Apparatus for estimating state of hybrid secondary battery and method thereof

• US 10,088,529 B2
• Filed: 10/14/2014
• Issued: 10/02/2018
• Est. Priority Date: 10/14/2013
• Status: Active Grant

• Current Assignee: LG Energy Solution Limited (LG Corporation)
• Original Assignee: LG Chem Limited (LG Corporation)
• Inventors: Joe, Won-Tae
• Primary Examiner(s): King, Douglas
• Application Number:
  US15/028,974
• Publication Number:
  US 20160252583A1
• Time in Patent Office: 1,449 Days
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 16/00 Structural combinations of different types of electrochemical generators
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

An apparatus for estimating state of a hybrid secondary battery including a first secondary battery and a second secondary battery having different electrochemical characteristics from each other and being connected in parallel with each other, is provided. The apparatus includes a sensor unit which measures an operating voltage and an operating current of the secondary battery at time intervals, and a control unit which is electrically connected with the sensor unit and estimates the state of the hybrid secondary battery including at least one of a first state of charge of the first secondary battery and a second state of charge of the second secondary battery, by implementing an Extended Kalman Filter algorithm using a state equation and an output equation, in which the state equation includes, as a state parameter, at least one of the first state of charge of the first secondary battery and the second state of charge of the second secondary battery, and the output equation includes, as an output parameter, the operating voltage of the hybrid secondary battery.

Claims

1. An apparatus for estimating a state of a hybrid secondary battery, wherein the hybrid secondary battery comprises a first secondary battery and a second secondary battery having different electrochemical characteristics from each other and being connected in parallel with each other, the apparatus comprising:

a sensor unit configured to measure, at time intervals, an operating voltage and an operating current of the hybrid secondary battery; and

a battery management system (BMS) electrically connected with the sensor unit, and configured to estimate the state of the hybrid secondary battery, wherein the state comprises at least one of a first state of charge of the first secondary battery and a second state of charge of the second secondary battery, by implementing an Extended Kalman Filter algorithm using a state equation and an output equation, wherein the state equation comprises, as a state parameter, the first state of charge of the first secondary battery and the second state of charge of the second secondary battery, and the output equation comprises, as an output parameter, the operating voltage of the hybrid secondary battery,

wherein the state equation and the output equation are derived from a first circuit unit and a second circuit unit which correspond to the first secondary battery and the second secondary battery, respectively, and connected in parallel with each other, and

at least one of the first circuit unit and the second circuit unit comprises an open-circuit voltage element varying voltage according to a state of charge of a corresponding secondary battery connected in series with an impedance element varying voltage according to current flowing through a corresponding circuit unit,

wherein the open-circuit voltage element includes a first open-circuit voltage element and a second open-circuit voltage element,

wherein the first open-circuit voltage element varies voltage according to the state of charge of the first secondary battery,

wherein the second open-circuit voltage element varies voltage according to the state of charge of the second secondary battery,

wherein the BMS is configured to initiate charging and discharging of the hybrid secondary battery based on the estimated state of the hybrid secondary battery,

wherein the different electrochemical characteristics include;

a difference in a positive electrode material, a difference in a negative electrode material, or a difference in an electrolyte, and

a difference in battery capacity, a difference in a battery use voltage range, a difference in a range of charge rate or a difference in a range in discharge rate, and

wherein the BMS is further configured to increase a time index of said Extended Kalman Filter algorithm in response to a continued charging or discharging of the hybrid secondary battery.

2. The apparatus of claim 1, wherein the state parameter further includes at least one of:

a voltage formed by a first impedance element included in the first circuit unit; and

a voltage formed a second impedance element included in the second circuit unit.

3. The apparatus of claim 2, wherein the state equation is defined such that the voltage formed by the at least one impedance element varies according to time, by an impedance voltage formula derived from circuit analysis of the at least one impedance element included in the first circuit unit and the second circuit unit, respectively, and

the BMS time-updates the voltage formed by each impedance element, by implementing [state estimate time update] of the Extended Kalman Filter algorithm, by using the state equation.

4. The apparatus of claim 1, wherein the state equation includes, as an input parameter, a first current flowing through the first circuit unit, and a second current flowing through the second circuit unit, and the BMS determines the first current and the second current, by using a current distribution equation derived from the circuit model, and the current measured by the sensor unit.

5. The apparatus of claim 1, wherein the output equation is derived from voltage analysis of the circuit model, and includes a plurality of input parameters, and the plurality of input parameters include a current measured by the sensor unit.

6. The apparatus of claim 1, wherein the state equation is defined such that the first state of charge and the second state of charge are determined by adding up currents flowing through the first circuit unit and the second circuit unit according to time, respectively, and

the BMS time-updates the first state of charge and the second state of charge, by implementing [state estimate time update] of the Extended Kalman Filter algorithm, by using the state equation.

7. The apparatus of claim 1, wherein the BMS implements [error covariance time update] of the Extended Kalman Filter algorithm, by using Jacobian matrix derived from the state equation.

8. The apparatus of claim 7, wherein the BMS estimates the operating voltage of the hybrid secondary battery, by implementing [output estimate] of the Extended Kalman Filter algorithm, by using the output equation.

9. The apparatus of claim 8, wherein the BMS implements [Kalman gain determination] of the Extended Kalman Filter algorithm, by using Jacobian matrix derived from the output equation and the time-updated error covariance.

10. The apparatus of claim 9, wherein the BMS implements [state estimate measurement update] of the Extended Kalman Filter algorithm, by reflecting the determined Kalman gain to a difference between the measured operating voltage and the estimated operating voltage.

11. The apparatus of claim 10, wherein the BMS implements [error covariance measurement update] of the Extended Kalman Filter algorithm, by using the time-updated error covariance and the determined Kalman gain.

12. The apparatus of claim 1, wherein the state equation includes a process noise, and the output equation includes a sensor noise.

13. The apparatus of claim 1, wherein the impedance element included in the first circuit unit or the second circuit unit includes at least one resistor, at least one capacitor, at least one inductor or a combination thereof.

14. The apparatus of claim 13, wherein the impedance element includes:

a plurality of RC circuits, each RC circuit including a first resistor and a capacitor connected in parallel; and

a second resistor connected in series with each RC circuit.

15. An electrically-driven apparatus comprising the apparatus as defined in claim 1.

16. The apparatus of claim 1, wherein the output equation is as follows:

17. The apparatus of claim 1, wherein the output equation is derived from voltage analysis of the circuit model, and includes a plurality of input parameters, and the plurality of input parameters further include:

an impedance voltage of the first circuit unit; and

an impedance voltage of the second circuit unit.

19. The method of claim 17, further including storing, transmitting, or displaying the estimated state of charge of the hybrid secondary battery.

20. The method of claim 17, wherein the Extended Kalman Filter algorithm includes:

state estimate time update;

error covariance time update;

output estimation;

Kalman gain determination;

state estimate measurement update; and

error covariance measurement update.

18. A method for estimating state of a hybrid secondary battery, wherein the hybrid secondary battery comprises a first secondary battery and a second secondary battery having different electrochemical characteristics from each other and being connected in parallel with each other, the method comprising:

measuring, at time intervals, an operating voltage and an operating current of the hybrid secondary battery;

estimating the state of the hybrid secondary battery via a battery management system (BMS), wherein the state comprises at least one of a first state of charge of the first secondary battery and a second state of charge of the second secondary battery, by implementing an Extended Kalman Filter algorithm using a state equation and an output equation, wherein the state equation comprises, as a state parameter, the first state of charge of the first secondary battery and the second state of charge of the second secondary battery, and the output equation comprises, as an output parameter, the operating voltage of the hybrid secondary battery,

wherein the state equation and the output equation are derived from a circuit model, and the circuit model comprises a first circuit unit comprising a first open-circuit voltage element corresponding to the first secondary battery connected in series with a first impedance element corresponding to the first secondary battery, and a second circuit unit connected in parallel with the first circuit unit, and comprising a second open-circuit voltage element corresponding to the second secondary battery connected in series with a second impedance element corresponding to the second secondary battery, and

initiating, via the BMS, the charging and discharging of the hybrid secondary battery based on the estimated state of the hybrid secondary battery,

wherein the different electrochemical characteristics include;

a difference in a positive electrode material, a difference in a negative electrode material, or a difference in an electrolyte, and

a difference in battery capacity, a difference in a battery use voltage range, a difference in a range of charge rate or a difference in a range in discharge rate,

wherein the first open-circuit voltage element varies voltage according to the state of charge of the first secondary battery,

wherein the second open-circuit voltage element varies voltage according to the state of charge of the second secondary battery, and

wherein the BMS is further configured to increase a time index of said Extended Kalman Filter algorithm in response to a continued charging or discharging of the hybrid secondary battery.

21. A computer-readable recording medium recording therein a program for implementing the method as defined in claim 18.

22. The method of claim 18, wherein the output equation is as follows: