Ali Sari

Improved Supercapacitor Floating Ageing Interpretation Through Multipore Impedance Model Parameters Evolution

Like any electric energy storage system, supercapacitors have a limited lifetime. Indeed, they degrade with time because of parasitic reactions between electrodes and electrolyte. Porous electrodes are complex structures and pores have size dispersion because of manufacturing processes. This paper proposes to study the specific impact of supercapacitor floating ageing on different pore sizes using a multipore model. The multipore model is an equivalent electrical circuit model, capable of representing impedance behavior of supercapacitor in full range of its operating frequencies and classifying different sized pores by their impedance parameters. This paper first presents a link between pore sizes and impedance parameters of the modeling circuit. Then, floating ageing experiments are carried out using three samples from two different manufacturers. Multipore model impedance parameters evolution is monitored and discussed. Finally, a new representation of ageing processes is proposed by pore size and for different ageing phases.

Accelerated Ageing of Metallized Film Capacitors Under High Ripple Currents Combined With a DC Voltage

In view of their potential for high dielectric breakdown strengths, low dissipation factors, and good dielectric stability over a wide range of frequencies and temperature, metallized films capacitors are very used components for aeronautic applications. Nevertheless, capacitors remain unreliable components; a good acquaintance of their deterioration over time would enable us to perform a predictive maintenance on the component and thus improve the availability of the whole system. This operation requires the knowledge of the capacitor ageing law and their failure mechanisms associated with the application. In a standard six pulses rectifier-fed pulse width modulation inverter, dc-link capacitors are generally subjected to gradients of temperature due to the encountered electrical stresses. Since traditional floating ageing tests, which consist on applying constant voltages and temperature across the component, do not reflect the normal ageing of the component, we propose in this paper to study the degradation kinetics of metallized films capacitors under high ripple currents, alone or combined with a dc voltage across the devices terminals. It will therefore reproduce with a more representative way the ageing of the component in comparison with the traditional floating ageing tests. Based on the resonant circuit properties, the ageing test bench especially developed for our study provides high currents and voltages from a low power source. Through the study and analysis of the capacitors parameters evolution under high ripple currents, an original ageing law is proposed to model the capacitance decrease with time based on the electrochemical corrosion of the capacitors electrodes. The adequacy between the experimental points and the model proved the validity of the proposed law.

Metallized polymer film capacitors ageing law based on capacitance degradation

Abstract Passive components, particularly capacitors, are very used devices in power electronics applications providing key function on board. Nevertheless, capacitors breakdowns can have catastrophic consequences on the financial and human scale; a good acquaintance of their deterioration over time would contribute in the improvement of the availability of the whole system by performing a predictive maintenance on the component. This operation requires the knowledge of the capacitor ageing law and their failure mechanisms associated to the application. Capacitance loss can be mainly attributed to the self-healing process occurring in metallized film capacitors when used under high steady electrical and thermal stresses. In this paper, a capacitance ageing law is proposed based on the identification of voltage and temperature degradation kinetics from three experimental floating ageing tests performed at different voltage and temperature constraints. A total of 34 capacitors provided from different manufacturers using polyester film as dielectric have been studied and compared to validate the proposed law.

Supercapacitors ageing prediction by neural networks

Supercapacitors are devices used in wide range of applications, for example in automotive applications. Therefore, it is important to monitor and track their ageing. This paper presents a new approach for predicting the ageing of supercapacitors based on the neo-fuzzy neuron in association with the one-step ahead time series prediction. Ageing information collected from the measurement of the equivalent series resistance and the double layer capacitance are used to train the neo-fuzzy neuron. The obtained model is used as a prognostic tool in order to forecast the ageing of supercapacitors. The performance of the proposed approach is evaluated by using an experimental platform for ageing supercapacitors. The experimental results show that the neo-fuzzy prediction model can track the ageing of supercapacitors.

Comparison of EDLC impedance models used for ageing monitoring

Electrochemical double layer capacitors (EDLC) electrodes are made with pores of different geometric characteristics. This particularity is called pore size distribution. During EDLC ageing monitoring, it is necessary to know precisely the evolution of impedance. Firstly, this article deals with classical impedance models like single pore or constant phase element (CPE) for EDLC and exposes their strengths and their drawbacks. Then a more recent model grouping pores of the same geometric capacities is presented. Each group can be modeled by an electrical branch and has its own impedance expression. The resulting electrode impedance is obtained by putting n branches in parallel. This new model, called multi-pores model (MP), has been recently presented by A. Hammar [3] and is highly hoped to be used for more precise health monitoring of EDLC. The physical advantage is to take into account the pore heterogeneity. The models precision is finally compared using experimental results.

LiFePO4 Battery State of Health Online Estimation Using Electric Vehicle Embedded Incremental Capacity Analysis

This paper presents a fully embedded State of Health estimator for widely used lithium iron phosphate batteries. The study was done including technical and cost constraints of automotive industry. An online estimator using Incremental Capacity Analysis and a Butterworth filter is studied. Cells were aged using pure electric vehicle cycles and were monitored with an automotive Battery Management System. Using this electronic platform and considering incomplete charge/discharge cycles, a 2% accurate State of Health estimator is proposed.

Low temperature aging tests for lithium-ion batteries

This paper presents the aging test results of a 100Ah prismatic LiFeMnPO4 battery cell at low temperatures. Accelerated aging tests have been carried out on 4 cells to address the effect of cold temperatures on Lithium-ion (Li-ion) batteries. Three of them were aged through a normalized driving cycle at three temperature tests (-20°C, 0°C and 25°C). The calendar test was carried out on one single battery at -20°C and mid-range of SOC (50%). Their capacities were continuously measured every two or three days. From the analysis, this paper shows that it is mandatory to consider the impact of cold temperatures on a battery pack lifespan. Therefore, there is a need for having a proper thermal strategy in order to keep the battery cell in the most appropriate operating condition and thus reduce the cold effect on the battery performances.

Ageing Law for Supercapacitors Floating Ageing

Supercapacitors are energy storage systems appreciated as high power short duration power sources. As any electrochemical devices, supercapacitors are subject to ageing processes. Ageing is characterized by supercapacitors electrical performances loss (capacitance fades and Equivalent Series Resistance increases). In this article, we focus on capacitance fade with time for different sets of floating ageing constraints (constant temperature and voltage). This article deals with the best way for modeling capacitance fading with time for supercapacitors. Firstly, we present the approach of Eyring which predicts time for failure apparition. Then, we study two recent and uncommon ways for predicting capacitance evolution based on Langmuir isotherms and on the growth of a surface electrolyte interface. According to our study surface electrolyte interface approach appears more suitable for floating ageing modeling.

Improved model of metalized film capacitors

Metalized film capacitors are commonly used components in power electronics applications and their characteristics are drastically dependent on their operating frequency. Parasitic parameters could appear at low and high frequencies and disturb substantially the behavior of the component. Proper design of metalized film capacitors requires an understanding of all parasitic parameters sources and their impacts on the circuit operation. This paper presents a modeling approach based on the complex form of the capacitor impedance to build its equivalent electrical circuit. This approach proved to be more accurate than the traditional modeling technique of identifying the electrical parameters using the modulus of the component impedance. Two different types of capacitors were tested; experimental results allowed to validate our model from 10 kHz to 35 MHz.

Balancing circuit control for supercapacitor state estimation

In this paper, an original technique for monitoring the aging of supercapacitor energy storage system is proposed. The aging of supercapacitor is represented by the degradation of its internal parameters as the loss of capacitance and the increase of the Equivalent Series Resistance (ESR). This degradation is continuous until reaching the end of life criteria. The proposed approach is based on estimating the current ESR, of each storage system element with a fast control of the balancing circuit present at the terminal of each storage element. The fast control is applied for a short moment and could be applied at any storage system state with no incidence on the system. The information about this current parameter makes the state of health monitoring possible. The analysis is performed using simulation with realistic storage system models in order to demonstrate and validate the effectiveness and the accuracy of the proposed technique. The results presented covers storage system such as supercapacitor but could be also applied to batteries.