 scaled HTS model magnet is being developed in CIAE. First, the design and fabrication of the 1:4 scaled prototype HTS magnet with concave edges will be described in detail. Then, each double pancake (DP) was tested by liquid nitrogen (LN) immersion. The terminal voltage and magnetic field variation were measured and simulated. Finally, the whole assembled HTS magnet was cooled down to 23 K using helium gas pipeline contact cooling and operated on 300 A for over 24 hours. The central magnetic field reached 719.5 mT, without iron. More detailed electromagnetic characteristics of the magnet during the excitation will be illustrated, which is much helpful for the fabrication of the final full-size HTS magnets.

An enhanced multi-constraint state of power estimation algorithm for lithium-ion batteries in electric vehicles

In this paper, an enhanced multi-constraint (MC) state of power (SOP) estimation algorithm in a prediction window up to 120 s is developed for lithium-ion batteries in electric vehicles (EVs). First, a novel regression-based algorithm (RBA) incorporating a model parameter forward prediction is devised for voltage-constraint SOP estimation to reduce battery linearization error and improve model accuracy by estimating model parameters to the end of a prediction window. The convergence condition is analytically formulated and can be satisfied over a whole battery operating range. Second, an improved state of energy (SOE)-constraint SOP estimation algorithm is proposed from a more practical perspective by considering battery terminal voltage variation in a prediction window. Together with the other constraints, the enhanced MC SOP estimation algorithm is achieved, which specifies a dynamic safe operating area for power regulation in EVs. Moreover, an incremental pulse test is designed to obtain reference SOPs in high fidelity under static conditions and dynamic load profiles. Simulations and experimental results demonstrate the improved accuracy of the enhanced MC SOP estimation algorithm over the conventional MC online SOP estimation algorithm.

Effects of State-of-Charge and Penetration Location on Variations in Temperature and Terminal Voltage of a Lithium-Ion Battery Cell during Penetration Tests

The nail penetration test has been widely adopted as a battery safety test for reproducing internal short-circuits. In this paper, the effects of cell initial State-of-Charge (SOC) and penetration location on variations in cell temperature and terminal voltage during penetration tests are investigated. Three different initial SOCs (10%, 50%, and 90%) and three different penetration locations (one is at the center of the cell, the other two are close to the edge of the cell) are used in the tests. Once the steel cone starts to penetrate the cell, the cell terminal voltage starts to drop due to the internal short-circuit. The penetration tests with higher initial cell SOCs have larger cell surface temperature increases during the tests. Also, the penetration location always has the highest temperature increment during all penetration tests, which means the heat source is always at the penetration location. The absolute temperature increment at the penetration location is always higher when the penetration is close to the edge of the cell, compared to when the penetration is at the center of the cell. The heat generated at the edges of the cell is more difficult to dissipate. Additionally, a battery cell internal short-circuit model with different penetration locations is built in ANSYS Fluent, based on the specifications and experimental data of the tested battery cells. The model is validated with an acceptable discrepancy range by using the experimental data. Simulated data shows that the temperature gradually reduces from penetration locations to their surroundings. The gradients of the temperature distributions are much larger closer to the penetration locations. Overall, this paper provides detailed information on the temperature and terminal voltage variations of a lithium-ion polymer battery cell with large capacity and high power under penetration tests. The presented information can be used for assessing the safety of the onboard battery pack of electric vehicles.

Comparative assessment of supercapacitor bank switching techniques under constant resistor, constant current, and constant power loads

High specific power density and longer cycle life features made the supercapacitors as the most prominent option in managing the transient demands of the pulsed power loads. However, the discharging characteristics of supercapacitors confine them from the utilisation of their entire energy. Reflecting on these concerns, this study aims to provide an extensive review of various bank switching circuits of supercapacitors to enhance their energy utilisation. Also, a comprehensive analysis of these switching circuits in terms of power delivery duration, SC cell energy utilisation, terminal voltage variations, system efficiency, and total cost is carried out for the constant resistor, constant power, and constant current loads.

A Simple Three-Level Switching Architecture to Enhance the Power Delivery Duration of Supercapacitor Banks in Electrified Transportation

Hybridization of supercapacitors (SCs) with batteries in electric vehicular applications improves battery life, acceleration, and driving range. However, the efficiency of the power electronic interface that unites batteries and SCs is affected due to wide voltage variations at the SC bank terminals. Moreover, the SCs in a bank offer low storage capacity that restricts them from serving a series of transients on a single charge. This article aims at improving the power delivery duration and energy utilization of SCs with controlled terminal voltage variations using a new bank switching configuration. A simple three-level transition control scheme is implemented for charge and discharge of the SC bank. The effectiveness of the proposed topology is validated using PLECS simulations and experimental studies on a laboratory-developed prototype. Furthermore, the suitability of the proposed SC bank in a hybrid energy storage system (HESS) for an electric vehicle is verified in accordance with varying load demands. The superiority of the proposed architecture is shown in terms of the SC bank voltage variations and depth of discharge under standard urban and highway drive cycles.

Investigation of transient energy storage sources for support of future electrical power systems

The connection of renewable energy sources to local low-voltage networks is becoming more accepted as electrical power networks progress to higher renewable penetration. Renewable energy resources, for example, wind and solar are highly dynamic and intermittent compared with more traditional generation sources, which imposes increasing challenges to the electrical network operator in terms of effectively managing the resource to maximise energy transfer and maintaining system stability. Therefore, transient energy storage systems (TESSs), for example, electrochemical batteries with fast charging/discharging capabilities are suitable candidates to improve the availability and reliability of connected renewable systems. In this study, two potential TESS technologies are presented, the lithium-ion (Li-ion) and sodium–nickel chloride (NaNiCl2) battery, and their feasibility to improve power systems in terms of power delivery and frequency fluctuations are compared. Experimentally validated battery models are presented and used to investigate the TESS performance in terms of state-of-charge, terminal voltage variation, peak current, power, energy and efficiency. The models and general design procedure may be applied to systems of different ratings and duty variations.

A delay-dependent anti-windup compensator for wide-area power systems with time-varying delays and actuator saturation

In this paper, a delay-dependent anti-windup compensator is designed for wide-area power systems to enhance the damping of inter-area low-frequency oscillations in the presence of time-varying delays and actuator saturation using an indirect approach. In this approach, first, a conventional wide-area damping controller is designed by using H&#x221E output feedback with regional pole placement approach without considering time-varying delays and actuator saturation. Then to mitigate the effect of both time-varying delays and actuator saturation, an add-on delay-dependent anti-windup compensator is designed. Based on generalized sector conditions, less conservative delay-dependent sufficient conditions are derived in the form of a linear matrix inequality &#x0028 LMI &#x0029 to guarantee the asymptotic stability of the closed-loop system in the presence of time-varying delays and actuator saturation by using Lyapunov-Krasovskii functional and Jensen integral inequality. Based on sufficient conditions, the LMI-based optimization problem is formulated and solved to obtain the compensator gain which maximizes the estimation of the region of attraction and minimizes the upper bound of L2-gain. Nonlinear simulations are performed first using MATLAB &#x002F Simulink on a two-area four-machine power system to evaluate the performance of the proposed controller for two operating conditions, e.g., 3-phase to ground fault and generator 1 terminal voltage variation. Then the proposed controller is implemented in real-time on an OPAL-RT digital simulator. From the results obtained it is verified that the proposed controller provides sufficient damping to the inter-area oscillations in the presence of time-varying delays and actuator saturation and maximizes the estimation of the region of attraction.

Urchin-like NiO-NiCo2O4 heterostructure microsphere catalysts for enhanced rechargeable non-aqueous Li-O2 batteries.

Urchin-like NiO-NiCo2O4 microspheres with heterostructures were successfully synthesized through a facile hydrothermal method, followed by thermal treatment. The unique structure of NiO-NiCo2O4 with the synergetic effect between NiCo2O4 and NiO, and the heterostructure favour the catalytic activity towards Li-O2 batteries. NiCo2O4 is helpful for boosting both the oxygen reduction reaction and oxygen evolution reaction for the Li-O2 batteries and NiO is likely to promote the decomposition of certain by-products. The special urchin-like morphology facilitates the continuous oxygen flow and accommodates Li2O2. Moreover, benefitting from the heterostructure, NiO-NiCo2O4 microspheres are able to promote the transport of Li ions and electrons to further improve battery performance. Li-O2 batteries utilizing a NiO-NiCo2O4 microsphere electrode show a much higher specific capacity and a lower overpotential than those with a Super P electrode. Moreover, they exhibit an enhanced cycling stability. The electrode can be continuously discharged and charged without obvious terminal voltage variation for 80 cycles, as the discharge capacity is restricted at 600 mA h g-1, suggesting that NiO-NiCo2O4 is a promising catalyst for Li-O2 batteries.

Control Method for Maximizing Fault Voltage of Wind Generation-Integrated Power Systems With Consideration of DFIG–Grid Coupling

In the last decade, wind generation techniques have been actively developed, and wind farms comprising doubly-fed induction generators (DFIGs) have been widely deployed. As a result of the increasing penetration of wind generation, the output power of DFIGs requires adjustment to ensure an adequate supply of reactive current under fault conditions. Many studies show that the reactive capability of a DFIG is constrained by the rotor current and terminal voltage. However, the power adjustment of DFIGs changes the grid power flow and the terminal voltage of DFIGs due to the coupling between DFIGs and the grid. The permissible power range of DFIGs also changes because of the terminal voltage variation. The DFIG–grid coupling has not been considered, and the permissible power range is not accurate. The control methods based on the existing permissible power range do not maximize the power controllability of DFIGs. In this paper, the fault power characteristics of DFIGs under the constraints of rotor current and rotor speed are analyzed on the basis of a fault model. The permissible power range of DFIGs with consideration of internal and external constraints is established by analyzing the terminal voltage under the effect of the grid power flow. A control method for maximizing fault voltage is proposed on the basis of the established permissible power range. The simulation results verify the accurate calculation of the permissible power range. The power controllability of DFIGs could be fully utilized to improve fault voltage by adopting the proposed method.

Study on survivability of 18650 Lithium-ion cells at cryogenic temperatures

Abstract Passive survivability of Commercially-off-the-shelf 18650 lithium-ion cells is tested in a thermal scenario similar to lunar night. Survivability of cells in particular and battery pack in general is crucial for resumption of function of any lunar exploration rover after hibernation at every lunar night. The test is designed to include a batch of Commercial lithium-ion cells from different manufacturers, with different nameplate capacities and different States of Charge. The cell behaviour during the test is monitored in-situ using cell terminal voltage measurements. To comprehend the effect of exposure to extreme low temperatures some complementary tests like visual examination, dimensional measurements, Residual Gas Analysis to detect any leakage, electrical tests to appraise electrical performance and 3 dimensional x-ray computed tomography analysis to view cell internal features are carried out at ambient conditions on cells both prior-to and after soaking at low temperatures. Results indicate successful survivability of tested cells after extreme thermal soak without any significant physical or internal damage or electrical performance degradation. Variation in cell terminal voltage with temperature is a reversible change attributed to the reversible phenomenon of freezing of cell electrolyte which furthermore is confirmed through ex-situ measurement of freezing point of electrolyte extracted from tested cells.

Energy storage system utilisation to increase photovoltaic penetration in low voltage distribution feeders

This work introduces a new droop control for energy storage system (ESS) dispatch commands generation. The droop characteristic generates the ESS dispatch commands as a function of the power surplus at the substation transformer. The ESS with the new droop control aims to increase the level of Photovoltaic (PV) penetration in low voltage (LV) distribution networks, for the most economical solution in terms of ESS placement and sizing. The new droop control maintains two independent modes of operation; the first mode is fixed droop (FD) control, and the second mode is variable droop (VD) control. When FD control is employed, the droop characteristic remains invariable during hours of excessive PV generation, while the dispatch commands maintain the total of the grid parameters within the allowable range at all times. When VD control is performed, the slope of the droop characteristic was modified hourly, providing a sound grid operation at all times, while the accuracy of the dispatch commands was enhanced compared to the FD control mode. For the research, a real-life LV network case study that maintains a loop arrangement was utilised for modelling purposes. The operational grid constraints include transmission lines loading, terminal voltage variation, and substation transformer loading. Simulation results revealed that both of the proposed control modes maintain a sound grid operation for 70% PV penetration. The VD control performed better resulting in a lower cost ESS. The study demonstrated that an ESS located in the LV network performed a number of positive functions, including load management, peak load levelling and voltage support.

Small-signal model for the single-electron transistor: part I

A simple small-signal model of the single-electron transistor is presented. The terminal voltage variations are considered to be sufficiently small to result in small current variations that can be expressed using linearized relations. The derivation of such relations and the development of an equivalent circuit to represent them are presented. Two-port analysis of the small-signal circuit of the single-electron transistor is proposed and explained using various parameters such as impedance parameters, admittance parameters, and hybrid parameters. The variation of the magnitude of these parameters is plotted with respect to frequency. The transconductance and drain resistances and their frequency variation are also discussed. The effect of parasitic capacitance on the proposed small-signal model is also analyzed.

Origin of terminal voltage variations due to self-mixing in terahertz frequency quantum cascade lasers

We explain the origin of voltage variations due to self-mixing in a terahertz (THz) frequency quantum cascade laser (QCL) using an extended density matrix (DM) approach. Our DM model allows calculation of both the current-voltage (I-V) and optical power characteristics of the QCL under optical feedback by changing the cavity loss, to which the gain of the active region is clamped. The variation of intra-cavity field strength necessary to achieve gain clamping, and the corresponding change in bias required to maintain a constant current density through the heterostructure is then calculated. Strong enhancement of the self-mixing voltage signal due to non-linearity of the (I-V) characteristics is predicted and confirmed experimentally in an exemplar 2.6 THz bound-to-continuum QCL.

Bidirectional Battery Charger for PV Using Interleaved Fourport DC-DC Converter

In this paper, a four-port bidirectional dc-dc converter is proposed for grid-interactive photovoltaic (PV) system application. The four-phase topology is suitable for residential pumping, aerospace power requirements. The control of battery and different capacities of PV modules are naturally decoupled. In addition, the port interface with PV is current type which can implement maximum power point tracking (MPPT) and soft switching under wide variation of PV terminal voltage. Finally, simulation results are proposed to verify the power control in different operation modes. DOI: http://dx.doi.org/10.11591/telkomnika.v14i3.7894

Single-Source, Single-Destination Charge Migration in Hybrid Electrical Energy Storage Systems

In spite of extensive research it is still quite expensive to store electrical energy without converting it to a different form of energy. As of today, no single type of electrical energy storage (EES) element can fulfill all the desirable features of an ideal storage device, e.g., high-efficiency, high-power/energy capacity, low-cost, and long-cycle life. A hybrid EES system (HEES) consists of two or more heterogeneous EES elements, realizing the advantages of each EES element while hiding their weaknesses. HEES systems exhibit superior performance compared with homogeneous EES systems when appropriate charge allocation and replacement policies are developed and used. In addition, charge migration is mandatory because the optimal EES banks for charge allocation and replacement are in general different, and each EES bank has limited storage capacity. This paper formally describes the notion of charge migration efficiency and its optimization. We first define the charge migration architecture and the corresponding charge migration optimization problem. We provide a systematic solution for the single-source, single-destination charge migration problem considering the efficiency variation of the converters, the rate capacity and internal power loss of the storage element, the terminal voltage variation of the storage elements as a function of their state of charge, and so on. We also introduce the optimal solutions for both the time-constrained and -unconstrained versions of the charge migration problem formulations. Experimental results demonstrate significant charge migration efficiency improvement of up to 83.4%.

Online estimation of lithium-ion battery remaining discharge capacity through differential voltage analysis

The estimation of battery remaining discharge capacity (QRDC) is essential for the remaining driving range prediction on pure electric vehicles. A traditional QRDC estimation method is based on the determination of battery state of charge (SOC), in which the estimation accuracy could be affected by the variation in discharge conditions. In this research, a novel QRDC estimation method through differential voltage (dV/dQ) analysis is introduced for lithium-ion batteries. Through analyzing the characteristics of terminal voltage variation, the present QRDC could be estimated by the dV/dQ value, which is capable to provide an accurate estimation result under various discharge conditions. On a commercial lithium-ion battery, the dV/dQ method is implemented for QRDC estimation under pulse discharge profiles and dynamic profiles. The result shows that the dV/dQ method could provide accurate QRDC estimation results under various discharge profiles in the latter part of the discharge process, and the QRDC estimation accuracy could hence be improved by combining the differential voltage analysis with the SOC-based method. Owing to the simple computation process, the dV/dQ-based estimation method is very competitive in onboard applications.

Nonlinear fractional‐order power system stabilizer for multi‐machine power systems based on sliding mode technique

SummaryThis paper presents two novel nonlinear fractional‐order sliding mode controllers for power angle response improvement of multi‐machine power systems. First, a nonlinear block control is used to handle nonlinearities of the interconnected power system. In the second step, a decentralized fractional‐order sliding mode controller with a nonlinear sliding manifold is designed. Practical stability is achieved under the assumption that the upper bound of the fractional derivative of perturbations and interactions are known. However, when an unknown transient perturbation occurs in the system, it makes the evaluation of perturbation and interconnection upper bound troublesome. In the next step, an adaptive‐fuzzy approximator is applied to fix the mentioned problem. The fuzzy approximator uses adjacent generators relative speed as own inputs, which is known as semi‐decentralized control strategy. For both cases, the stability of the closed‐loop system is analyzed by the fractional‐order stability theorems. Simulation results for a three‐machine power system with two types of faults are illustrated to show the performance of the proposed robust controllers versus the conventional sliding mode. Additionally, the fractional parameter effects on the system transient response and the excitation voltage amplitude and chattering are demonstrated in the absence of the fuzzy approximator. Finally, the suggested controller is combined with a simple voltage regulator in order to keep the system synchronism and restrain the terminal voltage variations at the same time. Copyright © 2014 John Wiley & Sons, Ltd.