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EP-4738644-A1 - CELL BALANCING CIRCUIT AND BATTERY DEVICE

EP4738644A1EP 4738644 A1EP4738644 A1EP 4738644A1EP-4738644-A1

Abstract

A cell balancing circuit (100, 200, 300, 400, 500) controls cell balancing between a first battery cell (11) that generates a first cell voltage (V1) and a second battery cell (12) which is connected in series with the first battery cell and generates a second cell voltage (V2). The cell balancing circuit includes: a first voltage divider circuit (103) that outputs a first voltage divider voltage (Vdl) as an average voltage of the first battery cell and the second battery cell; a first differential voltage-to-current converter (101) that discharges from the first battery cell a first cell balancing current (Ibl) generated according to a voltage difference obtained by subtracting the second cell voltage from the first voltage divider voltage; and a second differential voltage-to-current converter (102) that discharges from the second battery cell a second cell balancing current (Ib2) generated according to the voltage difference with polarity reversed.

Inventors

  • MIYAMOTO, YASUHIRO

Assignees

  • ABLIC Inc.

Dates

Publication Date
20260506
Application Date
20251007

Claims (9)

  1. A cell balancing circuit (100, 200, 300, 400, 500), controlling cell balancing between a first battery cell (11) that generates a first cell voltage (V1) and a second battery cell (12) which is connected in series with the first battery cell (11) and generates a second cell voltage (V2), the cell balancing circuit (100, 200, 300, 400, 500) comprising: a first voltage divider circuit (103) that outputs a first voltage divider voltage (Vd1) as an average voltage of the first battery cell (11) and the second battery cell (12); a first differential voltage-to-current converter (101) that discharges from the first battery cell (11) a first cell balancing current (Ib1) generated according to a voltage difference obtained by subtracting the second cell voltage (V2) from the first voltage divider voltage (Vd1); and a second differential voltage-to-current converter (102) that discharges from the second battery cell (12) a second cell balancing current (Ib2) generated according to the voltage difference with polarity reversed.
  2. The cell balancing circuit (100, 200, 300, 400, 500) according to claim 1, wherein the first differential voltage-to-current converter (101) and the second differential voltage-to-current converter (102) do not discharge the first cell balancing current (Ib1) and the second cell balancing current (Ib2) in response to the voltage difference being within a predetermined range including 0.
  3. The cell balancing circuit (100, 200, 300, 400, 500) according to claim 1, wherein the first differential voltage-to-current converter (101) and the second differential voltage-to-current converter (102) make the cell balancing current constant in a range where an absolute value of the voltage difference is larger than a predetermined value.
  4. The cell balancing circuit (100, 200, 300, 400, 500) according to claim 1, further comprising: a current monitoring circuit (104) which is connected to both ends of a current sense resistor (Rs) connected in series to a main current path, monitors a current value flowing through the current sense resistor (Rs), and determines whether the first battery cell (11) and the second battery cell (12) are in a discharging state, a charging state, or an open-circuited state; and a switching element (SW1, SW2, SW3, SW4) that turns on/off according to a signal output from the current monitoring circuit (104), short-circuits such that the voltage difference does not occur in response to turning on, and does not short-circuit such that the voltage difference occurs in response to turning off, wherein the current monitoring circuit (104) turns on the switching element (SW1, SW2, SW3, SW4) in response to determining the discharging state, and turns off the switching element (SW1, SW2, SW3, SW4) in response to determining the charging state or the open-circuited state.
  5. The cell balancing circuit (100, 200, 300, 400, 500) according to claim 1, further comprising: a first current mirror circuit (109) that discharges from the first battery cell (11) a current corresponding to a supply current from the first differential voltage-to-current converter (101) as the first cell balancing current (Ib1); and a second current mirror circuit (110) that discharges from the second battery cell (12) a current corresponding to a supply current from the second differential voltage-to-current converter (102) as the second cell balancing current (Ib2).
  6. The cell balancing circuit (100, 200, 300, 400, 500) according to claim 5, further comprising: a first balance detection part (116) that compares the first cell voltage (V1) and an input voltage of the first current mirror circuit (109) and detects an operating state of the first current mirror circuit (109); a second balance detection part (117) that compares the second cell voltage (V2) and an input voltage of the second current mirror circuit (110) and detects an operating state of the second current mirror circuit (110); and a diagnostic circuit (115) that outputs an error signal to outside in response to diagnosing that either the first current mirror circuit (109) or the second current mirror circuit (110) is abnormal based on a detection result of the first balance detection part (116) and a detection result of the second balance detection part (117).
  7. The cell balancing circuit (100, 200, 300, 400, 500) according to claim 6, further comprising; an external signal input terminal by which an OFF signal for stopping discharge of the first cell balancing current (Ib1) and the second cell balancing current (Ib2) is received, wherein in a case that the OFF signal is received by the external signal input terminal, the first balance detection part (116) and the second balance detection part (117) detect that the cell balancing current is being discharged, and the diagnostic circuit (115) outputs the error signal to outside.
  8. The cell balancing circuit (100, 200, 300, 400, 500) according to claim 1, wherein in a case that a third battery cell (13) that generates a third cell voltage (V3) is connected in series to a negative electrode side of the second battery cell (12), the cell balancing circuit (100, 200, 300, 400, 500) further comprises: a second voltage divider circuit (107) that outputs a second voltage divider voltage (Vd2) as an average voltage of the second battery cell (12) and the third battery cell (13); a third differential voltage-to-current converter (105) that discharges from the second battery cell (12) a third cell balancing current (Ib3) generated according to a voltage difference obtained by subtracting the third cell voltage (V3) from the second voltage divider voltage (Vd2); and a fourth differential voltage-to-current converter (106) that discharges from the third battery cell (13) a fourth cell balancing current (Ib4) generated according to the voltage difference with polarity reversed, wherein the second cell balancing current (Ib2) and the third cell balancing current (Ib3) are added in the second battery cell (12).
  9. A battery device, comprising at least: a first battery cell (11) that generates a first cell voltage (V1); a second battery cell (12) connected in series with the first battery cell (11) and generating a second cell voltage (V2); and the cell balancing circuit (100, 200, 300, 400, 500) according to any one of claims 1 to 8.

Description

BACKGROUND Technical Field The present invention relates to a cell balancing circuit and a battery device. Related Art There is a battery pack in which multiple battery cells of rechargeable secondary batteries are connected in series. Each cell voltage of the multiple battery cells in the battery pack is not the same due to, for example, manufacturing variation of the battery cells, variation in self-leakage current of the battery cells, and the like. Also, each cell voltage may differ according to ambient temperature. Furthermore, in response to degradation progressing in this battery pack through repeated charge-discharge cycles, the degradation state (SOH: State of Health) becomes different for each battery cell, and deviation occurs in the cell voltage of each battery cell. As degradation progresses, the cell voltage of the battery cells becomes higher during charging but becomes lower during discharging. In the case that each cell voltage of each battery cell differs greatly, in response to a charge-discharge control circuit being respectively connected to each battery cell, a battery cell with high cell voltage immediately becomes overcharged and charge stops during charging, and a battery cell with low cell voltage immediately becomes over-discharged and discharge stops during discharging. For this reason, efficient charge-discharge may not be performed. Various proposals have been made to regulate the balance of cell voltage of each battery cell in such a battery pack. For example, a battery pack control device has been proposed that respectively measures the cell voltage of each battery cell with an ADC (Analog to Digital Converter), performs calculations with a signal processing circuit such as an MPU (Micro Processing Unit), and equalizes the cell voltage of each battery cell (see Patent Document 1). Also, a voltage regulation device for a battery pack has been proposed that uses a comparator to selectively discharge battery cells higher than the average voltage of the battery pack, and finally equalizes the cell voltage of all battery cells (see Patent Document 2). Furthermore, a voltage balance correction circuit has been proposed that forms a negative feedback loop with a comparator to make the potential difference between the average voltage of two adjacent battery cells and the intermediate voltage of the two battery cells zero, and discharges the battery cell with high cell voltage in response to a voltage difference occurring (see Patent Document 3). Citation List Patent Document [Patent Document 1] International Publication No. WO 2015/029283[Patent Document 2] Japanese Patent Application Laid-Open Publication No. 2000-83327[Patent Document 3] Japanese Patent Application Laid-Open Publication No. 2010-63264 SUMMARY Technical Problem In one aspect of the present invention, an object is to provide a cell balancing circuit capable of performing cell balancing operation by current control for each battery cell connected in series. Solution to Problem The present invention provides a cell balancing circuit in one embodiment for controlling cell balancing between a first battery cell that generates a first cell voltage and a second battery cell which is connected in series with the first battery cell and generates a second cell voltage. The cell balancing circuit includes: a first voltage divider circuit that outputs a first voltage divider voltage as an average voltage of the first battery cell and the second battery cell; a first differential voltage-to-current converter that discharges from the first battery cell a first cell balancing current generated according to a voltage difference obtained by subtracting the second cell voltage from the first voltage divider voltage; and a second differential voltage-to-current converter that discharges from the second battery cell a second cell balancing current generated according to the voltage difference with polarity reversed. Effects According to one aspect of the present invention, it is possible to provide a cell balancing circuit capable of performing cell balancing operation by current control for each battery cell connected in series. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram illustrating a battery device (during discharging) using a cell balancing circuit according to a first embodiment of the present invention.FIG. 2 is a graph illustrating cell balancing current-voltage difference characteristics of a differential voltage-to-current converter according to the first embodiment of the present invention.FIG. 3 is a graph illustrating cell balancing current-voltage difference characteristics of the differential voltage-to-current converter according to the first embodiment of the present invention.FIG. 4 is a graph illustrating cell balancing current-voltage difference characteristics of the differential voltage-to-current converter according to the first embodiment of the present invention.FIG. 5 is a circuit diagram ill