S. Buller

Modeling the dynamic behavior of supercapacitors using impedance spectroscopy

This paper presents a new approach of modeling the dynamic behavior of supercapacitors using impedance spectroscopy. The new Matlab/Simulink model can be used in simulating the voltage response and energy efficiency, e.g. for automotive power systems. The model in the frequency domain, the parameter calculation as well as the inverse transformation into the time domain are discussed in detail. Furthermore, simulation results are compared with measured data obtained on a test bench.

Impedance-based non-linear dynamic battery modeling for automotive applications

This paper presents a systematic approach to employ electrochemical impedance spectroscopy for determining model structure and parameters of a simulation model for a VRLA battery. It focuses on the interpretation of the impedance data in terms of equivalent circuit models and describes the Matlab/Simulink implementation of the model as well as its time-domain verification. Furthermore, the advantages and limits of the impedance-based model as well as the possible simplifications are discussed.

A method for measurement and interpretation of impedance spectra for industrial batteries

Abstract Impedance spectroscopy is a promising tool for the modeling and diagnosis of industrial batteries. This paper discusses methodological questions connected with the measurement and interpretation of the impedance of such batteries, especially nonlinearity, voltage drift, stability, reproducibility, half-cell measurements, model structure and parameter extraction with respect to quantities like state of charge (SOC). On the basis of this discussion, a specialized impedance spectroscope for industrial batteries has been developed, as well as modifications of the standard electrochemical impedance spectroscopy (EIS) algorithm. A mini-cycle technique is suggested that gains additional information compared to classical measurements with continuous dc current offset. Impedance spectra from lead/acid batteries for different dc currents, SOCs, and temperatures are presented and analyzed. Reference-electrode measurements allow for separation of the half-cell impedances. Emphasis is placed on the limits of experimental reproducibility due to “history” of the battery.

A frequency-domain approach to dynamical modeling of electrochemical power sources

Electrochemical impedance spectroscopy can be used to obtain simulation models for the non-linear, non-stationary dynamic behavior of electrochemical power sources. Some extensions of porous-electrode theory are necessary for this purpose, which are not provided by standard EIS data evaluation software. This paper presents experimental data and consistent equivalent-circuit models for different dc conditions, regarding three electrochemical systems: supercapacitors as almost ideally blocking porous electrodes, lead/acid batteries under overcharge (water electrolysis) operation, and the same battery type under discharge/charge operation. The series inductance which masks the electrochemical behavior for frequencies as low as 100 Hz for a 100 Ah cell can be attributed mainly to the macroscopic cell geometry. The dependence of impedance parameters on direct current (non-linearity), temperature, state-of-charge, and previous discharge/charge regime is investigated. It is shown that model parameters extracted from the impedance spectra are closely linked with the charge-transfer kinetics, double-layer capacitance, transport limitation, and porous structure of the electrodes. Consequences for impedance-based determination of the batterys state-of-charge or state-of-health are discussed.

Impedance based battery diagnosis for automotive applications

In this paper, a procedure is presented, which determines and predicts the pulse power capability of a battery by means of an impedance-based model. This is achieved by a passive impedance measurement technique, which allows using current ripple and fluctuations as a signal source. The advantage of the procedure is its direct determination of the pulse power capability while no indirect and difficult to determine state variables such as state of charge and state of health are needed.

Supercapacitors and lithium-ion batteries for power electronic applications

This article employs the method of electrochemical impedance spectroscopy (EIS) to extend the physics-based, nonlinear equivalent circuit models of supercapacitors (SCs) to describe lithium-ion batteries (Li-ion). The following section briefly introduces the method of electrochemical impedance spectroscopy and presents measured impedance spectra. From these spectra, appropriate equivalent-circuit models are deduced. After this, the MATLAB/Simulink implementation of the new simulation models is discussed, and simulation results, as well as verification measurements, are provided. Finally, conclusions are drawn, and future perspectives of the new impedance-based modeling approach are outlined.

Analysis and evaluation of charge balancing circuits on performance, reliability and lifetime of supercapacitor systems

Supercapacitors, also known as ultracapacitors or electric double layer capacitors (ELDC), are electrical energy storage devices, which offer high power density, extremely high cycling capability and mechanical robustness. Due to their electrical performance, supercapacitors have a high potential to be used in industrial applications. To improve the performance, reliability and lifetime of these capacitors, charge balancing circuits are employed. In this paper, different equalization concepts are analyzed and evaluated. In addition, a simulation approach for the design of supercapacitor systems is proposed. As an example, results from an automotive application are presented.Supercapacitors, also known as ultracapacitors or electric double-layer capacitors (ELDCs), are electrical energy storage devices, which offer high power density, extremely high cycling capability, and mechanical robustness. Due to their electrical performance, supercapacitors have a high potential to be used in industrial applications. To improve the performance, reliability, and lifetime of these capacitors, charge-balancing circuits are employed. In this paper, different equalization concepts are analyzed and evaluated. In addition, a simulation approach for the design of supercapacitor systems is proposed. As an example, results from an automotive application are presented.

LabView-based universal battery monitoring and management system

In this paper, the main principles and the general structure of battery monitoring and management systems (BMS) are explained. Furthermore, a newly developed, highly accurate and inexpensive data acquisition system for BMS is presented. The modular measuring system consists of two different types of monitoring units, a battery block-voltage monitoring unit and a battery current and temperature monitoring unit. Following the discussion of the measuring hardware, a LabView realization of a universal BMS software is described in detail. Due to the flexible design of the LabView BMS, the system is able to perform control and surveillance activities for any kind of battery application and battery technology (e.g. Pb, VRLA, Ni-Cd, Ni-MH etc.). The BMS was originally designed for VRLA batteries in uninterruptible power supply systems (UPS), but was also tested in electric vehicles (VW CityStromer, BMW).