STATE OF CHARGE CALCULATOR FOR MULTI-CELL ENERGY STORAGE SYSTEM HAVING CELL BALANCING

• US 20100171503A1
• Filed: 09/20/2007
• Published: 07/08/2010
• Est. Priority Date: 09/20/2007
• Status: Active Grant

• Current Assignee: Audi AG (Volkswagen AG)
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Fredette, Steven J.
• Granted Patent: US 8,358,136 B2
• Time in Patent Office: Days
• US Class Current: 324/428
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• 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 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H02J 2300/30 The power source being a fuel cell
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

An arrangement for monitoring the current or state of charge (SOC) of an energy system (230) having one or more series-connected strings (S₁, S₂, . . . S_n) of battery cells (C₁, C₂, . . . C_n). The battery cells each have respective dissipative devices (D₁, D₂, . . . D_n) selectively connectable in parallel therewith for balancing cell voltages in the string. The dissipative devices are of predetermined, typically equal, impedance value. The voltage across each cell (V_c1, V_c2, . . . V_cn) may be separately monitored, such that by dividing the monitored voltage across a cell by the impedance value of a dissipative device connected in parallel therewith, the dissipative current is determined. A summation of all of the dissipative currents yields an error value, which error value is then removed from the measured gross current (I_bat) flowing through the combined battery cells and dissipative devices to yield a corrected value of current (I_batnet). A corrected SOC value (Q_net) is obtainable in a similar manner.

Claims

1. In a rechargeable energy storage system (230) characterized by a series arrangement (S₁, S₂, . . . S_n) of multiple battery cells (C₁, C₂, . . . C_n), multiple individual energy dissipative devices (D₁, D₂, . . . D_n) each associated with and selectively connectable and disconnectable (SW₁, SW₂, . . . SW_n) in parallel with a respective one of the multiple battery cells (C₁, C₂, . . . C_n), circuitry (240, V_c1, V_c2, . . . V_cn) for measuring the voltage (V_cell—

_i) across each of the respective ones of the multiple battery cells (C₁, C₂, . . . C_n), and circuitry (240, 36) for measuring the magnitude and direction of current (I_bat) flowing through the series arrangement of multiple battery cells and any dissipative devices connected in parallel therewith, a method of providing a measure of current flow (I_batnet) through substantially only the multiple battery cells comprising the steps of;

a) establishing a respective predetermined impedance (R) for each of the energy dissipative devices (D₁, D₂, . . . D_n);

b) determining (240, 246, SW₁, SW₂, . . . SW_n) which of the multiple individual energy dissipative devices (D₁, D₂, . . . D_n) are actually connected in parallel with respective ones of said battery cells (C₁, C₂, . . . C_n);

c) determining (240, 310, 244, V_c1, V_c2, . . . V_cn) the voltage across each of said battery cells to which said energy dissipative devices are actually connected in parallel;

d) determining (240, 420) the current (I_dis) in said respective connected dissipative devices;

e) summing (240, 430) the said currents (I_dis) in the respective said connected dissipative devices to provide a measure (I_distot) of the total dissipated current; and

f) subtracting (240, 460) the summed dissipated currents (I_distot) of the said connected dissipative devices from the current (I_bat) measured through the combined series arrangement of multiple battery cells and any energy dissipative devices connected in parallel therewith to provide a compensated measure of current (I_batnet) in substantially only the series arrangement of multiple battery cells.

2. The method of claim 1 wherein the respective predetermined impedance (R) for each of the energy dissipative devices (D₁, D₂, . . . D_n) is the same, and the step of determining the current (I_dis) in each of said respective connected dissipative devices comprises dividing (240, 420) the voltage (V_cell—

_i) for the respective battery cell by the impedance (R).

3. In a rechargeable energy storage system (230) characterized by a series arrangement (S₁, S₂, . . . S_n) of multiple battery cells (C₁, C₂, . . . C_n), multiple individual energy dissipative devices (D₁, D₂, . . . D_n) each associated with and selectively connectable and disconnectable (SW₁, SW₂, . . . SW_n) in parallel with a respective one of the multiple battery cells (C₁, C₂, . . . C_n), circuitry (240, V_c1, V_c2, . . . V_cn) for measuring the voltage (V_cell—

_i) across each of the respective ones of the multiple battery cells (C₁, C₂, . . . C_n), and circuitry (240, 36) for measuring the magnitude and direction of current (I_bat) flowing through the series arrangement of multiple battery cells and any dissipative devices connected in parallel therewith, a method of providing a measure of net charge (Q_net) to substantially only the multiple battery cells comprising the steps of;

a) establishing a respective predetermined impedance (R) for each of the energy dissipative devices (D₁, D₂, . . . D_n);

b) determining (240, 246, SW₁, SW₂, . . . SW_n) which of the multiple individual energy dissipative devices (D₁, D₂, . . . D_n) are actually connected in parallel with respective ones of said battery cells (C₁, C₂, . . . C_n);

c) determining (240, 310, 244, V_c1, V_c2, . . . V_cn) the voltage (V<sub>cell—

i</sub>) across each of said battery cells to which said energy dissipative devices are actually connected in parallel;

d) determining (240, 320) the dissipative charge (Q_cell) dissipated in each of said connected dissipative devices;

e) summing (240, 330) the said dissipative charge (Q_cell) in the respective said connected dissipative devices to provide a measure (Q_tot) of the total charge dissipated;

f) from the measure of the magnitude and direction of current (I_bat) flowing through the series arrangement of multiple battery cells and any dissipative devices connected in parallel therewith, determining (240, 350) the gross charge (Q_gross); and

g) subtracting (240, 360) the summed dissipated charges (Q_tot) of the said connected dissipative devices from the gross charge (Q_gross) determined for the combined series arrangement of multiple battery cells and any energy dissipative devices connected in parallel therewith to provide a compensated measure of charge (Q_net) for substantially only the series arrangement of multiple battery cells.

4. The method of claim 3 wherein the respective predetermined impedance (R) for each of the energy dissipative devices (D₁, D₂, . . . D_n) is the same, and the step of determining the dissipative charge (Q_cell) dissipated in each of said respective connected dissipative devices comprises dividing (240, 320) the time integral of the respective battery cell voltage (∫

V<sub>cell—

i</sub>·

dt) by the impedance (R).

5. The method of claim 3 wherein the step (350) of determining the gross charge (Q_gross) comprises determining the time integral (∫

I_bat·

dt) of the magnitude and direction of current (I_bat) flowing through the series arrangement of multiple battery cells and any dissipative devices connected in parallel therewith.

6. In a rechargeable energy storage system (230) characterized by a series arrangement (S₁, S₂, . . . S_n) of multiple battery cells (C₁, C₂, . . . C_n), multiple individual energy dissipative devices (D₁, D₂, . . . D_n) each associated with and selectively connectable and disconnectable (SW₁, SW₂, . . . SW_n) in parallel with a respective one of the multiple battery cells (C₁, C₂, . . . C_n), circuitry (240, V_c1, V_c2, . . . V_cn) for measuring the voltage (V_cell—

_i) across each of the respective ones of the multiple battery cells (C₁, C₂, . . . C_n), and circuitry (240, 36) for measuring the magnitude and direction of current (I_bat) flowing through the series arrangement of multiple battery cells and any dissipative devices connected in parallel therewith, the improvement comprising;

a) each of the energy dissipative devices (D₁, D₂, . . . D_n) being a respective predetermined impedance (R);

b) circuitry (240, 246, SW₁, SW₂, . . . SW_n) configured to determine which of the multiple individual energy dissipative devices (D₁, D₂, . . . D_n) are actually connected in parallel with respective ones of said battery cells (C₁, C₂, . . . C_n);

c) circuitry (240, 310, 244, V_c1, V_c2, . . . V_cn) configured to determine the voltage across each of said battery cells to which said energy dissipative devices are actually connected in parallel;

d) circuitry (240, 420) configured to determine the current (I_dis) in said respective connected dissipative devices;

e) circuitry (240, 430) configured to sum the said currents (I_dis) in the respective said connected dissipative devices to provide a measure (I_distot) of the total dissipated current; and

f) circuitry (240, 460) configured to subtract the summed dissipated currents (I_distot) of the said connected dissipative devices from the current (I_bat) measured through the combined series arrangement of multiple battery cells and any energy dissipative devices connected in parallel therewith and to thereby provide a compensated measure of current (I_batnet) in substantially only the series arrangement of multiple battery cells.

7. The rechargeable energy storage system (230) of claim 6 wherein each of said energy dissipative devices (D₁, D₂, . . . D_n) is a resistance of equal value.