JP2014044111A - Secondary battery device and charging state measurement method - Google Patents

Abstract

A secondary battery device and a state of charge measurement method are provided that are inexpensive and can improve the accuracy of SOC measurement.
According to an embodiment, a current measurement circuit measures the discharge current and the charge current based on a voltage generated in a resistor affected by the charge current and the discharge current of the secondary battery circuit. The switch circuit is provided between the input terminal of the current measurement circuit and the resistor, and the resistance measurement circuit is configured so that the current measurement circuit measures a discharge current in a first period and a charge current in a second period. The measurement connection state of the current measurement circuit is switched. A control part calculates the charge condition of the said secondary battery circuit using the output of the said current measurement circuit.
[Selection] Figure 5

Description

  Embodiments described herein relate generally to a secondary battery device and a charging state measurement method.

  The secondary battery device has a current measurement circuit that measures a current value. The current measurement circuit has an amplifier circuit. For example, the amplifier circuit amplifies a voltage generated at both ends of a low-resistance shunt resistor connected in series to the current path, and obtains an output based on the measurement voltage. This output is input to, for example, a microprocessor (MPU) and converted from digital to analog (A / D), and a value corresponding to the converted data is set as a measured current value. In the current measurement circuit, the measurement current value is integrated and reflected in the state of charge (SOC). In particular, a method is used in which the current values are integrated in a region where the open circuit voltage (OCV) -SOC curve is flat.

  Various techniques relating to the secondary battery device and its charge state measurement have been proposed, for example, as shown in the patent literature.

JP-A-9-297163 JP 2006-87160 A JP 2011-47820 A

  However, the conventional secondary battery device and the charge state measuring method are designed on the assumption that all the circuit elements used are normal and have a certain performance. For this reason, for example, there is a problem that an offset voltage is included in the output voltage of the measurement circuit due to the influence of variation of transistors constituting the operational amplifier and the error of the SOC is accumulated. In addition, an operational amplifier having a small offset voltage is expensive, and there is a problem of increasing the cost of the entire apparatus.

  Therefore, an object of the present embodiment is to provide a secondary battery device and a charge state measurement method that can improve the SOC measurement accuracy at low cost.

  According to the embodiment, a resistance affected by a charging current and a discharging current of a secondary battery circuit, a current measuring circuit that measures the discharging current and the charging current based on a voltage generated in the resistance, and the current measurement Provided as a connection circuit between an input terminal of the circuit and the resistor, the resistor and the current measurement circuit so that the current measurement circuit measures a discharge current in a first period and a charge current in a second period A switch circuit for switching the measurement connection state, and a control unit for calculating the charge state of the secondary battery circuit using the output of the current measurement circuit.

It is a figure which shows the example of 1 structure of the secondary battery apparatus used as the premise of this embodiment. It is a figure which shows the relationship between the output voltage of the electric current measurement circuit of FIG. 1, an offset voltage, and measurement current. It is a figure which shows the secondary battery apparatus by one structural example of this embodiment. It is a figure explaining the accumulation | storage state of the measurement error at the time of charge current / discharge current measurement of the secondary battery apparatus of FIG. 1 and FIG. It is a figure which shows the electric current measurement apparatus of a secondary battery apparatus in the other structural example of this embodiment. It is a figure which shows the relationship between the output voltage of the electric current measurement circuit of FIG. 5, an offset voltage, and measurement current.

  Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 shows a configuration example of a current measuring device for a secondary battery device which is a premise of the embodiment.

  In FIG. 1, BT is a secondary battery circuit in which a plurality of cells Cell-1, Cell-2, Cell-3... Cell-n are connected in series. A shunt resistor Rsh is inserted in series in the current path of the secondary battery circuit BT. The terminal T11 is a plus side terminal of the secondary battery circuit BT, and the terminal T12 is a minus side terminal of the secondary battery circuit BT. The shunt resistor Rsh is connected between the terminal T12 and the negative electrode of the secondary battery circuit BT.

  One input terminal 1-1 and the other input terminal 1-2 of the first current measuring circuit 101 are respectively connected to one terminal a and the other terminal b of the shunt resistor Rsh. One input terminal 2-1 and the other input terminal 2-2 of the second current measurement circuit 102 are connected to the other terminal b and one terminal a of the shunt resistor Rsh, respectively.

  In the first current measurement circuit 101, the one input terminal 1-1 is connected to one input terminal (for example, negative input terminal) of the differential amplifier circuit DA1 via the resistor R1, and the other input terminal. 1-2 is connected to the other input terminal (for example, positive side input terminal) of the differential amplifier circuit DA1 via the resistor R3. A feedback bias resistor R2 is connected between the output terminal and the negative input terminal of the differential amplifier circuit DA1. A reference bias resistor R4 is connected between the ground potential and the positive input terminal of the differential amplifier circuit DA1. These resistors are provided to construct a first operational amplifier.

  In the second current measuring circuit 102, the one input terminal 2-1 is connected to one input terminal (for example, negative input terminal) of the differential amplifier circuit DA2 via the resistor R5, and the other input terminal. 202 is connected to the other input terminal (for example, positive side input terminal) of the differential amplifier circuit DA2 via the resistor R7. A feedback bias resistor R6 is connected between the output terminal and the negative input terminal of the differential amplifier circuit DA2. A reference bias resistor R8 is connected between the ground potential and the positive input terminal of the differential amplifier circuit DA2. These resistors are provided to construct a second operational amplifier.

  Each output (current or voltage) of the current measurement circuit 101 and the current measurement circuit 102 is input to a microprocessing unit (MPU) 400. The analog / digital (A / D) conversion module in the MPU 400 converts the output (current or voltage) into a digital value and uses it for the SOC calculation. The remaining battery level (charged state SOC) increases or decreases by the accumulated charge or discharge current. Therefore, the MPU 400 integrates the measured digital current value, and grasps the integrated operation value for a preset period as the state of charge (SOC). The SOC information obtained by the above integration calculation is transmitted to the external connection device via the interface (I / F) circuit 500. Examples of the external connection device include a display for displaying the remaining battery level and a warning device.

  In the above apparatus, the current measurement circuit 101 can measure only the discharge current, and the output Vout1 of the discharge current measurement circuit 101 is expressed by the following equation (1) based on the discharge current value Id and the shunt resistance value Rsh.

Vout 1 = Id × Rsh × Av + ΔV1 ... (1)
At this time, the output voltage error ΔV1 is expressed by the following equation (2) based on the offset voltage Voff1 of the first operational amplifier and the voltage gain Av of the differential amplifier circuit DA1. ΔVoff1 is a unique value of the first operational amplifier and varies depending on the conditions of the individual, voltage, and temperature.

ΔV1 = Voff1 (1 + Av) (2)
The offset voltage Voff1 causes an error in the current measurement value by ΔV1.

  Similarly, when the current measurement circuit 102 is also shown, the current measurement circuit 102 can measure only the charging current, and the output Vout2 of the charging current measurement circuit is expressed by the following equation (3) based on the discharge current value Ic and the shunt resistance value Rsh.

Vout 2 = Ic × Rsh × Av + ΔV2 ・ ・ ・ ・ (3)
Due to the offset voltage Voff2 of the operational amplifier and the gain Av of the differential amplifier circuit DA2 at this time, the output voltage error ΔV2 is expressed by the following equation (4). Δvoff2 is a unique value of the operational amplifier and varies depending on the voltage and temperature.

ΔV2 = Voff2 (1 + Av) (4)
Therefore, an error in the current measurement value is caused by ΔV2.

  From the above, when the constant current discharge Id flows for the period t1, and then the constant current charge Ic flows for the period t2, the total Q of the current value integrated value becomes the equation (5), and the error ΔQ due to the offset voltage becomes the following equation (6).

Q = (Id x Rsh x Av + ΔV1) x t1 + (Ic x Rsh x Av + ΔV2) x t2 (5)
ΔQ = ΔV1 × t1 (Discharge time) ― ΔV2 × t2 (Charge time) (6)
(ΔV1 and ΔV2 in this equation are treated as current count values after A / D conversion in the MPU.)
The magnitudes and positive and negative directions of the errors ΔV1 and ΔV2 differ depending on the operational amplifier. Therefore, when the offset directions of the current measuring circuits 101 and 102 are different, the error becomes larger because the positive and negative of ΔV1 and ΔV2 are different.

  When the values of the discharge current and the charging current are small with respect to the measurement current range, the influence of the offset voltage is large and the current integration error is also large.

  FIG. 2 shows an image example of the charging or discharging current and the output voltage. Actually, the offset voltage depends on the current (input voltage characteristics) depending on the design of the operational amplifier and individual characteristics. When the values of the discharge current and the charging current are small, the offset voltage with respect to the output voltage of the current measuring circuit 101 or 102 is relatively large. This can also increase the error.

  FIG. 3 is a circuit that solves the above problem. Parts similar to those in the circuit of FIG. A different part from the circuit of FIG. 1 is demonstrated.

  One input terminal 1-1 and the other input terminal 1-2 of the current measuring circuit 101 are connected to either one input terminal side or the other input terminal side of the differential amplifier circuit DA1 via the switch circuit 100. Switching connection is possible.

  Switch circuit 100 includes switch elements SW1, SW2, SW3, SW4. The switch element SW1 can connect the input terminal 1-1 to one input terminal of the differential amplifier circuit DA1 via the resistor R1, and the switch SW2 differentially connects the input terminal 1-1 via the resistor R3. It can be connected to the other input terminal of the amplifier circuit DA1. The switch element SW3 can connect the input terminal 1-2 to one input terminal of the differential amplifier circuit DA1 via the resistor R1, and the switch SW4 connects the input terminal 1-2 via the resistor R3. It can be connected to the other input terminal of the differential amplifier circuit DA1.

  One input terminal 2-1 and the other input terminal 2-2 of the current measuring circuit 102 are connected to either the one input terminal side or the other input terminal side of the differential amplifier circuit DA2 via the switch circuit 200. Switching connection is possible.

  Switch circuit 200 includes switch elements SW5, SW6, SW7, and SW8. The switch element SW5 can connect the input terminal 2-1 to one input terminal of the differential amplifier circuit DA2 via the resistor R5, and the switch SW6 differentially connects the input terminal 2-1 to the input terminal 2-1 via the resistor R7. It can be connected to the other input terminal of the amplifier circuit DA2. The switch element SW7 can connect the input terminal 2-2 to one input terminal of the differential amplifier circuit DA2 via the resistor R5. The switch SW8 connects the input terminal 2-2 via the resistor R7. It can be connected to the other input terminal of the differential amplifier circuit DA2. The switch circuits 100 and 200 may be semiconductor elements or electromagnetic switches.

  The switch circuits 100 and 200 are controlled as follows. This control is executed by a control signal from the MPU 400, for example. During a certain period A, SW1, SW4, SW5, and SW8 are turned on, and SW2, SW3, SW6, and SW7 are turned off. In this period A, the current measurement circuit 101 can measure only the discharge current, and the current measurement circuit 102 can measure only the charging current.

  At this time, the MPU 400 calculates the output of the current measuring circuit 101 as a discharge current and the output of the current measuring circuit 102 as a charging current.

  Next, in another period B, SW2, SW3, SW6, and SW7 are turned on, and SW1, SW4, SW5, and SW8 are turned off. In this period B, the current measurement circuit 101 can measure only the charging current, and the current measurement circuit 102 can measure only the discharge current.

  At this time, the MPU 400 calculates the output of the current measuring circuit 101 as a charging current and the output of the current measuring circuit 102 as a discharging current.

By repeating the above period A and period B, the error of the current integrated value can be canceled. Specifically, after a constant current discharge current Id is passed for a period t1 in a period A, a constant current charge current Ic is supplied for a period t2, and in the next period B, the switching circuits 100 and 200 are switched and controlled. It is assumed that the constant current charging current Ic flows for the period t2 ′ after flowing for the period t1 ′. Then
The error in period A is the discharge period t1: ΔV1 = Voff1 (1 + Av),
Charging period t2: ΔV2 = Voff2 (1 + Av)
The error in period B is the discharge period t'1: ΔV2 '= Voff2' (1 + Av),
Charging period t2 ′: ΔV1 ′ = Voff1 ′ (1 + Av).

When calculating the error ΔQAB of the current integrated values in the period A and the period B,
Error ΔQAB = ΔV1 × t1 (discharge time) −ΔV2 × t2 (charge time) + ΔV2 ′ × t1 ′ (discharge time) −ΔV1 ′ × t2 ′ (charge time).

Here, if Id = Ic, Voff1 = Voff1 ′, Voff2 = Voff2 ′ becomes ΔV1 = ΔV1 ′, ΔV2 = ΔV2 ′,
ΔQAB = ΔV1 (t1−t2 ′) + ΔV2 (t1′−t2). Further, when the A and B periods and the charge / discharge period are equal, if t1 = t2 = t1 ′ = t2 ′, ΔQAB = 0. Accordingly, it is possible to suppress the offset of the current measuring circuit and / or cancel the offset.

  FIG. 4A shows a period in which the current measurement circuits 101 and 102 in FIG. 3 perform current measurement in the periods A and B described above. FIG. 4B shows a state where current measurement errors caused by the current measurement circuits 101 and 102 in FIG. 1 are accumulated in the periods A and B described above. FIG. 4C shows a state in which the current measurement errors of the current measurement circuits 101 and 102 in FIG. 3 are canceled in the periods A and B described above. FIG. 4C shows that the error ΔQ is canceled after the period A and the period B when the discharge current and the charge current are equal and the discharge current measurement period and the charge current measurement period are equal.

  In the above embodiment, the two current measurement circuits 101 and 102 are provided. However, the idea of the present invention may be configured as shown in FIG. In the embodiment of FIG. 5, the current measurement circuit 102 is omitted and the current measurement circuit 102 is adopted as compared with the embodiment of FIG. 3. Further, one end of the resistor R4 is connected to the other input terminal (for example, negative input terminal) of the differential amplifier circuit DA1, and the other end of the resistor R4 is connected to the reference voltage Vref.

In this example, using Vref as a reference voltage,
When Vout> Vref, discharge (charge) is performed, when Vout <Vref, charge (discharge), and when Vout = Vref, no current is measured, and the measurement current is calculated.

  The current value is calculated based on the absolute value of Vout−Vref. Therefore, the relationship between the output voltage of the current measuring circuit, the charge / discharge current, the reference voltage, and the offset voltage is as shown in FIG.

  For example, assume that an operational amplifier has a positive offset. Then, if the measured current value is a current value in the range of Vout> Vref, it is measured as a value larger than the original current value. Conversely, if the measured current value is in the range of Vout <Vref, In this case, it is measured as a value smaller than the original current value. In order to reduce the error due to the offset, the switch elements SW1 to SW4 are controlled. That is, since SW1 and SW4 are turned on and SW2 and SW3 are turned off during a certain period A, the MPU 400 calculates when the output of the current measuring circuit is discharged when Vout> Vref and charged when Vout <Vref. In the next period B, SW2 and SW3 are turned on, and SW1 and SW4 are turned off. Therefore, the MPU 400 calculates when the output of the current measurement circuit is Vout> Vref and discharges when Vout <Vref.

  By repeating the period A and the period B, an error included in the current integrated value can be canceled. Specifically, after a constant current discharge Id is allowed to flow for a period t1 in a period A, a constant current charge Ic is allowed to flow for a period t2. After that, the constant current charging Ic is assumed to flow for the period t2 ′.

  The offset voltage of the current measurement circuit 100 in the period A is the discharge region Voff1 and the charge Voff2, and the offset voltage in the period B is the discharge Voff1 'and the charge Voff2'. Therefore, the error is as follows.

The errors in period A are as follows: discharging period t1: ΔV1 = Voff1 (1 + Av), charging period t2: ΔV2 = Voff2 (1 + Av)
The respective errors in the period B are the discharge period t1 ′: ΔV2 ′ = Voff2 ′ (1 + Av) and the charging period t2 ′: ΔV1 ′ = Voff1 ′ (1 + Av).

Therefore, the error ΔQAB between the current integrated values in period A and period B is
ΔQAB = ΔV1 × t1 (discharge time) −ΔV2 × t2 (charge time) + ΔV2 ′ × t1 ′ (discharge time) −ΔV1 ′ × t2 ′ (charge time)

Here, if Id = Ic, Voff1 = Voff1 ′ and Voff2 = Voff2 ′ are changed to ΔV1 = ΔV1 ′ and ΔV2 = ΔV2 ′, and ΔQAB = ΔV1 (t1−t2) + ΔV2 (t1−t2). Further, when the A and B periods A and B are equal and the charge and discharge periods are equal, if t1 = t2 = t1 ′ = t2 ′, ΔQAB = 0. Further, if t1 = t2, ΔQAB = 0. Therefore, the offset of the current measuring circuit can be suppressed or canceled.

  In actual use, it is desirable that the period A and the period B be switched frequently so that the current measurement circuit makes the period corresponding to the current in one direction equal to the period corresponding to the other. For example, the control is performed so that the period A and the period B are switched at a timing at which no current continues for a certain time, a timing at which the apparatus is activated, or the like. This is particularly effective in an apparatus having a constant charge / discharge pattern and period.

  When the above-described current measurement circuit is connected to the charge / discharge path of the secondary battery circuit, the current measurement circuit is not necessarily limited to the locations shown in FIGS. 1, 3, and 5. In short, it may be the same place (charge / discharge detection path) where changes in charge current and discharge current for the secondary battery circuit can be detected. The current measurement circuit and the switch may be integrated with a semiconductor integrated circuit, and the switch may be controlled by a control signal from the control circuit.

  Of course, this apparatus can be applied to various apparatuses (vehicles such as automobiles and trains). Therefore, the timing for controlling the switch circuits 100 and 200 can be determined by the MPU 400. In this case, the MPU 400 can detect the charging period and the discharging period for the battery circuit BT. Then, the MPU 400 sets the period A and the period B, and performs switch control for the above-described measurement. Although FIG. 4 shows the theoretical period A and the period B, the period A and the period B may be distributed on the time axis.

  As described above, according to the present embodiment, the offset in the SOC calculation can be canceled and the SOC accuracy can be improved by switching the offset of the current measurement circuit in the direction of the measurement current every certain period. Therefore, further improvement in SOC accuracy can be expected. Moreover, the SOC accuracy can be improved only by adding an inexpensive switch without using an expensive operational amplifier.

  Although several embodiments of the present invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 100,200 ... Switch circuit, 101,102 ... Current measuring circuit, 400 ... MPU, 500 ... I / F circuit, BT ... Secondary battery circuit, Rsh ... Shunt resistance .

Claims (6)

A resistance affected by the charging current and discharging current of the secondary battery circuit;
A current measuring circuit for measuring the discharging current and the charging current based on the voltage generated in the resistor;
Provided as a connection circuit between the input terminal of the current measuring circuit and the resistor, the resistor and the resistor so that the current measuring circuit measures the discharge current in the first period and the charging current in the second period. A switch circuit for switching the measurement connection state of the current measurement circuit;
A secondary battery device comprising: a control unit that calculates a state of charge of the secondary battery circuit using an output of the current measurement circuit. A resistance affected by the charging current and discharging current of the secondary battery circuit;
A first current measuring circuit for measuring the discharge current and the charging current based on a voltage generated in the resistor;
A second current measuring circuit for measuring the discharge current and the charging current based on a voltage generated in the resistor;
In the first period, the first current measuring circuit measures the discharge current, the second current measuring circuit measures the charging current, and in the second period, the first current measuring circuit measures the charging current, A switch circuit for switching a connection state between the resistor and the first and second current measurement circuits so that a second current measurement circuit measures the discharge current;
A secondary battery device comprising: a control unit that calculates a state of charge of the battery circuit using outputs of the first and second current measurement circuits.   The timing of switching the measurement current direction by the switch circuit is when it is determined that the charging current and the discharging current do not flow for a certain period of time, or when a device using the voltage of the secondary battery circuit is activated. Item 3. The secondary battery device according to Item 1 or 2.   The secondary battery device according to claim 1, wherein the switch circuit includes a semiconductor element. A resistance that is affected by a charging current and a discharging current of the secondary battery circuit; a current measuring circuit that measures the discharging current and the charging current based on a voltage generated at the resistor; A method for measuring a state of charge, wherein the controller is
The connection state between the input terminal of the current measurement circuit and the resistor is switched so that the current measurement circuit measures the discharge current in the first period and the charge current in the second period,
A charge state measurement method for calculating a charge state of the secondary battery circuit using an output of the current measurement circuit. A resistance affected by the charging current and discharging current of the secondary battery circuit, a first current measuring circuit for measuring the discharging current and the charging current based on the voltage generated at the resistance, and a voltage generated at the resistance A second current measuring circuit for measuring the discharge current and the charging current, and a method for measuring a charging state of the secondary battery circuit including a control unit, the control unit comprising:
In the first period, the first current measuring circuit measures the discharge current, the second current measuring circuit measures the charging current, and in the second period, the first current measuring circuit measures the charging current, The connection state of the resistor and the first and second current measurement circuits is switched so that the second current measurement circuit measures the discharge current,
A charge state measurement method for calculating a charge state of the battery circuit using outputs of the first and second current measurement circuits.

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