METHOD FOR CHARACTERIZATION OF ACCUMULATORS AND RELATED DEVICES

• US 20140172334A1
• Filed: 12/16/2013
• Published: 06/19/2014
• Est. Priority Date: 12/18/2012
• Status: Abandoned Application

• Current Assignee: Calbatt S.r.l.
• Original Assignee: Calbatt S.r.l.
• Inventors: AMOROSO, Francesco Antonio, CAPPUCCINO, Gregorio
• Application Number:
  US14/108,228
• Publication Number:
  US 20140172334A1
• Time in Patent Office: Days
• US Class Current: 702/63
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/385 Arrangements for measuring battery or accumulator variables for monitoring G01R31/382

Abstract

A method for characterization of the parameters of an equivalent model of an accumulator is described. The method is based on an accumulator equivalent circuit modelling primary and secondary chemical reactions. The method includes: a step of identification of the accumulator equivalent circuit; a step of characterization of the primary reactions during an accumulator charging process, wherein measurements of a given number of electric parameters of primary reactions branch in absence of secondary reactions are performed; a step of characterization of the secondary reactions during the charging process when also the secondary reactions are active; and a calculation step, that can be performed subsequently to the charging process, wherein mathematical functions allowing to extrapolate the values of the electric parameters in correspondence of a given state of charge are determined. A charging system, a charge control system, a computer and a storing device related to the method are also described.

Claims

1. A method for characterization of electric parameters of an equivalent circuit of an accumulator as a function of its state of charge, comprising

a step A.1 of identification of an equivalent electric model of the accumulator,

a step A.2 of characterization of primary chemical reactions of the accumulator,

a step A.3 of characterization of secondary chemical reactions of the accumulator, and a step A.4 of calculation of electric parameters, said steps being as follows:

A.1) defining an equivalent electric circuit characterized by a set of electric parameters, said circuit comprising at least one primary branch including elements that during a charging process are traversed by current even in presence of only primary chemical reactions of the accumulator and to which primary branch respective primary parameters P_i are associated, i being a positive integer, and at least one secondary branch including elements that during a charging process are traversed by current only in presence of secondary chemical reactions of the accumulator and to which secondary branch respective secondary parameters are associated;

A.2) characterizing the primary parameters P_i of the primary branch, by repetitively executing, during an initial step of at least one accumulator charging process wherein the secondary reactions are negligible, whenever the accumulator state of charge is incremented of a pre-determined quantity obtained by a measurement of a state of charge during an overall accumulator charging process, the following sub-steps;

A.2.1) applying to the accumulator a pre-determined current and/or voltage waveform;

A.2.2) measuring, during a time interval, a pre-determined number of voltage values at the terminals of the accumulator and/or values of current flowing into the accumulator;

A.2.3) interpolating said voltage and/or current values measured in step A.2.2, determining an interpolating function reconstructing a time response of the voltage or current on the accumulator as a consequence of application of said waveform, and from said function obtaining the values of the electrical parameters of said at least one primary branch,

thus obtaining a set of values for each primary parameter P_i, and executing subsequently the following sub-step;

A.2.4) for each primary parameter P, of said at least one primary branch, determining, by interpolation of said set of values, a function linking the value of the parameter to the generic increment of state of charge during the charging process when only the primary reactions are active;

A.3) characterizing the parameters of the at least one secondary branch, by repetitively executing, during time instants subsequent to said initial step of the at least one accumulator charging process, the following subsequent steps;

A.3.1) a testing step for testing presence of secondary reactions wherein, in a given instant, the voltage and current at the accumulator terminals are measured, and the presence of secondary reactions is determined if said voltage and current values deviate of a pre-determined quantity from the voltage and current values as calculated by means of the equivalent circuit of step A.1, assuming that the current absorbed in the at least one secondary branch vanishes and determining the parameters of the at least one primary branch by extrapolating the functions determined in step A.2.4, and storing;

a first time instant t_g wherein the presence of secondary reaction is determined, current I_B(t_g) measured at the accumulator terminals at instant t_g and increment of state of charge Δ

SOC(t_g) obtained from the beginning of the charging process up to time instant t_g as coming from the state of charge measurements of step A.2;

A.3.2) a sampling step wherein a pre-determined number of voltage and current values at the accumulator terminals in correspondence of time instants subsequent to said time instant t_g is stored;

A.4) determining, in any time instant subsequent to the end of said step A.3, mathematical functions allowing to calculate, for a hypothetical charging process, the primary electrical parameters P_i of the accumulator in correspondence of any value of the state of charge both in absence and in presence of secondary reactions, performing the following sub-steps;

A.4.1) determining, on the basis of a value of the initial state of charge SOC₀ of said at least one charging process and the values of t_g, I_B(t_g) and Δ

SOC(t_g) stored in step A.3.1, a function I_acc(SOC), linking the maximum current I_acc that can be absorbed by the at least one primary branch and the state of charge SOC, that satisfies the condition;

I_ace[SOC₀+Δ

SOC(t_g)]=I_B(t_g)

A.4.2) determining, on the basis of the function I_acc(SOC) and the accumulator equivalent circuit, the values of the voltage and current at the terminals of the at least one secondary branch in correspondence of the values of voltage and current at the terminals of the accumulator stored in step A.3.2, and, by interpolating such values, determining a function V_g(I_g) expressing a relationship between voltage V_g and current I_g at the terminals of the at least one secondary branch;

A.4.3) determining mathematical functions connecting primary parameters P_i and the state of charge both in absence and in presence of secondary reactions, performing for each primary parameter P, the following sub-steps;

A.4.3.1) determining, by interpolation of the values of said set of values of the parameters of step A.2, an interpolating function f_pi(SOC), expressing a relationship between the primary parameter P_i and the state of charge when only the primary reactions are active, and

A.4.3.2) determining a function f_si(SOC) expressing a relationship between the primary parameter P_i and the state of charge when also the secondary reactions are active, said function coinciding with f_pi(SOC) if the value of the primary parameter P_i as a function of SOC is not influenced by the presence of secondary reactions, said function being otherwise determined by circuit analysis on the basis of the accumulator equivalent electric circuit of step A.1, the function I_acc(SOC), the function V_g(I_g) and the parameters whose function f_si(SOC) coincides with f_pi(SOC).

2. The method according to claim 1, wherein the initial state of charge SOC₀ is not known before said at least one charging process, and in place of step A.4.1 the following step is executed:

A.4.1bis) determining the initial state of charge SOC₀ of said at least one charging process and a mathematical function I_acc(SOC) connecting the maximum current I_acc that can be absorbed by the at least one primary branch and the state of charge SOC, performing an iterative procedure comprising the following steps;

A.4.1.1) assuming a value of SOC₀;

A.4.1.2) on the basis of the assumed value of SOC₀ and the values of t_g, I_B(t_g) and Δ

SOC(t_g) stored in step A.3.1, calculating a function I_acc(SOC) satisfying the condition;

I_acc[SOC₀+Δ

SOC(t_g)]=I_B(t_g)

A.4.1.3) calculating the state of charge increment Δ

SOC_S obtained by integrating the current I_acc, calculated according to the function determined in step A.4.1.2, from instant t_g up to a pre-determined instant of said at least one charging process of steps A.2 and A.3, and calculating the state of charge SOC_f of the charging process in said pre-determined instant, estimated on the basis of the following relationship;

SOC_f=SOC₀+Δ

SOC(t_g)+Δ

SOC_S

A.4.1.4) calculating a difference between the state of charge actually achieved in said pre-determined instant of said at least one charging process and the state of charge SOC_f estimated in step A.4.1.3;

A.4.1.5) if the difference calculated in step A.4.1.4 exceeds a pre-determined quantity, increasing the assumed value of SOC₀ by a quantity that is function of said difference, in particular proportional to said difference, and repeating steps A.4.1.2-A.4.1.5, otherwise terminating the iterative procedure.

3. The method according to claim 1, wherein for a pre-determined number of repetitions of step A.2.2 a first group of measurements is performed wherein:

the duration of the time interval wherein each measurement is performed is such to allow the measurement of all the parameters of said at least one primary branch, and wherein the measured parameters values are also used to define mathematical functions expressing a subset of the parameters of said at least one primary branch as a function of a different subset of the parameters of said at least one primary branch assumed as set of reference parameters;

and wherein the remaining repetitions of step A.2.2 comprise a second group of measurements, wherein;

the duration of the time interval is such to allow only measurement of said reference parameters, and wherein the values of the remaining parameters of said at least one primary branch are obtained from the values of said reference parameters by extrapolation using the functions calculated during the first group of measurements.

4. The method according to claim 1, wherein function I_acc(SOC) is:

5. The method according to claim 2, wherein function I_acc(SOC) is:

6. The method according to claim 1, wherein function V_g(I_g) determined in step A.4.2 is:

7. The method according to claim 1, wherein the at least one primary branch of the accumulator equivalent circuit of step A.1 comprises a determined number of resistors and at least one voltage generator whose value V_OC models the open-circuit voltage of the accumulator.

8. The method according to claim 7, wherein, for each resistor belonging to the at least one primary branch of the accumulator equivalent circuit, the function f_pi(SOC) determined in step A.4.3.1 is:

f_pi=α

m_Ri0(SOC−

SOC_i)+R_i0,

SOC_i being the initial state of charge of said hypothetical charging process, m_Ri0 and R_i0 being real-value constant coefficients determined by means of interpolation of at least two values of said resistor as measured in step A.2, and α

being a coefficient whose value is determined each time for each charging process according to the relationship;

9. The method according to claim 7, wherein function f_pi(SOC) as determined in step A.4.3.1 and function f_si(SOC) as determined in step A.4.3.2 for the voltage generator of value V_OC coincide and are of the type:

f_pi(SOC)=f_si(SOC)=m_VSOC+q_V,

m_v and q_v being real-value constant coefficients determined by interpolation of at least two values of V_OC determined in step A.2.

10. The method according to claim 1, wherein steps A.2 and A.3 are performed in correspondence of a given number of accumulator working temperature T in order to characterize the parameters of the accumulator equivalent circuit even as a function of the working temperature, determining in step A.4, by interpolation of the measured values:

a function I_acc(SOC, T) expressing the relationship between the maximum current that can be absorbed by the at least one primary branch and any values pair (SOC,T), and a function V_g(I_g, T) expressing the relationship between the voltage at the terminals of the at least one secondary branch and any values pair (I_g, T),

and, for each parameter of the at least one primary branch, determining;

a function f_pi(SOC, T), each time different depending on the parameter P_i, that expresses the relationship between the parameter and any values pair (SOC,T) when only the primary reactions are active, and a function f_si(SOC,T), each time different depending on the parameter P_i, expressing the relationship between the parameter and any values pair (SOC,T) when also the secondary reactions are active, such a function f_si(SOC,T) coinciding with f_pi(SOC,T) if the value of the parameter as a function of (SOC,T) is not influenced by the presence of secondary reactions, otherwise being determined by circuit analysis on the basis of the accumulator equivalent circuit, the functions I_acc(SOC,T), V_g(I_g, T) and the parameters whose function f_si(SOC,T) coincides with f_pi(SOC,T).

11. A charging system for electric energy accumulators, such a system provided with an input section and an output section and being able to take energy from a source by the input section and to give energy to the accumulator by the output section, the system comprising the following elements:

a power section, suitable to provide electric energy to the accumulator and to apply to the same accumulator pre-determined voltage and/or current waveforms,

a voltage measurement device for measuring voltage at the terminals of the accumulator,

a current measurement device for measuring current flowing into the terminals of the accumulator,

a memory device, and

an electronic calculation device,

said system being suitable to perform any charging process of the accumulator and the method of characterization of the electric parameters of the electric equivalent circuit according to claim 1, wherein;

said power section is configured to apply to the accumulator a current and/or voltage waveform according to step A.2.1;

said voltage measurement device and said current measurement device are configured to perform the measurements of steps A.2.2, A.3.1, A.3.2;

said calculation device performs the calculations of steps A.2, A.3 and A.4;

said memory device is used to store the data calculated by the method.

12. A charge control system for an electric energy accumulator receiving energy from an external battery charger, which includes an input section and an output section and is able to take energy from a source by the input section and to give energy to the accumulator by the output section having two terminals, said charge control system comprising two control terminals suitable to be connected, directly or by means of one or more devices in series, at the two terminals of said output section of the battery charger, said charge control system further comprising:

a load device suitable to absorb electric current by said two control terminals;

a voltage measurement device for measuring the voltage at the terminals of the accumulator;

a current measurement device for measuring the current flowing into the accumulator terminals,

a memory device, and

a calculation device,

said system being suitable to execute the method of characterization of the electrical parameters of the accumulator electric equivalent circuit according to claim 1, wherein;

said load device is configured to absorb electric current by said two control terminals during pre-defined time intervals in such a way that a pre-defined current and/or voltage waveform is applied to the accumulator, according to step A.2.1;

said voltage measurement device and said current measurement device are configured to perform the measurements of steps A.2.2, A.3.1, A.3.2;

said calculation device performs the calculations of steps A.2, A.3 and A.4;

said memory device is configured to store the data calculated in the method.

13. The charge control system according to claim 12, further comprising at least one switching block connected in series between the terminals of the output section of the battery charger and the accumulator terminals, such a switching block being configured in such a way to electrically disconnect the accumulator from the output section of the battery charger during the time intervals wherein the load device absorb current, and to electrically connect the accumulator to the output section of the battery charger in the remaining time intervals, said system further comprising the following elements:

a voltage generator provided with two terminals suitable to be electrically connected, directly or by one or more devices in series, to the terminals of the output section of the battery charger, said voltage generator being suitable to establish a voltage difference between its terminals;

at least one switching block connected in series between the terminals of said voltage generator and the terminals of the output section of the battery charger, such switching block being configured in such a way to electrically connect the voltage generator to the output section of the battery charger during the time intervals wherein the load device absorbs current, and to electrically disconnect the voltage generator from the output section of the battery charger in the remaining time intervals.

14. The charge control system according to claim 12, further comprising a power section suitable to supply current by said two control terminals.

15. A computer device comprising a processor, the processor configured to execute instructions of a computer program that performs the calculations of steps A.2, A.3 and A.4 of the method according to claim 1.

16. A non-transitory memory support, storing a computer program that performs, when executed on a computer, the calculations of steps A.2, A.3 and A.4 of the method according to claim 1.