Constant Voltage Charging Research Articles

Numerical study on thermal characteristics comparison between charge and discharge process for lithium ion battery

The comparison of thermal characteristics between charge and discharge processes for lithium ion battery is usually neglected but has a strongly effect on its performance and safety. In this paper, an electrochemical-thermal cycling model is presented for a 5 Ah LiNi1/3Co1/3Mn1/3 26650 type lithium ion battery to evaluate and compare the thermal characteristics, includes the temperature distribution, heat generation and contribution during charge and discharge processes. The model is validated during cycling by experiment firstly. The results show that the constant current charge process displays a shorter duration, a higher peak temperature, and a quicker temperature rise rate compared with the corresponding discharge process. The heat generated at charge process is larger than that at discharge of lower rate (0.5 C and 1 C), while that of discharge accounts for 52.97%, exceeding the charge process at 1.5 C. The constant current charge ends at state of charge of 91.31%, 84.62% and 78.06% for 0.5 C, 1 C and 1.5 C, respectively, which means that more capacity is charged and more heat is generated during constant voltage charge at higher rate. Moreover, the dominant heat generation in charge process is the polarization heat of negative electrode, while the dominant heat generation in discharge process is the polarization heat of positive electrode.

Reconfigurable Hybrid Resonant Topology for Constant Current/Voltage Wireless Power Transfer of Electric Vehicles

This paper proposes a reconfigurable hybrid topology (RHT) for the constant current (CC)/constant voltage (CV) charging of electric vehicles. The proposed system combines the series–series and the inductor and double capacitors-series topologies. Two AC switches (ACSs) are utilized to change the CC and CV charging modes, without requiring an additional resonant network. A detailed analysis for designing the hybrid topology parameters is also presented; a three-kilowatt prototype was configured based on this analysis in order to validate the proposed system. The constructed prototype confirmed the stable mode changes, load fluctuations, CC/CV output characteristics and efficiency of the proposed system. The maximum efficiency of the proposed RHT was found to be 92.58%.

Hybrid charging strategy with adaptive current control of lithium-ion battery for electric vehicles

Abstract The synergy of electric vehicles (EVs) and renewable energy (RE) can improve the energy consumption, and participate in grid regulation by vehicle-to-grid (V2G) technology. In this paper, a hybrid charging strategy with adaptive current control for EVs is proposed in this synergistic process. First, the battery parameters are tested by the hybrid pulse power characteristic. Then, the equivalent circuit model is established and the charging characteristics are obtained. Second, inspired by the multi-stage constant current (MS-CC) method, a constant current-constant current-constant voltage (CC-CC-CV) charging strategy is proposed to moderate the temperature of the battery by suddenly dropping the charging rate in the second constant current stage. Third, for the first constant current stage, the adaptive current profile is utilized based on the variable internal resistance of the battery, which can effectively reduce the ohmic losses during the charging process. The comparative experiments show that the CC-CC-CV strategy can alleviate the maximum temperature of the battery. Without harming the charging time and capacity, the hybrid charging strategy can effectively reduce the ohmic losses by 1.2%. Moreover, these advantages are more significant as the charging current increases. Finally, the application of the proposed charging strategy in the smart building with RE is discussed.

PH Dependence of Phosphorus Speciation and Transport in Flow-Electrode Capacitive Deionization.

Electrochemical processes such as capacitive deionization have shown great promise for salt removal and nutrient recovery, but their effectiveness on phosphate removal was lower than other charged ions. This study hypothesized that the speciation and transport behaviors of phosphate ions are highly influenced by electrolyte pH, and it used experimental and modeling approaches to elucidate such impacts in flow-electrode capacitive deionization (FCDI) cells. Phosphate removal was investigated in either constant current (CC) or constant voltage (CV) charging mode with pH ranged from 5 to 9 in the feed solution. Results showed that the average P removal rate increased from 20.8 (CC mode) and 16.8 mg/min (CV mode) at pH 9 to 38.3 (CC mode) and 34.3 mg/min (CV mode) at pH 5 (84-104% in improvement), respectively. Correspondingly, the energy consumption reduced from 1.04 kWh/kg P at pH 9 to 0.59 kWh/kg P at pH 5 (42.9-56.1% in saving). Such benefits were attributed to the shift in dominant P-species from HPO42- to H2PO4-. Conversely, high-electrolyte pH (pH = 11) for flow-electrode led to ∼74.8% higher phosphate recovery during discharge compared with pH 5, which was associated with the higher distribution of phosphate ions in the electrolyte versus on the flow-electrodes due to surface charge change. These results improved our understanding in ion distribution and migration and indicate that solution pH is critical for operating FCDI reactors. It shed lights on the best practices on electrochemical phosphate removal and recovery.

Performance evaluation of constant current and constant voltage charge control modes of an inductive power transfer circuit with double-sided inductor-capacitor-capacitor and inductor-capacitor/series compensations for electrical vehicle battery charge applications

For electric vehicle (EV) battery chargers, inductive power transfer (IPT) has become popular day by day due to its features such as being safe, comfortable and weather proof. The constant current (CC) and the constant voltage (CV) charge control modes are important for high-efficiency charging and long-life use of Lithium-ion (Li-ion) batteries commonly used in EVs. However, IPT method requires a wide range of operating frequency in order to provide CC/CV charge control modes. In IPT applications, CC and CV charge control modes are mainly achieved with dc-dc circuits using compensation networks at the transmitter and receiver sides. In this study, performances of inductor-capacitor/series compensation and double-sided inductor-capacitor-capacitor compensation topologies are evaluated based on CC/CV charge control modes. The analytical evaluation is presented in terms of voltage and current regulations during the entire charge control period. Finally, presented analytical evaluation is confirmed with ANSYS software providing field-electric common simulation to predict real response of compensation topologies. In the simulation work, both compensation topologies are operated for the maximum 2.5 kW output power and at the 250 V-450 V output voltage range.

Constant-Frequency and Noncommunication-Based Inductive Power Transfer Converter for Battery Charging

Compared with conductive charging, wireless inductive-power-transfer (IPT) charging exhibits higher potential as it avoids physical contact and provides convenient user experience. Regrettably, it is challenging for IPT converters to comply with the constant current (CC) and constant voltage (CV) charging profiles, while optimizing power efficiency. To achieve such goals, the existing IPT converters can apply multistage converter, dual side, or variable frequency modulation with feedback wireless communication. However, applying multistage converter increases cost and loss, while the stability of the IPT converter with dual side or variable frequency modulation can be at risk if communication fails. This article proposes a single-stage IPT converter for battery charging. With a constant operating frequency and without feedback wireless communication, the receiver side directly regulates the output to comply with the CC/CV charging profile, while the transmitter side aids in the reduction of the modulated phase shift angle at the receiver side, thus improving the efficiency. No wireless communication between the transmitter and receiver sides benefits both the hardware cost and stability. Also, we implement implicitly an output voltage regulation, further avoiding the need of an extra dc–dc converter. We verify experimentally the proposed control method in a 1-KW charging platform with a measured peak efficiency up to 94.35%.

Actively temperature controlled health-aware fast charging method for lithium-ion battery using nonlinear model predictive control

Previous research has shown that a drastic reduction of charging time compared to constant current constant voltage (CC/CV) charging protocol is possible while suppressing degradation causes by combining constant charging and pulse discharging current. However, effects of temperature variation on side reaction and lithium plating and effects of the frequency of pulse current on lithium stripping have not been considered. In fact, charging currents and operating temperatures dominantly affect the cycle life of battery, where both side reaction and lithium plating are competing. In this paper, reduced order electrochemical life models are developed and validated against experimental data collected at different currents and temperatures and then used to find out optimal temperatures at given charging currents with respect to degradation rates. Thereafter, an optimal charging current at different SOCs has been found using nonlinear model predictive control and then the optimal temperature is determined from the relationship obtained by the models, which reduces side reaction rate and lithium plating rate. In addition, pulse discharging current is added to promote the lithium stripping that recovers ions out of the plated lithium, where the amplitude and frequency of the pulse current are optimized using the models. Finally, the proposed charging method and the 1 C CC/CV charging method were tested in Battery-In-the-Loop using a large format pouch type lithium ion battery to compare each other, where 61% and 39% of charging time is reduced up to 80% and 100% SOC, respectively, while the capacity fade is comparable.

Diffusion stress modeling of micro hollow spherical shell electrode

Lithium-ion batteries (LIBs) can be used in the field of electronics widely. It is of great significance to understand the mechanism of diffusion-induced stress and then to enhance the performance of LIBs. This study aims to investigate the diffusion-induced stress (DIS) of a novel electrode material, i.e., carbon nano-spherical shell electrode. Firstly, we introduce single-phase diffusion model to analyze the influence factors on DIS under constant voltage charge and discharge conditions, to name a few, initial concentration of lithium ions and electrode size. To investigate how lithium ion concentration evolves in the spherical shell electrode, the initial concentration of lithium ions is controlled. To analyze the influence of electrode size, we alter the size and compute the corresponding radial and circumferential stress. It shows that lower initial lithium ion concentration and smaller electrode size give smaller DIS.

Extreme Fast Charging: The Current State of Understanding

Enabling fast charging between 10 to 15 minutes has been identified as one of the key challenges to facilitate rapid penetration of battery electric vehicles in the mass market. 1,2 Fast charging in 10 to 15-minute, however, could create multiple performance and safety consequences for the conventional graphite-based lithium ion batteries. Our earlier studies have identified the key bottlenecks of enabling extreme fast charging for a low loading (⁓2 mAhcm-2) cell (high power design).3–5 This presentation will discuss the effects of extreme fast charging on moderate loading cells (⁓3 mAhcm-2). The key cell limitations during such high rate charging will be revisited for moderately loaded graphite/NMC532 single layer pouch cells. The long-term performance and aging issues for 4C to 6C charging rates will be shown with experimental data. The identified dominating aging mechanisms will also be presented for the two different fast charging rates.The benefits of using different charging protocols, e.g., constant current- constant voltage and several multistep charging protocols will also be shown. Lastly, the opportunities and challenges of Li plating detection via electrochemical means will also be discussed.

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

An Integrated Inductive Power Transfer System Design With a Variable Inductor for Misalignment Tolerance and Battery Charging Applications

Inductive power transfer (IPT) technology is useful for electric vehicle (EV) charging because of safe, flexible, and convenient features. In this paper, an integrated IPT system design employing variable inductor control is proposed to achieve a target constant current (CC) and constant voltage (CV) battery charging profile with misalignment tolerance. The system is implemented under a fixed switching frequency in both CC and CV modes. Soft switching of the primary inverter can be achieved over the entire charging process and allowed misalignment range without additional switches or dc–dc converters. Theoretical circuit analysis and the system design process are presented. A 3.3-kW prototype is implemented with a 210-mm air gap to demonstrate the validity of the proposed method. Experimental results show that the target CC and CV charging profile can be achieved by adjusting the variable inductor with up to 120 mm of lateral and 300 mm of vertical misalignment. The maximum efficiency of the proposed system is 96.1% at full output power and stays above 95% throughout CC operation.

Thermodynamic reversible cycles of electrochemical desalination with intercalation materials in symmetric and asymmetric configurations

Conventional capacitive deionization (CDI) with carbon electrodes is a desalination process based on the formation of electrical double layer. Intercalation capacitive deionization (ICDI), a category of CDI based on intercalation materials as electrodes, achieves desalination by inserting ions into the crystal lattice of the electrode when a voltage is applied. It has been proven numerically that a thermodynamically reversible CDI cycle always consumes electrical work that equals the Gibbs free energy of the separation. We conducted a thermodynamic analysis of a four-stage reversible cycle for both symmetric and asymmetric ICDI using Frumkin isotherm to describe the electrode-solution chemical equilibrium. We provided both analytical and numerical proof showing the electrical work to complete a four-stage ICDI cycle is exactly identical to the Gibbs free energy of separation. Our thermodynamic analysis also shows ICDI is typically more energy efficient than CDI if constant voltage charging and discharge are performed to complete the same separation.

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.

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 communication-free WPT system based on transmitter-side hybrid topology switching for battery charging applications

A communication-free wireless power transfer system based on transmitter-side hybrid topology switching for various battery charging applications is proposed in this paper. The method realizes the stable and reliable constant current (CC) and constant voltage (CV) outputs by the inherent characteristics of the designed hybrid topology. Besides, the zero phase angle condition can be obtained, which enhances the power transmission capability and improves system efficiency. The transition point from the CC to CV charging mode is determined by the battery charging voltage, which is estimated in real-time by measuring the root-mean-square value of high-frequency inverter output current. Then, the whole charging process can be operated by the transmitter-side controller; hence, the receiver-side controller is unnecessary. The advantages are that wireless communication links for real-time feedback of charging parameters between the transmitter and receiver are avoided, sophisticated control strategies are no longer required, and a lightweight, miniaturized, and compact receiver is guaranteed. Finally, to verify the effectiveness and practicability of the proposed approach, a confirmatory experimental setup with 80 V charging voltage and 5 A charging current is constructed. The experimental results match the theoretical analysis.

An Aqueous Conducting Redox-Polymer-Based Proton Battery that Can Withstand Rapid Constant-Voltage Charging and Sub-Zero Temperatures.

Electrodes based on organic matter operating in aqueous electrolytes enable new approaches and technologies for assembling and utilizing batteries that are difficult to achieve with traditional electrode materials. Here, we report how thiophene‐based trimeric structures with naphthoquinone or hydroquinone redox‐active pendent groups can be processed in solution, deposited, dried and subsequently polymerized in solid state to form conductive (redox) polymer layers without any additives. Such post‐deposition polymerization offers efficient use of material, high mass loading (up to 10 mg cm−2) and good flexibility in the choice of substrate and coating method. By employing these materials as anode and cathode in an acidic aqueous electrolyte a rocking‐chair proton battery is built. The battery shows good cycling stability (85 % after 500 cycles), withstands rapid charging, with full capacity (60 mAh g−1) reached within 100 seconds, allows for direct integration with photovoltaics, and retains its favorable characteristics even at −24 °C.

An analytical model for the CC-CV charge of Li-ion batteries with application to degradation analysis

Abstract While the constant current charge time (CCCT) and constant voltage charge time (CVCT) are increasingly used for the state of health (SOH) estimation of Li-ion batteries, their correlations with battery degradation are not investigated comprehensively. This paper develops an analytical model to quantify the chargeable capacity of a Li-ion battery under a CC-CV profile, in which CCCT and CVCT are identified as two uncoupled parameters. The model is verified using a battery dataset of cycling tests subjected to 19 different test conditions with different discharge currents, ambient temperatures, and rest times. The behaviors of CCCT and CVCT during battery degradation are studied in terms of chargeable capacity fade. A new health indicator, the CV-CC time ratio, is developed for degradation analysis. Two partial CC-CV cases are also considered in the studies: in one case, the partial CC-CV charge starts after different discharged depths, and in the other case, different fast charging policies are executed before the partial CC-CV charge.

A Control Approach Integrating Electric Vehicle Charger and Dynamic Response of Demand-Side Resource Aggregators

Regardless of whether level 1, level 2, or dc fast charging, several methods are under development or available as an aftermarket option for Plug-in electric vehicles (EVs). While confining the charging behavior of EVs to low-load periods is difficult, it leads to significant and uncertain load peaks and valleys in the utility power network. Therefore, this paper proposes a new method for an electric vehicle charger. The proposed charging method involves power supervisory characteristics on the basis of the paradigm of a constant-current and a constant-voltage (CC–CV) charger so that the external commands from the demand-side resource aggregator in the smart grid can be executed. In the method, first, a feedback loop is included in the controller to formulate the relationship between battery voltage and charging power as a quadratic concave downward polynomial. The controlled output power at the beginning of constant voltage charging is then set to the maximum value of the quadratic polynomial because the charging power requirement near this point is closed to the highest. Hence, if the charging power is lower than the allowable maximum power, the proposed charger is determined to have followed the traditional CC–CV charging steps. On contrast, the proposed circuit launches the power control loop when the actual charging power is beyond the maximum power limitation of aggregator. The proposed charger can keep the power consumption inside an allowable range of aggregator. That is the power consumption at the EV charging sites becomes directly programmable by their aggregators. The proposed method is examined by conducting an interactive test of a remote energy management system and the proposed controller. The results revealed that the proposed method provide an easy method to dynamically control consumption pattern of the EV charging for demand-side power management.

Analysis and Design of an LCCC/S-Compensated WPT System With Constant Output Characteristics for Battery Charging Applications

The wireless power transfer (WPT) system has been extensively studied for its safety, convenience, and esthetics and has gradually been introduced into our life applications. In order to maintain battery performance, constant-current (CC) and constant-voltage (CV) charging outputs are generally regarded as the dominant charging modes. However, battery equivalent resistance changes significantly during the charging, so it is difficult to simultaneously achieve load-independent CC and CV charging outputs and zero phase angle (ZPA) condition. This article proposes a new LCCC/S topology and its corresponding parameter tuning method to obtain CC and CV charging modes at two different ZPA operating frequency points, respectively. In addition, it is worth mentioning that the receiver has only one compensation capacitor, which follows the principle that the receiver of the WPT system should remain compact and portable. Furthermore, a simple frequency modulation controller is designed to solve the problem of inaccuracies of the charging outputs due to parasitic losses of components and fluctuations of dc input voltage. Finally, a verification setup with 3-A output current in the CC mode and 48-V output voltage in the CV mode was built to validate the feasibility and rationality of the proposed LCCC/S-compensated WPT system and the corresponding control method.

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.