JP2009284591A - Charge controller for battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charge controller for battery pack that equalizes the voltage of each cell even if the voltage of a capacitor changes. <P>SOLUTION: The charge controller 1 for battery pack includes: a battery pack 10, where four cells 11A-11D are connected in series; a capacitor 20, MOS transistors 21 and 22; a step-down regulator 23; switches 24A-24D; cell voltage detectors 25A-25D; sample and hold circuits 26A-26D; a current detector 27; and a controller 35, which detects a plurality of voltage values and current values, about each of cells 11A-11D, by the sample and hold circuits 26A-26D and the current detector 27, and gets a voltage, where the amount of voltage drop by internal resistance is eliminated, as a corrective cell voltage, and extracts the lowest value of the corrective cell voltages as the lowest voltage, and charges the capacitor 20 by the battery pack 10, when this lowest voltage is at or under a predetermined value, and charges the cell 11 of the lowest voltage from the capacitor 20. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an assembled battery charge control device having an assembled battery in which a plurality of single cells are connected in series.

Conventionally, large capacity secondary batteries have been used as power sources for electric vehicles, hybrid vehicles, and the like. This secondary battery is an assembled battery in which a plurality of single cells are connected in series, and is an assembled battery that outputs a desired voltage necessary as a power source.
By the way, each single battery constituting the secondary battery has a variation in capacity due to an individual deviation at the time of manufacture and a use history. If the assembled battery is charged or discharged in a state where the capacity varies, the unit battery having a small capacity may be overcharged or overdischarged, and the performance of the assembled battery may be deteriorated.

Therefore, various methods have been proposed in order to make the voltage of each cell uniform.
For example, there is a method of aligning the voltage of each cell with the cell having the lowest voltage. That is, a bypass resistor is connected to a cell having a high voltage so that the energy of this cell is consumed and the voltage of each cell is made uniform. However, this method consumes energy wastefully, resulting in low energy efficiency.

Further, there is a method of aligning the voltage of each cell with the cell having the highest voltage (see, for example, Patent Document 1).
That is, the power supply device disclosed in Patent Document 1 includes a plurality of battery cells connected in series, an inverter that supplies regenerative power from a motor, a capacitor connected in parallel to the inverter, a capacitor and a plurality of capacitors. Battery cell selection means for selectively connecting one or more of the battery cells.

According to this method, the regenerative power from the inverter is stored in the capacitor, and when the voltage of the battery cell decreases, the battery cell having the decreased voltage is selected by the battery cell selection means and charged with the power of the capacitor. . According to this method, the voltage of each cell can be made uniform without reducing energy efficiency.
JP-A-6-319287

  However, in the method disclosed in Patent Document 1, since the number of cells connected to the capacitor changes according to the voltage of the capacitor, it is difficult to accurately charge a cell having a low voltage.

  An object of the present invention is to provide an assembled battery charge control device that can equalize the voltage of each cell even if the voltage of the capacitor changes.

  An assembled battery charge control device (for example, a later-described assembled battery charge control device 1) of the present invention includes an assembled battery (for example, a later-described assembled battery) in which a plurality of single cells (for example, cells 11A to 11D) are connected in series. Battery 10), one capacitor (for example, a capacitor 20 described later) connected in parallel to the assembled battery, and first switching means (for example, MOS transistors 21, 22 described later) for intermittently connecting the capacitor to the assembled battery. ), And a step-down regulator (for example, step-down regulator 23 described later) that is connected in parallel to the capacitor and outputs the step-down voltage of the capacitor, and the step-down regulator and each of the plurality of single cells are intermittently connected. Second switching means (for example, switches 24A to 24D described later) and a plurality of cell voltage detectors (for example, detecting voltages of the plurality of unit cells) , Cell voltage detectors 25A to 25D described later), a sample and hold circuit (for example, sample and hold circuits 26A to 26D described later) that holds a plurality of voltages detected by the cell voltage detector, and the assembled battery A plurality of voltage values and current values are detected for each of the single cells by a current detector (e.g., a current detector 27 described later) that detects a current flowing through the cell, and the sample and hold circuit and the current detector. Based on the plurality of voltage values and current values, corrected cell voltage calculation means for obtaining a voltage obtained by removing the voltage drop due to the internal resistance from the voltage value of each unit cell as a corrected cell voltage (for example, a control unit 35 described later) And extracting the lowest value of the correction cell voltage as the lowest voltage, and connecting the first switching means when the lowest voltage is not more than a predetermined value. Charging the capacitor with the assembled battery, and then connecting the second switching unit to the lowest voltage unit cell to charge the lowest voltage unit cell from the capacitor (for example, described later) Control unit 35).

According to the present invention, since only the battery with the lowest voltage is charged by the capacitor, the amount of charge necessary for charging the battery with the lowest voltage can be supplied at one time, and even if the voltage of the capacitor changes, The battery can be charged accurately and in a short time. Therefore, the voltage of each cell can be made uniform, and the performance of the assembled battery can be maintained over a long period of time.
In addition, a step-down regulator that steps down the voltage of the capacitor and outputs it is provided, so even if the capacitor voltage becomes higher than the standard value of the cell voltage, the voltage of the capacitor is stepped down by the step-down regulator to charge the cell. By using the voltage, pulse charging can be performed and the charging time can be shortened.

  In this case, a regulator voltage detector (for example, regulator voltage detector 28 described later) for detecting the output voltage of the step-down regulator, a voltage of the step-down regulator detected by the regulator voltage detector, and the cell voltage detector An error correction means for calculating the error of the cell voltage detector and the sample and hold circuit by comparing the voltage of each single cell detected and held by the sample and hold circuit, and correcting the calculated error ( For example, it is preferable to include a control unit 35) described later.

  According to the present invention, the regulator voltage detector is provided, and the voltage of the step-down regulator detected by the regulator voltage detector, and the voltage of each single cell detected by the cell voltage detector and held by the sample and hold circuit, In comparison, the error of the cell voltage detector and the sample and hold circuit was calculated. Therefore, errors in the cell voltage detector and the sample and hold circuit can be easily detected.

  According to the present invention, since only the battery with the lowest voltage is charged by the capacitor, the amount of charge necessary for charging the battery with the lowest voltage can be supplied at once, and even if the voltage of the capacitor changes, The battery can be charged accurately and in a short time. Therefore, the voltage of each cell can be made uniform, and the performance of the assembled battery can be maintained over a long period of time. In addition, a step-down regulator that steps down the voltage of the capacitor and outputs it is provided, so even if the capacitor voltage becomes higher than the standard value of the cell voltage, the voltage of the capacitor is stepped down by the step-down regulator to charge the cell. By using the voltage, pulse charging can be performed and the charging time can be shortened.

Hereinafter, an embodiment of the present invention will be described.
FIG. 1 is a diagram showing a configuration of an assembled battery charge control device 1 according to an embodiment of the present invention.
The assembled battery charge control device 1 includes an assembled battery 10, one capacitor 20, MOS transistors 21 and 22 as first switching means, a step-down regulator 23, and switches 24A to 24D as second switching means, Four cell voltage detectors 25A to 25D, four sample and hold circuits 26A to 26D, a current detector 27, a regulator voltage detector 28, an assembled battery charging circuit 31, a capacitor charge / discharge control circuit 32, A cell voltage measurement circuit 33, a cell selection circuit 34, and a control unit 35 as cell voltage correction means, charge control means, and error correction means are provided.

  The assembled battery 10 is configured by connecting cells 11A to 11D as four unit cells in series. These cells 11A to 11D are lithium ion batteries.

The capacitor 20 is connected to the assembled battery 10 in parallel and charges and discharges charges.
The MOS transistors 21 and 22 are switches that intermittently connect the capacitor 20 and both ends of the assembled battery 10, and the MOS transistors 21 and 22 can frequently charge and discharge the capacitor 20.

The step-down regulator 23 is connected in parallel to the capacitor 20 and steps down the voltage of the capacitor 20 and outputs it.
FIG. 2 is a diagram illustrating a configuration of the step-down regulator 23.
This step-down regulator 23 monitors a switching transistor 231, a coil 232 and a capacitor 233 that form a filter for smoothing a switched waveform, a Zener diode 234 for suppressing overvoltage, a diode 236, and an output voltage. And a switching control circuit 235 for switching the transistor 231.

The switches 24A to 24D intermittently connect the step-down regulator 23 and each of the four cells 11A to 11D, and each includes a pair of transistors.
The cell voltage detectors 25A to 25D detect the terminal voltages of the four cells 11A to 11D.
The sample and hold circuits 26A to 26D hold a plurality of voltages detected by the cell voltage detectors 25A to 25D.

The current detector 27 detects a current flowing through the assembled battery 10.
The regulator voltage detector 28 detects the output voltage of the step-down regulator 23.

The assembled battery charging circuit 31 charges the assembled battery 10 with regenerative power from the motor of the automobile.
The capacitor charge / discharge control circuit 32 charges the capacitor 20 with the power of the assembled battery 10 or charges the cells 11A to 11D with the power stored in the capacitor.
The cell voltage measurement circuit 33 receives the output signals of the sample and hold circuits 26A to 26D and detects the voltages of the cells 11A to 11D.
The cell selection circuit 34 opens and closes 24A to 24D of the cells 11A to 11D.

  The control unit 35 controls the assembled battery charging circuit 31, the capacitor charge / discharge control circuit 32, the cell voltage measurement circuit 33, and the cell selection circuit 34 to charge the cell 11A to 11D having the lowest voltage value. By repeating the process, the voltages of the cells 11A to 11D are averaged.

The process of averaging the cell voltages of the battery pack charge control device 1 will be described with reference to the flowchart of FIG.
Since a voltage drop due to internal resistance occurs in the cells 11A to 11D, it becomes lower than the actual inter-terminal voltage. Therefore, the voltage excluding the voltage drop of each cell is obtained as a corrected cell voltage, and the cell with the lowest corrected cell voltage is charged.

Specifically, the battery pack charging circuit 31 supplies current to the battery pack 10 with at least two types of current values, the current detector 27 detects the current values of the cells 11A to 11D, and the cell voltage measurement circuit. 33 detects the voltage values of the respective cells 11A to 11D with respect to the respective current values.
Next, based on the plurality of voltage values and current values, a voltage obtained by removing the voltage drop due to the internal resistance from the voltage values of the cells 11A to 11D is obtained as a corrected cell voltage.
Next, the lowest value of the corrected cell voltage is extracted as the lowest voltage. When this lowest voltage is equal to or lower than the predetermined value, the MOS transistors 21 and 22 are connected to charge the capacitor 20 with the assembled battery 10, and then The switch 24 of the lowest voltage cell 11 is connected to charge the lowest voltage cell 11 from the capacitor 20.

That is, in step S1, it is determined whether or not the value of the current flowing through the assembled battery 10 is equal to or less than a predetermined value, that is, whether or not the assembled battery 10 is charged / discharged with a large current. If this determination is YES, the process moves to step S2, and if NO, the process returns to step S1.
This is because, when the current value exceeds a predetermined value, the voltage greatly fluctuates and an error is likely to occur, and the inter-terminal voltages of the cells 11A to 11D greatly fluctuate due to the internal resistance of the cells 11A to 11D. It is.

  In step S2, the cell voltage detectors 25A to 25D detect the voltage, and the detected voltages are held by the sample and hold circuits 26A to 26D, and the current flowing through the assembled battery 10 is detected by the current detector 27.

In step S <b> 3, the control device 35 stores the voltage value held by the sample and hold circuits 26 </ b> A to 26 </ b> D and the current value detected by the current detector 27.
In step S4, it is determined whether or not a plurality of voltage values and current values have been acquired for each of the cells 11A to 11D. If this determination is NO, the process returns to step S2, and if YES, the process proceeds to step S5.

In step S5, an internal resistance is calculated to obtain a corrected cell voltage.
For example, for the cell 11A, when the correction cell voltage is E, the internal resistance is r, the acquired current values are I1 and I2, and the acquired voltage values are V1 and V2, the following expressions (1) and (2) are established. .
V1 = E−r × I1 (1)
V2 = E−r × I2 (2)

Therefore, from the expressions (1) and (2), the internal resistance r becomes the following expression (3).
r = (V1-V2) / (I1-I2) (3)

  Then, the corrected cell voltage E of the cell 11A is calculated by substituting Equation (3) into Equation (1) or Equation (2).

  In step S6, the cell 11 having the lowest correction cell voltage is extracted from the cells 11A to 11D. Hereinafter, the cell 11 having the lowest correction cell voltage is defined as the lowest voltage cell 11n.

In step S7, it is determined whether or not the voltage value of the lowest voltage cell 11n is in a normal range.
Specifically, when the voltage value of the lowest voltage cell 11n is lowered to a preset lower limit value, it is determined that the voltage is out of the normal range. Alternatively, when the voltage value of the lowest voltage cell 11n rises to a preset upper limit value, it is determined that the voltage range is out of the normal range.
If this determination is YES, the process returns to step S2, and if NO, the process proceeds to step S8.

In step S <b> 8, the capacitor 20 is charged by the assembled battery 10.
In step S9, only the switch 24A to 24D corresponding to the lowest voltage cell 11n is turned on by the control device 35, the charge is transferred from the capacitor 20 to the lowest voltage cell 11n, and the process returns to step S1.

Here, the charging voltage from the capacitor 20 to the lowest voltage cell 11n becomes high, and there is a possibility that the overvoltage is temporarily generated. Therefore, the step-down regulator 23 controls the charging voltage to the lowest voltage cell 11n to perform efficient charging.
That is, since the cell 11 is a lithium ion battery, the first half of the charging period of the cell 11 is charged with a constant current, and the second half is charged with a constant voltage. However, since the current decreases in the second half of the charging period, the charging time is prolonged.
Therefore, the step-down regulator 23 sets the voltage exceeding the standard value of the cell 11 for a short time and increases the current to perform pulse charging and shorten the charging time.

  By repeating the charging process of steps S1 to S9 described above, the voltages of the cells 11A to 11D constituting the assembled battery 10 are averaged.

  The above charging process needs to be repeated many times before the voltages of the cells 11A to 11D are averaged. However, the transfer effect decreases exponentially as the number of processing increases. Thus, by limiting the number of transfers to a preset number, the transfer efficiency within the battery pack 10 can be improved.

Further, since the capacity of the capacitor 20 is small, it takes a long time to transfer charges from the capacitor 20 and to completely average the voltages of the cells 11A to 11D.
Therefore, averaging may be repeated until the potential difference between the highest voltage cell and the lowest voltage cell falls within a preset range.

  Alternatively, the averaging may be repeated until the voltage value of the lowest voltage cell is within a preset range. In this case, for example, since there are four cells, the second highest cell voltage is set as the upper limit value, and the third highest cell voltage is set as the lower limit value.

  Alternatively, the averaging may be repeated until it falls within a predetermined range centered on the average voltage value of all cells.

By the way, in the sample-and-hold circuits 26A to 26D, an accuracy error occurs due to a temperature change or an individual deviation at the time of manufacture, so that there is a possibility that the charging accuracy of each of the cells 11A to 11D is lowered.
Therefore, errors in the sample and hold circuits 26A to 26D are corrected.

  Specifically, the controller 35 detects the voltage of the step-down regulator 23 detected by the regulator voltage detector 28 and the voltages of the cells 11A to 11D detected by the cell voltage detectors 25A to 25D and the sample and hold circuits 26A to 26D. To calculate the error of the cell voltage detectors 25A to 25D and the sample and hold circuits 26A to 26D, and correct the calculated error.

  Processing for correcting errors of the cell voltage detectors 25A to 25D and the sample and hold circuits 26A to 26D will be described with reference to the flowchart of FIG.

That is, after performing the process of averaging the voltages of the cells 11A to 11D described above, the following process is performed.
In step S11, the lowest voltage cell 11n is set as the correction target cell 11m.
In step S12, the voltage Vr of the step-down regulator 23 is detected.
In step S13, the switch 24m of the correction target cell 11m is turned on, and the voltage Vm of the correction target cell 11m is detected by the cell voltage detector 25m.

In step S14, the switch 24m corresponding to the correction target cell 11m is turned off.
In step S15, the voltage Vr of the step-down regulator is compared with the voltage Vm of the correction target cell 11m.
In step S16, a correction value of the voltage Vm of the correction target cell 11m is calculated.

In step S17, the correction value of the voltage Vm of the correction target cell 11m is set.
In step S18, cells 11A to 11D that are not connected for a certain period are extracted. This is because there is a high possibility that an error has occurred in the sample and hold circuit 26 of the cell 11 that has not been connected for a certain period.

In step S19, it is determined whether there are any cells 11A to 11D that are not connected for a certain period. If this determination is NO, the process ends. If YES, the process moves to step S20.
In step S20, the cells 11A to 11D that are not connected for a certain period are set as the correction target cell 11m, and the process returns to step S12.

According to this embodiment, there are the following effects.
(1) Since only the switch 24A to 24D corresponding to the lowest voltage cell 11n is turned on and only the lowest voltage cell 11n is charged by the capacitor 20, the amount of charge necessary for charging the lowest voltage cell 11n is once Even if the voltage of the capacitor 20 changes, the low voltage cell can be charged accurately and in a short time. Therefore, the voltage of each cell 11A-11D can be equalized, and the performance of the assembled battery 10 can be maintained over a long period of time.

  (2) By providing sample-and-hold circuits 26A to 26D in the voltage detection circuits of the cells 11A to 11D and simultaneously sampling the voltages of the cells 11A to 11D, a voltage can be obtained in an excessive state such as during charging or discharging. Even if fluctuates, the voltages of the cells 11A to 11D can be compared with high accuracy.

  (3) Since the step-down regulator 23 that steps down and outputs the voltage of the capacitor 20 is provided, even if the voltage of the capacitor 20 becomes higher than the standard value of the voltages of the cells 11A to 11D, the voltage of the capacitor 20 is reduced by the step-down regulator 23. By reducing the voltage to the charging voltage of the cells 11A to 11D, pulse charging can be performed and the charging time can be shortened.

  (4) A regulator voltage detector 28 is provided, and the voltage of the step-down regulator 23 detected by the regulator voltage detector 28 and each cell 11A detected by the cell voltage detectors 25A to 25D and held by the sample and hold circuits 26A to 26D The errors of the cell voltage detectors 25A to 25D and the sample and hold circuits 26A to 26D were calculated by comparing the voltages of ˜11D. Therefore, the errors of the cell voltage detectors 25A to 25D and the sample and hold circuits 26A to 26D can be easily detected.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

It is a figure which shows the structure of the charge control apparatus of the assembled battery which concerns on one Embodiment of this invention. It is a figure which shows the structure of the pressure | voltage fall regulator of the charge control apparatus of the assembled battery which concerns on the said embodiment. It is a flowchart of the process which averages the voltage of the cell of the charge control apparatus of the assembled battery which concerns on the said embodiment. It is a flowchart of the process which correct | amends the error of the cell voltage detector and sample-and-hold circuit of the charging control apparatus of the assembled battery which concerns on the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charge control apparatus of assembled battery 10 Assembled battery 11A-11D Cell (single cell)
20 Capacitor 21, 22 MOS transistor (first switching means)
23 Step-down regulator 24A-24D Switch (second switching means)
25A-25D Cell voltage detector 26A-26D Sample and hold circuit 27 Current detector 28 Regulator voltage detector 35 Control unit (correction cell voltage calculation means, charge control means, error correction means)

Claims (2)

An assembled battery in which a plurality of cells are connected in series;
One capacitor connected in parallel to the battery pack;
First switching means for intermittently connecting the capacitor to the assembled battery;
A step-down regulator connected in parallel to the capacitor and stepping down and outputting the voltage of the capacitor;
Second switching means for intermittently connecting the step-down regulator and each of the plurality of unit cells;
A plurality of cell voltage detectors for detecting respective voltages of the plurality of unit cells;
A sample and hold circuit for holding a plurality of voltages detected by the cell voltage detector;
A current detector for detecting a current flowing in the assembled battery;
The sample and hold circuit and the current detector detect a plurality of voltage values and current values for each of the unit cells, and based on the plurality of voltage values and current values, the voltage value of each unit cell is internally Correction cell voltage calculating means for obtaining a voltage excluding a voltage drop due to resistance as a correction cell voltage;
When the lowest value of the corrected cell voltage is extracted as the lowest voltage and the lowest voltage is less than or equal to a predetermined value, the first switching means is connected to charge the capacitor with the assembled battery, and then the lowest voltage And a charge control unit configured to connect the second switching unit to the unit cell and charge the unit cell having the lowest voltage from the capacitor. In the assembled battery charge control device according to claim 1,
A regulator voltage detector for detecting an output voltage of the step-down regulator;
By comparing the voltage of the regulator detected by the regulator voltage detector and the voltage of each single cell detected by the cell voltage detector and held by the sample and hold circuit, the cell voltage detector and the sample An assembled battery charge control apparatus comprising: an error correction unit that calculates an error of the hold circuit and corrects the calculated error.

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