Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
  • G01R31/367—Software therefor, e.g. for battery testing using modelling or look-up tables

Definitions

• the present invention relates to a method for estimating an internal state of an electrochemical system for storing electrical energy, such as a battery (lead, Ni-MH, Li-ion, etc.).
• the method makes it possible to manage batteries used in stationary or onboard applications, and in particular during their operation.
• the battery is one of the most critical components in the case of hybrid or electric vehicle applications, or the storage of solar photovoltaic energy.
• the correct operation of these applications is based on an intelligent battery management system (BMS) which is responsible for making the battery work at the best compromise between the different levels of dynamic solicitation.
• BMS battery management system
• SoC state of charge
• SoH health status
• SoC state of charge of a battery
• the state of charge of a battery corresponds to its available capacity, and is expressed as a percentage of its nominal capacity indicated by the manufacturer, or as a percentage of its total capacity measured under given conditions when this measurement is possible.
• the knowledge of the SoC allows to estimate the time during which the battery can continue to supply energy to a given current before the next recharge, or until when it can absorb it before the next discharge. This information conditions the operation of systems using batteries.
• SoH state of health
• SoC and SoH For example, a precise and reliable estimation of the SoC and SoH for a vehicle makes it possible for the supervisor of the vehicle not to behave in a way that is too conservative in the use of the battery's energy potential. , Or vice versa. A poor diagnosis of state of charge can lead to overestimate the number of kilometers that can be traveled, and put the motorist in difficulty. A good estimate of these indicators also makes it possible to avoid overdimensioning the safety of the batteries, thus saving weight on board and, consequently, the fuel consumed. The estimation of the SoC and SoH also reduces the total cost of the vehicle. A correct estimator is therefore a guarantee for efficient and safe operation of the battery capacity throughout the vehicle's operating range.
• SoC state of charge
• SoH state of health
• RC models are also described in document EP880710, the description of the electrochemical and physical phenomena at the electrodes and in the electrolyte serving as a support for the development of the RC model, the temperature of the battery being simulated by the model, in order to gain in precision, compared to an external measurement.
• SoC estimation method is based on the mathematical description of the reactions of a electrochemical system. SoC is calculated from system state variables. This description is based on material balances, load, energy, as well as on semi-empirical correlations.
• the document FR2874701 describes a method using a temporal electrical perturbation in order to compare the response obtained with a reference response.
• this method is more difficult to implement for li-ion type elements whose response variations following this type of disturbance are very small, and therefore can not give rise to an accurate measurement of SoH.
• the object of the invention relates to an alternative method for estimating an internal state of an electrochemical system for storing electrical energy, such as a battery.
• the method is based on measuring the impedance of the system to reconstruct its internal state by means of a predetermined statistical model depending on the battery model and its application.
• the method makes it possible to estimate the state of charge (SoC) and the state of health (SoH) of an electrochemical battery, which are the most interesting internal characteristics for the majority of applications using batteries, that they are stationary or on board.
• SoC state of charge
• SoH state of health
• the subject of the invention relates to a method for estimating an internal state of a first electrochemical system for storing electrical energy, such as a battery, in which at least one property relating to the state is estimated.
• internal of said first electrochemical system from electrical measurement by impedance spectroscopy. The method comprises the following steps:
• said property relating to the internal state of said second system is measured; and an electrical measurement is made by impedance spectroscopy of said second electrochemical system at different frequencies;
• an equivalent electrical circuit including at least one parameter is defined for modeling said electrical responses of said second system
• an electrical response of said first electrochemical system for different frequencies is determined which is modeled by means of said equivalent electrical circuit by determining said parameter so that an electrical response of said equivalent electrical circuit is equivalent to said electrical response of said first electrical circuit; electrochemical system;
• the internal state of said first electrochemical system is estimated by calculating said property relating to the internal state of said electrochemical system by means of said relationship.
• the different internal states can be obtained by performing an accelerated aging of a second electrochemical system of storage of electrical energy of the same type as the first electrochemical system.
• the different internal states can also be obtained by selecting a set of second electrochemical systems of the same type as the first electrochemical system, the systems of the set having different internal states.
• At least one of the following properties relating to the internal state of the electrochemical system can be calculated: a state of charge (SoC) of the system, a state of health (SoH) of the system.
• SoC state of charge
• SoH state of health
• the equivalent electrical circuit can be defined by several parameters chosen from the following parameters: resistance, capacitance, temperature, or any combination of these parameters.
• an electrical response for different frequencies can be determined by measuring electrical impedance diagrams obtained by adding an electrical signal to a current flowing through the electrochemical system.
• These electrical impedance diagrams can be measured by applying sinusoidal current disturbance to the electrochemical system, and measuring a sinusoidal voltage induced across the electrochemical system.
• These electrical impedance diagrams can also be measured by applying a disturbance in the form of a superposition of several sinusoids or in the form of a white noise, on the electrochemical system, and by measuring a sinusoidal voltage induced across the system. electrochemical.
• the electrochemical system can be at rest (vehicle stationary or parked), or in operation.
• the invention also relates to a system for estimating an internal state of an electrochemical system for storing electrical energy, comprising:
• a sensor including means for measuring electrical impedance by impedance spectroscopy of said electrochemical system
• a memory for storing an equivalent electrical circuit and a relation between a property relating to the internal state of said system electrochemical and said parameters of the equivalent electrical circuit, said relation being previously calibrated by means of measurements for different internal states of at least a second electrochemical system of a same type as said electrochemical system;
• the electrical impedance measuring means comprises:
• a galvanostat for applying to said electrochemical system a sinusoidal current disturbance, or a disturbance in the form of a superposition of several sinusoids or a disturbance in the form of a white noise;
• the invention also relates to an intelligent system for managing a battery (Battery Management System) comprising a system for estimating an internal state of the battery according to the invention.
• Battery Management System a system for estimating an internal state of the battery according to the invention.
• the invention also relates to a vehicle comprising a battery and an intelligent system for managing a battery according to the invention.
• the invention also relates to a photovoltaic system for storing electrical energy, comprising a system for estimating its internal state according to the invention.
• FIG. 1 represents the logic diagram of the method according to the invention.
• FIG. 3 shows a comparison between the impedances obtained for several states of aging representative of a VEH application at a state of charge of 20% for a Li4Ti5012 / LiFePO4 type battery.
• FIG. 4 illustrates an example of equivalent electrical circuit representative of an electrochemical accumulator.
• Figure 5 shows an exemplary model fit for an impedance between 65 kHz and 0.1 Hz on a Li4Ti5012 / LiFePO4 to 20% SoC battery in a Nyquist (a) representation and in a Bode (b) representation and using the equivalent circuit model of Figure 4.
• Figure 6 illustrates a comparison between an impedance obtained by imposing sinusoidal signals (SS), and an impedance obtained by white noise (BB).
• SS sinusoidal signals
• BB white noise
• Figure 7 illustrates the calculation right of the battery capacity from the estimation relation of SoH vs. measured capacity of the battery (a), and residuals (b) representing the difference between the capacity calculated from the impedance diagrams, and the measured capacitance of the battery.
• FIG. 8 illustrates a measurement of the capacity of a battery by a complete cycle during check-ups at 20 ° C (CK), and by impedance at 50 ° C during aging (VI).
• FIG. 9 illustrates the computation line of the SoC of the battery from the estimation relation of the SoC vs. measured values of the SoC (a), and residuals (b) representing the difference between SoC calculated from impedance diagrams and measured SoC.
• the method according to the invention makes it possible to produce a charge state or health status gauge of a model and technology battery previously identified for use in a transport application (traction battery) or for the storage of batteries. renewable energies.
• the proposed principle consolidates the SoC and SoH estimates made by the BMS as these data are not directly measurable.
• the method is potentially embedded in a vehicle, or used to store energy in the context of grid-connected photovoltaic solar systems, making it possible to quantitatively determine the state of charge (SoC) and the state of health (SoH) of batteries, and in particular Li-ion batteries, from a measurement of the electrical impedance across the electrodes of the system, non-intrusive and temperature-controlled measurement.
• SoC state of charge
• SoH state of health
• the flow diagram of the process is shown in FIG. 1.
• the method according to the invention comprises the following steps:
• Stage El a laboratory test campaign is carried out on a batch of batteries (Bat.) In order to measure impedance diagrams (Z) as a function of SoC, SoH and T.
• Step E2 a model (RC circuit) chosen (mod.) Is fitted with the measured impedance diagrams (Z) to determine a set of parameters (para.) Functions of SoC, SoH and T.
• RC circuit chosen (mod.) Is fitted with the measured impedance diagrams (Z) to determine a set of parameters (para.) Functions of SoC, SoH and T.
• Step E3 SoC and SoH quantities are calculated from a multivariate combination of parameters. We obtain a relation for the calculation of SoC and / or a relation for the calculation of SoH (Rel.l and Rel.2).
• Step E4 the model chosen and the calculated relations are used in a gauge (G) consisting of an instrument (IMI) for measuring the impedance Z by adding an electrical signal in the battery studied (BatE.), D. a software part (LOG) allowing the adjustment of the model chosen (mod.) to the measured impedance Z, then the calculation of the SoC and / or SoH (CALC) from the parameters (para.) obtained and the relations previously calculated.
• G consisting of an instrument (IMI) for measuring the impedance Z by adding an electrical signal in the battery studied (BatE.), D. a software part (LOG) allowing the adjustment of the model chosen (mod.) to the measured impedance Z, then the calculation of the SoC and / or SoH (CALC) from the parameters (para.) obtained and the relations previously calculated.
• a battery of the same type (BatE.) Is used.
• electrical response measurements are made for different states of charge and health of this battery.
• accelerated aging representative of the intended application can be achieved.
• the battery undergoes an accelerated aging protocol in the laboratory that simulates a hybrid vehicle-type embedded application or an accelerated aging protocol simulating a photovoltaic energy storage application connected to the electrical network.
• Measurement of the impedance diagrams can be obtained by applying a sinusoidal disturbance current (preferably) on a battery using a galvanostat and measure the sinusoidal voltage induced at the terminals.
• the perturbation can be applied in the form of a superposition of several sinusoids or even in the form of a white noise (where all the frequencies are superimposed in the same signal), rather than in the form of a simple sinusoidal disturbance, which then allows to analyze several or all frequency responses at the same time.
• the measurement of the impedance diagrams according to the SoC can be made on the full SoC range or on the SoC range corresponding to that used for the application.
• the variation of the impedance diagrams with the temperature over the operating temperature range of the application is also measured.
• the electrical impedance Z of the electrochemical system is measured by applying a current disturbance by means of a galvanostat.
• the complex quantity Z (of real part ReZ and of imaginary part ImZ) can be represented in the form of a Nyquist diagram, where Im (Z) is a function of ReZ, and where each point corresponds to a frequency.
• a Nyquist diagram where Im (Z) is a function of ReZ, and where each point corresponds to a frequency.
• FIG. 3 Such a diagram is illustrated in FIG. 3.
• the responses to fast phenomena internal resistance at high frequencies
• intermediate phenomena such as reactions to electrodes
• slow phenomena diffusion of ions in the medium at low frequencies
• These different phenomena are more or less sensitive to SoC and SoH.
• the impedance response changes depending on the state of charge and aging; the difficulty is to decouple the effects.
• the Nyquist diagrams obtained for all states are preferably modeled from an equivalent electrical circuit (series of resistors and capacitors in series and / or parallel) knowing that the resistances and capacitors will be dependent SoC and SoH but not proportionally simple.
• FIG. 4 illustrates an example of equivalent electrical circuit representative of an electrochemical accumulator.
• R 0 represents the high frequency resistance or series resistance of the element
• Ri a resistance of charge transfer
• Qi Constant Phase Element
• W Warburg impedance representing the diffusive phenomena.
• the equivalent circuit is chosen to best model the impedance of the system for all states of the battery, limiting the number of components, and keeping as much as possible a physical sense.
• the model chosen (mod) is adjusted to each impedance diagram of the test campaign corresponding to each state of SoC, SoH and temperature (T) of the battery, by varying the parameters of the model.
• a geometric approach modeling is coarser but faster (to obtain for example the diameter of the semicircle and the slope of the linear diffusive part at low frequency).
• the temperature can be added as a parameter to the model parameters.
• the battery voltage can be added as a parameter to the model parameters. This relationship is therefore established following the laboratory test campaign for the selected battery type and for the intended application, by controlling the parameters T, SoC and SoH, via a mathematical treatment, such as the PCA of the parameters of the model.
• the electrical response of the electrochemical system studied for different frequencies is determined. This response is modeled using the equivalent electrical circuit, determining the parameters so that the electrical response of the equivalent electrical circuit is equivalent to the determined electrical response.
• the internal state of the electrochemical system is then estimated by calculating the property relating to the internal state of the electrochemical system by means of the relation.
• the relation obtained in the previous step is used in a sensor (G) consisting on the one hand of an impedance measuring system (IMI) using indifferently a method described in step 1, and on the other hand, a software part allowing:
• the steps of the method according to the invention are applied to two batteries (Li-ion accumulators) of pairs of different materials:
• a more conventional commercial torque accumulator based on the use of lithiated iron oxyphosphate (LiFePO 4 ) for the positive electrode and C 6 graphite for the negative electrode.
• the batteries have undergone, depending on the case, an accelerated aging protocol simulating an on-board application of the hybrid vehicle type, or an accelerated aging protocol simulating a photovoltaic energy storage application connected to the electrical network.
• check-up In order to validate the method for diagnosing both SoC and SoH batteries, a test procedure called "check-up” is defined. This procedure makes it possible to characterize the batteries at room temperature, before and after aging, typically every four weeks.
• This test is composed of four consecutive cycles, as illustrated in FIG. 2.
• the cycle number is indicated by a digit preceded by the prefix NCy, and the curves represent the state of charge.
• the first cycle (NCyl) consists of a residual discharge followed by a full charge to ensure that the battery is fully charged.
• the second cycle (NCy2) is a test to evaluate the loss of capacity, and therefore the state of health of the battery. This test also allows to adapt the charge-discharge current during the next two cycles.
• the purpose of the 3rd cycle is to use potentiostatic impedance spectroscopy (noted SIP in the figure) after a period of rest
• the purpose of the 4th cycle is to measure the impedance without interruption of current involving the measurement of impedance in galvanostatic mode (denoted SIG in the figure) during the phases of charge and discharge.
• the potentiostatic mode is however used by obligation when the end of regulated load in tension.
• the impedances obtained for different aging rates can be represented on the same Nyquist diagram (example in FIG. 3) in order to observe the different effects of aging on the total impedance of the battery.
• FIG. 3 illustrates a comparison between the impedances obtained for several states of aging representative of an application VEH at a state of charge of 20% for a Li 4 Ti 5 O 12 / LiFePO 4 type battery.
• VI initial state
• V2 after 2 weeks of aging
• V3 after 4 weeks
• V4 after 6 weeks
• V5 after 8 weeks.
• Figure 5 shows an exemplary model fit for an impedance between 65 kHz and 0.1 Hz on a Li 4 Ti 5 O 12 / LiFePO 4 to 20% SoC battery in a Nyquist (a) representation and in a representation of Bode (b), where the frequency is denoted "freq.”, And using the equivalent circuit model of figure 4.
• EX experimental measurement
• MA adjusted model.
• the previous impedances were obtained by successively using sinusoidal signals of different frequency.
• the impedances can be obtained in different ways, for example by superimposing white noise on the charge / discharge signals of the batteries.
• Figure 6 shows an impedance measured by the traditional channel (sine wave signals), as well as an impedance measured by white noise (SS). It is remarkable to note the much larger number of points obtained by white noise, which makes it possible to obtain a more precise adjustment.
• the impedances are adjusted with a non-linear model consisting of simple electrical elements such as resistors, capacitors (or CPE constant-phase elements) and Warburg elements (example Figure 4).
• impedance measurements were also performed during the aging periods.
• FIG. 7 represents: on the graph of the top (a), the capacitance (Qcalc) estimated from the estimation relation of SoH on the ordinate, and the capacity of the measured battery (Q) on the abscissa.
• the line corresponds to a linear regression; on the bottom graph (b), on the ordinate the residuals (AQcalc) representing the difference between the capacity calculated from the impedance diagrams, and on the abscissa, the capacity of the measured battery (Q).
• the residuals must have a random dispersion (this is the case here).
• a non-random dispersion would reflect a lack of adequacy of the relationship.
• the standard error due to the model is 0.25%, this value is very low, and indicates the accuracy of the model.
• Analysis of variance also indicated that the adjustment factors were all representative of the model.
• Figure 8 shows the capacities (Q) determined by the two methods as a function of time (r) in hours: cycling during check-ups at 20 ° C (CK) and impedances at 50 ° C measured during aging ( VI).
• the bias from the temperature difference is regular, and has estimated capacity values always higher than the measured capacitance values. This result is consistent because the capacity of a battery always increases with temperature.
• the SoH (represented by capacity) during aging can be estimated by the method applied to impedance diagrams measured during aging, despite the difference in temperature. In fact, in the example used, the temperature parameter has not been studied. The integration of this parameter would improve the accuracy of the estimate.
• the experimental protocol consisted in using a lithia iron graphite / lithium phosphate commercial lithium-ion battery fully charged with 2.3 Ah capacity and discharging it in steps of 5% state of charge. At each state of charge, the battery is idle until stabilization and then an impedance measurement in galvanostatic mode is performed. The processing of the data is similar to that used for the determination of the state of health.
• R0, R1, C1, garlic, L0, W representing the impedance electrical parameters adjusted as previously indicated (RO is the electrolyte resistance, RI the transfer resistance, Cl the Ql size of the CPE, the exponent of the CPE element, LO high frequency inductance, W Warburg impedance).
• FIG. 9 represents: on the graph of the top (a), the estimated SoC (SoC wedge) from the estimation relation of the SoC on the ordinate, and the SoC of the measured battery (SoC) on the abscissa.
• the line corresponds to a linear regression; on the bottom graph (b), on the ordinate the residuals (ASoC wedge) representing the difference between the calculated from the impedance diagrams, and on the abscissa, the SoC of the measured battery (SoC).
• the standard error due to the model is 4%, this value is very low (4% uncertainty on the SoC of a battery), and indicates the accuracy of the model.
• Analysis of variance also indicates that the adjustment factors are all representative of the model.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Secondary Cells (AREA)
• Tests Of Electric Status Of Batteries (AREA)
• Measurement Of Resistance Or Impedance (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=42782311

Family Applications (1)

Country Status (6)

Cited By (1)

Families Citing this family (56)

Family Cites Families (32)

• 2010
  • 2010-02-11 US US13/579,357 patent/US20130069660A1/en not_active Abandoned
  • 2010-02-17 FR FR1000665A patent/FR2956486B1/fr not_active Expired - Fee Related
• 2011
  • 2011-02-11 CN CN2011800100413A patent/CN102859378A/zh active Pending
  • 2011-02-11 EP EP11709980A patent/EP2537040A1/de not_active Withdrawn
  • 2011-02-11 JP JP2012553364A patent/JP2013519893A/ja active Pending
  • 2011-02-11 WO PCT/FR2011/000083 patent/WO2011101553A1/fr active Application Filing

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events