SOC estimation system

Abstract

To provide a state of charge (SOC) estimation system capable of accurately estimating SOC of a secondary battery.SOLUTION: There is provided a state of charge (SOC) system of a secondary battery 10 provided on an unmanned vehicle 1, the system comprises: a current measurement part 22 for measuring a discharge current of the secondary battery 10; a voltage measurement part 21 for measuring a voltage between terminals of the secondary battery 10; and an SOC estimating part 23 for estimating SOC of the secondary battery 10 from the current measurement value by the current measurement part 22 and the voltage measurement value by the voltage measurement part 21. In a period in which, the unmanned vehicle 1 travels in a determined travel time measurement section A1, and in which a discharge current value of the secondary battery 10 is increased, the current measurement part 22 measures a current value and the voltage measurement part 21 measures a voltage value, and the SOC estimating part 23 estimates SOC of the secondary battery 10.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a SOC estimation system. [Background technology]

[0002] For example, automated guided vehicles are used to transport vehicles that have been assembled. Automated guided vehicles are equipped with electric motors and secondary batteries, and transport vehicles by traveling along a set route while repeatedly discharging and charging the battery.

[0003] In this type of automated guided vehicle, it is important to estimate the SOC (State Of Charge) of the secondary battery in order to prevent overcharging when charging the secondary battery.

[0004] One method for estimating SOC is to predict power consumption according to the driving pattern. For example, in Patent Document 1, the power consumption during driving is estimated taking into account the SOC fluctuations in the acceleration and deceleration sections of an automated guided vehicle. Then, the SOC fluctuations are kept small by charging and discharging the power storage device based on this estimation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-133431 Summary of the Invention [Problem to be solved by the invention]

[0006] When estimating the SOC while an automated guided vehicle is traveling, it is difficult to accurately estimate the SOC because the load required for transporting the automated guided vehicle varies depending on factors such as the road surface condition and whether or not the vehicle is carrying a load.

[0007] An object of the present invention is to provide an SOC estimation system that can accurately estimate the SOC of a secondary battery. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a system for estimating an SOC of a secondary battery provided in an automated guided vehicle, the system comprising: a current measurement unit that measures a discharge current of the secondary battery; a voltage measurement unit that measures a terminal voltage of the secondary battery; and an SOC estimation unit that estimates an SOC of the secondary battery from a current measurement value by the current measurement unit and a voltage measurement value by the voltage measurement unit, wherein, while the automated guided vehicle travels in a predetermined travel measurement section, in a process of increasing a discharge current value of the secondary battery, the current measurement unit measures a current value and the voltage measurement unit measures a voltage value, and the SOC estimation unit estimates a linear correlation between the current value and the voltage value of the secondary battery to estimate the SOC of the secondary battery. the current measurement unit measures a current value of a charging current to the secondary battery, and a charging measurement section is provided in which the charging current to the secondary battery is measured; in the running measurement section, the current measurement unit measures a discharging current of the secondary battery; in the charging measurement section, the current measurement unit measures a current value and the voltage measurement unit measures a voltage value; and the SOC estimation unit estimates the SOC of the secondary battery based on the measurement results of the running measurement section and the measurement results of the charging measurement section. It is characterized by:

[0009] According to the present invention, by providing a dedicated section for measurement, it is possible to perform measurements under uniform conditions. In other words, it is possible to eliminate variations in measurements due to differences in road conditions, such as road surface irregularities, slope, and whether the road is straight or curved. Furthermore, by measuring the current and voltage values ​​during the process of increasing the discharge current value in this measurement section, it is possible to measure the voltage value for each current value. As a result, it is possible to plot a current-voltage line with little variation. Then, by estimating the SOC of the secondary battery from this result, it is possible to improve the accuracy of the SOC estimation.

[0010] In the SOC estimation system, the current measurement unit measures the current value of the charging current to the secondary battery, a charging measurement section is provided in which the charging current to the secondary battery is measured, and in the charging measurement section, the current measurement unit measures the current value and the voltage measurement unit measures the voltage value, and the SOC estimation unit can estimate the SOC of the secondary battery based on the measurement results in the driving measurement section and the measurement results in the charging measurement section. Since the SOC can be estimated from a plot of current and voltage values ​​on both the discharge side and the charge side, it is possible to estimate the SOC more accurately. [Effects of the Invention]

[0011] According to the SOC estimation system of the present invention, the SOC of a secondary battery can be estimated with high accuracy. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a plan view showing an automatic transport system that automatically transports vehicles from a factory to a container yard. [Figure 2] 1 is a schematic configuration diagram of an automated guided vehicle according to an embodiment of the present invention; [Figure 3] FIG. 10 is a diagram showing the transition of load when the automatic guided vehicle is traveling. [Figure 4] 1A and 1B show the relationship between the current and voltage values ​​of a secondary battery measured while an automated guided vehicle is traveling, where (a) shows the results when traveling the entire route, and (b) shows the results when traveling within the measurement section. [Figure 5] FIG. 10 is a diagram showing the difference in measurement results between an unloaded state and a loaded state of an automated guided vehicle. [Figure 6] 1A and 1B are diagrams showing the transition of the state of a secondary battery during charging, in which FIG. 1A shows the current value charged into the secondary battery, and FIG. 1B shows the voltage value of the secondary battery. [Figure 7] FIG. 10 is a diagram showing the relationship between the current value and the voltage value of the secondary battery of the automatic guided vehicle, and shows the results of measurements on both the discharge side and the charge side. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] As shown in Fig. 1, an automated guided vehicle 1 according to one embodiment of the present invention transports a vehicle C completed in a factory F to a container yard Y, which is a waiting area for the vehicles. The automated guided vehicle 1 travels back and forth between the factory F and the container yard Y in accordance with wireless commands (dotted arrows) from a system control unit S.

[0015] A charging station 2 is placed on the travel path of the automatic guided vehicle 1, for example, before the position where the vehicle C is loaded in a factory F. At the charging station 2, the secondary battery provided in the automatic guided vehicle 1 is charged.

[0016] A travel-time measurement section A1 is provided before the automatic guided vehicle 1 with respect to the charging station 2. The travel-time measurement section A1 is a section dedicated to measurements for estimating the SOC of the secondary battery. The travel-time measurement section A1 is a route along which the automatic guided vehicle 1 travels straight, and a section with a flat road surface is selected. The travel-time measurement section A1 is also provided upstream of the travel route from the position where the automatic guided vehicle 1 loads the vehicle C. In other words, the automatic guided vehicle 1 does not load the vehicle C in the travel-time measurement section A1. However, the arrangement of the travel-time measurement section A1 is not limited to that of this embodiment.

[0017] As shown in FIG. 2, the automated guided vehicle 1 includes a secondary battery 10, drive wheels 11, a traction motor 12 and a regenerative motor 13 as electric motors, a receiver 14, a control unit 20, and the like.

[0018] The secondary battery 10 is, for example, a lithium-ion battery. The secondary battery 10 supplies power to a traction motor 12. The power-supplied traction motor 12 drives drive wheels 11. When the automated guided vehicle 1 decelerates, a regenerative motor 13 converts the driving force of the drive wheels 11 into electrical energy, which is then charged into the secondary battery 10. An inverter (not shown) is provided between the secondary battery 10 and the traction motor 12 or between the regenerative motor 13 and the secondary battery 10.

[0019] The control unit 20 includes a voltage measurement unit 21, a current measurement unit 22, an SOC estimation unit 23, etc. The control unit 20 constitutes an SOC estimation system that estimates the SOC of the secondary battery 10 in the automated guided vehicle 1. The voltage measurement unit 21 measures the terminal voltage of the secondary battery 10. The current measurement unit 22 measures the value of the current discharged from the secondary battery 10 or the value of the current charged to the secondary battery 10. The SOC estimation unit 23 estimates the SOC of the secondary battery 10 (hereinafter also simply referred to as SOC) based on the measured values ​​of the voltage measurement unit 21 and the current measurement unit 22.

[0020] The receiver 14 receives a wireless command from the system control unit S (see FIG. 1) and transmits it to the control unit 20. The control unit 20 operates the drive wheels 11 in accordance with the wireless command from the system control unit S, causing the automatic guided vehicle 1 to travel within a predetermined route.

[0021] Next, the measurement of the current and voltage values ​​of the secondary battery 10 in the measurement section A1 during travel (see FIG. 1) and the method of estimating the SOC will be described with reference to FIGS. 3 and 4. FIG. 3 is a diagram showing the load on the secondary battery 10 (the value of the current discharged from the secondary battery 10) while the automated guided vehicle 1 is traveling, with the horizontal axis representing the travel time (s) and the vertical axis representing the current value (A) discharged from the secondary battery 10. FIG. 4 also shows the relationship between the current and voltage values ​​measured when the automated guided vehicle 1 is travelling at 5 km / h, with (a) representing the values ​​when travelling the entire route and (b) representing the values ​​when travelling in the measurement section A1. In each diagram, the horizontal axis represents the current value measured by the current measurement unit 22, and the vertical axis represents the voltage value measured by the voltage measurement unit 21.

[0022] As shown in FIG. 3 , in the travel measurement section A1, the load on the secondary battery 10, in other words, the current value discharged from the secondary battery 10, is increased for a short period of time (see range B in FIG. 3 ). The length of range B is approximately 1 second, and the maximum current value is set to approximately 100 to 150 A. In this embodiment, particularly, only the measured values ​​in range B in FIG. 3 are used to estimate the SOC. That is, only the current value during the process in which the current value is rapidly increased in a short period of time (1 second or less) and the maximum current value after the increase are measured and used to estimate the SOC. Note that in range B, the current value decreases immediately after reaching the maximum current. On the other hand, in the normal travel section (to the right of the travel measurement section A1 in FIG. 3 ), the load for traveling the automated guided vehicle 1 varies depending on the conditions of the travel route, such as the size of the unevenness, whether the road is uphill or downhill, or whether the road is straight or curved, and the current value discharged from the secondary battery 10 also varies.

[0023] 4 shows the plot of voltage and current values ​​measured at predetermined intervals while the automated guided vehicle 1 was traveling. As shown in FIG. 4(a), the measured voltage value decreases as the current value discharged from the secondary battery 10 increases.

[0024] Then, the SOC estimation unit 23 can estimate the SOC of the secondary battery 10 based on the open circuit voltage value, which is the voltage value when the current value is 0 A in FIG.

[0025] However, as shown in Figure 4(a), the measurement results for the entire route vary depending on the conditions of the road surface on which the automated guided vehicle 1 travels (unevenness of the road surface, uphill or downhill road, straight or curved road, etc.), and whether the automated guided vehicle 1 is carrying a load, etc. In other words, there is a range in the voltage value at 0 A indicated by the plotted line in Figure 4(a), and the SOC cannot be estimated with high accuracy.

[0026] In contrast, as shown in Figure 4(b), by performing measurements in a dedicated driving measurement section A1, it is possible to perform measurements under the same conditions each time, thereby reducing the variation in the measured values. In other words, the set of plotted points shown in Figure 4(b) forms a single straight line with little variation. Due to this less varied measurement value, the variation in the voltage value at 0 A is also smaller than in Figure 4(a). Therefore, by having the SOC estimator 23 estimate the SOC using the open-circuit voltage value in the driving measurement section A1, the estimation accuracy can be improved.

[0027] In particular, in this embodiment, the driving conditions in the in-travel measurement section A1 (particularly the driving conditions in range B) are set to conditions that reduce variation in the measurement results, thereby further improving the accuracy of SOC estimation. Specifically, the in-travel measurement section A1 is a section where the road surface is flat with few irregularities, the automatic guided vehicle 1 is unladen, and the automatic guided vehicle 1 moves straight. This reduces variation in the driving conditions. However, it is not necessary to satisfy all of the above conditions; satisfying any one of the conditions can improve the accuracy of SOC estimation. Furthermore, the accuracy of SOC estimation can be improved if the weight and shape of the load carried by the automatic guided vehicle 1 are constant, but it is preferable that the load is unladen.

[0028] As an example of the variation in measurements, Fig. 5 shows the magnitude of variation in measurement results depending on whether or not the vehicle is loaded. The horizontal axis of Fig. 5 represents the current value measured by the current measuring unit 22, and the vertical axis represents the voltage value measured by the voltage measuring unit 21. The gray plots in Fig. 5 represent the case where the unloaded AGV 1 is traveling at 10 km / h, and the black plots represent the case where the loaded AGV 1 is traveling at 10 km / h.

[0029] 5, in measurements with no load, a current-voltage straight line with little variation is plotted, whereas in measurements of the automated guided vehicle 1 with a heavy load, the plot varies vertically (the line has thickness above and below). As such, the magnitude of variation in the measurement results varies depending on the traveling state of the automated guided vehicle 1 in the measurement section, so providing the measurement section A1 as in this embodiment is preferable for estimating the SOC with high accuracy.

[0030] Next, a case where a dedicated measurement section is provided to estimate the SOC when charging the secondary battery 10 at the charging station 2 (see FIG. 1) will be described using FIG. 6. FIG. 6 shows the charging current value to the secondary battery or the voltage value of the secondary battery during charging, with the horizontal axis of FIG. 6(a) and FIG. 6(b) representing time (s), the vertical axis of FIG. 6(a) representing the current value measured by the current measuring unit 22, and the vertical axis of FIG. 6(b) representing the voltage value measured by the voltage measuring unit 21. The left end of each figure indicates the time when the automated guided vehicle 1 is connected to the charging station 2 and charging begins.

[0031] As shown in FIGS. 6(a) and 6(b), in this embodiment, a charging measurement section A2 is provided in which the secondary battery 10 is charged for a short period of time before normal charging begins.

[0032] Then, in the charging measurement section A2, the voltage measurement unit 21 measures the voltage value, and the current measurement unit 22 measures the current value. As a result, in addition to the plot of values ​​greater than 0 A shown in FIG. 4(b), values ​​less than 0 A can be plotted. For example, as shown by the dashed-dotted line in FIG. 7, points to the left of 0 A can be plotted. This can be combined with the results plotted in the running measurement section A1 (i.e., points to the right of 0 A in FIG. 7) to calculate the voltage value (open-circuit voltage) at 0 A, enabling more accurate estimation of the SOC. Note that in this embodiment, the maximum absolute value of the current value in the charging measurement section A2 is set to be the same as the maximum absolute value of the current value in the running measurement section A1. This allows the contribution rates of the charging side and the discharging side to be equal when calculating the open-circuit voltage, thereby improving the accuracy of estimating the open-circuit voltage value and, therefore, the accuracy of estimating the SOC. The current values ​​of the secondary battery 10 during discharge and charge have opposite signs, and the current values ​​on the horizontal axis of Fig. 7 are shown with the current values ​​discharging the secondary battery 10 as positive values ​​and the current values ​​charging the secondary battery 10 as negative values. Also, a dashed line is drawn to show the outline of the plots on the charge side, but in reality, the current and voltage values ​​on the discharge side are shown by a set of plotted points, just like the discharge side.

[0033] Based on the SOC estimated in this way, the secondary battery 10 is charged so as not to exceed a preset charge capacity. Therefore, by accurately estimating the SOC, it is possible to prevent problems such as the automatic guided vehicle 1 becoming unable to run due to overcharging of the secondary battery 10 by the charging station 2 or shortening the life of the secondary battery 10.

[0034] Furthermore, when charging the secondary battery 10, CCCV (Constant Current, Constant Voltage) charging is performed to prevent overcharging. Specifically, as shown in range D in FIG. 6, control is performed to reduce the current value while maintaining a constant voltage. However, by accurately estimating the SOC as described above, it is possible to charge the secondary battery 10 to a sufficient extent without CCCV charging and to prevent overcharging. This allows the charging time to be shortened.

[0035] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0036] 1. Automated guided vehicle 2 Charging Station 10 Secondary battery 12. Drive motor 13 Regenerative motor 20 Control unit (SOC estimation system) 21 Voltage measurement section 22 Current measurement section 23 SOC measurement section A1 Measurement section during driving A2 Charging measurement section

Claims

1. A system for estimating an SOC of a secondary battery provided in an automatic guided vehicle, a current measuring unit for measuring a discharge current of the secondary battery; a voltage measurement unit for measuring a voltage between the terminals of the secondary battery; an SOC estimation unit that estimates an SOC of the secondary battery from a current measurement value by the current measurement unit and a voltage measurement value by the voltage measurement unit; While the automated guided vehicle is traveling within a predetermined travel measurement section, in the process of increasing a discharge current value of the secondary battery, the current measurement unit measures a current value and the voltage measurement unit measures a voltage value, and the SOC estimation unit estimates a linear correlation between the current value and voltage value of the secondary battery to estimate an SOC of the secondary battery; the current measurement unit measures a current value of a charging current to the secondary battery, providing a charging measurement section for measuring a charging current to the secondary battery; In the measurement section during driving, the current measurement unit measures a discharge current of the secondary battery, an SOC estimation system, characterized in that, in the charging measurement section, the current measurement unit measures a current value and the voltage measurement unit measures a voltage value, and the SOC estimation unit estimates the SOC of the secondary battery based on the measurement results of the driving measurement section and the measurement results of the charging measurement section.

2. 2. The SOC estimation system according to claim 1, wherein the SOC estimation unit calculates an open circuit voltage value of the secondary battery based on a linear correlation between the estimated current value and voltage value of the secondary battery, thereby estimating the SOC of the secondary battery.

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