Backup electric power supply device and detection method

Abstract

A backup electric power supply device (1) comprises: an electric power storage unit (20); an electric power conversion unit (10); a voltage detection unit (30) that detects the voltage of the electric power storage unit (20); a control unit (50) that performs constant electric current control and constant voltage control of the electric power conversion unit (10); a target electric current setting unit (60) that switches a target electric current value for the constant electric current control; and an internal resistance detection unit (80) that detects the internal resistance of the electric power storage unit (20). When the electric power storage unit (20) is being charged by the constant electric current control of the electric power conversion unit (10), the target electric current setting unit (60) switches the target electric current value for the constant electric current control from a first electric current value to a second electric current value in a first measurement section, and switches the target electric current value from the second electric current value to the first electric current value in a second measurement section.

Description

Backup power supply device and detection method

[0001] The present disclosure relates to backup power supplies and the like.

[0002] When the internal resistance of a power storage unit such as a lithium ion capacitor or an electric double layer capacitor increases due to aging, loss due to the internal resistance increases during discharge, and the power supply capacity may decrease. For this reason, it is necessary to detect the internal resistance of the power storage unit to detect deterioration of the power storage unit. Patent Document 1 discloses a technique for detecting the internal resistance of the power storage unit.

[0003] Japanese Patent Application Laid-Open No. 2020-30085

[0004] In the technology disclosed in Patent Document 1, the capacitance value of the power storage unit is required to detect the internal resistance, so it is necessary to prepare a function to detect the capacitance value of the power storage unit or to store the capacitance value of the power storage unit in advance in a non-volatile memory. Furthermore, if the accuracy of the capacitance value detection or the accuracy of the stored capacitance value is poor, the accuracy of the internal resistance detection will also be poor.

[0005] A backup power supply device according to the present disclosure includes a power storage unit, a power conversion unit that converts power supplied from a power supply unit to the power storage unit, a voltage detection unit that detects a voltage of the power storage unit, a control unit that performs constant current control of the power conversion unit and constant voltage control of the power conversion unit, a target current setting unit that switches a target current value for the constant current control, and an internal resistance detection unit that detects an internal resistance of the power storage unit, and when a charging operation to the power storage unit is performed by the constant current control of the power conversion unit, the target current setting unit changes the target current value for the constant current control from a first current value to a second current value in a first measurement interval. and after the target current value is switched from the first current value to the second current value, in a second measurement interval having the same length as the first measurement interval, the target current value is switched from the second current value to the first current value, and the internal resistance detection unit detects the internal resistance of the storage unit based on the amount of change in voltage of the storage unit detected in the first measurement interval and the amount of change in current flowing through the storage unit in the first measurement interval, and the amount of change in voltage of the storage unit detected in the second measurement interval and the amount of change in current flowing through the storage unit in the second measurement interval.

[0006] A detection method according to the present disclosure is a method for detecting the internal resistance of a storage unit of a backup power supply device that includes a storage unit and a power conversion unit that converts power supplied from a power supply unit to the storage unit, wherein when a charging operation to the storage unit is being performed by constant current control of the power conversion unit, in a first measurement interval, a target current value of the constant current control is switched from a first current value to a second current value, and after the target current value is switched from the first current value to the second current value, in a second measurement interval whose length is the same as the first measurement interval, the target current value is switched from the second current value to the first current value, and the internal resistance of the storage unit is detected based on the amount of change in voltage of the storage unit detected in the first measurement interval and the amount of change in current flowing through the storage unit in the first measurement interval, and the amount of change in voltage of the storage unit detected in the second measurement interval and the amount of change in current flowing through the storage unit in the second measurement interval.

[0007] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0008] According to the backup power supply device and the like according to one aspect of the present disclosure, the internal resistance of the power storage unit can be detected without using the capacitance value of the power storage unit.

[0009] FIG. 1 is a block diagram showing an example of a backup power supply device according to an embodiment. FIG. 2 is an equivalent circuit diagram showing an example of a power storage unit according to an embodiment. FIG. 3 is a block diagram showing an example of a realization of a backup power supply device according to an embodiment. FIG. 4 is a block diagram showing an example of a realization of a backup power supply device according to an embodiment. FIG. 5 is a flowchart showing an example of operation of a backup power supply device according to an embodiment. FIG. 6 is a diagram showing an example of an operation waveform for detecting internal resistance in an embodiment. FIG. 7 is a diagram for explaining a problem when the target current value is changed only once.

[0010] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0011] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, materials, components, arrangement and connection of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0012] (Embodiment) A backup power supply device according to an embodiment will be described below.

[0013] FIG. 1 is a block diagram showing an example of a backup power supply 1 according to an embodiment. In addition to the backup power supply 1, FIG. 1 also shows a power supply unit 100 and a load 200. For example, the backup power supply 1 is mounted on a vehicle or the like. Under normal circumstances, power is supplied from the power supply unit 100, such as a lead-acid battery, to a load 200, such as an auxiliary device of the vehicle. Under normal circumstances, power is also supplied from the power supply unit 100 to the backup power supply 1, and the power storage unit 20 is charged. On the other hand, in the event of an abnormality in the power supply unit 100 (for example, a battery failure), power is supplied from the backup power supply 1 to the load 200. Note that the application of the backup power supply 1 is not limited to vehicles, and the backup power supply 1 can be applied to any system requiring a power backup.

[0014] The backup power supply 1 includes a power conversion unit 10 , a power storage unit 20 , a voltage detection unit 30 , a current detection unit 40 , a control unit 50 , a target current setting unit 60 , a measurement interval setting unit 70 , and an internal resistance detection unit 80 .

[0015] The power conversion unit 10 converts the power supplied from the power supply unit 100 to the power storage unit 20. For example, the power conversion unit 10 is a DC-DC converter capable of bidirectional voltage step-up and step-down. The power conversion unit 10 normally supplies power from the power supply unit 100 to the power storage unit 20, and supplies power from the power storage unit 20 to the load 200 when an abnormality occurs in the power supply unit 100.

[0016] The power storage unit 20 is charged and discharged via the power conversion unit 10. The power storage unit 20 is, for example, a lithium ion battery (LiB), a lead storage battery, a lithium ion capacitor, or an electric double layer capacitor (EDLC).

[0017] FIG. 2 is an equivalent circuit diagram showing an example of the power storage unit 20 according to the embodiment.

[0018] As shown in FIG. 2 , the power storage unit 20 is composed of an internal resistance and a capacitance. In FIG. 2 , the resistance value of the internal resistance is indicated by R, and the capacitance value of the capacitance is indicated by C. The charging voltage of the power storage unit 20 is the voltage across the internal resistance and capacitance. If the resistance value (direct current resistance: DCR) of the internal resistance of the power storage unit 20 increases due to aging degradation, the loss in the internal resistance during discharge may increase, resulting in a decrease in the power supply capacity. For this reason, it is necessary to detect the internal resistance of the power storage unit 20 to detect degradation of the power storage unit 20. For this reason, the backup power supply device 1 is equipped with functions such as an internal resistance detection unit 80.

[0019] The voltage detection unit 30 detects the voltage (charging voltage) of the power storage unit 20. There are no particular limitations on how the voltage detection unit 30 is implemented, but it may be implemented, for example, by a voltage dividing resistor. The detected charging voltage is output from the voltage detection unit 30 to the control unit 50 and the internal resistance detection unit 80.

[0020] The current detection unit 40 detects the current flowing through the power storage unit 20. The current detection unit 40 may be, for example, a contactless current sensor using a magnetic core as shown in FIG. 1 . The current detection unit 40 may also be implemented using a Hall element or a shunt resistor. FIG. 1 shows an example in which the charging current of the power storage unit 20 is detected when the power storage unit 20 is being charged, and the detected charging current is output from the current detection unit 40 to the control unit 50 and the internal resistance detection unit 80. The control unit 50 performs constant current control and constant voltage control of the power conversion unit 10. Specifically, the control unit 50 feeds back the output current and output voltage of the power conversion unit 10, i.e., the charging current and charging voltage of the power storage unit 20, and outputs a PWM (Pulse Width Modulation) signal to a switch element included in the power conversion unit 10 so that these become constant current and constant voltage.

[0021] The target current setting unit 60 sets a target current value for the constant current control performed by the control unit 50. The target current setting unit 60 has a function of switching the target current value. The switching of the target current value is a function for detecting the internal resistance.

[0022] The measurement interval setting unit 70 sets a first measurement interval and a second measurement interval during which the current (charging current) flowing through the power storage unit 20 and the voltage (charging voltage) of the power storage unit 20, which are used by the internal resistance detection unit 80 to detect the internal resistance, are measured. Specifically, the measurement interval setting unit 70 sets the first measurement interval and the second measurement interval using a timer counter. More specifically, the measurement interval setting unit 70 sets the start and end timings of the first measurement interval and the start and end timings of the second measurement interval as the timings for measuring the charging current and charging voltage. The second measurement interval has the same length as the first measurement interval. Note that "same" here does not necessarily mean a perfect match; for example, the length of one interval may be allowed to differ from the length of the other interval depending on the required internal resistance detection accuracy. For example, the second measurement interval starts after the first measurement interval ends.

[0023] When a charging operation to the power storage unit 20 or a discharging operation from the power storage unit 20 is being performed by the constant current control of the power conversion unit 10, the target current setting unit 60 switches the target current value of the constant current control from a first current value to a second current value in the first measurement interval, and then switches the target current value from the second current value to the first current value in the second measurement interval. This operation of the target current setting unit 60 will be described in detail below. Note that, although an example in which the target current value of the constant current control is switched from the first current value to a second current value smaller than the first current value in the first measurement interval will be described below, the target current value of the constant current control may also be switched from the first current value to a second current value larger than the first current value.

[0024] The internal resistance detection unit 80 detects the internal resistance of the power storage unit 20. Specifically, the internal resistance detection unit 80 detects the internal resistance of the power storage unit 20 based on the amount of change in the voltage of the power storage unit 20 detected by the voltage detection unit 30 in the first measurement interval and the amount of change in the current flowing through the power storage unit 20 in the first measurement interval, and the amount of change in the voltage of the power storage unit 20 detected by the voltage detection unit 30 in the second measurement interval and the amount of change in the current flowing through the power storage unit 20 in the second measurement interval. For example, the amount of change in the current flowing through the power storage unit 20 in the first measurement interval is the amount of change in the current flowing through the power storage unit 20 detected by the current detection unit 40 in the first measurement interval, and the amount of change in the current flowing through the power storage unit 20 in the second measurement interval is the amount of change in the current flowing through the power storage unit 20 detected by the current detection unit 40 in the second measurement interval. This operation of the internal resistance detection unit 80 will be described in detail later.

[0025] Note that internal resistance detection unit 80 does not need to use the current detected by current detection unit 40. For example, the amount of change in the current flowing through power storage unit 20 in the first measurement interval may be the amount of change from the first current value to the second current value, and the amount of change in the current flowing through power storage unit 20 in the second measurement interval may be the amount of change from the second current value to the first current value. In other words, since the current flowing through power storage unit 20 becomes the target current value by performing constant current control, the target current value set by target current setting unit 60 may be used instead of the current detected by current detection unit 40.

[0026] Next, examples of how the control unit 50, target current setting unit 60, measurement interval setting unit 70, and internal resistance detection unit 80 included in the backup power supply 1 will be described with reference to FIGS. 3 and 4. FIG.

[0027] 3 and 4 are block diagrams showing examples of the backup power supply device 1 according to the embodiment.

[0028] 3, the measurement interval setting unit 70 and the internal resistance detection unit 80 may be realized by a microcomputer 91. For example, the control unit 50 is configured with hardware such as a control IC, and the target current setting unit 60 has a circuit configuration that can change the voltage level of the target current value output to the control unit 50 by switching a voltage dividing resistor. For example, when adding the internal resistance detection function of the present disclosure to an existing backup power supply device, the backup power supply device 1 may be realized by implementing the microcomputer 91 in an existing backup power supply device that has the control unit 50 and the target current setting unit 60.

[0029] 4, the control unit 50, target current setting unit 60, measurement interval setting unit 70, and internal resistance detection unit 80 may be realized by a microcomputer 92. For example, the setting and control of the target current are realized by calculations of the microcomputer 92. In this case, the control unit 50, target current setting unit 60, measurement interval setting unit 70, and internal resistance detection unit 80 can be realized by a single microcomputer 92, which enables cost reduction and size reduction.

[0030] Next, the operation of the backup power supply 1 will be described in detail with reference to FIGS.

[0031] 5 is a flowchart showing an example of the operation of the backup power supply device 1 according to the embodiment, which illustrates the operation for detecting the internal resistance when the power storage unit 20 is being charged by the constant current control of the power conversion unit 10.

[0032] FIG. 6 is a diagram showing an example of operational waveforms for detecting internal resistance in the embodiment. FIG. 6 shows time waveforms of the charging voltage, charging current, and target current when charging operation to power storage unit 20 is performed by constant current control of power conversion unit 10. As shown in FIG. 6, when charging operation is performed, power storage unit 20 is charged and the charging voltage increases. Furthermore, when charging operation is performed, the target current value is set to a first current value. In FIG. 6, the first current value is I1. Furthermore, to detect the internal resistance, the target current value is temporarily set to a second current value. In FIG. 6, the second current value is I2.

[0033] First, internal resistance detection unit 80 measures the charging voltage and charging current at the start timing of the first measurement interval set by measurement interval setting unit 70, and target current setting unit 60 starts a timer (step S11). For example, internal resistance detection unit 80 measures the charging voltage and charging current by acquiring the charging voltage and charging current from voltage detection unit 30 and current detection unit 40. As shown in Fig. 6 , the target current value is set to the first current value, and power storage unit 20 continues to be charged even after the start of the first measurement interval, so the charging voltage gradually increases.

[0034] The target current setting unit 60 determines whether the timer counter has exceeded a count value T1 (step S12). The count value T1 is a preset count value corresponding to the time from the start of the first measurement interval until the target current value is switched from the first current value to the second current value. If the timer counter has not exceeded the count value T1 (NO in step S12), the process in step S12 is repeated. In other words, the target current setting unit 60 waits until the timer counter has exceeded the count value T1.

[0035] When the timer counter exceeds the count value T1 (YES in step S12), the target current setting unit 60 switches the target current value from the first current value (I1) to the second current value (I2) and resets and starts the timer (step S13). As shown in FIG. 6 , because the target current value has switched from the first current value to the second current value, the charging current also decreases from the first current value to the second current value. As the charging current decreases, the current flowing through the internal resistance of the power storage unit 20 also decreases, lowering the voltage across the internal resistance. As shown in FIG. 2 , the voltage across the internal resistance constitutes part of the charging voltage, so the charging voltage also decreases as the voltage across the internal resistance decreases. In FIG. 6 , the decrease in charging voltage, specifically the decrease in the voltage across the internal resistance, is designated ΔV. Furthermore, because the charging current has decreased from the first current value to the second current value, the increase in charging voltage is more gradual than before the decrease in charging current.

[0036] The target current setting unit 60 determines whether the timer counter has exceeded a count value T2 (step S14). The count value T2 is a preset count value corresponding to the time from when the target current value is switched in the first measurement interval to when the first measurement interval ends. If the timer counter has not exceeded the count value T2 (NO in step S14), the process in step S14 is repeated. In other words, the target current setting unit 60 waits until the timer counter has exceeded the count value T2.

[0037] If the timer counter exceeds count value T2 (YES in step S14), internal resistance detection unit 80 measures the charging voltage and charging current (step S15). That is, internal resistance detection unit 80 measures the charging voltage and charging current at the end timing of the first measurement interval set by measurement interval setting unit 70. Internal resistance detection unit 80 calculates the difference between the charging voltage measured in step S11 and the charging voltage measured in step S15 and the difference between the charging current measured in step S11 and the charging current measured in step S15, thereby obtaining the amount of change in the voltage of power storage unit 20 detected in the first measurement interval and the amount of change in the current flowing through power storage unit 20 in the first measurement interval. That is, the amount of change in the voltage of power storage unit 20 detected in the first measurement interval is the amount of change from the voltage of power storage unit 20 at the start timing of the first measurement interval to the voltage of power storage unit 20 at the end timing of the first measurement interval. The amount of change in the current flowing through power storage unit 20 during the first measurement interval is the amount of change from the current value of the current flowing through power storage unit 20 at the start timing of the first measurement interval to the current value of the current flowing through power storage unit 20 at the end timing of the first measurement interval. In Fig. 6, the amount of change in the voltage of power storage unit 20 detected during the first measurement interval is denoted as ΔV1, and the amount of change in the current flowing through power storage unit 20 during the first measurement interval is denoted as ΔI.

[0038] Next, the internal resistance detection unit 80 measures the charging voltage and charging current at the start timing of the second measurement period set by the measurement period setting unit 70, and the target current setting unit 60 resets and starts the timer (step S21).

[0039] The target current setting unit 60 determines whether the timer counter has exceeded a count value T2 (step S22). The count value T2 is a preset count value corresponding to the time from the start of the second measurement period until the target current value is switched from the second current value to the first current value. If the timer counter does not exceed the count value T2 (NO in step S22), the process in step S22 is repeated. In other words, the target current setting unit 60 waits until the timer counter exceeds the count value T2.

[0040] The count value T2 in the second measurement interval is the same as the count value T2 in the first measurement interval (see the x marks in FIG. 6 ). Therefore, the amount of charge of power storage unit 20 due to the charging current of the second current value in the first measurement interval (i.e., the amount of increase in charging voltage) is the same as the amount of charge of power storage unit 20 due to the charging current of the second current value in the second measurement interval (i.e., the amount of increase in charging voltage).

[0041] When the timer counter exceeds the count value T2 (YES in step S22), the target current setting unit 60 switches the target current value from the second current value (I2) to the first current value (I1) and resets and starts the timer (step S23). As shown in FIG. 6 , since the target current value has switched from the second current value to the first current value, the charging current also increases from the second current value to the first current value. As the charging current increases, the current flowing through the internal resistance of the power storage unit 20 also increases, and the voltage generated across the internal resistance increases. As shown in FIG. 2 , the voltage generated across the internal resistance constitutes part of the charging voltage, so the charging voltage also increases as the voltage generated across the internal resistance increases. In FIG. 6 , the increase in charging voltage, specifically the increase in the voltage generated across the internal resistance, is designated ΔV. Because the amount of decrease in charging current in the first measurement interval is the same as the amount of increase in charging current in the second measurement interval, the amount of decrease in voltage generated across the internal resistance in the first measurement interval is the same as the amount of increase in voltage generated across the internal resistance in the second measurement interval.

[0042] The target current setting unit 60 determines whether the timer counter has exceeded a count value T1 (step S24). The count value T1 is a preset count value corresponding to the time from when the target current value is switched in the second measurement interval to when the second measurement interval ends. If the timer counter has not exceeded the count value T1 (NO in step S24), the process in step S24 is repeated. In other words, the target current setting unit 60 waits until the timer counter has exceeded the count value T1.

[0043] The count value T1 in the second measurement interval is the same as the count value T1 in the first measurement interval (see the circles in FIG. 6 ). Therefore, the amount of charge of power storage unit 20 due to the charging current of the first current value in the first measurement interval (i.e., the amount of increase in charging voltage) is the same as the amount of charge of power storage unit 20 due to the charging current of the first current value in the second measurement interval (i.e., the amount of increase in charging voltage).

[0044] In this way, the period in the first measurement interval during which the target current value is the first current value and the period in the second measurement interval during which the target current value is the first current value are the same length, and the period in the first measurement interval during which the target current value is the second current value and the period in the second measurement interval during which the target current value is the second current value are the same length. Note that "same" here does not only mean a perfect match, but also allows for a deviation in the length of one interval relative to the other interval depending on the required internal resistance detection accuracy, for example.

[0045] If the timer counter exceeds the count value T1 (YES in step S24), the internal resistance detection unit 80 measures the charging voltage and the charging current (step S25). That is, the internal resistance detection unit 80 measures the charging voltage and the charging current at the end timing of the second measurement interval set by the measurement interval setting unit 70. The internal resistance detection unit 80 calculates the difference between the charging voltage measured in step S21 and the charging voltage measured in step S25 and the difference between the charging current measured in step S21 and the charging current measured in step S25, thereby obtaining the amount of change in the voltage of the power storage unit 20 detected in the second measurement interval and the amount of change in the current flowing through the power storage unit 20 in the second measurement interval. That is, the amount of change in the voltage of the power storage unit 20 detected in the second measurement interval is the amount of change from the voltage of the power storage unit 20 at the start timing of the second measurement interval to the voltage of the power storage unit 20 at the end timing of the second measurement interval. The amount of change in the current flowing through the power storage unit 20 in the second measurement interval is the amount of change from the current value of the current flowing through the power storage unit 20 at the start timing of the second measurement interval to the current value of the current flowing through the power storage unit 20 at the end timing of the second measurement interval. In Fig. 6 , the amount of change in the voltage of the power storage unit 20 detected in the second measurement interval is denoted as ΔV2, and the amount of change in the current flowing through the power storage unit 20 in the second measurement interval is denoted as ΔI. In the second measurement interval, the target current value switched in the first measurement interval is restored, so the amount of change in the current flowing through the power storage unit 20 in the first measurement interval and the amount of change in the current flowing through the power storage unit 20 in the second measurement interval are the same.

[0046] Then, the internal resistance detector 80 detects the internal resistance (step S31). The increase in the charging voltage in the first measurement interval and the second measurement interval (specifically, ∫I(t)dt / C) can be offset by the difference between ΔV2 and ΔV1, and as a result, ΔV can be extracted, and the internal resistance ΔV / ΔI can be detected.

[0047] In the present disclosure, to detect the internal resistance, the target current value is changed from a first current value to a second current value in the first measurement interval, and then changed from the second current value to the first current value in the second measurement interval. In other words, to detect the internal resistance, the target current value is changed twice. Here, a problem that occurs when the target current value is changed only once will be described with reference to FIG. 7 .

[0048] 7 is a diagram for explaining the problem that occurs when the target current value is changed only once, showing the time waveforms of the charging voltage and the charging current.

[0049] If it were possible to measure the change in voltage of the power storage unit 20 at the moment when the charging current changes by ΔI due to a change in the target current value, ΔV could be accurately measured even if the target current value was changed only once. However, because the interval between voltage measurements is limited by the sampling period, it is difficult to measure ΔV at the moment when the charging current changes by ΔI. Since the charging voltage rises momentarily, as shown in FIG. 7 , the measurable ΔV becomes ΔV', which deviates from the actual ΔV. Thus, when the target current value is changed only once, there is a problem that the voltage change cannot be accurately measured and the accuracy of internal resistance detection deteriorates. Therefore, in the present disclosure, the target current value is changed twice. As described above, when the target current value is changed twice, the difference between ΔV2 and ΔV1 offsets the increase in charging voltage, allowing only the voltage change in the internal resistance to be extracted.

[0050] The period of the first measurement interval after the target current value is switched and the period of the second measurement interval before the target current value is switched may overlap. That is, the second measurement interval may start after the first measurement interval starts and before the first measurement interval ends. This shortens the time during which the target current value is the second current value, thereby preventing the charging time from becoming longer.

[0051] Furthermore, if either the voltage of the power storage unit 20 detected in the first measurement interval or the voltage of the power storage unit 20 detected in the second measurement interval is not within a predetermined voltage range, the internal resistance detection unit 80 may not detect the internal resistance. For example, if the detected voltage is abnormal due to the occurrence of noise or the like, the detection accuracy of the internal resistance will decrease, and therefore, in such a case, the internal resistance may not be detected.

[0052] As described above, by changing the current flowing through the power storage unit 20 while the power storage unit 20 is being charged, the internal resistance can be detected while the power storage unit 20 is being charged. Specifically, if the amount of change in the current flowing through the power storage unit 20 is ΔI and the amount of change in the voltage generated in the power storage unit 20 due to the change in the current flowing through the power storage unit 20 is ΔV, the internal resistance can be detected by calculating ΔV / ΔI. However, because the interval between voltage measurements is limited by the sampling period, it is difficult to measure the amount of change in voltage at the moment when the current flowing through the power storage unit 20 changes. For this reason, the amount of change in voltage measured at intervals corresponding to the sampling period is affected by the charging voltage of the power storage unit 20, which increases over time while the power storage unit 20 is being charged, and therefore deviates from the actual amount of change that occurs at the moment when the current changes.

[0053] Therefore, in the present disclosure, the amount of change in voltage is detected in each of the first and second measurement intervals, which have the same interval length. Because the amount of change detected in each of the first and second measurement intervals, which have the same interval length, includes the same amount of increase in the charging voltage of the power storage unit 20, the increase in the charging voltage of the power storage unit 20 can be offset by calculating the difference between the amounts of change, and the amount of change in voltage at the moment when the current flowing through the power storage unit 20 changes can be extracted. Therefore, the internal resistance of the power storage unit 20 can be detected using only the voltage value and the current value. In other words, the internal resistance of the power storage unit 20 can be detected without using the capacitance value of the power storage unit 20.

[0054] Note that the greater the difference between the first current value and the second current value, the smaller the amount of charge to the power storage unit 20 during the period when the target current value is the second current value, resulting in a longer charging time. However, in the present disclosure, the internal resistance can be detected even if there is a small difference between the first current value and the second current value. In other words, the internal resistance can be detected regardless of the magnitude of the difference between the first current value and the second current value. Therefore, by reducing the difference between the first current value and the second current value, it is possible to prevent the charging time from becoming longer due to the need to detect the internal resistance.

[0055] (Other Embodiments) As described above, the embodiments have been described as examples of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present disclosure.

[0056] For example, in the above embodiment, an example has been described in which the backup power supply 1 includes the current detection unit 40 , but the backup power supply 1 does not necessarily have to include the current detection unit 40 .

[0057] For example, in the above embodiment, an example was described in which the first current value and the second current value are positive values, but one of the first current value and the second current value may be a negative value and the other may be a positive value.

[0058] For example, in the above embodiment, the case where the target current value of the constant current control is switched from the first current value to the second current value that is smaller than the first current value in the first measurement interval has been described, but the target current value of the constant current control may be switched from the first current value to the second current value that is larger than the first current value. In this case, the magnitude relationship between ΔV1 and ΔV2 is reversed, but the internal resistance detection unit 80 treats the difference between ΔV1 and ΔV2 as being positive.

[0059] For example, in the above embodiment, an example has been described in which, when the power storage unit 20 is being charged by the constant current control of the power conversion unit 10, the target current setting unit 60 switches the target current value of the constant current control from the first current value to the second current value in the first measurement interval, and then switches the target current value from the second current value to the first current value in the second measurement interval. However, this is not limiting. For example, when the power storage unit 20 is being discharged by the constant current control of the power conversion unit 10, the target current setting unit 60 may switch the target current value of the constant current control from the first current value to the second current value in the first measurement interval, and then switch the target current value from the second current value to the first current value in the second measurement interval.

[0060] For example, the present disclosure can be realized not only as the backup power supply 1 but also as a detection method including steps (processing) performed by the components that make up the backup power supply 1 .

[0061] The detection method is a method for detecting the internal resistance of the storage unit 20 of a backup power supply device 1 that includes the storage unit 20 and a power conversion unit 10 that converts power from a power supply unit 100 to the storage unit 20. As shown in FIG. 5, when a charging operation to the storage unit 20 is performed by constant current control of the power conversion unit 10, in a first measurement interval, the target current value of the constant current control is switched from a first current value to a second current value (step S13). Thereafter, in a second measurement interval whose length is the same as that of the first measurement interval, the target current value is switched from the second current value to the first current value (step S23). The internal resistance of the storage unit 20 is detected based on the amount of change in voltage of the storage unit 20 detected in the first measurement interval and the amount of change in current flowing through the storage unit 20 in the first measurement interval, and the amount of change in voltage of the storage unit 20 detected in the second measurement interval and the amount of change in current flowing through the storage unit 20 in the second measurement interval (step S31).

[0062] For example, the present disclosure can be realized as a program for causing a computer (processor) to execute the steps included in the detection method. Furthermore, the present disclosure can be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0063] For example, when the present disclosure is realized as a program (software), each step is performed by running the program using hardware resources such as a computer's CPU, memory, input / output circuits, etc. In other words, each step is performed by the CPU acquiring data from memory or input / output circuits, etc., performing calculations, and outputting the calculation results to memory or input / output circuits, etc.

[0064] In the above embodiment, each component included in the backup power supply 1 may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may also be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0065] Some or all of the functions of the backup power supply 1 according to the above embodiment are typically realized as an LSI, which is an integrated circuit. These may be individually integrated into single chips, or some or all of them may be integrated into a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. It is also possible to use an FPGA (Field Programmable Gate Array), which can be programmed after LSI manufacture, or a reconfigurable processor, which allows the connections and settings of circuit cells within the LSI to be reconfigured.

[0066] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, it is natural that each component included in the backup power supply device 1 can be integrated using that technology.

[0067] In addition, this disclosure also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope that does not deviate from the intent of this disclosure.

[0068] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0069] (Technology 1) A charging device includes a power storage unit, a power conversion unit that converts power supplied from a power supply unit to the power storage unit, a voltage detection unit that detects a voltage of the power storage unit, a control unit that performs constant current control of the power conversion unit and constant voltage control of the power conversion unit, a target current setting unit that switches a target current value of the constant current control, and an internal resistance detection unit that detects an internal resistance of the power storage unit, wherein when a charging operation to the power storage unit is performed by the constant current control of the power conversion unit, the target current setting unit switches the target current value of the constant current control from a first current value to a second current value in a first measurement interval, a backup power supply device in which, after the current value is switched from the first current value to the second current value, in a second measurement interval having the same length as the first measurement interval, the target current value is switched from the second current value to the first current value, and an internal resistance detection unit detects the internal resistance of the storage unit based on the amount of change in voltage of the storage unit detected in the first measurement interval and the amount of change in current flowing through the storage unit in the first measurement interval, and the amount of change in voltage of the storage unit detected in the second measurement interval and the amount of change in current flowing through the storage unit in the second measurement interval.

[0070] By changing the current flowing through the power storage unit while the power storage unit is being charged, the internal resistance can be detected while the power storage unit is being charged. Specifically, if the change in current flowing through the power storage unit is ΔI and the change in voltage generated in the power storage unit due to the change in current flowing through the power storage unit is ΔV, the internal resistance can be detected by calculating ΔV / ΔI. However, because the interval between voltage measurements is limited by the sampling period, it is difficult to measure the change in voltage at the moment the current flowing through the power storage unit changes. Therefore, the measured change in voltage is affected by the charging voltage of the power storage unit, which increases over time while the power storage unit is being charged, and therefore deviates from the actual change that occurs at the moment the current changes.

[0071] Therefore, in the present disclosure, the amount of change in voltage is detected in each of the first and second measurement intervals, which have the same interval length. Because the amount of change detected in each of the first and second measurement intervals, which have the same interval length, includes the same amount of increase in the charging voltage of the power storage unit, calculating the difference between the amounts of change can cancel out the increase in the charging voltage of the power storage unit, and the amount of change in voltage at the moment when the current flowing through the power storage unit changes can be extracted. Therefore, the internal resistance of the power storage unit can be detected using only the voltage value and the current value, i.e., the internal resistance of the power storage unit can be detected without using the capacitance value of the power storage unit.

[0072] Note that the greater the difference between the first current value and the second current value, the smaller the amount of charge to the power storage unit during the period when the target current value is the second current value, resulting in a longer charging time. However, in the present disclosure, even a small difference between the first current value and the second current value is sufficient to detect the internal resistance. In other words, the internal resistance can be detected regardless of the magnitude of the difference between the first current value and the second current value. Therefore, by reducing the difference between the first current value and the second current value, it is possible to prevent the charging time from becoming longer due to the need to detect the internal resistance.

[0073] (Technology 2) The backup power supply device according to Technology 1 further includes a current detection unit that detects the current flowing in the storage unit, wherein the amount of change in the current flowing in the storage unit in the first measurement interval is the amount of change in the current flowing in the storage unit detected in the first measurement interval, and the amount of change in the current flowing in the storage unit in the second measurement interval is the current value of the current flowing in the storage unit detected in the second measurement interval.

[0074] In this way, the amount of change in current detected by the current detection unit may be used to detect the internal resistance.

[0075] (Technology 3) A backup power supply device according to Technology 1, wherein the amount of change in the current flowing through the storage unit during the first measurement interval is the amount of change from the first current value to the second current value, and the amount of change in the current flowing through the storage unit during the second measurement interval is the amount of change from the second current value to the first current value.

[0076] In this way, the amount of change in the target current value switched by the target current setting unit may be used to detect the internal resistance.

[0077] (Technology 4) A backup power supply device according to any one of technologies 1 to 3, wherein the period of the first measurement section after the target current value is switched and the period of the second measurement section before the target current value is switched overlap.

[0078] This makes it possible to shorten the time during which the target current value is the second current value, thereby preventing the charging time from becoming too long.

[0079] (Technology 5) A backup power supply device according to any one of Technologies 1 to 4, wherein the internal resistance detection unit does not detect the internal resistance if either the voltage of the storage unit detected in the first measurement section or the voltage of the storage unit detected in the second measurement section is not included in a predetermined voltage range.

[0080] For example, if the detected voltage is abnormal due to the occurrence of noise or the like, the detection accuracy of the internal resistance will decrease, and in such a case, the internal resistance may not be detected.

[0081] (Technology 6) A backup power supply device according to any one of Techniques 1 to 5, wherein, when a discharge operation from the power storage unit is being performed by constant current control of the power conversion unit, the target current setting unit switches the target current value from the first current value to the second current value in the first measurement interval, and after the target current value has been switched from the first current value to the second current value, switches the target current value from the second current value to the first current value in the second measurement interval.

[0082] According to this, the internal resistance of the power storage unit can be detected without using the capacitance value of the power storage unit during a discharging operation as well as during a charging operation.

[0083] (Technology 7) A backup power supply device according to any one of Technologies 1 to 6, wherein one of the first current value and the second current value is a negative value and the other is a positive value.

[0084] In this way, the first current value or the second current value may be a negative value.

[0085] (Technology 8) A method for detecting an internal resistance of a power storage unit of a backup power supply device including a power storage unit and a power conversion unit that converts power supplied from a power supply unit to the power storage unit, the method comprising: when a charging operation to the power storage unit is being performed by constant current control of the power conversion unit, switching a target current value of the constant current control from a first current value to a second current value in a first measurement interval; after the target current value is switched from the first current value to the second current value, switching the target current value from the second current value to the first current value in a second measurement interval having the same interval length as the first measurement interval; and detecting the internal resistance of the power storage unit based on an amount of change in voltage of the power storage unit detected in the first measurement interval and an amount of change in current flowing in the power storage unit in the first measurement interval, and an amount of change in voltage of the power storage unit detected in the second measurement interval and an amount of change in current flowing in the power storage unit in the second measurement interval.

[0086] This provides a detection method that can detect the internal resistance of the power storage unit without using the capacitance value of the power storage unit.

[0087] The present disclosure can be applied to systems that require backup power supplies.

[0088] REFERENCE SIGNS LIST 1 Backup power supply device 10 Power conversion section 20 Power storage section 30 Voltage detection section 40 Current detection section 50 Control section 60 Target current setting section 70 Measurement section setting section 80 Internal resistance detection section 91, 92 Microcomputer 100 Power supply section 200 Load

Claims

1. A storage battery comprising: a power conversion unit that converts power supplied from a power supply unit to the storage battery unit; a voltage detection unit that detects the voltage of the storage battery unit; a control unit that performs constant current control of the power conversion unit and constant voltage control of the power conversion unit; a target current setting unit that switches a target current value for the constant current control; and an internal resistance detection unit that detects internal resistance of the storage battery unit, wherein when a charging operation to the storage battery unit is performed by the constant current control of the power conversion unit, the target current setting unit switches the target current value for the constant current control from a first current value to a second current value in a first measurement interval, and after the target current value has been switched from the first current value to the second current value, switches the target current value from the second current value to the first current value in a second measurement interval whose length is the same as that of the first measurement interval, and the internal resistance detection unit a backup power supply device that detects an internal resistance of the power storage unit based on an amount of change in voltage of the power storage unit detected in the first measurement interval and an amount of change in current flowing through the power storage unit in the first measurement interval, and an amount of change in voltage of the power storage unit detected in the second measurement interval and an amount of change in current flowing through the power storage unit in the second measurement interval.

2. The backup power supply device according to claim 1, further comprising a current detection unit that detects a current flowing through the storage battery unit, wherein the amount of change in the current flowing through the storage battery unit in the first measurement interval is the amount of change in the current flowing through the storage battery unit detected in the first measurement interval, and the amount of change in the current flowing through the storage battery unit in the second measurement interval is the current value of the current flowing through the storage battery unit detected in the second measurement interval.

3. The backup power supply device according to claim 1, wherein the amount of change in current flowing through the storage unit during the first measurement interval is the amount of change from the first current value to the second current value, and the amount of change in current flowing through the storage unit during the second measurement interval is the amount of change from the second current value to the first current value.

4. A backup power supply device according to any one of claims 1 to 3, wherein the period of the first measurement period after the target current value is switched and the period of the second measurement period before the target current value is switched overlap.

5. A backup power supply device according to any one of claims 1 to 4, wherein the internal resistance detection unit does not detect the internal resistance if either the voltage of the storage unit detected in the first measurement period or the voltage of the storage unit detected in the second measurement period is not included in a predetermined voltage range.

6. The backup power supply device according to any one of claims 1 to 5, wherein, when a discharging operation from the power storage unit is being performed by the constant current control of the power conversion unit, the target current setting unit switches the target current value from the first current value to the second current value in the first measurement interval, and after the target current value has been switched from the first current value to the second current value, switches the target current value from the second current value to the first current value in the second measurement interval.

7. The backup power supply device according to any one of claims 1 to 6, wherein one of the first current value and the second current value is a negative value, and the other is a positive value.

8. A method for detecting the internal resistance of a power storage unit of a backup power supply device comprising a power storage unit and a power conversion unit that converts power supplied from a power supply unit to the power storage unit, the method comprising: when a charging operation to the power storage unit is being performed by constant current control of the power conversion unit, switching a target current value of the constant current control from a first current value to a second current value in a first measurement interval; after the target current value has been switched from the first current value to the second current value, switching the target current value from the second current value to the first current value in a second measurement interval having the same interval length as the first measurement interval; and detecting the internal resistance of the power storage unit based on the amount of change in voltage of the power storage unit detected in the first measurement interval and the amount of change in current flowing in the power storage unit in the first measurement interval, and the amount of change in voltage of the power storage unit detected in the second measurement interval and the amount of change in current flowing in the power storage unit in the second measurement interval.

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