Apparatus for estimating voltage of hybrid secondary battery and method thereof

• US 10,073,146 B2
• Filed: 10/14/2014
• Issued: 09/11/2018
• 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): Quigley, Kyle R
• Application Number:
  US15/027,459
• Publication Number:
  US 20160245871A1
• Time in Patent Office: 1,428 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: G01R 31/396 Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
• CPC Class Codes: H01M 10/4207 for several batteries or cells simultaneously or sequentially
• 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 16/00 Structural combinations of different types of electrochemical generators
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

An apparatus and a method for estimating voltage of a hybrid secondary battery are provided, in which the hybrid secondary battery includes 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 includes a sensor unit which measures an operating current of the hybrid secondary battery, and a control unit which estimates the voltage of the hybrid secondary battery using the operating current, and a voltage equation derived from a circuit model including a first circuit unit which simulates a voltage variation of the first secondary battery by a first open-circuit voltage element and optionally, a first impedance element, and a second circuit unit which is connected in parallel with the first circuit unit and simulates a voltage variation of the second secondary battery by a second open-circuit voltage element and optionally, a second impedance element.

Claims

1. An apparatus for estimating voltage 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 including a sense resistor configured to measure an operating current of the hybrid secondary battery; and

a battery management system including a processor and a memory, wherein the battery management system is electrically coupled to the hybrid secondary battery and wherein the battery management system is configured to estimate the voltage of the hybrid secondary battery using the operating current, and a voltage equation derived from a circuit model stored in the memory of the battery management system, the circuit model comprising a first circuit unit configured to simulate a voltage variation of the first secondary battery by a first open-circuit voltage element and optionally, a first impedance element, and a second circuit unit connected in parallel with the first circuit unit and configured to simulate a voltage variation of the second secondary battery by a second open-circuit voltage element and optionally, a second impedance element,

wherein the battery management system is configured to initiate charging and discharging of the hybrid secondary battery based on the estimated voltage,

wherein the voltage equation is described by the following expression;

2. The apparatus of claim 1, wherein the first secondary battery and the second secondary battery are packaged in different packages from each other as independent batteries, or packaged together in a single package.

3. The apparatus of claim 1, wherein at least one of the first secondary battery and the second secondary battery includes a plurality of unit cells or a plurality of battery modules.

4. The apparatus of claim 2, wherein at least one of the first secondary battery and the second secondary battery includes a plurality of unit cells or a plurality of battery modules.

5. The apparatus of claim 1, wherein the control unit:

determines a first open-circuit voltage formed by the first open-circuit voltage element, based on a pre-defined first correlation between a first state of charge of the first secondary battery and the first open-circuit voltage, and

determines a second open-circuit voltage formed by the second open-circuit voltage element, based on a pre-defined second correlation between a second state of charge of the second secondary battery and the second open-circuit voltage.

6. The apparatus of claim 5, wherein the first correlation is a look-up table or a look-up function obtained from an open-circuit voltage profile according to state of charge variation of the first secondary battery, and

the second correlation is a look-up table or a look-up function obtained from an open-circuit voltage profile according to state of charge variation of the second secondary battery.

7. The apparatus of claim 1, wherein the first impedance element and the second impedance element includes at least one resistor, at least one capacitor, at least one inductor, or a combination thereof.

8. The apparatus of claim 7, wherein the first impedance element and the second impedance element includes at least one RC circuit in which a resistor and a capacitor are connected in parallel, and a resistor connected in series thereto.

9. The apparatus of claim 1, wherein the first open-circuit voltage element and the first impedance element are connected in series with each other, and

wherein the second open-circuit voltage element and the second impedance element are connected in series with each other.

10. The apparatus of claim 1, wherein the control unit:

determines a first impedance voltage formed by the first impedance element, by using a first impedance voltage equation derived from a connection relation and electrical characteristic values of circuit elements included in the first impedance element, and

determines a second impedance voltage formed by the second impedance element, by using a second impedance voltage equation derived from a connection relation and electrical characteristic values of circuit elements included in the second impedance element.

11. The apparatus of claim 1, wherein the control unit:

determines, from the circuit model, a first current and a second current flowing through the first circuit unit and the second circuit unit, respectively,

time-updates a first state of charge of the first secondary battery and a second state of charge of the second secondary battery, by adding up the first current and the second current, respectively,

time-updates a first impedance voltage formed by the first impedance element and a second impedance voltage formed by the second impedance element, by using the time-updated first state of charge and the time-updated second state of charge, and the first current and the second current,

determines a first open-circuit voltage of the first secondary battery and a second open-circuit voltage of the second secondary battery corresponding to the time-updated first state of charge and the time-updated second state of charge, and

estimates the voltage of the hybrid secondary battery by substituting the determined first open-circuit voltage and the determined second open-circuit voltage, the time-updated first impedance voltage and the time-updated second impedance voltage, and the measured operating current, into the voltage equation.

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

13. A method for estimating voltage of a hybrid secondary battery comprising 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:

providing a battery management system electrically coupled to the hybrid secondary battery and including a processor and a memory, the memory including a circuit model comprising a first circuit unit configured to simulate a voltage variation of the first secondary battery by a first open-circuit voltage element and optionally, a first impedance element, and a second circuit unit connected in parallel with the first circuit unit and configured to simulate a voltage variation of the second secondary battery by a second open-circuit voltage element and optionally, a second impedance element;

measuring an operating current of the hybrid secondary battery;

determining, from the circuit model, a first current and a second current flowing through the first circuit unit and the second circuit unit, respectively;

time-updating a first state of charge of the first secondary battery and a second state of charge of the second secondary battery, by adding up the determined first current and the determined second current, respectively;

time-updating a first impedance voltage formed by the first impedance element and a second impedance voltage formed by the second impedance element, by using the time-updated first state of charge and the time-updated second state of charge, and the first current and the second current;

determining a first open-circuit voltage of the first secondary battery and a second open-circuit voltage of the second secondary battery corresponding to the time-updated first state of charge and the time-updated second state of charge, respectively; and

estimating the voltage of the hybrid secondary battery by substituting the determined first open-circuit voltage and the determined second open-circuit voltage, the time-updated first impedance voltage and the time-updated second impedance voltage, and the measured operating current, into a voltage equation derived from the circuit model; and

initiating, via the battery management system, the charging and discharging of the hybrid secondary battery based on the estimated voltage,

wherein the voltage equation is described by the following expression;

14. The method according to claim 13, further including measuring an operation initiating voltage of the hybrid secondary battery;

and

determining initial conditions for the state of charge of the first secondary battery and the state of charge of the second secondary battery based on the states of charge corresponding to the operation initiating voltage.

15. The method according to claim 13, further including determining initial conditions for the first impedance voltage and the second impedance voltage.

16. The method according to claim 13, wherein the first current and the second current are respectively determined based on a first current distribution equation and a second current distribution equation, wherein the first and the second current distribution equations include input parameters including the first open-circuit voltage and the second open-circuit voltage, the first impedance voltage and the second impedance voltage, and the operating current.

17. A non-transitory computer-readable recording medium recording therein a program for implementing the method as defined in claim 13.