JP2004245673A - Method and device for predicting residual capacity of storage capacitor, and storage capacitor pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately provide the residual capacity of a storage capacitor such as lithium ion secondary battery mounted on a hybrid car at any time interval. <P>SOLUTION: The discharging/charging current of the secondary battery 11 is monitored, and summation calculation is performed based on the discharging/charging current to continuously calculate a first residual capacity value. At the same time, a timing when the charging and discharging of the secondary battery 11 is switched is detected and, at the detected timing, the terminal voltage of the secondary battery 11 at the detected timing is regarded as an open circuit voltage and, based on the open circuit voltage, a second residual capacity value is obtained. Then, the first residual capacity value is updated by the second residual capacity value. The first residual capacity value is outputted to the outside as the residual capacity of the secondary battery 11. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for estimating a state of charge (SOC) of a power storage unit such as various secondary batteries typified by a lithium ion secondary battery and a large capacity capacitor, and an estimation of such a state of charge. The present invention relates to a power storage pack such as a battery pack incorporating a device.
[0002]
[Prior art]
2. Description of the Related Art In recent years, secondary batteries such as lithium ion secondary batteries and nickel-metal hydride batteries have come to be used as power sources for electric motors for power applications. Further, large-capacity capacitors such as electric double-layer capacitors have also been used as power sources for driving motors. In this specification, a device that accumulates electric energy by charging and discharges electric energy by discharging, such as a secondary battery or a capacitor, is referred to as a power storage unit.
[0003]
As an application of such a motor drive of a power storage unit such as a lithium ion secondary battery or a large capacity capacitor, there is, for example, an application in a hybrid electric vehicle (hereinafter, simply referred to as a hybrid vehicle). A hybrid vehicle generally includes an engine that is an internal combustion engine, a generator driven by the engine, a power storage unit, and an electric motor. There are several types of driving methods for hybrid vehicles.For example, when a power storage unit is charged with electric power obtained by a generator, and when the vehicle is accelerating or climbing a slope, the power storage unit is used in addition to the power from the generator. Is supplied to the electric motor. In addition, there is an engine in which the driving wheels are directly driven by an engine, and the driving of the driving wheels is assisted by an electric motor output during acceleration or climbing a hill. In these hybrid vehicles, in order to further improve the energy efficiency, when braking the vehicle, the electric motor is operated as a generator to function as a regenerative brake, and the energy storage device is also charged with the obtained energy. I have.
[0004]
In the case of a hybrid vehicle, in practice, control is performed such that the remaining capacity of the power storage unit is always within a predetermined range. Specifically, for example, when the remaining capacity becomes 20% or less, the engine is started, power is generated by the generator, and the power is charged by the power. Then, for example, when the remaining capacity becomes 80% or more, the power storage unit is prevented from being charged any more. As described above, since it is necessary to control charging and discharging according to the remaining capacity of the power storage unit, the remaining capacity of the power storage unit must be constantly monitored. Specifically, the remaining capacity is obtained at time intervals of several tens of milliseconds to several seconds.
[0005]
In principle, the remaining capacity of a power storage unit can be obtained by the difference between the charged amount and the discharged amount of charge.Conventionally, the value of the charge / discharge current of the power storage unit is measured at regular time intervals, By integrating the measured values, the remaining capacity of the power storage unit has been obtained. Further, when the power storage unit is a lithium ion secondary battery or a large capacity capacitor, there is a certain relationship between the open circuit voltage of the power storage unit (voltage when the charge / discharge current is 0) and the remaining capacity. It is also known to measure the open circuit voltage of the power storage unit to estimate the remaining capacity. However, when the power storage device is applied to a hybrid vehicle, a large current may flow in a short time due to an inrush current of an electric motor or the like, and it is difficult to obtain a current sensor that is inexpensive, has high linearity, and has high accuracy. If the charge and discharge current values are integrated to determine the remaining capacity for reasons such as, the accumulated error that cannot be ignored may occur. On the other hand, when estimating the remaining capacity based on the open circuit voltage of the power storage unit, the problem of accumulation of errors does not occur, but in operation in a hybrid vehicle, charging and discharging are controlled based on the remaining capacity. Since the timing at which the charge / discharge current becomes zero cannot be set at the required time intervals, there is a problem that this method cannot practically determine the remaining capacity value.
[0006]
Japanese Patent Application Laid-Open No. 11-206028 (Patent Document 1) discloses that a charge / discharge current value for a power storage device is integrated to obtain a remaining capacity, and before and after switching from charging to discharging or from discharging to charging. , A charge / discharge I (current) -V (voltage) characteristic curve of the power storage body was obtained from the terminal voltage value and the charge / discharge current value, and an open circuit voltage was estimated from the charge / discharge IV characteristic curve. It is disclosed that the remaining capacity is determined based on the open circuit voltage. Then, the remaining capacity obtained by integrating the charge / discharge current value is compared with the remaining capacity obtained from the estimated open circuit voltage, and when the difference becomes a predetermined value or more, the remaining capacity is obtained from the estimated open circuit voltage. The remaining capacity value is replaced by the remaining capacity value obtained by integrating the charging and discharging current values. However, the method based on Patent Document 1 requires an operation for calculating a charge / discharge IV characteristic curve, which increases the amount of operation, and the open circuit voltage itself is only an estimated value. There is a problem that accuracy is not very good.
[0007]
In the case where a power storage unit such as a lithium ion secondary battery or a large capacity capacitor is used, the cells of these power storage units are rarely used alone, and a plurality of single cells are used so that a desired discharge voltage and discharge current can be obtained. It is common to configure them as power storage packs connected in series and / or in parallel. The power storage pack includes, in addition to the power storage cells (battery cells and capacitor cells), a safety circuit such as an overcharge prevention circuit, a circuit that measures the remaining capacity and outputs the measured value, and the like. There are many.
[0008]
[Patent Document 1]
JP-A-11-206028
[0009]
[Problems to be solved by the invention]
As described above, in the conventional method for obtaining the remaining capacity of the power storage unit, it is necessary to solve the problem that the error is large, the latest remaining capacity value cannot be obtained at a required time interval, or the amount of calculation increases. Challenges remain.
[0010]
An object of the present invention is to provide a remaining capacity estimating method and a remaining capacity estimating apparatus capable of estimating the latest remaining capacity of a power storage unit at a desired time interval with high accuracy and with a small amount of calculation. It is another object of the present invention to provide a power storage pack incorporating such an estimation device.
[0011]
[Means for Solving the Problems]
The remaining capacity estimating method of the present invention monitors a charge / discharge current of a power storage unit, performs an integration operation based on the charge / discharge current, continuously calculates a first remaining capacity value, and performs charging and discharging of the power storage unit. Is switched, and at that timing, a second remaining capacity value is obtained based on the terminal voltage of the power storage unit at that timing, and the first remaining capacity value is replaced with the second remaining capacity value, and replaced. The integration operation is continued based on the subsequent first remaining capacity value, and the first remaining capacity value is set as the remaining capacity of the power storage unit.
[0012]
The remaining capacity estimating device of the present invention includes a current detecting means for detecting a charging / discharging current in the power storage device, a voltage measuring means for detecting a terminal voltage of the power storage device, a storage means for holding a value of the remaining capacity, A calculating means for continuously executing an integration calculation on the value stored in the storage means based on the charging / discharging current; and a timing for detecting a timing of switching between charging and discharging in the power storage unit based on an output of the current detecting means. Detecting means, having a remaining capacity value obtaining means for obtaining a remaining capacity value based on the terminal voltage at the detected timing, and at the detected timing, by the remaining capacity value obtained by the remaining capacity value obtaining means, The value in the storage means is replaced.
[0013]
The power storage pack of the present invention includes a power storage unit, a current detection unit that detects a charge / discharge current in the power storage unit, a voltage measurement unit that detects a terminal voltage of the power storage unit, and a storage that holds and outputs a value of a remaining capacity. Means, an arithmetic means for continuously performing an integration operation on the value stored in the storage means based on the detected charging / discharging current, and charging and discharging of the power storage unit based on an output of the current detecting means. A timing detecting means for detecting a switching timing; and a remaining capacity value obtaining means for obtaining a remaining capacity value based on a terminal voltage at the detected timing, wherein the remaining capacity value obtaining means obtains the remaining capacity value at the detected timing. The value in the storage means is replaced by the remaining capacity value.
[0014]
In applications such as hybrid vehicles, the present invention frequently switches between discharging and charging in a power storage unit, and switches the direction of current flowing in the power storage unit.When the switching is performed, the charging / discharging current instantaneously becomes zero. It is noted that an open circuit voltage of the power storage unit can be obtained by measuring the terminal voltage of the power storage unit at a timing. If the open circuit voltage of the power storage unit is obtained, the remaining capacity can be accurately estimated as described above. However, the interval at which switching between charging and discharging occurs is not constant. In the case of a hybrid vehicle, the interval may be as short as about 1 second, and as long as about several tens of minutes. , The interval is too long to be used as it is. Therefore, in the present invention, for example, charge / discharge control is performed by the first remaining capacity value obtained assuming that the remaining capacity is continuously calculated by integrating the charging / discharging current, and charging and discharging are performed. Every time the switching occurs, the first remaining capacity value by integrating the charge / discharge current is rewritten by the remaining capacity (second remaining capacity value) based on the open circuit voltage measured at that timing. Thereafter, until the next switching between charge and discharge occurs, the integration calculation of the charge / discharge current is performed based on the rewritten first remaining capacity value.
[0015]
With this configuration, in the present invention, the first remaining capacity value based on the integration of the charging / discharging current is more accurately calculated based on the open circuit voltage every time the switching between the charging and discharging of the power storage unit occurs. Since it is updated by the capacity value, the accumulated error in the integration of the charge / discharge current is reset each time. Therefore, according to the present invention, it is possible to acquire the remaining capacity at an arbitrary timing with high accuracy and little influence of the accumulated error. When considering the application to hybrid vehicles, switching between charging and discharging occurs after a few tens of minutes at the longest, and the remaining capacity value is updated to an accurate value based on the open circuit voltage. The accumulated error in the integration of the discharge current is not so great as to have a bad effect when performing charge / discharge control based on the remaining capacity. Further, according to the present invention, it is not necessary to use an expensive sensor having good linearity as a current sensor used for detecting the charging / discharging current, and the overall cost of the configuration for estimating the remaining capacity is reduced. Can be reduced.
[0016]
In the present invention, for example, a secondary battery such as a lithium ion secondary battery or a large capacity capacitor such as an electric double layer capacitor can be used as the power storage unit.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a power storage device remaining capacity estimating apparatus according to one embodiment of the present invention, and is illustrated as a power storage pack in which a remaining capacity estimating device 10 is incorporated. Here, a secondary battery 11 that is, for example, a lithium ion secondary battery is used as a power storage unit. Therefore, the power storage unit pack is configured as a battery pack 12.
[0018]
The remaining capacity estimating device 10 includes a current detector 21 that detects a charging current and a discharging current for the secondary battery 11, a voltage measuring unit 22 that measures and outputs a terminal voltage of the secondary battery 11, A / D converter 23 which samples the output and performs analog / digital conversion, and polarity detection which shapes the output waveform of current detector 21 and detects the polarity of charge / discharge current (whether charge or discharge). Unit 24, an edge detection unit 25 that detects an edge in the output of the polarity detection unit 24 and outputs a trigger signal, and a remaining capacity value based on an open circuit voltage of the secondary battery 11 (here, a lithium ion secondary battery). , A remaining capacity storage unit 27 that stores the current value of the remaining capacity, and a remaining capacity value that is stored in the remaining capacity storage unit 27 based on the output from the A / D converter 21. To A totalizing section 28 for totalizing Te, and a.
[0019]
Specifically, the current detector 21 may be an open loop type using a Hall sensor, or a type having a shunt resistance and measuring the voltage between both ends. The current detector 21 generates a voltage that is proportional to the magnitude of the charge / discharge current and that is negative for charging and positive for discharging, for example. The difference between the charging current and the discharging current is distinguished by the direction of the current with respect to the secondary battery 11. For example, as shown on the right side of FIG. 2, the polarity detection unit 24 determines whether the output of the current detector 21 is positive or negative, whether discharging or charging. During the discharging period, the logical level is “1”. And outputs “0” during the charging period. As such a polarity detector 24, one having a comparator 31 can be used as shown in FIG. The waveform from the current detector 21 is input to the (+) terminal of the comparator 31, and 0 V is supplied to the (-) terminal as a reference potential. The edge detection unit 25 outputs a trigger signal at the rising edge (the edge that transitions from “0” to “1”) and the falling edge (the edge that transitions from “1” to “0”) of the output of the polarity detection unit 24. I do.
[0020]
When the open circuit voltage of the secondary battery 11 is input, the remaining capacity value acquiring unit 26 obtains and outputs the remaining capacity value corresponding to the open circuit voltage. The measured voltage value (digital value) and a trigger signal generated by the edge detection unit 25 are input. Then, a voltage value is fetched at the timing when the trigger signal is input, and a remaining capacity value corresponding to the fetched voltage value is output. Actually, a look-up table showing the relationship between the open circuit voltage value and the remaining capacity of the lithium ion secondary battery is provided, and the obtained voltage value is referred to as the open circuit voltage value, and the remaining capacity value is referred to. Is output. When the power storage object whose remaining capacity is to be estimated is a power storage element other than the lithium ion secondary battery, a look-up table corresponding to the characteristics of the power storage element is provided. Of course, when the relationship between the open-circuit voltage value and the remaining capacity can be expressed by a simple function formula such as when the power storage unit is a large-capacity capacitor, the remaining capacity is obtained by calculation based on the function formula. You may do so.
[0021]
The remaining capacity storage unit 27 that holds the current remaining capacity of the secondary battery 11 also functions as a calculation memory when calculating the remaining capacity by integrating the charge / discharge current by the integration calculation unit 28. The current remaining capacity (SOC) is output to the outside in real time. Further, the value of the remaining capacity in the remaining capacity storage unit 27 is replaced with the output value when the trigger signal is output and the remaining capacity value is output from the remaining capacity value acquiring unit 26. The integration operation unit 28 performs an integration operation on the remaining capacity value stored in the remaining capacity storage unit 27 according to the output of the A / D converter 23 for each sampling of the A / D converter 23. Here, if the value of the remaining capacity stored in the remaining capacity storage unit 27 is [SOC], at the time of discharging,
[SOC] ← [SOC]-(discharge current) (1)
[SOC] is updated by
[SOC] ← [SOC] + (magnitude of charging current) × charging efficiency (2)
[SOC] is updated. Here, the reason why the charging efficiency is multiplied at the time of charging is that not all the charge amount corresponding to the charging current is stored in the secondary battery 11. Charging efficiency is generally a function of temperature. Therefore, the integration operation may be performed by changing the value of the charging efficiency according to the temperature.
[0022]
FIG. 3 schematically shows the operation of the remaining capacity estimating apparatus 10.
[0023]
The current detector 21 constantly monitors the charge / discharge current for the secondary battery 11 serving as a power storage unit, and supplies a voltage signal corresponding to the detected current to the A / D converter 23 and the polarity detection unit 24. The A / D converter 23 and the multiplying operation unit 28 calculate the remaining capacity value [SOC] stored in the remaining capacity storage unit 27 by the above equation (1) for each sampling in the A / D converter 23. ) And (2), an integration operation is performed by adding or subtracting the charge / discharge current. As a result, the latest remaining capacity value is stored in the remaining capacity storage unit 27 every time sampling is performed by the A / D converter 23.
[0024]
The voltage signal from the current detector 21 is also input to the polarity detector 24, where the waveform is shaped, and is a signal whose logic level is "1" during the discharge period and "0" during the charge period. , Both the rising edge and the falling edge are detected by the edge detecting unit 25. The remaining capacity value acquiring unit 26 acquires the remaining capacity value corresponding to the terminal voltage of the secondary battery 11 at the timing when the trigger signal is input from the edge detector 25, that is, at the timing when the edge trigger is applied. Then, the remaining capacity value [SOC] stored in the remaining capacity storage unit 27 is replaced with the remaining capacity value. The timing at which the edge trigger is applied is the timing at which the secondary battery 11 switches from charging to discharging or from discharging to charging. At this time, the charging / discharging current of the secondary battery 11 is substantially zero. The terminal voltage of the secondary battery 11 can be regarded as the open circuit voltage of the secondary battery 11 at that time. As a result, the remaining capacity value acquisition unit 26 outputs an accurate remaining capacity value based on the open circuit voltage at the timing of switching from charging to discharging or from discharging to charging. Therefore, according to the remaining capacity estimating apparatus 10, the remaining capacity of the secondary battery 11 is continuously calculated by the integration calculation of the charge / discharge current, and the remaining capacity used in the integration calculation is changed at the timing when the charge and the discharge are switched. The capacity value is updated with the correct remaining capacity value. As a result, accumulation of errors in the integration operation is eliminated, and it is possible to know an accurate remaining capacity at any time.
[0025]
The above-described remaining capacity estimation device 10 of the present embodiment is generally implemented using a microcomputer. In this case, the functions of the edge detection unit 25, the remaining capacity value acquisition unit 26, the remaining capacity storage unit 27, and the integration calculation unit 28 are realized by a microcomputer. Specifically, the microcomputer continuously performs the integration operation based on the charging / discharging current, and the output signal of the waveform shaping unit 24 is input to the input capture terminal of the microcomputer, and the rising edge and the falling edge are detected. Then, if an edge is detected, an interrupt task may be generated to refer to the look-up table of the remaining capacity value.
[0026]
FIG. 4 is a flowchart showing an example of the operation of such a microcomputer. First, as an initial setting, an initial value is substituted for the remaining capacity value [SOC] in the remaining capacity storage unit 27 (step 101), and it is determined whether or not the timing of switching between charging and discharging, that is, whether or not an edge has been detected. (Step 102). If it is not the switching timing, the current value I is read from the A / D converter 23 (step 103), [SOC] is updated by integrating the charging / discharging current (step 104), and the process returns to step 102. Further, when it is the switching timing in step 102, since the interrupt task is generated as described above, the open circuit voltage is fetched (step 105), and the remaining capacity value is obtained from the lookup table (step 106). Then, the obtained remaining capacity value is substituted for [SOC] (step 107), and the process returns to step 102.
[0027]
1 uses the polarity detection unit 24 and the edge detection unit 25 to detect the timing of switching between charging and discharging in the secondary battery 11, but the present invention is not limited to this. It is not done. For example, when the sampling rate of the A / D converter 23 is sufficiently high, the switching timing between charging and discharging can be detected from the output of the A / D converter 23. FIG. 5 shows the configuration of such a remaining capacity estimation device. The remaining capacity estimating apparatus 10A is different from the remaining capacity estimating apparatus 10 shown in FIG. 1 in that a zero-cross detector 29 is provided instead of the polarity detector 24 and the edge detector 25. The zero-cross detector 29 monitors the output of the A / D converter 23, and outputs the trigger signal at the timing when the output value of the A / D converter 23 switches from positive to negative or from negative to positive. Output to In the normal case, the most significant bit (MSB) of the digital value output by the A / D converter 23 is a sign bit. Therefore, by detecting the switching between “0” and “1” in the sign bit, , The switching between positive and negative in the output of the A / D converter 23 can be detected.
[0028]
【The invention's effect】
As described above, the present invention monitors the charge / discharge current of the power storage unit, performs an integration operation based on the charge / discharge current, continuously calculates the first remaining capacity value, and simultaneously performs the charge in the power storage unit. And a discharge switching timing. At the detected timing, a second remaining capacity value is obtained based on the terminal voltage of the power storage unit at the detected timing, and the second remaining capacity value is calculated based on the second remaining capacity value. By updating the remaining capacity value of 1, there is an effect that accumulation of errors in the integration operation is eliminated, and it becomes possible to know an accurate remaining capacity of the power storage unit at any time. .
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a remaining capacity estimation device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating an example of the configuration and operation of a polarity detection unit.
FIG. 3 is a diagram schematically showing an operation of remaining capacity estimation.
FIG. 4 is a flowchart illustrating an operation of remaining capacity estimation.
FIG. 5 is a block diagram illustrating a configuration of a remaining capacity estimation device according to another embodiment of the present invention.
[Explanation of symbols]
10, 10A Remaining capacity estimating device 11 Secondary battery 12 Battery pack 21 Current detector 22 Voltage measuring unit 23 A / D converter 24 Polarity detecting unit 25 Edge detecting unit 26 Remaining capacity value acquiring unit 27 Remaining capacity storage unit 28 Integration calculation Section 29 zero cross detection section 31 comparators 101 to 107 step

Claims (7)

A remaining capacity estimation method for estimating a remaining capacity of a power storage unit,
The charge / discharge current of the power storage unit is monitored, and an integration operation based on the charge / discharge current is executed to continuously calculate a first remaining capacity value,
Detecting a timing at which the power storage device switches between charging and discharging, and at this timing, obtaining a second remaining capacity value based on the terminal voltage of the power storage device at the timing and obtaining the second remaining capacity value; Replacing the first remaining capacity value;
A remaining capacity estimation method, wherein the integration operation is continued based on the first remaining capacity value after replacement, and the first remaining capacity value is used as the remaining capacity of the power storage unit. The remaining capacity estimation method according to claim 1, wherein the second remaining capacity value is obtained by referring to a look-up table describing a relationship between an open circuit voltage and a remaining capacity in the power storage unit. The remaining capacity estimating method according to claim 1, wherein the power storage unit is a lithium ion secondary battery. A remaining capacity estimating device for estimating a remaining capacity of a power storage unit,
Current detection means for detecting a charge / discharge current in the power storage unit,
Voltage measuring means for detecting a terminal voltage of the power storage unit,
Storage means for holding a value of the remaining capacity;
Calculating means for continuously performing an integration calculation on the value stored in the storage means, based on the detected charging / discharging current;
Based on the output of the current detection means, timing detection means for detecting the timing of switching between charging and discharging in the power storage,
Having a remaining capacity value obtaining means for obtaining a remaining capacity value based on the terminal voltage at the detected timing,
At the detected timing, the remaining capacity value obtained by the remaining capacity value obtaining means replaces the value in the storage means with the remaining capacity value. The remaining capacity value acquiring means has a look-up table describing a relationship between an open circuit voltage and a remaining capacity value of the power storage unit, and refers to the look-up table based on the terminal voltage to obtain the remaining capacity value. The remaining capacity estimating device according to claim 4, which obtains the remaining capacity. The remaining capacity estimating device according to claim 4 or 5, wherein the power storage unit is a lithium ion secondary battery. Power storage,
Current detection means for detecting a charge / discharge current in the power storage unit,
Voltage measuring means for detecting a terminal voltage of the power storage unit,
Storage means for holding and outputting the value of the remaining capacity;
Calculating means for continuously performing an integration calculation on the value stored in the storage means, based on the detected charging / discharging current;
Based on the output of the current detection means, timing detection means for detecting the timing of switching between charging and discharging in the power storage,
Having a remaining capacity value obtaining means for obtaining a remaining capacity value based on the terminal voltage at the detected timing,
The power storage pack, wherein at the detected timing, the value in the storage means is replaced with the remaining capacity value obtained by the remaining capacity value obtaining means.

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