JP2008151745A - Residual capacity computing device for charge accumulating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely compute the residual capacity of a charge accumulating device. <P>SOLUTION: A terminal voltage V, a current I and a cell temperature T are read in (step S1), in this residual capacity computing device, and a release voltage Vo is estimated based on the terminal voltage V (step S2). A sampling time Ts is also calculated based on a current change rate di/dt (step S3), and an average current value Ai is calculated using the sampling time Ts (step S5). Then, a full charge capacity FAh of a capacitor 20 is calculated by referring to a prescribed current capacity table, based on the average current value Ai and the cell temperature T (step S6). A current capacity Ah remaining in the capacitor 20 is calculated based on the full charge capacity FAh, the release voltage Vo, an upper limit voltage Vmax and a lower limit voltage Vmin (step S7), and an energy amount Wh remaining in the capacitor 20 is calculated by multiplying the current capacity Ah with the release voltage Vo (step S8). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a remaining capacity computing device for an electricity storage device that computes the remaining capacity of an electricity storage device.

  High energy density and high output density are required for energy storage devices mounted on electric vehicles and hybrid vehicles, and power devices assembled in various power tools, so lithium ion secondary batteries, electric double layer capacitors, etc. It is listed as a candidate. In order to improve both energy density and power density, an electricity storage device called a lithium ion capacitor that combines the electricity storage principles of a lithium ion secondary battery and an electric double layer capacitor has also been proposed. This lithium ion capacitor uses activated carbon of an electric double layer capacitor for the positive electrode, and charges are accumulated using the electric double layer for the positive electrode, while the carbon material of the lithium ion secondary battery is used for the negative electrode. In the negative electrode, a carbon material is loaded with lithium ions to accumulate electric charges. By adopting such a power storage mechanism, the output density and energy density can be improved.

By the way, in order to effectively use these power storage devices, it is important to accurately grasp the remaining capacity in the power storage devices. In view of this, there have been proposed a technique for obtaining the remaining capacity by integrating charge / discharge currents of the electricity storage device and a technique for obtaining the remaining capacity based on the open circuit voltage of the electricity storage device. In general, calculation methods based on current integration are resistant to load fluctuations such as inrush currents, but have a problem that errors are likely to accumulate. While the effectiveness is high in a situation where the voltage is accurately estimated, it has a problem that it is vulnerable to load fluctuations such as inrush current. Therefore, using the weight set according to the charge / discharge state, the remaining capacity based on the current integration and the remaining capacity based on the open circuit voltage are weighted and synthesized to improve the calculation accuracy of the remaining capacity. A technique has been proposed (see, for example, Patent Document 1).
JP 2005-201743 A

  However, in the above-described power storage device such as a lithium ion capacitor, the capacity is less than that of a conventional secondary battery, so that the capacity tends to fluctuate greatly depending on the charge / discharge rate. It has been difficult to calculate the remaining capacity with high accuracy.

  In addition, an electricity storage device such as a lithium ion capacitor has a predetermined lower limit voltage even when a usable capacity is discharged, so that it can be further discharged below the lower limit voltage. However, since discharging exceeding the allowable amount may cause deterioration or damage of the electricity storage device, it is important to accurately grasp the remaining capacity and control it so as not to fall below the lower limit voltage.

  An object of the present invention is to accurately calculate the remaining capacity of an electricity storage device.

  The remaining capacity computing device for an electricity storage device of the present invention includes an open-circuit voltage estimating means for estimating an open-circuit voltage of the electricity storage device based on a terminal voltage of the electricity storage device, and the electricity storage device based on the current and temperature of the electricity storage device. Current capacity calculation means for calculating the current capacity of the power storage device, and energy amount calculation means for calculating the amount of energy remaining in the power storage device by multiplying the current capacity of the power storage device by an open circuit voltage.

  The remaining capacity computing device for an electricity storage device according to the present invention is characterized in that the open-circuit voltage estimating means estimates an open-circuit voltage based on a terminal voltage, a current and an impedance.

  In the remaining capacity calculation device for an electricity storage device according to the present invention, the current capacity calculation means calculates a current average value based on a sampling time that is increased or decreased according to a current change rate, and at the time of full charge based on the current average value and temperature. A current capacity is calculated, and a current capacity remaining in the power storage device is calculated based on a full-charge current capacity and an open circuit voltage.

  The remaining capacity calculation device for an electricity storage device according to the present invention is characterized in that the current capacity calculation means increases the sampling time when the current change rate increases, and decreases the sampling time when the current change rate decreases. .

  The remaining capacity computing device for an electricity storage device according to the present invention is characterized in that a lower limit voltage of the electricity storage device exceeds 0V.

  According to the present invention, the current capacity of the power storage device is calculated based on the current and temperature, and the amount of energy remaining in the power storage device is calculated by multiplying the current capacity by the open circuit voltage. The capacity can be calculated with high accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a drive control system for a hybrid vehicle. As shown in FIG. 1, the power unit 10 of the hybrid vehicle is provided with an engine 11 and a motor generator 12 as drive sources, and a transmission 14 is connected to the rear side of the motor generator 12 via a torque converter 13. ing. The power output from the engine 11 and the motor generator 12 is shifted through the transmission 14 and then distributed to the drive wheels 16 through the differential mechanism 15. The illustrated power unit 10 is a parallel type power unit 10, and an engine 11 is driven as a main drive source, while a motor generator 12 is driven in an auxiliary manner when starting or accelerating. Further, when the motor generator 12 is driven to generate power during deceleration or steady running, kinetic energy can be converted into electric energy and recovered.

  In such a hybrid vehicle, a lithium ion capacitor (hereinafter referred to as a capacitor) 20 is mounted as an electric storage device that supplies electric power to the motor generator 12 and stores electric power generated by the motor generator 12. This capacitor 20 has a positive electrode formed using activated carbon capable of reversibly supporting lithium ions and anions, and a negative electrode formed using a carbon-based material capable of reversibly supporting lithium ions. An organic solvent solution in which a lithium salt is dissolved is used as the electrolytic solution. In addition, by preloading (pre-doping) lithium ions with respect to the negative electrode, the negative electrode potential can be lowered, the negative electrode capacity can be increased, and the energy density of the capacitor 20 can be increased.

  In addition, a capacitor control unit 21 is connected to the capacitor 20 in order to execute charge / discharge control of the capacitor 20. A voltage sensor 22 for detecting the terminal voltage V of the capacitor 20 is connected to the capacitor control unit 21, and a current sensor 23 for detecting the current I of the capacitor 20 is connected to detect the cell temperature T which is the temperature of the capacitor 20. A temperature sensor 24 is connected. Then, the capacitor control unit 21 that functions as an open-circuit voltage estimating means, a current capacity calculating means, and an energy amount calculating means calculates the remaining capacity, that is, the energy amount Wh remaining in the capacitor 20 in accordance with a calculation process described later.

  In addition, the hybrid vehicle is provided with a hybrid control unit 25 that cooperatively controls the engine 11, the motor generator 12, and the like based on the energy amount Wh of the capacitor 20, the traveling state of the vehicle, and the like. The hybrid control unit 25 is connected to an inverter 26 that controls the torque and the rotational speed of the motor generator 12, and an engine control unit 27 that controls the torque and the rotational speed of the engine 11. Further, an accelerator pedal sensor, a brake pedal sensor, and the like (not shown) are connected to the hybrid control unit 25, and various information indicating the traveling state of the vehicle is input to the hybrid control unit 25. Each control unit 21, 25, 27 includes a CPU that calculates control signals and the like, and also includes a ROM that stores control programs, arithmetic expressions, map data, and the like, and a RAM that temporarily stores data. .

  Next, the calculation process of the energy amount Wh executed by the capacitor control unit 21 will be described. FIG. 2 is a flowchart showing a calculation procedure of the energy amount Wh. As shown in FIG. 2, first, in step S1, the terminal voltage V, current I, and cell temperature T of the capacitor 20 are read. In the subsequent step S2, the open circuit voltage Vo is estimated based on the terminal voltage V. In step S2, in order to estimate the open circuit voltage Vo from the terminal voltage V, the impedance Z of the capacitor 20 is obtained in advance by using an equivalent circuit model diagram of the capacitor 20 shown in FIG. This equivalent circuit model is an equivalent circuit model in which the parameters of resistance components R1 to R3 and capacitance components C1, CPE1, and CPE2 (where CPE1 and CPE2 are double layer capacitance components) are combined in series and in parallel. Each parameter can be determined by curve fitting a well-known Cole-Cole plot.

The impedance Z obtained from these parameters varies greatly depending on the cell temperature T of the capacitor 20, the electrochemical reaction rate, and the frequency component of the current I. Therefore, as a parameter for determining the impedance Z, the moving average value MAi of the current I per unit time is replaced with a frequency component, and impedance measurement is performed on the condition of the moving average value MAi and the cell temperature T to obtain data. After the accumulation, a table of impedance Z is created based on the moving average value MAi and the cell temperature T. Then, the impedance Z is obtained using the impedance table, and the open-circuit voltage Vo is estimated from the impedance Z, the measured terminal voltage V and the current I using the following formula (1).
V = Vo-I × Z (1)

  Subsequently, in step S3, the sampling time Ts is calculated based on the current change rate di / dt, and in step S4, it is determined whether or not the sampling time Ts has elapsed. If it is determined in step S4 that the sampling time Ts has elapsed, the process proceeds to the subsequent step S5, and the current average value Ai is calculated using the sampling time Ts. Here, FIG. 4A is a diagram showing the fluctuation state of the terminal voltage V, the current I, and the cell temperature T in a predetermined running state, and FIG. 4B is a current change rate di calculated from the current I. FIG. 4C is a diagram showing the sampling time Ts calculated based on the current change rate di / dt. As shown in FIGS. 4A to 4C, when the current I greatly increases and decreases and the current change rate di / dt appears to be large, the sampling time Ts is set long, while the current I decreases and increases and decreases. When the current change rate di / dt appears small, the sampling time Ts is set short. As a result, the current average value Ai can be calculated without being affected by temporary load fluctuations.

  In the subsequent step S6, by referring to a predetermined current capacity table based on the current average value Ai and the cell temperature T, the current capacity at full charge when the capacitor 20 is fully charged (hereinafter referred to as full charge capacity). FAh is calculated. Here, FIG. 5 is a diagram showing an example of a current capacity table. As shown in FIG. 5, the full charge capacity FAh of the capacitor 20 is calculated to be higher as the cell temperature T is higher and the current I is lower, while it is calculated to be lower as the cell temperature T is lower and the current I is higher. Yes.

In the subsequent step S7, the current capacity Ah remaining in the capacitor 20 is calculated from the full charge capacity FAh, the open circuit voltage Vo, the upper limit voltage Vmax, and the lower limit voltage Vmin using the following equation (2). Here, FIG. 6 is an explanatory diagram showing the relationship between the current capacity Ah and the open circuit voltage Vo at a predetermined current rate, and FIG. 7 is an explanatory diagram for explaining a correction coefficient when calculating the current capacity Ah. First, as shown in FIG. 6, the current capacity Ah and the open circuit voltage Vo maintain a substantially proportional relationship, and when the current capacity Ah is 0%, the open circuit voltage Vo becomes the lower limit voltage Vmin (eg, 2.2 V), and the current capacity When Ah is 100%, open circuit voltage Vo is upper limit voltage Vmax (for example, 3.8 V). Then, the current capacity Ah when the open circuit voltage Vo reaches the lower limit voltage Vmin is set to 0, and the current capacity Ah when the open circuit voltage Vo reaches the upper limit voltage Vmax is set to the full charge capacity FAh. As shown in equation (2), the full charge capacity FAh is multiplied by (Vo−Vmin) / (Vmax−Vmin) as a correction coefficient. That is, as shown in FIGS. 6 and 7, since the current capacity Ah and the open circuit voltage Vo are substantially proportional, by multiplying the full charge capacity FAh by b / a as a correction coefficient, the full charge capacity FAh is obtained. The current capacity Ah remaining in the capacitor 20 is calculated.
Ah = FAh × (Vo−Vmin) / (Vmax−Vmin) (2)

  In step S8, the current capacity Ah is multiplied by the open circuit voltage Vo, and the amount of energy Wh remaining in the capacitor 20 is calculated. Based on the calculated energy amount Wh, charge / discharge control of the capacitor 20 and drive control of the engine 11 and the motor generator 12 are executed. Thus, after calculating the current capacity Ah remaining in the capacitor 20 based on the average current value Ai, the current capacity Ah is multiplied by the open circuit voltage Vo to calculate the energy amount Wh remaining in the capacitor 20. Therefore, it is possible to improve the calculation accuracy of the remaining capacity. That is, even in an electric storage device whose capacity varies depending on the current rate at the time of charging / discharging, the full charge capacity FAh is calculated based on the average current value Ai indicating the current rate, and the remaining current based on the full charge capacity FAh. Since the capacity Ah is calculated, the calculation accuracy of the current capacity Ah can be increased, and the calculation accuracy of the remaining energy amount Wh can be increased. Further, instead of using the current capacity Ah as it is, the energy amount Wh calculated by multiplying the current capacity Ah by the open circuit voltage Vo is used, so that the power storage device has a lower limit voltage Vmin exceeding 0V. However, it is possible to accurately calculate the amount of energy Wh that can be used until the lower limit voltage Vmin is reached.

  In step S3, when the current change rate di / dt appears large, the sampling time Ts is set to be long. On the other hand, when the current change rate di / dt appears small, the sampling time Ts is set to be short. Even when the current I fluctuates greatly, it is possible to prevent vibration when calculating the current capacity Ah. When the load fluctuation is small, the accuracy when calculating the current capacity Ah can be improved. It becomes possible to improve. Here, FIG. 8 is a comparison diagram showing the energy amount Wh when the sampling time Ts is increased or decreased and when it is fixed. Note that the energy amount Wh shown in FIG. 8 is the energy amount Wh calculated based on the terminal voltage V, current I, and cell temperature T shown in FIG. As shown in FIGS. 4A and 8, when the current I greatly fluctuates due to load fluctuation, it is possible to suppress fluctuations in the calculated energy amount Wh by setting the sampling time Ts long. It becomes. Further, when the current I does not fluctuate greatly, the energy amount Wh can be calculated with high accuracy by setting the sampling time Ts short.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, in the case shown in the drawing, the present invention is applied to obtain the remaining capacity of the capacitor 20 mounted on the hybrid vehicle, but the present invention is not limited to this, and is mounted on other transportation equipment such as an electric vehicle. The present invention may be applied to a stored electricity storage device, or the present invention may be applied to an electricity storage device that functions as a power source for an electrical device or the like. Further, the power storage device is not limited to the lithium ion capacitor 20 described above, and the present invention may be applied to an electric double layer capacitor, and the present invention may be applied to a secondary battery such as a lithium ion secondary battery. You may make it apply invention.

  Further, as shown in FIG. 2, in step S2, the open circuit voltage Vo is estimated by multiplying the current I and the impedance Z and adding the terminal voltage V thereto. However, the present invention is not limited to this. Alternatively, the open circuit voltage Vo may be estimated by another method. For example, a kickback voltage indicating a difference between the terminal voltage V and the open circuit voltage Vo is calculated in advance by experiments or the like, and the open circuit voltage Vo is estimated based on the kickback voltage and the actually measured terminal voltage V. Also good. Further, the kickback voltage may be set for each cell temperature T to increase the accuracy, or the kickback voltage may be set as a coefficient.

It is the schematic which shows the drive control system of a hybrid vehicle. It is a flowchart which shows the calculation procedure of energy amount. It is an equivalent circuit model figure of a capacitor. (A) is a diagram showing the fluctuation state of the terminal voltage, current and cell temperature in a predetermined running state, (B) is a diagram showing the current change rate calculated from the current I, (C) is It is a diagram which shows the sampling time calculated based on a current change rate. It is a diagram which shows an example of a current capacity table. It is explanatory drawing which shows the relationship between the current capacity in a predetermined | prescribed current rate, and an open circuit voltage. It is explanatory drawing explaining the correction coefficient at the time of calculating a current capacity. It is a comparison figure which shows the energy amount when the sampling time is increased / decreased and when it is fixed.

Explanation of symbols

20 Lithium ion capacitor (electric storage device)
21 Capacitor control unit (open-circuit voltage estimating means, current capacity calculating means, energy amount calculating means)
V Terminal voltage Vo Open voltage I Current T Cell temperature (temperature)
Ah Current capacity Wh Energy amount Z Impedance Ts Sampling time Ai Current average value FAh Full charge capacity (current capacity at full charge)
di / dt Current change rate Vmin Lower limit voltage

Claims (5)

An open-circuit voltage estimating means for estimating an open-circuit voltage of the power storage device based on a terminal voltage of the power storage device;
Current capacity calculating means for calculating the current capacity of the electricity storage device based on the current and temperature of the electricity storage device;
An energy storage device remaining capacity computing device comprising: an energy amount calculating means for calculating an energy amount remaining in the energy storage device by multiplying an open circuit voltage by the current capacity of the energy storage device. The apparatus for calculating a remaining capacity of an electricity storage device according to claim 1,
The open-circuit voltage estimation means estimates an open-circuit voltage based on a terminal voltage, a current, and an impedance. The remaining capacity computing device for an electricity storage device according to claim 1 or 2,
The current capacity calculating means calculates a current average value based on a sampling time that is increased or decreased according to a current change rate, calculates a full charge current capacity based on the current average value and temperature, An apparatus for calculating a remaining capacity of a power storage device, wherein a current capacity remaining in the power storage device is calculated based on an open circuit voltage. The remaining capacity computing device for an electricity storage device according to claim 3,
The current capacity calculating means increases the sampling time when the current change rate increases, and decreases the sampling time when the current change rate decreases. In the remaining capacity calculation apparatus of the electrical storage device of any one of Claims 1-4,
An apparatus for calculating a remaining capacity of an electricity storage device, wherein a lower limit voltage of the electricity storage device exceeds 0V.

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