JP2007267559A - Charging method for secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging method for a secondary battery for finishing charging under one of a charging current and the predetermined current lower limit in the event of performing a constant-potential charge for charging at a constant voltage using a secondary battery system, equipped with a current sensor for measuring current supplied to a load during discharging and measuring charging current during charging between the secondary battery and an open end, in which the open end of the secondary battery is designed to be connected to either of a load or a charger, capable of obtaining an almost fully charged condition. <P>SOLUTION: This charging method of a secondary battery employs the current sensor 3 with two-stage switchable measuring ranges of which spans are wide and narrow. The measuring range with a narrow span is used during charging, while the measuring range with a wide span is used during discharging. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is configured to connect either one of a load and a charger to the open end of a secondary battery, measure a current supplied to the load at the time of discharging, and provide a current sensor for measuring a charging current at the time of charging. A secondary battery charging method using a secondary battery system provided between the secondary battery and the open end to terminate the charging when the charging current falls below a predetermined current lower limit value when performing constant voltage charging. In particular, the present invention relates to a device that can be brought closer to a fully charged state without being overcharged.

  Conventionally, either a load or a charger is connected to the open end of a secondary battery such as a lithium ion battery, and the current supplied to the load is measured during discharging and the charging current is measured during charging. Using a secondary battery system with a current sensor between the secondary battery and the open end, when charging at a constant voltage, charging is performed when the charging current falls below a predetermined current lower limit. There is known a method for charging a secondary battery that terminates (see, for example, Patent Document 1).

  FIG. 1 is a conceptual circuit diagram showing such a secondary battery system 90. FIG. 1 (a) shows a state in which a load is connected to the open end, and FIG. 1 (b) shows a charger at the open end. Each of the secondary battery systems 90 represents a connected state, and includes, for example, a secondary battery 91 in which a plurality of cells are combined, a charge / discharge control unit 92, a current sensor 93, and an open end 94. 94 is configured such that a load 96 is connected during discharging and a charger 97 can be connected during charging for charging the secondary battery 91.

  In such a secondary battery system 90, when charging a secondary battery by connecting a charger to the open end, after performing constant current charging in which the charge current is controlled to be constant, When the voltage reaches a predetermined voltage, constant voltage charging is performed by controlling the charging voltage to be constant, and at this time, the charging current that decreases with the passage of time is monitored, and if this current value falls below the predetermined value Charging is stopped.

FIG. 2 is a graph showing the charging voltage between the open ends and the charging current at the time of charging performed in this way. The horizontal axis represents time from the start of charging, and the vertical axis represents the charging voltage and charging current. In the figure, I is a curve showing the time change of the charging current, and E _app is a curve showing the time change of the voltage between the open ends. From the start of charging up to time t _1, it performs the constant current charging. During this time, the voltage E _app between the open ends becomes the actual voltage E _real appearing at both ends of the secondary battery plus the circuit voltage drop E _RI , so E _app becomes (E _real + E _RI ). If the charging is stopped at the same time, both ends of the secondary battery become E _{real and a} full charge state can be obtained, but in reality, the E _RI is unknown and the temperature rises abnormally when overcharged Therefore, the constant current charging is stopped at the time t ₁ when the voltage value E ₁ on the safe side, which is surely lower than the fully charged voltage, is reached.

However, since it is far from the fully charged state, constant voltage charging is subsequently performed so as to obtain a state as close to full charge as possible. If this process is continued, the battery 91 approaches full charge, so the current value of the charging current I gradually decreases. Because dangerous is this Wherever Continuing continued overcharged secondary battery 91, charging current is being performed to end the charging at the time t ₂ to below a predetermined value I _min.
JP 2000-14035 A

However, in the above charging method, for example, when charging a secondary battery having a large discharge current with respect to the charging current, such as an electric bicycle driving battery, the charging state of the secondary battery may be close to full charge. It was not possible to improve it. That is, in the conventional method, when charging is terminated, it is difficult to reduce the voltage difference ΔE ₁ (see FIG. 2) between the fully charged voltage and the voltage E ₂ at the end of charging.

This is because, as shown in FIG. 1, the current sensor 94 for detecting whether or not the charging current has fallen below a predetermined value _Imin is used to measure the discharging current and the charging current. The measurement range is set wide so that the range does not exceed when discharging, and if a current near the minimum current value _Imin is detected using the same range of the current sensor 94 as during discharging, the error will be large. In order to stop charging on a fairly safe side to avoid overcurrent, it was necessary to estimate the minimum current value I _min and set charging to a very short time before full charge. is there.

  The present invention has been made in view of such problems, and is configured to connect either the load or the charger to the open end of the secondary battery, and measures the current supplied to the load during discharging. When charging with constant voltage using a secondary battery system that has a current sensor for measuring the charging current between the secondary battery and the open end during charging, the charging current falls below a predetermined current lower limit value. An object of the present invention is to provide a charging method that can obtain a state that is closer to a full charge in a charging method of a secondary battery that terminates charging sometimes.

<1> is a current sensor configured to connect either the load or the charger to the open end of the secondary battery, measure the current supplied to the load during discharging, and measure the charging current during charging. When performing constant voltage charging using a secondary battery system provided between the secondary battery and the open end and charging at a constant voltage, the charging is terminated when the charging current falls below a predetermined current lower limit 2 In the next battery charging method,
As the current sensor, one that can be switched between a wide and narrow measurement range span is used, and a wide measurement range is used during discharging, and a narrow measurement range is used during charging. This is a charging method of a secondary battery to be used.

  <2> is a secondary battery that performs constant-current charging that charges at a constant current prior to the constant-voltage charging in <1> and shifts to the constant-voltage charging when a predetermined voltage is reached in constant-current charging. The charging method.

  <3> is a secondary battery charging method in which the current lower limit value used for terminating charging in <1> or <2> is set to 1/10 or less of the rated current value during discharge.

  <4> In any one of <1> to <3>, as the current sensor, a pair of shunt resistors having different resistance values are arranged in parallel, and a current in a charging direction is supplied to the shunt resistor having a smaller resistance value. This is a method of charging a secondary battery using a current value obtained by detecting the voltage at both ends of a composite circuit in which rectifiers to be disconnected are connected in series.

  <5> in any one of <1> to <3>, wherein the current sensor switches the measurement range by an FET that performs switching by detecting a charging voltage when the open end is connected to a charger. This is a method of charging a secondary battery using the one configured as described above.

  <6> is a method for charging a secondary battery in which the secondary battery is used for an electric bicycle in any one of <1> to <5>.

  <1> According to <1>, a current sensor having a measurement range span that can be switched between a wide range and a narrow range is used. At the time of discharge, a measurement range with a wide span is used. Since the measurement range with a narrow span is used, it is possible to accurately measure the current during constant voltage charging, which makes it possible to set the current lower limit value when stopping charging to be extremely low and to prevent overcharging. In addition to preventing, it is possible to obtain a state very close to full charge.

  <2> According to <2>, constant current charging is performed at a constant current prior to the constant voltage charging, and when the predetermined voltage is reached in constant current charging, the constant voltage charging is performed, so the charging time is shortened. can do.

According to <3>, since the current lower limit value used for terminating the charging is set to 1/10 or less of the rated current value during discharging, a state closer to full charging can be obtained.

  According to <4>, as the current sensor, a pair of shunt resistors having different resistance values are arranged in parallel, and a rectifier that cuts off current in a charging direction is connected in series to a shunt resistor having a smaller resistance value. Since the measurement range is switched by using the voltage detected at both ends of the synthesis circuit to obtain the current value, the range switching circuit can be simply configured and can be realized with low cost.

  <5> According to <5>, since the current sensor is configured to switch the measurement range by the FET that performs switching by detecting the charging voltage when connected to the charger at the open end, the range The switching current lower limit value can be set with higher accuracy.

  According to <6>, since the secondary battery is used for an electric bicycle, the effect of improving the charging method can be advantageously used.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a conceptual circuit diagram showing a secondary battery system used in the method for charging a secondary battery according to the present invention. The secondary battery system 10 controls the secondary battery 1 and charging / discharging of the battery 1. The charging / discharging control part 2 which performs, the discharge sensor at the time of discharge, the current sensor 3 which detects a charging current at the time of charge, and the open end 4 for connecting the load 6 or the charger 7 are comprised.

  The current sensor 3 includes a combined resistance unit 15. The combined resistance unit 15 connects a first shunt resistor 11 having a small resistance value and a second shunt resistor 12 having a large resistance value in parallel. 11, a rectifier 13 that cuts off only the charging current is connected in series, and the current sensor 3 converts a voltage generated at both ends of the combined resistance unit 15 into a physical quantity proportional to this voltage. It is comprised so that it may detect as a current value via.

  The output from the current sensor 14 is input to the charge / discharge control unit 2, and the charge / discharge control unit 2 functions to terminate charging when this value falls below a preset current Imin.

  Here, at the time of charging, only the second shunt resistor 12 having a large resistance value passes the current, so even if the charging current is small, the voltage V across the combined resistor 15 is large, while at the time of discharging with a large current, Since the current passing through the first shunt resistor 11 having a small resistance becomes dominant, the voltage V across the combined resistor 15 is small even when the current is large, and this causes the combined resistor 15 to have a maximum current during charging. The voltage V between both ends and the voltage V across the combined resistor 15 with respect to the maximum current at the time of discharge can be made substantially the same value. This means that the voltage V between both ends is converted via the converter 14 having a constant resolution. When the current value is input to the charge / discharge control unit 2, it means that measurement is performed in a measurement range with a narrow span during charging, and measurement is performed in a measurement range with a wide span during discharge. In this case, high accuracy can be ensured even if the current value is small, and it is possible to prevent the range from being exceeded even during the discharge even if the current value is large.

Conventionally, while charging, a small current was measured in a wide span measurement range, in the present invention, the current can be measured by switching to a narrow span measurement range in this way, More accurate current measurement is possible, and as a result, the error in the magnitude comparison with the current lower limit value Imin becomes smaller, and there is a risk of overcharging even if the current lower limit value Imin is much smaller than the conventional one For example, when the full span of the current measurement range during charging can be reduced to 1/10 of the conventional one, the error is also reduced to 1/10, and accordingly, Imin is also reduced to 1/10 of the conventional one. FIG. 4 is a graph showing the voltage value change and the current value change during charging in the present invention, as compared with the conventional case shown in FIG. Can be fully charged at that time Very small difference Delta] E ₂ of the voltage, it is possible to obtain a state close to the full charge.

  In place of the current sensor shown in FIG. 3, a current sensor 3 </ b> A having the configuration shown in FIG. 5 can be used. This current sensor 3 </ b> A is connected to the open end 4 from the charger 7. The FET 21 functioning as a switch is turned on by the voltage, and the internal resistance of the IC circuit 22 configured to be switchable is switched to a large resistance value. The voltage V between both ends when a current is passed through a large internal resistance of 22 is input to the charge / discharge control unit 2 as a current value, and the voltage V between both ends when a current is passed through a small internal resistance of the IC circuit 22 during discharging. As the current value is input to the charge / discharge control unit 2, the current value at the time of discharging is kept within the measurement range as described above, and high accuracy is maintained even at the time of charging at a small current value. It is possible.

  And when the said current lower limit Imin is made into 1/10 or less of the rated current value at the time of discharge, the secondary battery 1 can be charged to a state closer to full charge. In addition, a lithium ion battery, a lead acid battery, etc. can be mention | raise | lifted as a secondary battery charged in this way.

  And when the charging method is applied to the motor drive battery of an electric bicycle using such a secondary battery system, it is compared with the conventional method in which the charging amount can be charged only to a state far from being fully charged. Thus, the amount of charge can be greatly increased, and the troublesomeness required for charging can be greatly reduced by extending the charging cycle.

  The present invention can be used particularly for charging a secondary battery having a large rated capacity.

It is a conceptual circuit diagram which shows the conventional secondary battery system. It is a graph which shows the electric current change and voltage change with respect to time at the time of charge in the conventional charging method. It is a conceptual circuit diagram which shows the secondary battery system of embodiment which concerns on this invention. It is a graph which shows the electric current change and voltage change with respect to time at the time of charge in the conventional charging method of this invention. It is a conceptual circuit diagram which shows the secondary battery system of other embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Secondary battery 2 Charging / discharging control part 3, 3A Current sensor 4 Open end 6 Load 7 Charger 10 Secondary battery system 11 Shunt resistance with smaller resistance 12 Shunt resistance with larger resistance 13 Rectifier 14 Conversion part 15 Synthesis Resistor 21 FET
22 IC circuit

Claims (6)

It is configured to connect either the load or the charger to the open end of the secondary battery. A current sensor that measures the current supplied to the load during discharging and measures the charging current during charging is opened with the secondary battery. Rechargeable battery charging method that terminates charging when charging current falls below a predetermined current lower limit value when performing constant voltage charging with a constant voltage using a secondary battery system provided between the two ends In
As the current sensor, one that can be switched between a wide and narrow measurement range span is used, and a wide measurement range is used during discharging, and a narrow measurement range is used during charging. The charging method of the secondary battery to be used.   The charging method of the secondary battery according to claim 1, wherein constant current charging for charging at a constant current is performed prior to the constant voltage charging, and transition to the constant voltage charging is performed when a predetermined voltage is reached in constant current charging.   The method for charging a secondary battery according to claim 1 or 2, wherein the lower limit value of the current used for terminating the charging is 1/10 or less of the rated current value during discharging.   As the current sensor, a pair of shunt resistors having different resistance values are arranged in parallel, and a voltage across the composite circuit in which a rectifier that cuts off a current in a charging direction is connected in series to a shunt resistor having a smaller resistance value is detected. The method for charging a secondary battery according to claim 1, wherein a current value is used.   The said current sensor uses what was comprised so that the said measurement range may be switched by FET which detects the charging voltage when it connects to the open end with a charger, and performs switching. The secondary battery charging method. The secondary battery charging method according to claim 1, wherein the secondary battery is used for an electric bicycle.

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