JP2007333474A - Open voltage detection device and open voltage detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an open voltage detection device capable of accurately calculating an open circuit voltage in a short time. <P>SOLUTION: In this open voltage detection device used for detecting an open circuit voltage of a main battery 1 in a no-load state, the terminal voltage of the battery 1 is detected by a voltage sensor 5; a time-varied rate of the terminal voltage of the main battery 1 is calculated by a controller 4; and the open circuit voltage is calculated by adding a predetermined voltage value to the terminal voltage detected when the time-varied rate is set below a predetermined value. As a result, the open circuit voltage can be accurately calculated in a short time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an open-circuit voltage detection device and an open-circuit voltage detection method for detecting an open circuit voltage of a battery.

  In order to know the state of charge of the secondary battery, it is necessary to detect the open circuit voltage of the battery (the open voltage in the equilibrium state) using an open voltage detector or the like. Therefore, in the case of a driving battery mounted on an electric vehicle such as an electric vehicle or a hybrid vehicle, when the load and the battery are electrically disconnected, for example, charging / discharging after ignition off is not performed. The open circuit voltage is detected when there is no load.

  However, since it takes several hours to several days for the battery state to reach an equilibrium state after stopping charging and discharging, to reduce the detection time, the terminal voltage at three points is detected over time after the battery is in a no-load state, A method of calculating an approximate curve of voltage change from these data and estimating an open circuit voltage in an equilibrium state is known (see, for example, Patent Document 1).

JP 2004-109007 A

  However, in the method of estimating the open circuit voltage using such an approximate curve, it is necessary to detect the terminal voltage over a long period of time in order to obtain the required estimation accuracy. For this reason, when this method is employed in a battery for driving an electric vehicle, there is a problem that the power of the low-power battery as the power source is consumed for voltage detection after the ignition is turned off and for driving the arithmetic circuit. .

The invention of claim 1 is applied to an open-circuit voltage detection device for detecting an open circuit voltage of a battery in an unloaded state, and a voltage detection means for detecting a terminal voltage of the battery, and a change rate for detecting a time change rate of the terminal voltage. And a detection means, and an arithmetic means for calculating an open circuit voltage by adding a predetermined voltage value to a terminal voltage detected by the voltage detection means when the time change rate becomes a predetermined value or less. And
The invention of claim 3 is applied to an open-circuit voltage detection method for detecting an open circuit voltage of a battery in an unloaded state, detects a time change rate of the terminal voltage of the battery, and when the time change rate becomes a predetermined value or less. The open circuit voltage is calculated by adding a predetermined voltage value to the terminal voltage detected in (1).

  According to the present invention, the open circuit voltage is calculated by adding the predetermined voltage value to the terminal voltage when the detected time change rate becomes equal to or less than the predetermined value. The power consumption required for measurement and calculation processing can be reduced as much as possible.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of an open-circuit voltage detection device according to the present invention, and shows a block diagram when applied to an electric vehicle. A motor 3 for driving the vehicle is connected to the main battery 1 via the inverter 2. During traveling, the inverter 2 converts the DC power of the main battery 1 into three-phase AC power and supplies it to the motor 3. During braking, the motor 3 is regeneratively generated, the generated three-phase AC power is converted into DC power by the inverter 2, and the main battery 1 is charged.

  The main battery 1 is an assembled battery formed by connecting a plurality of lithium ion battery cells in series. The terminal voltage of the main battery 1 is detected by the voltage sensor 5, and the charge / discharge current is detected by the current sensor 6. The detected voltage value and current value are input to the controller 4. The controller 4 monitors the charge state of the main battery 1 and performs charge / discharge control. A switch 7 is provided between the main battery 1 and the inverter 2 for connecting and disconnecting them. When an ignition on / off signal is input from the ignition switch 10 to the controller 4, the switch 7 is turned on / off in response to the ignition on / off signal.

  In addition to the main battery 1, a low-electricity auxiliary battery 9 is mounted on the vehicle, and is used as a power source for control equipment such as the controller 4 and auxiliary equipment (air conditioner, audio, etc.). A lead acid battery is used for the auxiliary battery 9 and is charged by the main battery 1 via the DC / DC converter 8.

  As described above, conventionally, after the switch 7 is turned off due to the ignition off, it waits for the terminal voltage to reach the equilibrium state, or the equilibrium state is released from the approximate curve of the voltage change obtained by detecting the terminal voltage at three points. The open circuit voltage of the main battery 1 is detected by estimating the voltage. In the following, a method for detecting this open circuit voltage with higher accuracy in a shorter time than in the prior art will be described.

  FIG. 2 shows experimental data obtained by experimenting with one cell of a lithium ion battery used for the main battery 1, and is a diagram showing a voltage change after changing from a discharge state to a no-load state. In FIG. 2, (a) shows a case where discharge is performed at 20A, (b) shows a case of 40A, and (c) shows a case of 60A. After the discharge stops, the voltage suddenly rises and then slowly rises to approach the equilibrium state. The open circuit voltage was 3.550 V, 3.507 V, 3.602 V in the order of (a) to (c). The battery temperature is 40 ° C.

  The main battery 1 mounted on an actual vehicle includes a cooling device such as a cooling fan, and is controlled so that the battery temperature is close to a predetermined target temperature by controlling the cooling device. It is preferable to use data obtained by experiments in advance at a temperature near the target temperature. In the case of this embodiment, the temperature near the target temperature is 40 ° C.

  FIGS. 3A to 3C are enlarged views of the graphs of FIGS. 2A to 2C up to 20 seconds. 4A to 4C show the voltage change rate ΔV / t (mV / sec) with respect to each of FIGS. 3A to 3C. As shown in FIGS. 3A to 3B, it can be seen that the terminal voltage continues to change in the time range up to 20 seconds. On the other hand, in the case of the voltage change rate ΔV / t (mV / sec) shown in FIGS. 4 (a) to 4 (c), it rapidly decreases with the passage of time, and after about 10 seconds, the value reaches about 1mV / sec. Get smaller. In the experimental data shown in FIG. 4, it became 1 mV / sec in about 10 seconds, but the elapsed time until it reaches about 1 mV / sec depends on the battery usage conditions (charge amount, battery temperature, load, etc.). Different.

  FIG. 5 shows the voltage difference ΔV between the open circuit voltage and the terminal voltage while the voltage change rate changes from 5 mV / sec to 1 mV / sec after discharge. It was shown to. The average value of the voltage difference ΔV and the open circuit voltage are also shown. In addition, the column which shows "-" in a figure is a part with no experimental data. As can be seen from FIG. 5, the voltage difference ΔV at the same voltage change rate varies depending on the discharge current value. As the voltage change rate decreases, the variation of the voltage difference ΔV decreases, and at 2 mV / sec or less. It can be regarded as almost the same.

  Therefore, in this embodiment, the open circuit voltage is obtained by adding the predetermined voltage ΔV to the terminal voltage at the time when the voltage change rate becomes equal to or lower than the predetermined value. In the case of the experimental data shown in FIG. 5, since the average value of the voltage difference at the voltage change rate = 2 mV / sec is 31 mV, the value obtained by adding 30 mV to the terminal voltage when the voltage change rate becomes 2 mV / sec or less. Let open circuit voltage. In this case, the variation of the calculated open circuit voltage is about 0.1% (several mV) with respect to the actual open circuit voltage of 3.55 to 3.602 V, and the open circuit voltage can be calculated very accurately. Can do. Note that 25 mV may be added to the terminal voltage at the time of 1 mV / sec, and if the voltage change rate is 2 mV / sec or less, a voltage corresponding to the voltage change rate may be added to the terminal voltage.

  In the case of an assembled battery in which a plurality of cells are connected in series as in the main battery 1 of FIG. 1, the discharge current value of each cell is the same, so that the voltage difference ΔV of each cell can be regarded as the same. Therefore, if the number of cells connected in series is N, the voltage change rate may be increased N times, and the voltage value to be added may be increased N times. That is, when the voltage change rate becomes 2N (mV / sec) or less, 30N (mV) may be added to the terminal voltage.

  FIG. 6 is a flowchart illustrating a method for detecting an open circuit voltage. The process shown in FIG. 6 starts when the controller 4 receives an ignition off signal from the ignition switch 10. In step S1, the switch 7 is turned off to place the main battery 1 in a no-load state. In step S2, the terminal voltage of the main battery 1 is detected by the voltage sensor 5, and the detected voltage value is stored. In step S3, a voltage change rate ΔV / t (mV / sec) is calculated based on the detected terminal voltage. For example, the voltage change rate ΔV / t (mV / sec) is calculated by comparing the terminal voltage detected last time with the terminal voltage detected this time.

  In step S4, it is determined whether or not the voltage change rate ΔV / t (mV / sec) is equal to or less than a predetermined value α. When it determines with NO, it returns to step S2, and when it determines with YES, it progresses to step S5. Here, the predetermined value α is the voltage change rate in the case of the above-described assembled battery = 2N (mV / sec).

  In step S5, a preset voltage difference Δ is added to the terminal voltage value detected in step S2 to obtain an open circuit voltage. Here, the above-described 30 N (mV) is added. The calculated open circuit voltage is stored and used for calculating the battery state of the main battery 1 and the like. Thereafter, the power supply of the measurement system is turned off in step S6, and the series of processes is completed.

  Thus, in this embodiment. In an open circuit voltage detection device for detecting an open circuit voltage of a battery (main battery 1) in an unloaded state, voltage detection means (voltage sensor 5) for detecting a terminal voltage of the battery 1 and a time change rate of the terminal voltage are detected. Change rate detection means (controller 4) and an operation for calculating an open circuit voltage by adding a predetermined voltage value α to the terminal voltage detected by the voltage detection means 5 when the time change rate becomes a predetermined value or less. Since the means (controller 4) is provided, the open circuit voltage can be calculated accurately in a short time, and the power consumption required for the measurement and calculation processing can be reduced as much as possible.

  In the above-described embodiment, the open circuit voltage detection method has been described using the total voltage of the main battery 1. However, the open circuit voltage is calculated by detecting the voltage change rate for each cell. It doesn't matter. In that case, a voltage detection circuit may be provided for each cell to detect each terminal voltage. Moreover, although the lithium ion type battery has been described as an example, the present invention can be applied to any battery having the same characteristics as the above-described lithium ion battery. Furthermore, although the open voltage detection device for the main battery 1 of the electric vehicle has been described as an example, the open voltage detection device can be applied not only to the main battery of the electric vehicle but also to various battery open voltage detection devices.

  In the correspondence between the embodiment described above and the elements of the claims, the voltage sensor 5 constitutes voltage detection means, and the controller 4 constitutes change rate detection means and calculation means. The above description is merely an example, and when interpreting the invention, there is no limitation or restriction on the correspondence between the items described in the above embodiment and the items described in the claims.

It is a figure which shows one Embodiment of the open circuit voltage detection apparatus by this invention, and shows the block diagram at the time of applying to an electric vehicle. It is a figure which shows the voltage change after making it into a no-load state from a discharge state, (a) is a case where discharge current value = 20A, (b) is a case where discharge current value = 40A, (c) is a discharge current. The case of value = 60A is shown. (A)-(c) is the figure which expanded each part of Drawing 2 (a)-(c). It is a figure which shows the time change of a voltage change rate, (a)-(c) respond | corresponds to Fig.2 (a)-(c), respectively. It shows the voltage difference ΔV between the open circuit voltage and the terminal voltage while the voltage change rate changes from 5 mV / sec to 1 mV / sec after discharge. It is a flowchart explaining the detection method of an open circuit voltage.

Explanation of symbols

  1: main battery, 2: inverter, 3: motor, 4: controller, 5: voltage sensor, 6: current sensor, 7: switch, 8: DC / DC converter, 9: battery for auxiliary equipment, 10: ignition switch

Claims (3)

In an open voltage detection device that detects an open circuit voltage of a battery in an unloaded state,
Voltage detecting means for detecting the terminal voltage of the battery;
A change rate detecting means for detecting a time change rate of the terminal voltage;
Computation means for calculating an open circuit voltage by adding a predetermined voltage value to a terminal voltage detected by the voltage detection means when the time change rate becomes a predetermined value or less. Open voltage detection device. The time change rate is a predetermined change rate of 2 mV / sec or less,
2. The open-circuit voltage detection device according to claim 1, wherein the voltage value added to the terminal voltage is a predetermined voltage value corresponding to the predetermined rate of change. In an open circuit voltage detection method for detecting an open circuit voltage of a battery in an unloaded state,
A time change rate of the terminal voltage of the battery is detected, and an open circuit voltage is calculated by adding a predetermined voltage value to the terminal voltage detected when the time change rate becomes a predetermined value or less. Open voltage detection method.

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