Charging control device, charging / discharging system, and cyclic charging / discharging method for secondary battery

Abstract

When a charge / discharge cycle is repeated, charges are accumulated in a battery cell and the battery cell is in a fully charged state, and when the state is sustained, the battery cell is overcharged. The purpose of the present invention is to improve lifespan and reliability by preventing overcharging. The present invention contributes to "9. Industry, Innovation and Infrastructure" and "11. Sustainable Cities and Communities" which are the Sustainable Development Goals (SDGs). A charging device for charging a secondary battery is provided with: a first switch having a control terminal; a second switch having a control terminal; a circuit constituting an exclusive OR; and a control circuit having an input terminal and an output terminal. The first switch is connected between a charging circuit and a power supply terminal, and the second switch is connected between the secondary battery and the input terminal of the control circuit. The circuit constituting the exclusive OR is connected to the control terminal of the second switch, and the output terminal of the control circuit is connected to the control terminal of the first switch.

Description

Charging Control Device for Secondary Battery, Charge-Discharge System, and Method of Cyclic Charge-Discharge

[0001] The present invention relates to a charging control device for a secondary battery, a charge-discharge system, and a method of cyclic charge-discharge for appropriately controlling the charge state of a secondary battery in equipment that performs charge-discharge cycles and the like.

[0002] In equipment where a charge-discharge cycle is performed, such as charging for a certain period of time and discharging for a certain period of time, it is necessary to monitor the charge state of the secondary battery and control it so as not to over-discharge or over-charge while maintaining an appropriate charge state in order to ensure the life of the secondary battery. As a method for monitoring the charge state of a secondary battery, for example, the open-circuit voltage of the secondary battery is measured, the charging current of the secondary battery during charging is measured at any time, and an approximate function is derived from both measurement results and the time and time interval of the measurement at any time, and a method for estimating the charge state of the battery from the obtained approximate function is used, as described in the following patent documents.

[0003] Japanese Patent Application Laid-Open No. 2015-137916, Japanese Patent Application Laid-Open No. 2009-280175

[0004] However, in the disclosures of Patent Documents 1 and 2, a sensor circuit that monitors the voltage and charging current of a secondary battery at any time, an analog-digital conversion circuit that converts the measurement result of the sensor circuit into a digital value, a microcomputer that obtains a correlation from the measured digital value and calculates an approximate function, and a memory circuit that stores data are provided to grasp the charge state (SOC: State of Charge), and the charge amount is controlled according to the result. There are three problems with this method. The first problem is that it does not operate in a high-temperature environment exceeding 150°C. The second problem is that the circuit scale becomes large. The third problem is that a power supply system is required in addition to the power supply for charging the secondary battery.

[0005] To solve the above problems, one embodiment of the present invention provides, for example, a charging device for charging a secondary battery, comprising a first switch having a control terminal and a second switch having a control terminal, a circuit that constitutes an exclusive OR, and a control circuit having an input terminal and an output terminal. The first switch is connected between the charging circuit and the power supply terminal, and the second switch is connected between the secondary battery and the input terminal of the control circuit. The circuit that constitutes an exclusive OR is connected to the control terminal of the second switch, and the output terminal of the control circuit is connected to the control terminal of the first switch.

[0006] According to the present invention, a more suitable charge control device, charge / discharge system, and cycle charge / discharge method can be realized.

[0007] This is a diagram showing the configuration of an embodiment of a charging control device according to one embodiment of the present invention. This is a diagram showing the operation of a charging control device according to one embodiment of the present invention. This is a diagram showing the operating waveform of a charging control device according to one embodiment of the present invention. This is a diagram showing the operating voltage of a charging control device according to one embodiment of the present invention. This is a diagram showing the operating waveform of a charging control device according to one embodiment of the present invention.

[0008] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the examples described herein, and various modifications and alterations are possible by those skilled in the art within the scope of the technical ideas disclosed herein. Furthermore, in all the drawings used to illustrate embodiments of the present invention, components having the same function are generally given the same reference numerals, and repeated descriptions may be omitted.

[0009] Figure 1 shows the overall configuration of a charge-discharge cycle system using a charge control device according to one embodiment of the present invention. The charge-discharge cycle system includes a power terminal 101, a charge control device 102, a charge circuit 104, a secondary battery 105, a diode 106, a voltage conversion circuit 107, an output terminal 108, and a voltage terminal 115. The charge control device 102 consists of a control circuit 113, a charge switch 103, an EX-OR (EXCLUSIVE-OR) circuit 114, and a battery switch 109. The control circuit 113 includes a reference voltage generation circuit 110, a comparison circuit 111, and a delay circuit 112.

[0010] Specifically, the charging switch 103 has a control terminal and is connected between the charging circuit 104 and the power terminal 101. The output terminal of the control circuit 113 is connected to the control terminal of the charging switch 103. The charging switch 103 may also be called the first switch. The battery switch 109 has a control terminal and is connected between the secondary battery 105 and the input terminal of the control circuit 113. A circuit that constitutes an exclusive OR is connected to the control terminal of the battery switch 109. The battery switch 109 may also be called the second switch. In this embodiment, the EX-OR circuit 114 is a circuit that constitutes an exclusive OR. A comparison circuit 111 is connected between the reference voltage generation circuit 110 and the input terminal of the control circuit 113, and a delay circuit 112 is connected between the comparison circuit 111 and the output terminal of the control circuit 113. The comparison circuit 111 compares the voltage value of the reference voltage generation circuit 110 with the voltage value input from the input terminal of the control circuit 113, and the result of the comparison is input to the delay circuit 112.

[0011] Next, the operation will be explained using Figures 2 to 5. Figure 2 is a diagram with the charge control device 102 removed from Figure 1 in order to explain the operation of the basic charge-discharge cycle system. Figure 3 shows the voltage waveform against time in one charge-discharge cycle of the secondary battery 105 in Figures 1 and 2. Figure 4 is a diagram showing the relationship between a predetermined voltage and the SOC in the voltage waveform of Figure 3. Figure 5 is a diagram showing the increase in SOC with respect to time when a charge-discharge cycle is performed in the voltage waveform of Figure 3. In Figure 2, when power is supplied from the power supply terminal 101, it is converted to a predetermined voltage through the voltage conversion circuit 107 and output to the output terminal 108. Also, the necessary voltage and current are supplied to the secondary battery 105 through the charging circuit 104 to charge the secondary battery 105. The diode 106 is connected between the secondary battery 105 and the power supply terminal 101, but it is reverse-biased during charging, so no current flows from the secondary battery 105 to the voltage conversion circuit 107. Next, when the power supply from the power terminal 101 is cut off, current flows from the secondary battery 105 through the diode 106, which is forward-biased, to the voltage conversion circuit 107, where it is converted to a predetermined voltage and output to the output terminal 108.

[0012] In a charge-discharge cycle system, a predetermined charging time and a predetermined discharge time are repeatedly performed. An example of the voltage of the secondary battery 105 at this time is shown in Figure 3. The waveform in Figure 3 is the time waveform of the voltage terminal 115 representing one cycle of the charge-discharge cycle, and is shown as waveform 201. Period 202 represents the time of one cycle. Period 203 represents the charging time. Period 204 represents the discharge time. In addition, the dotted lines 205 to 210 represent the voltage at predetermined timings, with voltage 205 being the charging start voltage, voltage 206 being the charging end voltage, voltage 207 being the open-circuit voltage after charging is complete, voltage 208 being the voltage drop at the start of discharge, voltage 209 being the discharge end voltage, and voltage 210 being the open-circuit voltage after discharge is complete.

[0013] When repeating charge-discharge cycles, the integrated value of the charging current during the charging period 203 and the integrated value of the discharge current during the discharge period 204 are designed to be approximately equal, thereby ensuring that charging and discharging are performed without excess or deficiency. In this process, taking into account temperature variations, manufacturing variations of the secondary battery, the charging efficiency of the charging circuit 104, the conversion efficiency of the voltage conversion circuit 107, and the voltage drop across the diode 106, the integrated value of the charging current is designed to be greater than the integrated value of the discharge current to prevent the secondary battery 105 from becoming depleted. As a result, charge accumulates in the secondary battery 105 when the charge-discharge cycle is repeated.

[0014] This condition will be explained in detail using Figure 5. The vertical axis represents the amount of charge stored (unit: %), and the horizontal axis represents the cycle charge-discharge time. The amount of charge stored may also be called SOC (State of Charge). Graph (line) 401 shows the change in SOC with respect to cycle charge-discharge time. Region 402 of graph 401 is enlarged and shown in the dotted line frame 403. Graph 404 is an enlarged view of graph 401. The time range 405 represents the charging period and is the same as period 203 in Figure 3. The time range 406 represents the discharging period and is the same as period 204 in Figure 3. By repeatedly performing cycle charge-discharge, the accumulation of a small amount of charge prevents undercharging, but it can approach a fully charged state and potentially lead to overcharging. In particular, when cycle charging and discharging in a high-temperature environment, it is important to use an appropriate SOC range of 80% to 50% to prevent overcharging, in order to suppress the degradation of the secondary battery 105 and obtain a long lifespan.

[0015] The voltages 205 to 210 in waveform 201 are not always constant, but fluctuate depending on the state of charge (SOC) of the secondary battery 105. An example of the change in voltage 210 with respect to SOC is shown in waveform 301 of Figure 4. In Figure 4, waveform 301 shows the change in voltage 210 with respect to SOC, and the dotted line 302 shows the approximate curve when voltage 301 is linearly approximated. The dotted line 303 shows the case when SOC is 50%. The dotted line 304 shows the voltage 210 when SOC is 50%, clearly indicating that voltage 210 is voltage Vcg. Therefore, in each charge-discharge cycle, if the open-circuit voltage 210 at the end of discharge of the secondary battery 105 is Vcg or higher, charging in the next cycle can be stopped, making it possible to maintain SOC at around 50%.

[0016] Figure 1 shows the circuit configuration to achieve this. In Figure 1, when charging starts, the power input from the power terminal 101 is supplied to the control circuit 113, the EX-OR circuit 114, and the voltage conversion circuit 107. The voltage conversion circuit 107 converts the power to a predetermined voltage and outputs it to the output terminal 108. Because power is supplied to the control circuit 113, the reference voltage generation circuit 110 generates a voltage Vcg, and the comparison circuit 111 and delay circuit 112 are in operation. The EX-OR circuit 114 controls the battery switch 109 to the ON state when there is input from the power terminal 101 or the charging switch 103, and to the OFF state when there is input from both. When charging starts, the charging switch 103 is in the OFF state due to the operation of the delay circuit 112, so the battery switch 109 is controlled to be ON. When the battery switch 109 is turned ON, the comparison circuit 111 compares the voltage of the secondary battery 105 (let's call it Vbat) with Vcg, and is set to turn the output ON if Vbat < Vcg ... (1) and turn the output OFF if Vbat > Vcg ... (2).

[0017] In case (1), the charge switch 103 is turned ON through the delay circuit 112, power is supplied to the charge circuit 104, and the secondary battery 105 is charged. As soon as charging starts, there is an input to the EX-OR circuit 114, so the battery switch 109 is turned OFF, and there is no input to the comparison circuit 111, so (1) is met and charging continues.

[0018] In case (2), the charge switch 103 is turned OFF through the delay circuit 112, and power is not supplied to the charge circuit 104. As a result, the secondary battery 105 is not charged and remains in a non-charged state until the next charge / discharge cycle. The output of the EX-OR circuit 114 continues, the battery switch 109 remains ON, and the input to the comparison circuit 111 continues, waiting for charging to begin until (1) is met.

[0019] If the power supply to the power terminal 101 is cut off (i.e., it enters a discharge state), the control circuit 113 does not operate, the charge control device 102 does not operate, and the power from the secondary battery 105 is input to the voltage conversion circuit 107 via the diode 106, converted to a predetermined voltage, and output to the output terminal 108.

[0020] By repeating the above operations, the State of Charge (SOC) of the secondary battery 105 can be kept nearly constant even when the charge-discharge cycle continues for a long period of time, ensuring sufficient lifespan and reliability. Furthermore, even if the load condition becomes unstable, the power supplied from the output terminal 108 during the charge-discharge cycle does not have to worry about overcharging the secondary battery 105, and stable power supply can be provided. In addition, heat-sensitive elements such as microcomputers and memory elements are not used. For example, semiconductor elements such as MOS field-effect transistors can be used as switch elements, and discrete semiconductor elements capable of operating at around 175°C can be selected, making it possible to use the device in high-temperature environments.

[0021] In the embodiment of the present invention, at the timing when the secondary battery switches from discharge to charge, after a power supply for charging is secured, the voltage of the secondary battery is compared with a reference voltage. Depending on the comparison result, if charging is necessary, a first switch circuit provided between the power supply and the charging circuit is made conductive to start charging the secondary battery, and at the same time, a second switch circuit provided between the secondary battery and the comparison circuit is turned off to maintain charging. On the other hand, the voltage of the secondary battery is compared with the reference voltage, and depending on the comparison result, if charging is not necessary, the first switch circuit is turned off to avoid charging the secondary battery for one cycle. In the charge-discharge cycle, the voltage of the battery after discharge is compared with the reference voltage to determine if it exceeds the reference voltage, and if so, charging control is performed to stop charging in the next cycle, thereby suppressing overcharging when the charge-discharge cycle is continued and improving lifespan and reliability.

[0022] The charge control device according to the present invention is suitable for use with all-solid-state batteries (secondary batteries) because it can be applied over a wide temperature range. Applications include power supply systems for MWD (Measuring While Drilling) and LWD (Logging While Drilling) in underground resource exploration equipment, which sense the orientation, inclination, and geological layer evaluation of the drilling site while drilling and transmit the data. Such power supply systems are ideally suited for this charge control device because they involve a charge-discharge cycle where the MWD period is charging and the LWD period is discharging, and because the ambient temperature at the drilling site can reach high temperatures of 100-200°C.

[0023] Furthermore, the technology according to this embodiment makes it possible to provide an energy-efficient charging and discharging system. This contributes to the United Nations' Sustainable Development Goals (SDGs) "9. Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation" and "11. Make cities and human settlements inclusive, safe, and resilient."

[0024] Although various embodiments have been described in detail above, the present invention is not limited to the embodiments described above and includes various modifications. For example, the embodiments described above are detailed explanations of the entire system in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

[0025] 101...Power terminal, 102...Charging control device, 103...Charging switch, 104...Charging circuit, 105...Secondary battery, 106...Diode, 107...Voltage conversion circuit, 108...Output terminal, 109...Battery switch, 113...Control circuit, 114...EX-OR circuit

Claims

1. A charge control device for controlling the charge state of a secondary battery, comprising: a first switch having a control terminal; a second switch having a control terminal; a circuit that constitutes an exclusive OR; and a control circuit having an input terminal and an output terminal, wherein the first switch is connected between the charging circuit and a power terminal; the second switch is connected between the secondary battery and the input terminal of the control circuit; the circuit that constitutes an exclusive OR is connected to the control terminal of the second switch; and the output terminal of the control circuit is connected to the control terminal of the first switch.

2. A charging control device according to claim 1, wherein the control circuit comprises a reference voltage generation circuit, a comparison circuit, and a delay circuit.

3. A charging control device according to claim 2, wherein the comparison circuit is connected between the reference voltage generation circuit and the input terminal of the control circuit.

4. A charging control device according to claim 2, wherein the delay circuit is connected between the comparison circuit and the output terminal of the control circuit.

5. A charge / discharge system comprising: a power terminal; a charging circuit; a charge control device connected between the power terminal and the charging circuit; and a secondary battery connected to the charge control device via the charging circuit, wherein the charge control device comprises a circuit that constitutes an exclusive OR and a control circuit having input terminals and output terminals.

6. A cycle charge-discharge method for a secondary battery, comprising the steps of repeatedly charging the secondary battery for a set period of time and discharging it for a set period of time, the method comprising the steps of comparing the voltage of the secondary battery with a reference voltage, and determining whether or not to continue charging based on the comparison result in the first step, wherein, for each cycle of the cycle charge-discharge, if the voltage of the secondary battery is higher than the reference voltage, the charging cycle is stopped.

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