JP2001204141A - Detector for cell voltage of set battery and detecting method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a set battery voltage detector capable of freely setting the number of cells in series of a unit of measurement, and detecting cell voltage with high precision without the need of a highly precise A/D converter in the detector for the cell voltage of a set battery consisting of a plurality of cells connected in series, particularly, in the cell voltage detector which detects the cell voltage by shifting the respective cell voltages having different potentials to ground to the same one, using a flying capacitor method. SOLUTION: This detector, as a first step, charges a capacitor to the cell voltage in an arbitrary cell having a different potential to ground of the set battery in which a plurality of cells are connected in series by action of the flying capacitor circuit, as a second step, obtains a pulse having pulse width corresponding to the time when the voltage of the capacitor charged by the cell voltage attenuates and reach threshold voltage by action of the capacitor of the flying capacitor circuit, a discharge circuit, and a voltage comparator, and, as a third step, obtains the digital value of the cell voltage by action of a time measuring method of the pulse width and an operating means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for detecting a cell voltage of a battery pack comprising a plurality of cells connected in series, and more particularly, to shifting a voltage of each cell having a different ground potential to the same ground potential to achieve high accuracy. The present invention relates to a cell voltage detection device and a detection method capable of detecting a voltage by using the same.

[0002]

2. Description of the Related Art In an electric vehicle or a so-called hybrid car, an electric motor is used as a power source or an auxiliary power source, and a secondary battery in which many cells are connected in series is used as a power source. As an example, there is known a nickel-hydrogen secondary battery having a standard voltage of 1.2 V per cell in which 60 cells are connected in series. It is known that when a secondary battery in which a large number of cells are connected in series is used repeatedly by repeating charging and discharging, variations in cell voltage occur. Therefore, in addition to monitoring the total voltage of all cells, the voltage of each cell is monitored, and a secondary battery management method that prevents any cell from being continuously used in an overcharged or overdischarged state is necessary.

[0003] It is convenient to monitor the voltage by converting the voltage into a digital value by an A / D converter and taking it in.
To this end, it is necessary to shift a different ground potential to the same ground potential for each cell and then input the cell voltage to the A / D converter. From this viewpoint, in the case of the series of 60 cells described above, when the potential of the negative electrode of the lowermost cell is set to the ground potential, the ground potential of the positive electrode of the uppermost cell reaches 72 V, and the ground potential becomes the same potential as it is. Shifting design becomes difficult. Therefore, first, after dividing 60 cells into several blocks and reducing the number of serial cells in each block, the voltage of each cell is monitored in each block, and data such as the monitoring result of the cell voltage obtained in each block. Are integrated and managed by totalizing them through an insulated communication means such as a photocoupler. Of course, such block division has many disadvantages such as an increase in the number of circuit components including the A / D converter, but it is unavoidable to realize the functions.

Here, the cell voltage is a voltage difference between the positive electrode potential and the negative electrode potential of each cell, that is, a differential voltage. On the other hand, since the ground potential that differs for each cell is the same-mode voltage, a large number of cells The purpose of measuring the cell voltage of the batteries in series with each other corresponds to the purpose of measuring the differential voltage without being sensitive to the common-mode voltage.

In the case where the number of series cells in one block is 20 cells, the potential difference between the negative electrode potential of the lowermost cell and the negative electrode potential of the uppermost cell is 22.8 V. Under the severest conditions, the common mode voltage of 22.8 V It is required to accurately measure the differential voltage 1.2 V while eliminating the influence.

A level shift circuit using a differential amplifier or an operational amplifier is well known as a circuit for extracting a differential voltage while eliminating the influence of a common-mode voltage. Due to the effects of threshold voltage offset of the transistor pair and resistance ratio error of the level shift resistor, errors in the output voltage are likely to occur with respect to the ground potential, and it is difficult to obtain performance suitable for the intended use here. . As another circuit system, there is a circuit system called a flying capacitor (Flying Capacitor) among experts. The concept is disclosed in JP-A-8-24216.
Although described in No. 9, the basic operation is from the following (1)
This is a repetition of (3).

(1) A capacitor is connected to the voltage source to be measured and charged to the voltage of the voltage source to be measured.

(2) Disconnect both terminals of the capacitor from the voltage source to be measured.

(3) A capacitor is connected to a reference potential terminal (usually a ground terminal) and an input terminal of the A / D converter, and the voltage of the capacitor is converted into a digital value.

The above-described series of operations determines whether the capacitor is transferring the voltage of the voltage source to be measured to the input of the A / D converter while jumping between the voltage source to be measured and the A / D converter. Therefore, it seems to be called a flying capacitor. Although this is a term that is generally unfamiliar to hear, it is considered to be a term that expresses the concept of its operation well as described above, and a flying capacitor or a flying capacitor method will be used as a term in this specification.

An example in which the flying capacitor method is applied to the measurement of the cell voltage of a battery is disclosed in Japanese Unexamined Patent Publication No.
98702.

As described above, in the flying capacitor method, the voltage of the voltage source to be measured is charged and held in the capacitor, only the ground potential is shifted, and the charged voltage of the capacitor is directly transferred to the A / D converter. It can be said that this is a method suitable for extracting only the differential voltage while eliminating the influence of the common mode voltage.

On the other hand, in order to perform A / D conversion of a voltage whose ground potential has been shifted by a flying capacitor with high accuracy, the A / D converter itself has high accuracy with sufficient resolution. , The maximum input voltage of the A / D converter (ie, the full scale of the A / D converter) must be reasonably matched to the maximum voltage of the voltage source to be measured (ie, the full scale of the voltage source to be measured). It is. If the A / D converter full scale is too large with respect to the full scale of the voltage source to be measured, the substantial resolution is reduced. Looking at the compatibility between the flying capacitor method and the A / D converter receiving the output from this viewpoint, it can be said that the charging voltage of the capacitor charged to the voltage of the voltage source to be measured is directly transferred to the A / D converter. It can be seen that there are many obstacles to satisfying the above requirements. For example, A / D converters built into microcomputers often have a full-scale of 5 V, whereas a nickel-hydrogen secondary battery with a standard voltage of 1.2 V per cell is a series of 6 cells. Is the unit of measurement of the cell voltage, the voltage becomes 7.2 V as a standard, and a 5 V full-scale A / D converter cannot be used. Conversely, in order to use the 5V full-scale A / D converter, there is a constraint condition that the measurement unit must be limited to about 3 cells in consideration of the fluctuation of the cell voltage.

As described above, if the flying capacitor method is applied to cell voltage detection of a multi-cell series assembled battery and the output voltage of the flying capacitor circuit is A / D converted,
Since the range of the cell voltage to be measured is restricted, the device cannot be optimally designed from a comprehensive viewpoint. Also, a high-precision A / D converter is expensive.

An object of the present invention is to provide a cell voltage detecting device for an assembled battery in which a number of cells are connected in series. In particular, the voltage of each cell having a different ground potential by using a flying capacitor method is applied to the same ground potential. In the cell voltage detecting method, the number of cells as a unit of measurement can be freely set, and a high-precision A / D converter is not required, and the cell voltage can be detected with high precision. An object of the present invention is to provide a voltage detection device and a detection method.

[0016]

A cell voltage detecting device according to the present invention comprises an assembled battery in which a plurality of cells are connected in series, a flying capacitor circuit, a discharging circuit, a voltage comparator, a time measuring means, and a calculating means. Have.

The flying capacitor circuit includes a capacitor, a sampling switch for connecting both ends of a selected cell of the battery pack to the capacitor, and sampling and holding a voltage of the selected cell on the capacitor, A transfer switch that connects the capacitor in parallel with the discharge circuit after the switch has turned off and discharges the charge of the capacitor through the discharge circuit.

The discharge circuit is a constant current circuit or a simple resistor, one end of which is connected to a reference potential. The voltage between both terminals of the discharge circuit is a small voltage immediately before the transfer switch is turned on, and rises to the voltage of the capacitor when the capacitor is connected by turning on the transfer switch. The transition of the voltage after that differs depending on whether the discharge circuit is a constant current circuit or a simple resistor. In the case of the constant current circuit, the charge of the capacitor is discharged at a constant current, and the voltage decreases in proportion to the transition of the discharge time. In the case of a simple resistor, when the capacitance value of the capacitor is C and the resistance value of the resistor is R, the voltage decreases with the transition of the discharge time according to a well-known exponential function with CR as a time constant. I do.

The voltage comparator receives the voltage of the other end of the discharge circuit that is not connected to the reference potential and compares the voltage with a threshold voltage. Then, when the input voltage that decreases with the transition of the discharge time reaches the threshold voltage, the output voltage is changed from high to low (or from low to high). Therefore, a pulse having a pulse width from the time when the transfer switch is turned on to the time when the input voltage reaches the threshold voltage is generated at the output of the voltage comparator. This time is defined as a threshold arrival time (T).
Since the threshold arrival time (T) is determined by a function related to the voltage of the capacitor immediately before the start of the discharge, the voltage of the capacitor immediately before the start of the discharge based on the threshold arrival time (T), that is,
The cell voltage to be measured can be calculated.

The time measuring means obtains a digital value related to the threshold arrival time (T) described above, and converts the digital value into a digital value by counting the number of reference clock pulses within the time, for example. is there. More specifically,
The gate control of the pulse counter for counting the reference clock pulse is performed by the output pulse of the voltage comparator, or the gate control of the pulse counter is set to the on timing of the transfer switch and the output of the voltage comparator at the threshold voltage arrival time. A method of opening and closing control according to the timing of the generated voltage transition can be used. Alternatively, another method may be used instead of the above-described pulse counting method. In any case, at this stage the analog value associated with the cell voltage has been converted to a digital value.

The calculating means calculates a digital value of the cell voltage based on the digital value relating to the threshold arrival time measured by the time measuring means. The operation formula will be described later according to an embodiment.

To summarize the above, as a first step, the action of the flying capacitor circuit is used to charge a capacitor to a cell voltage for an arbitrary cell having a different ground potential of an assembled battery in which multiple cells are connected in series. By the action of the capacitor, the discharge circuit and the voltage comparator, a pulse having a pulse width corresponding to the time when the voltage of the capacitor charged to the cell voltage attenuates and reaches the threshold voltage is obtained. The digital value of the cell voltage is obtained by the operation of the calculation means.

With this arrangement, the cell voltage of a unit of measurement can be set freely for any cells having different ground potentials of a battery pack in which multiple cells are connected in series, without being restricted by the full scale of the A / D converter. A digital value of the cell voltage can be obtained with high accuracy without using an expensive high-precision A / D converter.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments.

FIG. 1 is a diagram showing a first embodiment of the present invention. In the figure, 1 is an assembled battery, 2 is a flying capacitor circuit, 3 is a discharge circuit, 4 is a voltage comparator, 5 is time measuring means, and 6 is arithmetic means. 21, 22 and 23 are components of the flying capacitor circuit, 21 is a capacitor, 22 is a sampling switch, and 23 is a transfer switch. Reference numerals 31 and 32 denote constituent means of the discharge circuit 3, reference numeral 31 denotes a resistor, and reference numeral 32 denotes a constant current circuit. 31
Either of 32 is used. Reference numeral 41 denotes a threshold voltage of the voltage comparator 4. 51 and 52 are time measuring means 5
, 51 is a pulse width measuring means, and 52 is a reference clock pulse. Also, 100 indicates a microcomputer,
101 is a switch pulse generating means.

The battery pack 1 is a series body of four cells # 1 to # 4, and each cell # 1 to # 4 itself is also made of a series body of a plurality of unit cells. Although the number of cells in series and the number of cells in series are not directly related to the establishment of the present invention, for the time being, each cell is composed of six nickel metal hydride cells having a standard voltage of 1.2 V in series. Then, assume that the standard cell voltage is 7.2 V and the standard total voltage is 28.8 V.

One of the switches φS1 to φS4 is selected by the sampling switch pulse supplied from the switch pulse generator 101, and the sampling switch 22 of the flying capacitor circuit is turned on / off. The switch pulse generating means 101 has
The four switch pulses of S4 may be individually supplied to the sampling switch. Alternatively, for example, a method in which a 2-bit code is supplied and decoded and used on the sampling switch side may be used. When the sampling switch is turned on, a cell connected to the selected switch is connected to the capacitor 21, and the capacitor 21 is charged to the voltage of the cell.

The transfer switch 23 is on / off controlled by the transfer switch pulse φT, and is turned on at the timing after the sampling switch 22 has transitioned from on to off. The switch timing is managed so that the sampling switch and the transfer switch are not turned on at the same time.

The discharge circuit 3 is composed of either a resistor 31 or a constant current circuit 32, and is functionally a two-terminal circuit. Further, the constant current circuit 32 can be realized by the circuit illustrated in the figure. One end of the discharge circuit 3 is biased to a reference potential (earth potential in the figure), and the other terminal is connected to a voltage comparator 4.
Is connected to the input terminal of The voltage of the other terminal connected to the input terminal of the voltage comparator 4 is defined as the voltage of the discharge circuit. The voltage of the discharge circuit is at a low voltage while the transfer switch 23 is off. When the transfer switch 23 is turned on, the capacitor 21 discharges the discharge circuit 3
, And the charge of the capacitor 21 is gradually discharged through the discharge circuit 3. Immediately after the start of discharging, the voltage of the discharging circuit increases to the initial charging voltage of the capacitor 21, and then gradually decreases with the transition of the discharging time.

The voltage comparator 4 compares the voltage of the discharge circuit applied to the input terminal with a threshold voltage 41. And
When the input voltage that decreases with the transition of the discharge time reaches the threshold voltage, the output voltage transitions from high to low. Therefore, a pulse having a pulse width from the time when the transfer switch is turned on to the time when the input voltage reaches the threshold voltage is generated at the output of the voltage comparator 4. This pulse is defined as a threshold arrival time pulse. The time from the discharge start time to the time when the input voltage reaches the threshold voltage is a threshold arrival time (T).
Is defined. Since the threshold arrival time (T) is determined by a function related to the voltage of the capacitor immediately before the start of discharge, the voltage of the capacitor immediately before the start of discharge, that is, the cell voltage to be measured, is determined based on the threshold arrival time (T). Can be calculated.

It is a necessary condition that the ON period of the transfer switch is set to be longer than the threshold arrival time (T). It is preferable to design so as to set a predetermined time with a margin in advance or to turn off at an appropriate time after the voltage of the discharge circuit reaches the threshold voltage.

FIG. 2 shows a sampling switch pulse, a transfer switch pulse,
FIG. 9 is a diagram illustrating an example of mutual timing of threshold arrival time pulses.

FIG. 3 is an explanatory diagram of the threshold arrival time (T). The discharge circuit is a resistor (R) and the constant current circuit (I
The case (c) is shown in (A) and (B), respectively.

First, the case where the discharge circuit is a resistor (R) will be described. In this case, the voltage (V (t)) of the discharge circuit according to the transition of the discharge time becomes the following exponential function.

[0035]

(Equation 1)

Here, Vc is the charging voltage of the capacitor 21 immediately before the start of discharging, that is, the cell voltage to be measured.
C is the capacitance value of the capacitor 21 and R is the resistance value of the resistor 31. In the figure, the voltage transition when Vc is a different voltage (V1, V2) is also shown. Threshold voltage 41
Is Vth, the time at which the voltage (V (t)) of the discharge circuit reaches Vth is indicated by T. V1, V2
Are T1 and T2, respectively.

If Vth and the CR product are known, Vc can be calculated by the following equation using the measured value of T.

[0038]

(Equation 2)

Next, the case where the discharge circuit is a constant current circuit (Ic) will be described. In this case, the voltage (V (t)) of the discharge circuit accompanying the transition of the discharge time becomes a linear function as follows.

[0040]

(Equation 3)

Here, Ic is the current value of the constant current circuit. In the figure, assuming that the threshold voltage 41 is Vth, the time when the voltage (V (t)) of the discharge circuit reaches Vth is T.
Indicated by T corresponding to V1 and V2 are T1 and T2, respectively.

If Vth and Ic are known, Vc can be calculated by the following equation using the measured value of T.

[0043]

(Equation 4)

Since Vth, C, R, and Ic are design parameters and are known and are basically fixed values, the threshold arrival time is calculated according to the above equation (2) or (4). The cell voltage can be calculated from the measured value of (T). In some cases, the design parameters are expected to change over time or due to temperature, and a method of dealing with such a case will be described in another embodiment described later.

Returning to the description of FIG.

The time measuring means 5 obtains a digital value related to the above-described threshold arrival time (T). For example, by counting the number of reference clock pulses within the threshold arrival time (T), the digital value is obtained. Is converted to As an example, the one constituted by the pulse width measuring means 51 and the reference clock pulse 52 is shown. The pulse width measuring means 51 controls opening and closing of the gate of the pulse counter by a pulse output from the voltage comparator 4, and counts a reference clock pulse during a period when a pulse having a pulse width T is applied. As another method of controlling the gate opening / closing of the pulse counter, a method of opening the gate at the ON timing of the transfer switch and closing the gate at the timing of the voltage transition generated at the output of the voltage comparator at the threshold voltage arrival time can be used. Some microcomputers incorporate such a function as input capture, and this function can also be used. In any case, by counting the number of reference clock pulses within the threshold arrival time (T), a digital value of the threshold arrival time (T) can be obtained.

The repetition period of the reference clock pulse is Tc
The digital value of the threshold arrival time (T) when the pulse count value is P at lk is obtained by the following equation.

[0048]

## EQU00005 ## For example, when the clock of the microcomputer is 5 MHz, T = P.Tclk ---------------------
The clk is appropriately 0.2 μsec. If each design parameter is set so that the threshold arrival time (T) is set to about 200 μsec, even if there is a counting error of ± 1, it will be 0.1 μsec. This is a calculation that can obtain an accuracy of about 1%.

The calculating means 6 calculates the digital value of the cell voltage based on the digital value relating to the threshold arrival time measured by the time measuring means 5. Specifically, the microcomputer 1 in which a program corresponding to an equation obtained by substituting the equation (5) into the equation (2) or (4) is incorporated.
00 does this. The digital value of the cell voltage obtained as a result of the operation is used for monitoring the cell voltage in the same microcomputer, or is notified to another host microcomputer and used for other purposes such as control of the entire apparatus.

The foregoing is summarized in a time series and expressed as follows. The case where the cell voltage of # 4 is measured is taken as an example.

(1) The sampling switch φS4 is turned on, and the cell # 4 is connected to the capacitor 21. At this time,
The capacitor 21 is charged to the cell voltage of the cell # 4.

(2) Turn off φS4. At this time, the capacitor 21 holds the cell voltage of the cell # 4.

(3) Turn on the transfer switch φT and connect the capacitor 21 to the discharge circuit 3 in parallel. At this time, discharging of the charge of the capacitor is started.

(4) With the charging voltage of the capacitor immediately before the start of discharging as an initial value, the voltage of the discharging circuit decreases with the transition of the discharging time.

(5) At the time when the voltage of the discharge circuit reaches the threshold voltage, the voltage comparator outputs a voltage transition. At this time, a threshold arrival time pulse having a pulse width equal to the threshold arrival time (T) is generated.

(6) The time measuring means counts the number of reference clock pulses during the period of the pulse, and calculates a threshold arrival time (T).
Is converted to a digital value.

(7) A digital operation is performed based on the digital value of the threshold arrival time (T) to calculate a digital value of the cell voltage.

(8) At an appropriate time after the time when the voltage of the discharge circuit reaches the threshold voltage, the transfer switch is turned off.

(9) Returning to the procedure (1), the process proceeds to the next cell voltage measurement sequence. In the embodiment of the present invention described above, for any cell having a different ground potential of a battery pack in which multiple cells are connected in series, the measurement unit can be measured without being restricted by the full scale of the A / D converter. The number of cells can be freely set, and a digital value of the cell voltage can be obtained with high accuracy without requiring an expensive high-precision A / D converter.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the initial variation of parameters such as C, R, Ic, and Vth in Equation (2) or Equation (4) derived as the cell voltage calculation equation in the description of the first embodiment, and It discloses a method for coping with those changes with time and temperature dependence.

The formula for calculating the cell voltage (Vc) is shown below again.

[0062]

(Equation 2)

[0063]

(Equation 4)

In the above cell voltage calculation formula, T is a measured value, and other C, R, Ic, and Vth are parameters. Generally, initial variation of each parameter, aging,
Factors such as temperature dependency vary in the degree and properties of the components depending on the material and structure of the components. For example, C, R
Is generally highly temperature-dependent, and Ic is also generally inversely proportional to the resistance value.

Considering these properties, C, R, Ic
The second embodiment provides a mechanism that does not directly depend on.

In FIG. 4, reference numeral 1 denotes a battery pack. The battery pack 1 is a series body of a plurality of cells like the battery pack in the first embodiment, but in order to facilitate understanding of the essence of the present embodiment, any cell (#n) in the battery pack 1 will be described. Are represented as representatives. Similarly, sampling switches connected to other than the cell (#n) are omitted. 7
Is a calibration voltage source. The voltage (Vo) of the calibration voltage source 7
Is newly added to the sampling switch 22. Reference numeral 8 denotes a voltage divider that divides the voltage (Vo) of the calibration voltage source 7 at a division ratio α to generate a voltage αVo. The voltage of αVo is used as a threshold voltage of the voltage comparator 4. Other configurations are the same as those of the first embodiment, and are not shown in FIG. As in the first embodiment, there are two types of the discharge circuit 3, that is, a resistor and a constant current circuit.

The calibration voltage source 7 is a voltage source whose output voltage is stabilized using a zener voltage or a band gap voltage of a semiconductor. Such a voltage source has a temperature dependency of 1
ICs having extremely stable characteristics of 0 ppm / degree C are distributed at relatively low cost. The voltage divider 8 is composed of two resistors, and the voltage division ratio α is determined by the resistance value ratio of the two resistors. 2
Since the resistors are of the same kind of material and of the same kind of structure, the resistance values have the same temperature dependence, and therefore the partial pressure ratio α has no temperature dependence. The initial value of the partial pressure ratio α can be accurately obtained by performing trimming as necessary. Therefore, in the present embodiment, the following description will be made on the assumption that the calibration voltage Vo and the voltage division ratio α are stable fixed values.

The cell voltage detection circuit according to the present embodiment has two operation modes, a cell voltage detection mode and a calibration mode. The operation in the cell voltage detection mode is the same as in the first embodiment. In the calibration mode, φSo of the sampling switch 22 operates to measure the voltage Vo of the calibration voltage source 7, and stores the threshold arrival time measured at that time as To. Hereinafter, the case where the discharge circuit is a resistor and the case where the discharge circuit is a constant current circuit will be described separately.

First, when the discharge circuit is a resistor, Vc is Vo, Vth is αVo, and T is T
The following equation corresponding to the calibration mode is established by substituting o.

[0070]

(Equation 6)

By solving the above equation for 1 / CR, the following equation is obtained.

[0072]

(Equation 7)

The above equation shows that the CR having a high temperature dependency is obtained by calculating the stable fixed value α and the measured value To of the threshold arrival time To in the calibration mode.
Means that it can be replaced by

By substituting this equation into Equation (2), the following cell voltage calculation equation in the cell voltage measurement mode is obtained.

[0075]

(Equation 8)

The above equation shows that the calibration voltage Vo is a stable fixed value.
It shows that the cell voltage can be calculated from the measured value of the threshold arrival time T in the cell voltage measurement mode, using the threshold arrival time To measured and stored in the calibration mode as the calculation parameters.

Next, when the discharging circuit is a constant current circuit, Vc is Vo, Vth is αVo, and T is T
The following equation is established by substituting for o.

[0078]

(Equation 9)

By solving the above equation for Ic / C, the following equation is obtained.

[0080]

(Equation 10)

The above equation means that C and Ic, which have a high temperature dependency, can be replaced with a stable fixed value α and a measured value To of the threshold arrival time To in the calibration mode.

By substituting this equation into Equation (4), the following cell voltage calculation equation in the cell voltage measurement mode is obtained.

[0083]

[Equation 11]

The above equation shows that the calibration voltage Vo is a stable fixed value.
It shows that the cell voltage can be calculated from the measured value of the threshold arrival time T in the cell voltage measurement mode, using the threshold arrival time To measured and stored in the calibration mode as the calculation parameters.

In either case of the above two types of discharge circuits, if the time interval between the calibration mode and the cell voltage measurement mode is appropriately shortened, the temperature change and the change over time within that time can be kept sufficiently small. Because it is possible, it is possible to eliminate the effects of temperature dependence of C, R, Ic, etc. and the change with time. Also, the initial variations of C, R, and Ic are completely absorbed.

In the above description, it is a necessary condition that the calibration voltage Vo and the voltage division ratio α are stable fixed values. However, if the following initial value calibration method is used together, it is not always necessary that the initial value completely matches the design target value. The initial value calibration method is a process close to the final process of the assembly process of the battery pack device embodying the present invention,
Perform the following procedure.

(1) The calibration voltage Vo of the calibration voltage source 7 and the divided voltage generated by the voltage divider 8 are read by an external precision voltmeter.

(2) The read digital value of the calibration voltage is stored in the memory of the battery pack device as the actual value of Vo.

(3) The ratio between the two voltages thus read is calculated and stored in the memory in the battery pack device as the actual value of α.

At the stage where the battery pack device is used, the actual value of Vo and the real value of α stored in the memory of the battery pack device are read out from the memory, and the above-mentioned formula (8) or (11) is read. Used for the calculation of

As a result, the initial accuracy of the calibration voltage source 7 and the voltage divider 8 does not have to be unduly strict.

Next, FIGS. 5A and 5B show the calibration voltages Vo and other means for generating a voltage α times the Vo. FIG. 2A is a diagram in which a voltage obtained by dividing the output of the operational amplifier by the voltage dividing ratio α is fed back to the inverting input terminal of the operational amplifier, and the voltage αVo is applied to the non-inverting input terminal. The output voltage of the operational amplifier becomes Vo, and Vo and αVo are used in the same manner as in the second embodiment.

FIG. 5B has another set of circuits of the same type as that of FIG. 5A, and the voltage applied to the operational amplifier is a voltage Vref different from Vo and αVo. By setting the voltage dividing ratio of each voltage divider to Vref / Vo, Vref / αVo, voltages of Vo and αVo are obtained at the output of the operational amplifier. Vo and αVo thus obtained are used in the same manner as in the second embodiment.

Either of the above means is equivalent in the function of obtaining the calibration voltage Vo and the voltage αVo obtained by multiplying the calibration voltage by the coefficient α.

The effect obtained by the second embodiment is effective even in a case where the cell voltage measurement target cell is limited to one specific cell. That is, the sampling switch 22 does not necessarily need to be able to select all the cells of the battery pack 1, and the same effect can be obtained even if only a specific cell is selected.

Next, a third embodiment of the present invention will be described with reference to FIG. In the figure, the difference from the first embodiment is that a common sampling switch φSc is newly added to the sampling switch 22. Others are the same. The meaning of the common of the common sampling switch is a sampling switch connected to the common terminals of the sampling switches φS1 to φS4 having a function of selecting a corresponding cell of the cell voltage measurement, and performing a common switching operation in any cell voltage measurement. It represents that. The sampling switch in the first embodiment has both a function of selecting a corresponding cell for cell voltage measurement and a function of turning on the switch for a predetermined time to sample the voltage of the corresponding cell and charge the capacitor 21. However, the sampling switch according to the third embodiment imposes the latter of the above functions on the common sampling switch.

FIG. 7 shows the switch drive timing in the third embodiment. Referring to the switch drive timing in the first embodiment shown in FIG. 2, the above difference can be understood, and the same cell voltage detection function as that of the first embodiment can be obtained by the third embodiment. Can understand.

On the other hand, the following new effects can be obtained by adding the common sampling switch. It focuses on the property that a flying capacitor circuit generates a voltage error under the influence of a parasitic capacitor due to its operation principle. That is, in an actual flying capacitor circuit configuration, an electronic switch group for switching a connection destination of a capacitor is essential, and is affected by a parasitic capacitor inevitably attached to this electronic switch.
As a result, there is a phenomenon that an error occurs in the voltage held in the capacitor 21. This phenomenon is particularly large when the number of cells to be measured is large, and accordingly the number of electronic switches and the total capacitance of the parasitic capacitors associated therewith are large.
It becomes important when the capacitance value of the capacitor 21 cannot be increased so much for various reasons such as IC.

Here, an error generated in the voltage of the capacitor 21 under the influence of the parasitic capacitor will be described with reference to FIGS. FIG. 8 shows, of the parasitic capacitors associated with the electronic switch, those related to the above-mentioned voltage error, in comparison with the case without the common sampling switch and the case with the common sampling switch. The capacitance value Cs for each electronic switch
Parasitic capacitor. Capacitor 2
Since a parasitic capacitor directly connected to the high-potential-side terminal 1 contributes to the voltage error, the total capacitance value of the parasitic capacitor is set to ΔCs. As can be seen from the figure, when there is no common sampling switch, ΔCs is 5Cs, while when there is a common sampling switch,
ΣCs is 2Cs. ΦS1 to φS1 where the common sampling switch performs the function of capacitor 21 and cell selection
It is located between the S4 switches and eliminates the influence of the parasitic capacitors associated with the φS1 to φS4 switches.

FIG. 9 illustrates the mechanism by which ΔCs causes a voltage error in the capacitor 21. When the sampling switch is on, ΔCs is charged to the positive potential of the cell under measurement #n. Then, when the transfer switch is turned on and the low-side electrode of the capacitor 21 is connected to the ground potential, the capacitor 21 The movement of the charged charge toward. This causes the capacitor 21 to generate a voltage error of ΔV. The magnitude of ΔV is represented by the calculation formula described in the figure, and is proportional to the magnitude of ΔCs. Therefore, when there is a common sampling switch that can reduce ΔCs, the voltage error remains at a smaller value.

It is clear that the common sampling switch described in the third embodiment can be applied to the second embodiment.

[0102]

As described above, according to the cell voltage detecting device and the detecting method of the present invention, as a first step, by the action of the flying capacitor circuit, an arbitrary battery having a series connection of multiple cells having different ground potentials is obtained. For the cell, the capacitor is charged to the cell voltage, and as a second step, the time required for the voltage of the capacitor charged to the cell voltage to attenuate to reach the threshold voltage by the action of the capacitor of the flying capacitor circuit, the discharge circuit, and the voltage comparator. In the third step, the digital value of the cell voltage is obtained by the operation of the time measuring means and the calculating means of the pulse width, so that the A / D converter is restricted by the full scale. The cell voltage of the unit of measurement can be set freely without
In addition, a digital value of an arbitrary cell voltage having a different ground potential can be obtained with high accuracy without requiring an expensive high-precision A / D converter.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing switch drive timing in the first embodiment.

FIG. 3 is an explanatory diagram of a threshold arrival time (T).

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram showing calibration voltages Vo and other means for generating a voltage α times the Vo;

FIG. 6 is a diagram showing a third embodiment of the present invention.

FIG. 7 is a diagram illustrating switch drive timing in a third embodiment.

FIG. 8 is a diagram illustrating the behavior of a parasitic capacitor in the flying capacitor circuit.

FIG. 9 is a diagram illustrating a capacitor voltage error due to the influence of a parasitic capacitor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... assembled battery, 2 ... flying capacitor circuit, 3 ... discharge circuit, 4 ... voltage comparator, 5 ... time measuring means, 6 ... arithmetic means, 21 ... capacitor, 22 ... sampling switch,
23: transfer switch, 31: resistor, 32: constant current circuit, 41: threshold voltage of voltage comparator 4, 51: pulse width measuring means, 52: reference clock pulse, 7: calibration voltage source, 8: voltage divider

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03M 1/50 H03M 1/50 F term (Reference) 2G016 CA03 CB11 CB12 CC01 CC04 CC12 CC27 CD10 CD14 5G003 BA03 CA11 CB10 CC02 CC07 EA02 EA06 GC05 5H030 AS06 AS08 FF43 FF44 5H115 PG04 PI16 PU01 QN03 QN12 TI05 TR19 TU16 TU17 5J022 AA07 BA01 CE02 CF01 CF04 CG01

Claims (10)

[Claims] A sampling switch, a capacitor,
A transfer switch, a discharge circuit, a voltage comparator,
A cell voltage detecting device for a battery pack comprising a time measuring means and a calculating means, wherein the sampling switch connects both ends of a selected cell of the battery pack to the capacitor and selects the selected cell. The transfer switch switches the capacitor in parallel with the discharge circuit after the sampling switch is turned off, and the discharge circuit connects the capacitor when the transfer switch is turned on. Then, the charge of the capacitor is discharged with the transition of the discharge time, the voltage comparator compares the voltage of the discharge circuit with the threshold voltage, and the voltage of the discharge circuit, which decreases with the transition of the discharge, is equal to the threshold voltage. When the threshold voltage is reached, the output voltage is changed to notify the time measuring means, and the time measuring means turns off the transfer switch. By counting the number of reference clock pulses within the time from the time when the discharge of the capacitor starts to discharge to the time when the voltage of the discharge circuit reaches the threshold voltage, this is related to the threshold arrival time. A cell value digital value, wherein the calculating means calculates a digital value of the cell voltage using a digital value related to the threshold arrival time measured by the time measuring means. . 2. A method for detecting a cell voltage of an assembled battery using a flying capacitor circuit including a sampling switch, a capacitor, and a transfer switch, a discharging circuit, a voltage comparator, a time measuring unit, and an arithmetic unit. The flying capacitor circuit charges the capacitor to the cell voltage of the assembled battery, and the voltage of the capacitor charged to the cell voltage reaches a threshold voltage by the action of the capacitor, the discharging circuit, and the voltage comparator. Obtaining a pulse of a pulse width corresponding to the time to perform, measuring the pulse width of the pulse as a digital value by the time measuring means, and obtaining a digital value of the cell voltage from the digital value related to the pulse width by the calculating means. A method for detecting a cell voltage of an assembled battery, comprising the steps of: 3. A sampling switch, a capacitor,
A transfer switch, a discharge circuit, a voltage comparator,
A cell voltage detecting device for an assembled battery, comprising a time measuring unit, a calculating unit, and a voltage generating unit, operating in a calibration mode and a cell voltage measuring mode, wherein the voltage generating unit includes a calibration voltage Vo and a calibration voltage Vo. Coefficient α (0
Generating a threshold voltage αVo multiplied by <α <1); in the calibration mode, the sampling switch connects the voltage generation means to the capacitor to sample and hold the calibration voltage Vo on the capacitor; The transfer switch connects the capacitor in parallel with the discharge circuit after the sampling switch has turned off, and the discharge circuit discharges the charge of the capacitor when the capacitor is connected by turning on the transfer switch. The voltage comparator discharges with time, and the voltage comparator compares the voltage of the discharge circuit with the threshold voltage αVo supplied from the voltage generating means. When the threshold voltage is reached, the output voltage is changed to notify the time measuring means, and the time measuring means To count the number of reference clock pulses within the time from the time when the discharge of the capacitor starts to be discharged to the time when the voltage of the discharge circuit reaches the threshold voltage. In the cell voltage measurement mode, the sampling switch connects both ends of the cell of the assembled battery to the capacitor and measures the digital value related to the arrival time (To). The transfer switch samples and holds the voltage on the capacitor, and the transfer switch connects the capacitor in parallel to the discharge circuit after the sampling switch has turned off, and the discharge circuit has the capacitor connected by turning on the transfer switch. Then, the charge of the capacitor is discharged with the transition of the discharge time, and the voltage comparator discharges the charge of the discharge circuit. The voltage is compared with the threshold voltage αVo supplied from the voltage generating means, and when the voltage of the discharge circuit, which decreases with the transition of the discharge, reaches the threshold voltage, the output voltage is shifted to measure the time. Means for notifying this, and the time measuring means sets the time within the time from the time when the discharge of the capacitor is started by turning on the transfer switch to the time when the voltage of the discharge circuit reaches the threshold voltage. The number of reference clock pulses is counted and measured as a digital value (T) related to the threshold arrival time. And calculating a digital value of the cell voltage using the threshold arrival time (To) in the calibration mode read from the memory. 4. A cell voltage of an assembled battery using a flying capacitor circuit including a sampling switch, a capacitor, and a transfer switch, a discharging circuit, a voltage comparator, a time measuring unit, a calculating unit, and a voltage generating unit. A detection method, wherein a calibration voltage Vo and a coefficient α
(0 <α <1) to generate a threshold voltage αVo, charge the capacitor to the calibration voltage Vo by the flying capacitor circuit, and operate the capacitor, the discharge circuit and the voltage comparator A pulse having a pulse width (Wo) corresponding to the time when the voltage of the capacitor charged to the calibration voltage Vo attenuates and reaches the threshold voltage is obtained, and the pulse width (Wo) of the pulse is measured by the time measuring means. The capacitor is charged to the cell voltage of the assembled battery by the flying capacitor circuit, and the capacitor is charged to the cell voltage by the action of the capacitor, the discharging circuit and the voltage comparator. Pulse width (W) corresponding to the time when the capacitor voltage attenuates and reaches the threshold voltage
The pulse width (W) of the pulse is measured as a digital value (T) by the time measuring means, and the cell is calculated by the calculating means using the digital value (To) and the digital value (T). A method of detecting a cell voltage of an assembled battery, comprising calculating a digital value of a voltage. 5. The cell voltage detecting device for an assembled battery according to claim 1, wherein the discharging circuit is a resistor. 6. The cell voltage detecting device for an assembled battery according to claim 1, wherein the discharging circuit is a constant current circuit. 7. The cell voltage detecting method according to claim 2, wherein said discharging circuit is a resistor. 8. The method for detecting a cell voltage of a battery pack according to claim 2, wherein the discharge circuit is a constant current circuit. 9. The cell voltage detecting device for an assembled battery according to claim 1, wherein the sampling switch is connected to one of the cells of the assembled battery. A cell voltage detection device for an assembled battery, comprising: a common sampling switch connected in series to a common terminal of a cell selection switch for selecting one of the cell selection switches. 10. A method for detecting a cell voltage of an assembled battery according to any one of claims 2, 4, 7, and 8, wherein the sampling switch comprises one of the cells of the assembled battery. A cell sampling switch connected in series to a common terminal of a cell selection switch for selecting one of the cell selection switches.