Current Constant Voltage Charge Research Articles

An improved resistance-based thermal model for prismatic lithium-ion battery charging

This study proposed a dynamic resistance-based thermal model to predict the temperature evolution of a prismatic lithium-ion battery in fast and regular charging strategies. The effects of battery temperature, state of charge (SOC), and charging current on resistance were investigated to form a dynamic heat generation model. This model included both the heat generation of battery body and the heat generation of electrodes. Then the charging resistance-based thermal model was used to predict the temperature distribution and temperature evolution of a 50 Ah prismatic battery under different charging strategies and ambient temperatures. The charging strategies included a multi-stage constant current-constant voltage (MSCC-CV) for fast charging and a constant current-constant voltage (CC-CV) for regular charging. Experiments verified the prediction accuracy of the proposed thermal model. The results showed that the dynamic thermal model accurately predicted the temperature distribution and its evolution under different charging strategies and ambient temperatures. With regard to temperature distribution prediction, the average root mean square errors (RMSEs) of temperature among the five test points were 0.43 °C for the MSCC-CV charging strategy and 0.3 °C for the CC-CV charging strategy. For the temperature prediction under various ambient temperatures, the average RMSEs at different ambient temperatures were 0.34 °C for the MSCC-CV strategy and 0.25 °C for the CC-CV strategy. Finally, the effect of the charging and discharging resistance on the temperature prediction under the MSCC-CV charging condition was studied. Although the discharging resistance-based thermal model could describe the temperature change with charging time, it showed higher predicted temperatures than the tested values and a larger estimation error than the charging resistance-based thermal model.

Pulsed Current Based Fast Charging Methods for Li-Ion Battery

The increasing rate of greenhouse gas emissions from conventional cars and its impact on global warming in the recent years has led to the technological advancements in the evolution of electric vehicles. Developing fast charging methods for Li-ion batteries is one such technological advancement and soon it will be imperative to promote the usage of electric vehicles in increased numbers. However, fast charging of Li-ion battery accelerates aging mechanisms [1] and triggers thermal runaway condition. As a result, this study investigates pulsed current based fast charging methods employed on C/NMC batteries. Pulses of current at low frequency (mHz) [2] and high frequency (KHz) are used with an extended pulse current period, thanks to higher voltage limit based on ohmic drop compensation [3]. The findings of the experimental investigation clearly establishes that a compromise has to be found between relaxation period and temperature in order to achieve fast charging. For instance, on one hand, a 2C current pulse with an on duration of 3s and relaxation duration of 1s allows to save 45% of recharging time when compared with standard constant current-constant voltage charging (CC-CV) at 0.5C as shown in the figure below. On the other hand, the temperature variation does not exceed 20°C beyond ambient which is lower than that of its counterpart CC-CV at 2C. Hence, the experimental investigation successfully opens the doors to implement fast charging methods on C/NMC batteries by limiting the temperature rise, there by arresting the ageing of batteries and thermal runaway condition.Keyword: Li-ion, Fast charging, Current pulse, Ohmic drop compensation, Temperature, Thermal runaway. Figure 1

A 6.78-MHz Single-Stage Wireless Charger With Constant-Current Constant-Voltage Charging Technique

A 6.78-MHz fully integrated single-stage wireless charger with constant-current constant-voltage (CC-CV) charging technique for resonant wireless power transfer applications is presented. Based on the principle of three-mode reconfigurable resonant regulating ( $R^{3}$ ) rectifier, the proposed charger achieves high efficiency and low cost by realizing power rectification, voltage regulation, and CC-CV charging in a single power stage. The power stage of the proposed charger consists of only four nMOS power transistors. A bootstrapping technique using a single-input-dual-output voltage doubler with adaptive phase control is also proposed to integrate bootstrap capacitors on-chip. The CC loop and the CV loop share the same pulsewidth modulation (PWM) controller with smooth transition from the CC mode to the CV mode. An on-chip current sensing and estimation circuit is specially designed for the CC loop. Fabricated in a standard 0.35- $\mu \text{m}$ CMOS process with a die area of 8 mm2, the charger delivered a maximum charging current of 1.5 A, and the measured peak efficiency reached 92.3% and 91.4% when the charging currents were 1 A and 1.5 A, respectively.

A Reconfigurable On-Board Power Converter for Electric Vehicle With Reduced Switch Count

This paper proposes a compact reconfigurable on-board power converter for low voltage electric vehicle. The proposed converter serves the purpose of a battery charger as well as a 3-phase voltage source inverter (VSI) to drive the traction motor. The 3-phase VSI is the backbone of this converter that can be either reconfigured to a propulsion unit or to a battery charger by adding few more power electronics components. During charging mode, the topology is reconfigured to form a front-end boost power factor correction rectifier which is cascaded by a DC-DC converter through a DC link. The same power stage is reconfigured to operate as a 3-phase VSI to drive the traction motor during propulsion mode. Thus, it reduces the switch count by eliminating the requirement of a separate inverter stage. Simultaneously the weight, volume, and cost of the overall system are reduced. Unified control technique is implemented which is capable to achieve near-unity power factor operation of front-end boost rectifier as well as optimal battery charging without sensing the DC link voltage. This control scheme implements a single control loop for both stages by eliminating the need of two separate control loop for each stage of the charger. A 470 W scaled-down prototype is developed and its performance is validated with Constant Current-Constant Voltage charging of a 24 V, 30Ah battery pack in charging mode and with a 400W BLDC motor in propulsion mode.

Model-Instructed Design of Novel Charging Protocols for the Extreme Fast Charging of Lithium-Ion Batteries Without Lithium Plating

Relatively long recharge time of high-energy density lithium-ion batteries (LIBs) is one of the major obstacles to the widespread deployment of electric vehicles (EVs). Excessive fast charge of LIBs can cause severe safety issues, the most significant of which is lithium plating. In addition to the consumption of cyclable lithium, dendrite-like lithium plating can cause short-circuiting within the cell, which could lead to catastrophic failure. In addition to the developments of advanced electrolytes, active materials and electrodes, the fast charging capability of LIBs can be improved by using optimized charging protocol. In this work, the Pseudo2D battery model is first used to screen some conventional charging protocols proposed for fast charging, including the constant-current constant-voltage charging (CCCV), constant-power constant-voltage charging (CPCV), multi-stage constant-current charging, and pulse current charging. A semi-optimal charging protocol is then developed by automatically modifying the charge current such that the cell is charged at close-to-maximum current without lithium plating. Based on the features of the semi-optimal protocol, two practical novel fast charging protocols are proposed which allow charging the cell at a higher rate without lithium plating. Through simulation, we show that the no-plating capacity after 10 min charge can be improved by up to ∼10.7% compared to CCCV charging for a 2.5 mAh cm−2 cell and ∼18.8% for a 4 mAh cm−2 cell, when the proposed charging protocols are used.

Evaluation of Charging Strategies for Valve Regulated Lead-Acid Battery

The present paper considers the evaluation of temperature regulated and unregulated charging strategies to select the appropriate one to ensure extended battery life with reduced charging time. Temperature regulated pulse charging (TRPC) and temperature regulated reflex charging (TRRC) are compared with the Constant current-constant voltage (CC-CV) charging strategy. In the case of CC-CV charging temperature of the battery rises with the magnitude of the current being injected and cannot be regulated without any external cooling arrangement. Impact on the State of health (SOH) and the expected lifespan of the battery are considered as the parameters of evaluation. Temperature regulated strategies are implemented through a discrete electro-thermal model, which acts as a temperature estimator. The co-efficient of the estimators corresponds to the battery parameters such as internal resistance and thermal time constants, entropy, etc. Temperature regulation is ensured in the three identified sections of charge deposited vs magnitude of the injected current. Three sections are identified as sections where the injected current is not sufficient to raise the battery temperature to set limit or not and the level of charge submitted as compared to normal charging. Experimentation is carried with 12 V, 26 Ah Valve regulated lead-acid battery to justify that increase in temperature reference of regulation allows submission of higher charge for the same charging rate. It is demonstrated that TRPC results in a significant reduction (≈60%) in charging time as compared to CC-CV and TRRC. For the same charging time as achieved with TRPC, TRPC results in almost double the expected life of operation and better SOH as compared to CC-CV and TRRC.

The Charging Control and Efficiency Optimization Strategy for WPT System Based on Secondary Side Controllable Rectifier

The equivalent resistance of the battery will change during charging in practical applications, so it is difficult to design a wireless power transfer (WPT) system with accurate constant current (CC) and constant voltage (CV) output characteristics. In addition, the WPT system efficiency is also affected by the change of equivalent resistance. Therefore, this paper studies the charging control and efficiency optimization strategy for the WPT system with dynamic loads. The WPT system with a structure of double-sided LCC compensation topology and containing controllable rectifier circuit at the secondary side is established, and the working process of full-bridge controllable rectifier circuit is analyzed. Then the output characteristics of the WPT system are analyzed. The expressions of the optimal transmission efficiency and the optimal equivalent impedance of the full-bridge rectifier are derived. The relationships between the equivalent impedance of the capacitor-filtered full-bridge controllable rectifier circuit and the phase shift angle, the charging current and the phase shift angle are also obtained. In this paper, the CC and CV charging strategies based on phase shift control of controllable rectifier circuit and efficiency optimization strategy based on dynamic equivalent impedance matching are proposed, which can improve the WPT system transmission efficiency while realizing CC and CV charging. Finally, the effectiveness of the proposed control strategy is verified by simulation and experiment. The WPT system realizes CC charging mode and CV charging mode in turn when the load resistance changes from $5~\Omega $ to $30~\Omega $ , and the overall efficiency is up to 90.71% at the transmission distance of 15cm.

Investigation of lithium-ion battery degradation mechanisms by combining differential voltage analysis and alternating current impedance

18650-type cells with 2.5 Ah capacity are cycled at both 25 °C and 0 °C separately, and at 25 °C two charging protocols (constant current, and constant current-constant voltage charge) are used. Differential voltage analysis (dV/dQ) and alternating current (AC) impedance are mainly used to investigate battery degradation mechanisms quantitatively. The dV/dQ suggests that active cathode loss and loss of lithium inventory (LLI) are the dominating degradation factors. Significant microcracks are observed in the fatigued cathode particles from the scanning electron microscopy (SEM) images. Crystal structure parameters of selected fatigued batteries at fully charged state are determined by in situ high-resolution neutron powder diffraction. Obvious increases of ohmic resistance and solid electrolyte interphase (SEI) resistance occur when the battery capacity fade falls beneath 20%. Continuous charge transfer resistance and Warburg impedance coefficient (W.eff) increase are observed in the course of cycling. Correlation analysis is performed to bridge the gap between material loss as well as LLI and impedance increase. The increase of the charge transfer resistance is related to both active cathode loss and LLI, and a functional relationship is revealed between LLI and W.eff regardless of the used cycling protocols.

Variable-Parameter T-Circuit-Based IPT System Charging Battery With Constant Current or Constant Voltage Output

Load-independent output characteristics of inductive power transfer (IPT) systems are increasingly popular in battery charging. This paper proposes a novel variable-parameter T-circuit (VT) for an IPT system charging a battery with constant current (CC) or constant voltage (CV) output. The VT can transfer a CC/CV input to a CC or CV output by using an ac switch and a passive component (inductor or capacitor). An IPT system with a VT for CC–CV charging can reduce the number of passive components and ac switches. Besides, the proposed VT merits more design freedom of charge current/voltage with the constraints imposed by the loosely coupled transformer parameters compared to that of the traditional one. In addition, there are three kinds of VTs for various IPT charging systems with different requirements. A 400 W laboratory-scale prototype with a 150 mm air gap was built to verify the theoretical analyses. Both electronic load and lead-acid battery are utilized to verify the charging profile of the proposed method. The experimental results of the IPT system indicate that the fluctuation of the charging current in CC mode is less than 2%, and the change rate of charging voltage in CV mode is within 2.9%. The maximum overall efficiency 93.93% of the charging system is achieved from a dc 110 V input to a dc 100 V output.

Phase-Locked Loop Combined With Chained Trigger Mode Used for Impedance Matching in Wireless High Power Transfer

In a wireless power transfer system (WPTS), the control technique of the active rectifier is vital for improving the transfer efficiency of the resonant network, expanding the operating range of the load, and increasing the power density. An indispensable component of such control technique is the accurate and reliable phase-locked method for the resonant current. However, the traditional phase-locked method based on the DSP controller tends to lose driver pulses, which might cause damage to the safe operation of the WPTS. This article illustrates the essential reason why the driver pulses lose and proposes a phase-locked loop combined with the chained trigger mode (PLL-CTM) that can lock the phase of the resonant current accurately and produce the driver pulses reliably. With the proposed PLL-CTM applied, the reliability of the WPTS can be enhanced tremendously. Furthermore, based on the PLL-CTM, this article also presents a double-side phase shift control (DPSC) strategy to achieve constant-current constant-voltage charging and minimize the power loss of the resonant network simultaneously. Finally, a 500-W WPT prototype is built to verify the feasibility of the DPSC with PLL-CTM. Benefiting from the DPSC with PLL-CTM, the WPTS not only obtains a high accuracy in steady state, but also achieves a good dynamic performance with the step change of R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> and R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Eref</sub> .

An Experimental Analysis on the Impacts of Different Pulse Charging Frequencies on Lithium Ion Batteries

Lithium ion batteries can be charged by different techniques. CCCV (constant current, constant voltage) charging is the conventional method that is predominantly employed for charging the lithium ion batteries. Pulsed current charging is seen as one of the promising techniques for fast charging and high energy efficiencies.1–3 However, the impacts on the batteries due to the variations in the frequency of pulses are seldom investigated on high energy batteries. The objective of this work is to experimentally investigate the impacts of current pulses at different frequencies on commercial LTO and NMC batteries. The results of charging time, overall cycle life and efficiency are then compared with the conventional charging method. In this experiment, pulsed current profile is controlled by varying the duty cycle and amplitude to maintain the average for effective comparison with CCCV charging. Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscope (SEM) are used in analyzing the impacts of both the charging protocols on different lithium battery chemistries. References J. M. Amanor-Boadu, M. A. Abouzied, and E. Sanchez-Sinencio, IEEE Trans. Ind. Electron., 65, 7383–7394 (2018).M. F. Hasan, C.-F. Chen, C. E. Shaffer, and P. P. Mukherjee, J. Electrochem. Soc., 162, A1382–A1395 (2015) http://jes.ecsdl.org/cgi/doi/10.1149/2.0871507jes.H. Z. Z. Beh, G. A. Covic, and J. T. Boys, 2013 IEEE Energy Convers. Congr. Expo. ECCE 2013, 315–320 (2013).

A Novel Fast Charging Method Based on Simplified Pseudo Two- Dimensional Model Considering Side Reactions for Lithium-ion Battery

A novel fast charging algorithm based on a simplified electrochemical thermal battery model considering side reactions is proposed in this paper. The method applies multistage charging strategies to charge the battery. The results of the testing on a high power NMC lithium-ion cell subjected to the method are reported. The presented charging curve permits a full recharging of the cell in approximately 35 minutes, nearly 50% of the Constant Current-Constant Voltage (CC-CV). The model is used to dynamically estimate the side reaction rate and degradation representatives at anode. The simulation and experimental results show that the proposed charging method reduces the side-effects generally accompanied by the normal CC-CV charging and slows down aging rate of a cell.

A Multi-Objective Adaptive Control Framework in Autonomous DC Microgrid

This paper presents a multi-objective adaptive power management scheme for an autonomous dc microgrid which consists of a novel adaptive gain-based proportionate charging/discharging strategy in order to provide energy balancing between battery energy storage systems (BESSs) of different capacities. As BESSs are a key component to maintain reliability and stability in an autonomous microgrid, control measures for longevity of these units should be properly investigated. Following the recommended way of charging for BESSs, i.e., constant current/constant voltage (CV) charging, the conventional methods undergo mode switching using a floating reference value to control CV charging which does not guarantee zero current when the battery is fully charged. To account for this issue, a novel progressive de-rating control scheme for PV in a seamless fashion to carry out CV charging of BESSs is done using the adaptive mechanism introduced by model reference adaptive control scheme for optimized power management between sources and loads. Furthermore, emergency events such as load shedding and load following operation of PV have also been discussed in detail. The proposed control strategy is simulated in MATLAB/SIMULINK environment and tested on a 1 kVA FPGA-based experimental prototype to validate the control approach under different scenarios.

An Efficient and Fast Li-Ion Battery Charging System Using Energy Harvesting or Conventional Sources

This paper presents a multi-input battery charging system that is capable of increasing the charging efficiency of lithium-ion (Li-ion) batteries. The proposed battery charging system consists of three main building blocks: a pulse charger, a step-down dc–dc converter, and a power path controller. The pulse charger allows charging via a wall outlet or an energy harvesting system. It implements charge techniques that increase the battery charge efficiency of a Li-ion battery. The power path controller (PPC) functions as a power monitor and selects the optimal path for charging either via an energy harvesting system or an ac adapter. The step-down dc–dc converter provides an initial supply voltage to start up the energy harvesting system. The integrated circuit design is implemented on a CMOS 0.18 μm technology process. Experimental results verify that the proposed pulse charger reduces the charging time of 100 mAh and 45 mAh Li-ion batteries respectively by 37.35% and 15.56% and improves the charge efficiency by 3.15% and 3.27% when compared to the benchmark constant current-constant voltage charging technique. The step-down dc–dc converter has a maximum efficiency of 90% and the operation of the PPC is also verified by charging the battery via a thermoelectric energy harvesting system.

Model Predictive Control for Lithium-Ion Battery Optimal Charging

Charging time and lifetime are important performances for lithium-ion (Li-ion) batteries, but are often competing objectives for charging operations. Model-based charging controls are challenging due to the complicated battery system structure that is composed of nonlinear partial differential equations and exhibits multiple time-scales. This paper proposes a new methodology for battery charging control enabling an optimal tradeoff between the charging time and battery state-of-health (SOH). Using recently developed model reduction approaches, a physics-based low-order battery model is first proposed and used to formulate a model-based charging strategy. The optimal fast charging problem is formulated in the framework of tracking model predictive control (MPC). This directly considers the tracking performance for provided state-of-charge and SOH references, and explicitly addresses constraints imposed on input current and battery internal state. The capability of this proposed charging strategy is demonstrated via simulations to be effective in tracking the desirable SOH trajectories. By comparing with the constant-current constant-voltage charging protocol, the MPC-based charging appears promising in terms of both the charging time and SOH. In addition, this obtained charging strategy is practical for real-time implementation.

An Improved Wireless Battery Charging System

This paper presents a direct wireless battery charging system. The output current of the series-series compensated wireless power transfer (SS-WPT) system is used as a current source, and the output voltage of AC-DC converter controls the current source. Therefore, the proposed wireless battery charging system needs no battery charging circuit to carry out charging profiles, and can solve space constraints and thermal problems in many battery applications. In addition, the proposed wireless battery charging system can implement easily most other charging profiles. In this paper, the proposed wireless battery charging system is implemented and the feasibility is verified experimentally according to constant-current constant-voltage charging profile or multi-step current charging profile.

An Experimental Analysis on the Impacts of Current Pulsing with Varying Current Amplitudes on Lithium-Ion Cells

Lithium-ion cells can be charged using different techniques. CCCV (constant current, constant voltage) charging is the standard method that is typically employed for charging the lithium ion batteries/cells. A theoretical analysis of pulse charging using varying current amplitudes with the relaxation periods has shown reduction in the charging time without reaching lithium saturation over the period [1]. It is based on the concept of increasing surface concentration of lithium at initial stages and maintaining the concentration value close to the saturation, resulting in enhanced performance. The objective of this work is to experimentally analyze the impacts of varying current pulse amplitudes on the lithium ion battery materials. This method comprises constant width charging, a rest period and decrease in applied current as the charging progress. Implementing the pulsed currents of different amplitudes on cathodic (Lithium Iron Phosphate, Lithium Manganese Dioxide) and anodic (Graphite and Li 4Ti5O12) half cells separately will impact the electrode materials in various ways. The results of charging time and effects on the electrode materials are compared with conventional charging method. Figures 1 and 2 show the constant current and a portion of pulsed current profile that are used in the analysis. In this experiment, pulsed current profile is controlled by varying the duty cycle and relaxation periods between pulses while the current amplitudes are reduced as the charging progress. SEM and equivalent circuit modelling based on EIS data are used in analyzing the impacts of both the charging protocols on the lithium-ion cells.

Multi-Objective Optimal Charging Method for Lithium-Ion Batteries

In order to optimize the charging of lithium-ion batteries, a multi-stage charging method that considers the charging time and energy loss as optimization targets has been proposed in this paper. First, a dynamic model based on a first-order circuit has been established, and the model parameters have been identified. Second, on the basis of the established model, we treat the objective function of the optimization problem as a weighted sum of charging time and energy loss. Finally, a dynamic programming algorithm (DP) has been used to calculate the charging current of the objective function. Simulation and experimental results show that the proposed charging method could effectively reduce the charging time and decrease the energy loss, compared with the constant-current constant-voltage charging method, under the premise of exerting little influence on the attenuation of battery capacity.

An Experimental Analysis on the Impacts of Current Pulsing with Varying Current Amplitudes on Lithium Ion Cells

Lithium ion batteries can be charged by different techniques. CCCV (constant current, constant voltage) charging is the conventional method that is predominantly employed for charging the lithium ion batteries. A theoretical analysis of pulse charging using varying current amplitudes with the relaxation periods has shown reduction in the charging time without reaching lithium saturation over the period [1]. It is based on the concept of increasing surface concentration of lithium at initial stages and maintaining the concentration value close to the saturation. The objective of this work is to experimentally investigate the impacts of varying current pulse amplitudes on the lithium ion battery materials. This method consists of constant width charging, rest period and the applied current is decreased as the charging progress. Implementing the pulsed currents of different amplitudes on cathodic (Lithium Iron Phosphate) and anodic (Graphite and Li 4Ti5O12) half cells separately creates varied impacts on the electrode materials. The results of charging time and overall cycle life are then compared with conventional charging method. Figures 1 and 2 show the constant current and a portion of pulsed current profile that are used in the analysis. In this experiment, pulsed current profile is controlled by varying the duty cycle, relaxation periods are included in between pulses and current amplitudes are reduced as the charging progress. EIS, SEM and XRD are used in analyzing the impacts of both the charging protocols on the lithium ion cells.

A LOW TEMPERATURE INCREASE TRANSCUTANEOUS BATTERY CHARGER FOR IMPLANTABLE MEDICAL DEVICES

Many medical groups have used wireless battery charging technology for rechargeable batteries used in implantable devices. During charging, battery heat is lost from the battery and other heat sources within an implantable device, which may be harmful to patients’ tissues. Therefore, charging batteries with minimum discomfort to patients while replenishing battery capacity as much as possible is a challenge. In this paper, a constant voltage with a different limiting current strategy for a lithium-ion polymer battery is proposed, thereby modulating the limiting current rate that reduces battery temperature increase. Experiments show that better safety charging performance for 260, 600, and 1000[Formula: see text]mAh lithium-ion polymer batteries can be obtained by the proposed current-limiting method. Compared with conventional constant-current–constant-voltage charging strategies, the maximum battery temperature increase is improved.