JP2001231173A - Charging circuit for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that reduction in the capacity of a secondary battery due to deterioration cannot be detected during trickle charging. SOLUTION: The charging circuit for secondary batteries comprises a first switch SW1 for turning on and off charging current from a DC-DC converter 1, a variable resistor VR1 for adjusting the crest value of pulse current, the secondary battery 2 to be charged, a low resistance R1 for measuring charging/ discharging current, a second switch SW2 series-connected with a variable resistor VR2 for adjusting discharging current, and a control circuit 10. The circuit is so constituted that the second switch SW2 is turned on/off when the first switch SW1 is off. Circuitry to judge any deterioration in the secondary battery 2 utilizing the off duration of trickle charge by pulse current is provided to detect reduction in the capacity of the secondary battery 2 due to deterioration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charging circuit for a secondary battery, and more particularly to a charging circuit for a secondary battery having a function of determining deterioration.

[0002]

2. Description of the Related Art A secondary battery for backup use is usually
In a standby state, when the supply of commercial power is stopped due to a power failure or the like, a discharging operation is performed to continue power supply to the load.
When the commercial power is restored, the secondary battery is quickly fully charged by the charging circuit. After the full charge, the secondary battery enters the standby operation again to prepare for a power failure. If the secondary battery is left standing during the standby operation, the capacity is reduced due to self-discharge. Therefore, the trickle charge compensates for a decrease in self-discharge capacity during standby.

Since a secondary battery (a nickel-cadmium battery, a nickel-metal hydride battery, etc.) is deteriorated by overcharging, it is desirable to perform trickle charging using a pulse current, and the average value of the pulse current is very small corresponding to the self-discharge amount. Is set so that the current is high. However, even when charging is performed with a pulse current, a reduction in capacity due to deterioration of the secondary battery is inevitable, and it is necessary to perform trickle charging while monitoring the deterioration of the secondary battery.

[0004] A charging method in which the secondary battery is disconnected from the load after full charge and a small current is constantly supplied to compensate for self-discharge is referred to as trickle charging. The trickle charging current may be a very small constant current, but a pulse current that is considered to be less affected by overcharging is recommended.

[0005] As a conventional example showing trickle charging by pulse current, (a) "Twicell sealed nickel-metal hydride storage battery technical data"-Sanyo Electric Co., Ltd. (June 1999)
Monday), (b) “Fast Charge IC” -Be
nchmarq (Data-Book, 1998),
(C) "Rechargeable battery charging method and charging device"
No. 182215.

(A) of the document specifically shows the on / off ratio of the pulse current at the time of trickle charging, and recommends the pulse charging method as a trickle charging method to avoid overcharging. (B) of the document shows a control circuit IC for performing pulse charging and a configuration of a charging circuit using the control circuit IC. In (C) of the document, the amount of heat generated at the end of the life of the secondary battery during rapid charging may be a problem. An invention for changing the on / off ratio is shown.

FIG. 8 is a circuit diagram of a charging circuit for a secondary battery in a conventional example. The charging circuits shown in the materials described above (especially (b) and (c)) are basically the same, and have the configuration shown in FIG. The figure shows a DC / DC converter 1 for converting a charging voltage value, polarity, quality, etc., and a DC / D converter.
A first switch SW1 for turning on / off the output current of the C converter 1, a variable resistor V for adjusting the peak value of the pulse current
R, a secondary battery 2 to be charged, a shunt resistor R (low resistance) for detecting a charging current, and a control circuit 30.

FIG. 9 is a diagram showing a charging current of a secondary battery in a conventional example. The figure shows conceptual diagrams of the quick charging current, the Top-Off charging current, and the trickle charging current shown in FIG. The pulse current during the trickle charge period is set so that the ON period is short and the average current (peak value of pulse current × duty ratio) is extremely small.

FIG. 10 is a flowchart for explaining the operation of a conventional charging circuit for a secondary battery. After the secondary battery 2 is discharged,
This is an operation flow starting from the time when rapid charging is started. [S21] The secondary battery 2 is connected to the charging circuit. [S22] Rapid charging is performed. At the time of rapid charging, a large charging current needs to flow to the secondary battery 2, so that the first switch SW1 keeps the ON state or the switching state in which the ON period is longer than the OFF period. [S23] It is checked whether the full charge of the secondary battery 2 has been detected by the quick charge. Rechargeable battery 2 by fast charging
Is fully charged, the peak voltage, -Δ
This is performed by detecting V, the maximum temperature, the rate of temperature rise and the like. If a full charge is detected, the process proceeds to S24; otherwise, S22
Return to That is, the quick charging operation is performed until the full charge of the secondary battery 2 is detected, and the next operation is performed when the full charge is detected.

[S24] The duty ratio and period of the pulse are changed to perform the finishing (Top-Off) charging. However,
In some cases, the Top-Off charging is omitted and the state immediately shifts to the trickle charging state by the pulse current. [S25] The duty ratio and cycle of the pulse are changed again to perform trickle charging. This trickle charging is performed by loading the secondary battery due to a power failure or a failure of the charging circuit (not shown in FIG. 8,
Usually, the battery is connected in parallel with the secondary battery). [S26] It is checked whether a quick charge signal has been received. If it has been received, the process returns to S22. If not, the process returns to S26. That is, when the secondary battery recovers to a chargeable state after discharging, the charging circuit shifts to the quick charge state, and returns to the starting point of the present flow for quick charging of the secondary battery.

[0011]

However, in a secondary battery for backup use, a trickle charge period corresponding to a standby time is much longer than a charge / discharge period. In the conventional invention, a charging circuit configuration and a charging method during a quick charging period are studied, but little consideration is given to deterioration of a secondary battery during a trickle charging period. As described above, since the conventional charging circuit does not have the function of determining the deterioration of the secondary battery during the trickle charging period, it is not possible to detect that the secondary battery has deteriorated and the capacity has decreased during the trickle charging period. For this reason, it was difficult to predict the backup time in an emergency when the secondary battery actually performs the discharging operation.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the conventional circuit, and has a circuit configuration for determining deterioration of a secondary battery using an off period of trickle charging by a pulse current. It is an object of the present invention to provide a battery charging circuit. In other words, the present invention relates to a deterioration diagnosis circuit for a charging circuit that performs trickle charging using a pulse current, and in particular, has a function of determining deterioration of a secondary battery using a property that a voltage drop at the time of discharge increases as deterioration of the secondary battery progresses. 3 is a charging circuit for a secondary battery.

[0013]

The discharge current of a secondary battery flowing through a discharge current adjusting resistor is controlled by a second switch that is turned on and off during an off period of a first switch that turns on and off a trickle charge current. To adjust. Adjustment of the discharge current of the secondary battery by the second switch is performed based on the deterioration determination of the secondary battery.

Since the first switch for flowing the trickle charge current to the secondary battery operates by detecting the OFF state, the discharge current of the secondary battery is not affected by the charging circuit. The capacity of the secondary battery decreases due to the discharging operation by the second switch, but the amount of reduction in the capacity can be arbitrarily determined by adjusting the ON period of the second switch and the discharge current adjusting resistance. it can. Further, in order to refresh the secondary battery having the memory effect, it is possible to set the average value of the pulse current by the discharge to be larger than the average value of the pulse current by the trickle charge.

During the ON period of the second switch, the discharge current, voltage drop, and temperature of the secondary battery are measured and stored as a database, and the degree of deterioration is compared with the previously measured database of the secondary battery. It can be determined. In order to determine the deterioration of the secondary battery using previously measured data, for example, fitting the voltage drop of the secondary battery as a function of the discharge current and temperature, the measured voltage drop and the voltage drop obtained by the function And means for comparing

Since the deterioration of the secondary battery progresses gradually, by configuring the measurement at every fixed number of pulses of the trickle current, the database held by the CPU becomes small, and the measurement at a low data acquisition speed is performed. Equipment can be used.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to solve the above-mentioned problems, a charging circuit for a secondary battery according to the present invention is a charging circuit for a secondary battery in which trickle charging of the secondary battery is performed with a pulse current. A first switch for turning off, a means for detecting an off period of the first switch, and a second switch for turning on and off during the off period of the first switch, wherein the second switch has a discharge current It is characterized in that it is connected in parallel to the secondary battery via an adjusting resistor. The second switch must be operated to complete on / off during the off period of the first switch.

Further, the charging circuit for a secondary battery according to the present invention includes a discharging current of the secondary battery during an ON period of the second switch and a discharging current of the secondary battery in order to determine the deterioration of the secondary battery. A voltage drop and a function of measuring the temperature of the secondary battery are provided, and a CPU having a storage circuit for sequentially storing the discharge current, the voltage drop, and the temperature is provided. I have. The voltage drop of the secondary battery is greatly affected by the temperature of the secondary battery and the discharge current of the secondary battery. When determining the deterioration of the secondary battery based on the measurement data, it is possible to extract similar data from data measured at the beginning and compare with the measured data to make the determination.

Further, in the charging circuit for a secondary battery according to the present invention, in order to determine the deterioration of the secondary battery with high accuracy, the CPU determines the temperature of the secondary battery or at least one of the discharge current of the secondary battery. Means for correcting a voltage drop, means for appending the output of the correcting means to a storage circuit, and means for comparing the output of the correcting means with an allowable maximum value, and judging deterioration between the standardized data It has special features.

Further, the charging circuit for a secondary battery of the present invention does not need to perform measurement every time trickle charging is completed by a pulse current. For this reason, it has a function of counting the trickle charge pulse of the secondary battery, and discharge current of the secondary battery after applying a specific number of trickle charge pulses, voltage drop of the secondary battery, and It is characterized by measuring the temperature of

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the present invention will be described. FIG.
FIG. 3 is an explanatory diagram illustrating the principle of the present invention. (A)
4 is a graph showing a relationship between an internal resistance and a capacity of a secondary battery (for example, N, KATO, K. YAMAMOTO, "Est
imation of the Capacityof Nickel-Cadmium Batteries
by Measuring Impedance using Electolyte-Deficient
Battery Characteristics ", Proceedings of lNTE
LEC'95, pp. 772-777). This indicates that as the battery deteriorates, the internal resistance increases and the capacity decreases.

(B) shows that a difference occurs in the voltage drop of the secondary battery. That is, since the voltage drop of the secondary battery is proportional to the discharge current of the secondary battery × the internal resistance, a difference occurs in the voltage drop of the secondary battery depending on the state of deterioration.
Therefore, under the situation where the discharge current and the temperature of the secondary battery are the same, the temporal transition of the voltage drop of the secondary battery is stored as data, and the deterioration is obtained by comparing the initially obtained data with the current data. The degree can be determined.

As a simple data correction method,
It is assumed that the voltage drop (Vd) is proportional to the discharge current (I) and is given by the following m-th order polynomial of the temperature (t) as follows. _{Vd / I = a 0 + a} 1 t + a 2 t 2 + ------- + a m t m (1) Vd, when the initial data for the I and t and n pieces acquired, is seeking a ₀ ~a _m For example, Vd at an arbitrary discharge current and temperature in the secondary battery to be measured can be estimated. As a method for obtaining a ₀ ~a _m, least square approximation and Chebishiefu approximation is generally used. Vd (Vds) or Vd / I (Rd) obtained from the equation (1)
s) is compared with the current measurement data, and when the current measurement data exceeds the calculated value of the equation (1) by a certain value or more,
It is determined that the secondary battery has deteriorated.

Instead of obtaining an approximate expression, interpolation is performed through these points from the (n + 1) data obtained in the early stage of use of the secondary battery, and the estimated value (V
ds or Rds). As the interpolation method, Lagrange interpolation or Newton interpolation can be applied.

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a charging circuit for a secondary battery according to a first embodiment of the present invention. FIG.
The same reference numerals denote the same elements, and a description thereof will be omitted. In this embodiment, a variable resistor VR2 for adjusting a discharge current is connected in series with the second switch SW2, and the second switch SW2 is turned on when the first switch SW1 is turned off. In the figure, when the first switch SW1 is turned on and the second switch SW2 is turned on at the same time, the low resistance R1 for charge / discharge current measurement becomes
Due to the influence of the current flowing from the DC / DC converter 1 side of the secondary battery 2, only the discharge current of the secondary battery 2 cannot be accurately measured. Therefore, when the first switch SW1 is turned on, the control circuit 10 supplies the second switch SW2
Provide a mechanism that never turns on. Such a mechanism is realized by the control circuit 10.

FIG. 2 is a diagram showing a configuration of a control circuit according to an embodiment of the present invention. IC 1 for pulse charging in the figure
Reference numeral 1 denotes a function of rapidly charging the secondary battery 2, a function of determining full charge, a function of performing Top-Off charging, a function of performing trickle charging with a pulse current, and a function of displaying a trickle charge mode. Having it is enough. Therefore,
A commercially available charging IC (for example, the aforementioned BENCHMA
RQ BQ2002 series IC) can also be used.

Hereinafter, in FIG. 2, the second switch SW
The mechanism for turning on and off the second 2 will be described in detail. A control signal is output from the pulse charging IC 11 to the first switch SW1. When the pulse charging IC 11 enters the trickle charge mode, it outputs a trickle charge mode signal. Therefore, the AND circuit 12 outputs and inputs an ON signal of the first switch SW1. The output of the AND circuit 12 is the delay circuit 1
4 and the NOT circuit 15 (or the order of the NOT circuit 15 and the delay circuit 14), a signal which is equal to the off period of the first switch SW1 and slightly delayed is obtained.

This signal is input as a clock signal of the counter 16, and when the number of clock signals exceeds a specific number, the counter 16 sets the one-shot multivibrator 1.
7 to the output. As described above, since the leading edge of the counter signal is delayed by the delay circuit 14, the first switch SW
However, the first switch SW1 and the second switch SW2 may be turned on at the same time because the trailing edge overlaps with the next ON signal of the first switch SW1.
Therefore, the one-shot multivibrator 1 is set so that the trailing edge of the signal output from the counter 16 is closer to the leading edge.
At 7, the pulse waveform is shaped. The shaped signal is output as a drive signal for turning on / off the second switch SW2 through the buffer 18. Note that the buffer 18 is a one-shot multivibrator 17 and the second switch S
This is necessary when driving power is insufficient when operating W2.

In FIG. 2, the second switch SW2
Is configured to operate the sampling circuit 19 in synchronization with the drive signal of the above, it is possible to measure the voltage drop, temperature, and discharge current of the secondary battery 2 when the second switch SW2 is turned on. . The measured data is stored in CPU1
3 and are sequentially recorded and, if necessary,
The CPU 13 sends a secondary battery deterioration warning to the outside.

FIG. 3 is a diagram showing an operation timing during trickle charging and a measured current of low resistance in the embodiment of the present invention. (A) shows the operation of the switch, and (b) shows the measured current. That is, it shows the polarity and timing of the charge current and the discharge current during trickle charging as viewed from the secondary battery 2. Mode 1: The charging current is measured while the first switch SW1 is on and the second switch SW2 is off. Mode 2: No current flows during the period when the first switch SW1 is off and the second switch SW2 is off. Mode 3: The discharge current is measured while the first switch SW1 is off and the second switch SW2 is on. Mode 4: No current flows while the first switch SW1 is off and the second switch SW2 is off.

FIG. 4 is a flowchart for explaining the operation of the charging circuit for a secondary battery in the first embodiment of the present invention. 3 is an operation flow when the control circuit 10 of FIG. 2 is applied to the secondary battery charging circuit in the first embodiment of the present invention shown in FIG. [S1] The control signal from the pulse charging IC 11 is output to the first switch SW1. [S2] Is trickle charge mode signal on? If it is on, the process proceeds to S3; otherwise, the process proceeds to S9. [S3] The AND circuit 12 operates. [S4] Delay circuit 14, NOT circuit 15, counter 16
Determines the number of cycles of the trickle charge signal to turn on the second switch SW2.

[S5] Is the cycle of turning on the second switch SW2? If so, proceed to S6, otherwise return to S4. [S6] The counter 16 is reset, and the one-shot multivibrator 17 determines the on / off time width of the second switch SW2. [S7] The synchronous circuit 20 is operated by the ON signal at the same time when the ON / OFF signal is transmitted to the second switch SW2, the gate of the sampling circuit 19 is opened, and the voltage, temperature,
The discharge current is sampled. [S8] The signal received by the sampling circuit 19 is
At U13, processing and an alarm signal are transmitted. [S9] The AND circuit 12 maintains the off state.

(Embodiment 2) FIG. 5 is a circuit diagram of a charging circuit for a secondary battery in a second embodiment of the present invention. As shown in FIG. 1, the charging current and the discharging current may be measured by one low resistance R1 for measuring the charging / discharging current. However, since the pulse width is short for the discharging current measurement, high frequency characteristics are required. There is. In the second embodiment, a low resistance R2 for measuring a discharging current is connected in series with the second switch SW2, and a low resistance R3 for measuring a charging current is separately provided.

FIG. 6 is a flowchart for explaining the operation of the secondary battery charging circuit according to the second embodiment of the present invention. [S11] The secondary battery 2 is connected to the charging circuit. [S12] Rapid charging is performed. [S13] It is checked whether the full charge of the secondary battery 2 has been detected by the quick charge. If detected, proceed to S14,
Otherwise, the process returns to S12. [S14] The duty ratio / period of the pulse is changed to perform finishing (Top-Off) charging. [S15] The duty ratio and cycle of the pulse are changed again to perform trickle charging. [S16] The second switch SW2 is turned on and off while the first switch SW1 is off. [S17] During the ON period of the second switch SW2, the current and voltage of the secondary battery 2 are stored in the storage / detection device. [S18] It is checked whether or not a quick charge signal has been received. If it has been received, the process returns to S12. If not, the process returns to S15.

[0035]

As described above, the present invention has a circuit configuration for judging the deterioration of the secondary battery by using the OFF period of the trickle charge by the pulse current, so that the secondary battery is deteriorated during the trickle charge period. Then, it can be detected that the capacity has decreased. Therefore, it is possible to predict the backup time in an emergency when the secondary battery actually performs the discharging operation.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a charging circuit for a secondary battery according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a control circuit according to an embodiment of the present invention.

FIGS. 3A and 3B are diagrams illustrating an operation timing during trickle charging and a measured current of a low resistance according to the embodiment of the present invention.

FIG. 4 is a flowchart illustrating the operation of a charging circuit for a secondary battery in the first embodiment of the present invention.

FIG. 5 is a circuit diagram of a secondary battery charging circuit according to a second embodiment of the present invention.

FIG. 6 is a flowchart illustrating the operation of a charging circuit for a secondary battery according to a second embodiment of the present invention.

FIGS. 7A and 7B are explanatory diagrams illustrating the principle of the present invention.

FIG. 8 is a circuit diagram of a charging circuit for a secondary battery in a conventional example.

FIG. 9 is a diagram showing a charging current of a secondary battery in a conventional example.

FIG. 10 is a flowchart illustrating the operation of a conventional secondary battery charging circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 DC / DC converter 2 secondary battery 10 control circuit 11 pulse charging IC 12 AND circuit 13 CPU 14 delay circuit 15 NOT circuit 16 counter 17 one-shot multivibrator 18 buffer 19 sampling circuit 20 synchronization circuit 30 control circuit R shunt resistor R1 Low resistance for charge / discharge current measurement R2 Low resistance for discharge current measurement R3 Low resistance for charge current measurement SW1 First switch SW2 Second switch VR Variable resistance VR1 Variable resistance for charge current adjustment VR2 Discharge current adjustment Variable resistor for

Claims (4)

[Claims] A first switch for turning on / off the trickle charging current; a means for detecting an off period of the first switch; ON during the off period of one switch
A charging circuit for a secondary battery, comprising: a second switch for turning off the second switch, wherein the second switch is connected in parallel to the secondary battery via a discharge current adjusting resistor. 2. The secondary battery charging circuit according to claim 1, wherein the secondary switch discharge current, the secondary battery voltage drop, and the secondary battery temperature during the ON period of the second switch. And a CPU having a storage circuit for storing the discharge current, the voltage drop, and the temperature. 3. The device according to claim 1, wherein the CPU corrects the voltage drop based on at least one of a temperature of the secondary battery and a discharge current of the secondary battery, a unit that stores an output of the correction unit in a storage circuit, A charging circuit for a secondary battery, comprising: means for comparing an output of a correction means with an allowable maximum value. 4. The charging circuit for a secondary battery according to claim 2 or 3, wherein the charging circuit has a function of counting trickle charge pulses, and outputs a discharge current of the secondary battery after outputting a specific number of trickle charge pulses. A charging circuit for a secondary battery, comprising: measuring a voltage drop of the secondary battery and a temperature of the secondary battery.