Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a metnod of
operating a secondary battery to recondition the battery, in
which the battery repeats charge and discharge cycles, and more
particularly a method of operating a secondary battery to
recondition the battery in which zinc (Zn) is used as the
negative electrode active material.
Examples of the secondary battery using zinc (Zn) as
the negative electrode active material include a zinc-bromine,
zinc-chlorine, nickel-zinc, air-zinc battery, etc. The
operation of this type of secondary battery to recondition the
battery is effected by a complete discharge method with intent
to completely dissolve the zinc on the negative electrode for
the purpose of increasing the charge and discharge battery
life. With this complete discharge operation, the secondary
battery is discharged until the battery voltage and the load
current are substantially reduced to zero.
However, even if the complete discharge operation is
performed, the zinc on the negative electrode is not completely
dissolved and some of the zinc remains on the negative
electrode. As a result, when the charge of the next cycle is
effected, the zinc is further electrodeposited on the remaining
zinc on the negative electrode. Depending on the conditions,
this electrodeposition of the zinc takes the form of an
abnormal electrodeposition which is called as a dendrite.
Thus, if the abnormal electrodeposition causes the zinc to
extend to the positive electrode this gives rise to a problem
of battery short-circuit. Moreover, where the battery has a
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large size and a large capacity, the above-mentioned complete
discharge operation consumes a large amount of electric po"er
wastefully.
SUMMARY OF THE INVENTIOM
It is an object of the present invention to prevent
the occurrence of any abnormal electrodeposition of zinc during
the charging of a secondary battery.
It is another object of the invention to increase the
charge and discharge cycle life of a secondary battery.
It is still another object of the invention to ensure
efficient use of the electric power of a secondary battery.
The invention is used in a method of operating a
secondary battery to recondition the battery, in which the
battery includes at least one unit cell using zinc as an active
material for a negative electrode in an electrolyte and adapted
to be charged and discharged repeatedly. The invention relates
to the improvement comprising the steps of: discharging the
secondary battery until a voltage of the battery has been
reduced to a predetermined positive value; electrically and
switchably connecting a positive electrode of the battery to a
negative output terminal of a direct current supply means and
connecting a negative electrode of the battery to a positive
output terminal of the direct current supply means; and flowing
a reversed charging current from the negative electrode to the
positive electrode in the electrolyte of the battery from the
direct current supply means until the battery voltage has been
further reduced below a zero value and has reached a
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predetermined negative value, to cause the zinc on tne negative
electrode to be completely dissolved into the electrolyte.
Thus, a reversed charge of a secondary battery is
performed after the completion of its normal discharge. The
reversed charge of the secondary battery is effected by
electrically connecting direct current supply means to the
secondary battery in opposite polarity relation with respect to
each other.
More specifically, the secondary battery subjected to
the reversed charge i5 also subjected to a reversed discharge
operation. ThiS reversed discharge operation is effected bDy
electrically connecting the direct current supply cans to the
secondary battery so that they have the same polarity.
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~3~7
During the reversed charge and discharge, the energy
generated prom the secondary battery is regenerated by means
which is capable of converting the dc power to a stepped-up
ac power.
The above and other objects, features and advantages of
the present invention will become apparent from the
following detailed description taken with the accompanying
drawings.
10 BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a circuit diagram for explaining a
conventional method of operating a secondary battery.
Figs. 2(A) to (C) are waveform diagrams showing the
conventional secondary battery operating method.
Fig. 3 is a circuit diagram for explaining an
embodiment of a method of operating a secondary battery
according to the invention
Fig. 4 shows waveforms useful for explaining the
embodiment of the invention.
Fig. 5 is a circuit diagram for explaining a second
embodiment of the invention.
Fig. 6 shows waveforms useful for explaining the
second embodiment of the invention.
Fig.7 is a circuit diagram showing detailed example of
25 the second embodiment shown in Fig. 5.
Fig. 8 is a circuit diagram showing another detailed
example of the second embodiment shown in Fig. 5.
~3~9~i7
DESCRIPTION OF THE PREFERRED EMBODIMENTS
While the secondary battery operating method of the
present invention is susceptible to numerous pnysical
embodiments, depending upon the environment and requirements of
use, substantial numbers of the herein shown and described
embodiments have been made, tested and used, and all have
performed in an eminently satisfactory manner. Firstly, the
conventional secondary battery operating method ill be
described with reference to Figs. 1 and 2 of the accompanying
drawings
Fig. l shows a circuit for effecting the complete
discharge of a battery stack of secondary cells lO. The
secondary battery lO is connected to a charging and discharging
circuit which is not shown. The charging and discharging
circuit includes a load which is supplied with the power from
the secondary battery 10. In Flg. 1, the secondary battery lO
is electrically connected to a series circuits of a switch 12
and a resistor 14.
Referring now to Fig. 2, there are illustrated
variations in the voltage and current of the secondary battery
10 when its charge, discharge and said complete discharge are
effected. Shown in (C) are the modes of operation of the
secondary battery 10. In Figs. 2(A) to (C), the secondary
battery 10 is charged from a time tl to a time t2 by the
charging and discharging circuit which is not shown. During
the time interval from t2 to t3, the charging and discharging
circuit is openedO During the time interval from t3 to t4, the
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power is supplied to the load from the secondary battery l
through the charging and discharging circuit and the secondary
battery 10 is discharged. During the interval from t4 to t5,
the charging and discharging circuit is again opened.
Then, during the interval from t5 to t6, the complete
discharge of the secondary battery 10 is effected. The s~,Jitsn
12 shown in Fig. 1 is closed first at the time t5. This
operation electrically switcnably connects the positive and
negative electrodes of the secondary battery 10 to the resistor
14 and the complete discharge of the secondary battery 10 is
started. Upon the discharge, the battery voltage is gradually
decreased as shown in Fig. I and also the battery çurrent is
decreased gradually as shown in (B). The battery voltage and
current of the secondary battery 10 become substantially equal
to zero at the time t6. At the time t6, the complete discharge
operation is completed and the charge of the next cycle is
effected.
In the case of a secondary battery using zinc as the
negative electrode active material, generally the zinc deposits
on the negative electrode during the charge and upon the
discharge the zinc on the negative electrode is dissolved into
the electrolyte. When the complete discharge is effected, the
zinc on the negative electrode must be dissolved into the
electrolyte. However, even if the battery voltage of the
secondary battery is reduced to zero as a result of the
complete discharge, some zinc on the negative electrode is not
dissolved completely into the electrolyte. Therefore, when the
charge of the next cycle is effected, the zinc is further
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electrodeposited on the remaining zinc on the negati-le
electrode. If this electrodeposition of the zinc develops to
an abnormal electrodeposition which is called as dendrite, then
the battery is short-circuited finally.
On the other hand, if the complete discharge of a
large-capaci~y secondary battery is effected, a considerable
amount of electric power is wasted.
Referring now to Figs. 3 to 6, a description will be
made of a novel and improved secondary battery operating method
according to the invention which has overcome the foregoing
disadvantages of the conventional operating method.
Fig. 3 shows an exemplary circuit for performing an
operating method according to an embodiment of the invention.
In the Figure, a positive electrode 10P of a battery stack of
secondary cells 10 is electrically connected to a contact 16A
of a switch 16. A negative electrode 10M of the secondary
battery 10 and the other contact 16B of the switch 16 are
electrically connected to a polarity switch 18.
The polarity switch 18 includes contacts 18A, 18B,
18C, 18D, 18E and 18F. With these contacts, the contacts 18A
and 18F are interconnected and the contacts 18C and 18D are
interconnected. The contact 16B of the switch 16 is connected
to each of the contacts 18C and 18D of the polarity switch 18.
The negative electrode 10M of the secondary battery 10 is
connected to each of the contacts 18A and 18F of the polarity
switch 18.
The contact 18B of the polarity switch 18 is
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electrically connected to a negative terminal 20M of a dc po,7er
source 20~ Also, the contact 18E of the polarity switch 18 is
electrically connected to a positive terminal 20P of the dc
power source 20. In the polarity reversing switch 18, the
contact 18B is switchably connected to either of the contacts
18A and 18C. AlSo, the contact 18E is switchably connected to
either of the contacts 18D and 18F. The interconnections of
these contacts are made in an interlocked manner. When the
contact 18B is connected to the contact 18A, the contact 18E is
connected to the contact 18Do Thus, the positive electrode 10P
of the secondary battery 10 is electrically connected to the
positive terminal 20P of the dc power source 20 and the
negative electrode 10M of the secondary battery 10 is
electrically connected to the negative terminal 20M of the dc
power source 20. On the other hand, when the contact 18B of
the polarity switch 18 is connected to the contact 18C the
contact 18E is connected to the contact 18F. Thus, the
positive electrode 10P of the secondary battery 10 is
electrically connected to the negative terminal 20M of the dc
power source 20 and the negative electrode 10M of the
secondary battery 10 is electrically connected to the
positive terminal 20P of the dc power source 20.
It is to be noted that the secondary battery 10 is
electrically connected to a charging and discharging circuit
which is not shown. The charging and discharging circuit
includes a load which is supplied with the power from the
secondary battery 10.
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3 3~
The operating method according to the embodiment ,will
now be described with reference to Fig. 3 as jell as jigs. 4(A~
to (C). Fig. 4(A) shows variations in the battery voltage of
the secondary battery 10 when the operating method of the
embodiment is performed. Shown in (B) are variations in the
battery current of the secondary battery 10 in the similar
case. Also, shown in (C) are the modes of operation in the
similar case.
The charge of the secondary battery 10 is effected
first during the interval from tlo to tll in Fig. 4. This
charge is effected with a constant voltage and current by the
charging and discharging circuit which is not shown. Note that
the polarity switch 18 shown in Fig. 3 is open. During the
interval from tll to tl2, the charging and discharging circuit
is opened. In this period, the battery voltage ev of the
secondary battery 10 is lower slightly than the battery
charging voltage value es.
Then, during the interval from tl2 to tl3, the
secondary battery 10 is discharged by the charging and
discharging circuit which is not shown. In this period, the
discharging current flows constantly throughout the period, the
discharging voltage remains essentially constant untll the
final stage of the period and then decreases gradually in a
small amount, and the power is supplied to the load. This
discharging voltage is lower than the open battery voltage ev
of the secondary batter 10. Note that the direction of the
battery current IL flowing upon the discharge is opposite to
the current flowing upon the charge.
8 --
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8~
Then, during the interval from tl3 to tl4, the
discharge is terminated and the charging and discnarging
circuit is again opened. In this period, the open battery
voltage en of the secondary battery 10 reaches gradually to a
voltage level corresponding to the open battery voltage value
at the open circuit period from tll to tl2 after the charging
operation.
Then, during the interval from tl4 to tl5, the
reversed charge of the secondary battery 10 is effected.
Firstly, at the time tl4, the contact 18B of the
polarity switch 18 is connected to the contact 18C and the
contact 18E is connected to the contact 18F. Then, the switch
16 is closed. As a result of these switch operations, the
positive electrode 10P of the secondary battery 10 is
electrically connected to the negative terminal 20M of the dc
power source 20 and the negative electrode 10M of the secondary
battery 10 is electrically connected to the positive terminal
20P of the dc power source 20. Thus r the reversed charge of
the secondary battery 10 is effected. When the reversed charge
is effected, the battery voltage ev of the secondary battery 10
is decreased gradually and it is eventually reversed in
polarity. On the other hand, the battery current IL f the
secondary battery 10 flows constantly in the same direction as
in the case of the discharge during the interval from tl2 to
tl3
At the time tl5, the battery voltage ev of the
secondary battery 10 becomes a predetermined negative voltage
_ g _
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--el as shown in Fig. 4(A). At this time, the polarity s"itch
18 is operated thereby reversing the polarity of the dc power
source 20 connected to the secondary battery 10. As a result
of this operation, the contact 18B of the polarity switch 18 is
connected to the contact 18A and the contact 18E is connected
to the contact 18Do Thus, the positive electrode 10P of the
secondary battery 10 is electrically connected to the positive
terminal 20P of the dc power source 20 and the negative
electrode 10M of the secondary battery 10 is electrically
connected to the negative terminal 20M of the dc power source
20. As a result of this operation, the reversed discharge of
the secondary battery 10 is effected starting at the time tl5.
When the reversed discharge is effected, the battery voltage ev
of the secondary battery 10 is gradually increased from the
negative voltage -el to approach zero and then it is eventually
reversed and restored to the original polarity. On the other
hand, the battery current IL of the secondary battery 10 flows
constantly in the same direction as in the case of the charging
during the interval from tlo to tll.
At the time tl6, the battery voltage ev of the
secondary battery 10 reaches the initial voltage es at the end
of the charging at the time tll as shown in Fig. 4(A~. At this
time, the switch 16 is opened and then the open battery voltage
decreases slightly. The open circuit of the secondary battery
10 by this operation is continued up to a time tl7, the
essential normal charge is effected by the charging and
discharging circuit which is not shown.
-- 10 --
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38~
As described hereinabove, in this embodiment tne
reversed charge of the secondary battery 10 is effected after
the termination of its normal discharge. This reversed charge
reverses the polarities of the electrodes lOP and lOM of the
secondary battery 10. As a result, the zinc remaining on each
negative electrode of the battery stack of secondary cells 10
upon the termination of the normal discharge at the time tl3 is
completely dissolved into the electrolyte by the reversed
charge. Thereafter, the reversed discharge is effected and the
secondary battery 10 is restored to the normal polarity and
state.
It is to be noted that in accordance with the present
embodiment the open-circuit mode (tl6 to tl7) exists between
the reversed discharge mode and the normal charge mode as shown
in Fig. 4(C). However, this open-circuit mode is not
especially required at all times. Therefore, it is possible to
arrange so that the normal charge of the secondary battery 10
is started at the time tl6. Also, where an electrolyte
circulation type battery stack of secondary cells is operated,
the electrolyte circulating pumps may be stopped during the
operation in the reversed charge mode and the reversed
discharge mode, respectively. If the electrolyte circulating
pumps are stopped, the electrolytes in each unit cell of the
secondary battery 10 are made stationary. For example, the
eIectrolyte circulating pumps which are not shown are stopped
at the time tl4 in Fig. 4 and the operation of the pumps is
restarted at the time tl7. The reversed charge and discharge
operations may be performed for every normal charge and
discharge cycle of the secondary battery 10 or at intervals of
-- 11 --
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several cycles.
Enumerated below are the results of the tests made 'oy
applying the operating method of the above-mentioned embodiment
to zinc-bromine battery (battery stack of 24 bipolar secondary
cells having each effective electrode area of 750 cm2 and
subject to an 8-ho~lr charge with a charging current of 15A and
an average charging voltage of 46.5 V and then to a discharge
with a discharging current of 13A until the battery voltage
decreasing to 24V) and the results obtained were satisfactory
in all the cases.
(1) After the discharge, the reversed charge was started with
the battery current of 5A. When the battery voltage reached
-~4V at the expiration of about 120 minutes, the secondary
battery was disassembled and the negative electrode surfaces
were observed showing that the zinc on the whole electrode
surfaces was dissolved completely.
(2) After the discharge, the reversed charge was started with
the battery current of 5A, and then the reversed discharge was
effected with the battery current of 5A when the battery
voltage reached -24V. Then, after the battery voltage had
reached +24V, the normal charge was effected
- 12 -
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with the battery current of lSA for 8 hours and the
secondary battery was disassembled. The observation of the
conditions of the electrodeposited zinc on the whole
negative electrode surfaces showed that the zinc was
5 electrodeposited uniformly and that there was no abnormal
electrodeposition.
(3) In the case of the above (2) where the electrolyte
circulating pumps were stopped during the reversed charge
and the reversed discharge, it was found that the time
10 required for the battery voltage to reach - 24V ,during the
reversed charge was reduced by about 50 minutes. Note that
the time required for the battery voltage to reach +24V
during the reversed discharge was conversely increased by
above 5 minutes.
15 (4) Where the normal charge and discharge were effected with
a battery current density of 20 mA/cm2, the relationship
between the battery current density (the reversed charging
current density) auring the reversed charge and the battery
voltage at the end of the reversed charge (the final
20 reversed charge voltage) showed the proper per-unit-cell
values as shown in Table 1.
Table 1
Reversed charging Final reversed charye
current density voltage
20 m~/cm2 -1.5 V or less
10 mA/cm -1.0 V or less
5 mA/cm -1.0 V or less
(5) In the case of a battery system composed of a plurality
of secondary batteries, the secondary battery which has been
subjected to the norMal discharge may be used as a dc power
source for reversed charging and discharging purposes so as
to improve the energy efficiency of the battery system on
the whole. This type of system is well suited for use as
standard battery system for electric power storing means.
Next, a second embodiment of the invention will be described
with reference to Figs. 5 and 6~
Fig. 5 shows an exemplary circuit for performing an
operating method according to the second embodiment of the
invention. In the Figure, a secondary battery 10 is elec-
trically connected to an ac-dc converter circuit 22 including
a step-up and step-down circuit (hereinafter simply referred
to as ac-dc converter circuit). The ac-dc converter circuit
22 is also electrically connected to a series circuit of a
switch 24 and an ac power source 26~
Electrically connected to the ac-dc converter circuit 22 is
a battery voltage detecting circuit 28, a battery current de-
tecting circuit 30 and a control circuit 32. The control
-- l --
jrc:eh~
-
circuit 32 controls the operation of the ac-dc converter
circuit 22 in accordance with the detection signals from the
battery voltage detecting circuit 28 and -the battery current
detecting circuit 30.
Next, the operating method according to the second
embodiment will be described with reference to Fig. 5 and
Figs. 6(A) to (C). Figs. 6(A) to (C) show the battery
voltage ev and the battery current IL of the secondary
battery 10 during its operation and the modes of operation
as in the case of Fig. 4.
Firstly, during the interval from t20 to t21 in Fig. 6,
the switch 24 is closed and the charge of the secondary
battery 10 is effected. The ac power from the ac power
source 26 is converted to a dc power by the ac-dc converter
circuit 22. The charge of the secondary battery 10 is effected
by this dc power. The charging voltage and the charging
current during the charge are respectively detected by the
battery voltage detecting circuit 28 and the battery current
detecting circuit 30. In response to the detection signals,
the control circuit 32 controls the ac-dc converter circuit
22. This control maintains the charging voltage and the
charging current at the desired values as shown in Figs.
6(A) and (B), respectively.
During the interval from t21 to t22, the switch 24 is
opened and an open~curcuit condition is established. It
is to be noted that this open-circuit mode is not always
required.
jrc~
Then, during the interval from t22 to t23, thP s~7itch
24 is again closed and the secondary battery 10 is dis-
charged. The dc power from the secondary battery 10 is
stepped-up and converted to an ac power by the ac-dc con-
verter circuit 22. Alternatively, the dc power is converted
to an ac power and then stepped-up.
Thus stepped-up ac power is returned to the ac power
source 26 or regenerated. The current flowing to the ac
power source 26 during the discharge is detected by the
battery current detecting circuit 30. In response to the
detection signal, the control circuit 32 controls the ac-dc
converter circuit 22. As a result of this control, the
current flowing to the ac power source 26 is controlled at
the desired value.
During the interval from t23 to t24, the switch 24 is
again opened and the open-circuit state is established.
Then, during the interval from t24 to t26, the reversed
charge of the secondary battery 10 is effected. In this
reversed charge mode, the battery ac-dc converter circuit 22
is electrically connected to the secondary battery 10 in
opposite polarity relation with each other. In other words,
the secondary battery 10 and the ac-dc converter circuit 22
are electrically connected opposite in polarity to the con-
nections during the charge in the interyal from t20 to t21
As a result of this reversed charge, the battery voltage ev f
the secondary battery 10 is decreased gradually and eventually
its polarity isreversed. On the other hand, the battery cur-
rent IL of the secondary battery 10 flows constantly in the same
- 16 -
jrc:~t
~8~7
direction as in the case of the discharge during the
interval from t22 to t23. At this time, the battery
voltage ev of the secondary battery 10 is detected by
the battery voltage detecting circuit 28 and its detection
signal is applied to the control circuit 32. Then, the
control circuit 32 controls the ac-dc converter circuit
22 in the following manner. Pirstly, the ac-dc converter
circuit 22 is controlled in such a manner that the dc
power from the secondary battery 10 is converted to a
stepped-up ac power until the battery voltage ev is
reduced to zero (the interval from t24 to t25). By
virtue of this control, the energy from the secondary
battery 10 is regenerated or returned to the ac power
source 26. Then, the ac-dc converter circuit 22 is
controlled in such a manner that the ac power from the
ac power source 26 is converted to a dc power until the
battery voltage ev reaches a predetermined negative
voltage - e2 (the interval from t25 to t26). As a
result of this control, the reversed-polarity charge of
the secondary battery 10 is effected with the energy from
the ac power source 26.
Then, during the interval from t26 to t28, the
reversed discharge of the secondary battery 10 is effected.
In this reversed discharge mode, the terminal connections
between the ac-dc converter circuit 22 and the secondary
battery 10 are electrically interchanged. In other words,
the secondary battery 10 and the ac-dc converter circuit 22
are electrically connected in the same polarity relation
as in the case of the charge during the interval from
t20 to t21. As a result of this reversed
- 17 -
, . f
~389~
discharge, the battery voltage ev of the secondary battery
10 is gradually increased from the negative voltage -e2
toward zero and it is eventually reversed to restore the
original polarity. On the other hand, the battery current
5 IL flows constantly in the same direction as in the case of
the charge during the interval from t20 to t2l. At this
time, the battery voltage ev of the secondary battery 10 is
detected by the battery voltage detecting circuit 28 and its
detection signal is supplied to the control circuit 32.
10 Then, the control circuit 32 controls the ac-dc converter
circuit 22 in the following manner. Firstly, the ac-dc
converter circuit 22 is controlled in such a manner that the
dc power from the secondary battery 10 is converted to a
stepped-up ac power until the battery voltage ev is
15 increased from the negative voltage -e2 to zero (the
interval from t26 to t27). As a result of this control, the
energy from the secondary battery 10 is xeturned to the ac
power source 26. Then, the ac-dc converter circuit 22 is
controlled in such a manner that the ac power from the ac
20 power source 26 is converted to a dc power until the battery
voltage ev is increased from xero to reach a normal-polarity
present voltage eT (the interval from t27 to t28 ) As a
result of this control, the normal charge of the secondary
battery 10 is effected by the energy from the ac power
25 source 26.
Then, at the time t28, the battery voltage ev of the
secondary battery 10 is restored to the original voltage eT
as shown in Fig. 6(A). At this time, the switch 24 is
- 18 -
~L~3~39~
opened. The open-circuit condition of the secondary
battery 10 by this operation is continued up to a time
t29. Then, at the time t29, the switch 24 is again
closed and the essential normal charge is effected.
Fig. 7 shows a detailed example of the embodiment
shown in Fig. 5. In Fig. 7, the ac-dc converter cir-
cuit 22 includes first and second converters 22A and
! 22B, a step-up clrruit 22C and dc reactor 22D. Of
these component parts, each of the converters 22A and
22B comprises switching elemen-ts such as thyristors or
transistors arranged in a three-phase bridge connection.
This connection is generally referred to as a thyristor
Ward-Leonard type. The first and second converters 22A
and 22B are electrically connected so that they are
opposite in polarity to each other, that is, they are
arranged in an inverse parallel connection. The convert-
ers 22A and 22B are electrically connected tothe ac power
source 26, In this emhodiment, the ac power source 26
comprises a three-phase power source.
The battery voltage detecting circuit 30 includes
current transformers 30A and a converter 30B. The current
transformers 30A are each proyided in a line for supplying
the three-phase ac current to the ac-dc converter circuit
22. Each current transformer 30A detects the current
f lowing in the supply line. In other words, a current
proportional to the current flowing in the three-phase ac
supply line is supplied to the converter 30B from each
current transformer 30A. The converter 30B converts the
-- 19 --
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~,,23~9L~71 ""' " ': '
value of the applied current to a form suitable for the
control by the control circuit 32 and applles the resulting
detection signal to the control circuit 32.
The control circuit 32 includes setting means 32A, a
S battery voltage controlling amplifier 32B~ a battery current
controlling amplifier 32C, a gate controller 32D and signal
generator 32E. Of these component parts, the setting.means
32A is provided to preset a desired charged voltage value of
the secondary battery lO. A suitable voltage is applied to
lO a terminal 32F and this voltage is divided by a variable
resistor thereby presetting the desired charged voltage
value. This desired charged voltage value is applied to
comparing means 32G. Also applied to the comparing means
32G is the detected value of the battery voltage generated
15 from the battery voltage detecting circuit 28. The detected
value and the desired charged voltage value are compared by
the comparing means 32G and the difference between the two
is applied to the battery voltage controlling amplifier 32B.
Then, the battery voltage control.ling amplifier 32B applies
20 its output to comparing means 32H. Also applied to the
comparing means 32H i5 the detection signal generated from
the converter 30B of the battery current detecting circuit
30. The comparing means 32H compares the inputs and the
resuI~ing difference is applied to the battery current
25 controlling amplifier 32C. Then, the battery current
controlling amplifier 32C applies its output to the gate
controller 32Do The gate controller 32D applies a gate
controlling signal or a gate signal to each of the
20 -
converters 22A and 22B. The generation of the gate signals
is controlled in accordance with the output from the signal
generator 32E. More specifically, the phase of the gate
signal i5 changed to effect the mode switching between the
S forward conversion and the inverse conversion operation of
the converters 22A and 22B, respectively. In addition, the
stopping of the conversion operations, etc., are also
effected.
The operation of the apparatus shown in Fig. 7 will now
10 be described. This operation corresponds to a case where
the operation shown in Fig. 6 is performed. Assume first
that the gate signal generated from the gate controller 32D
is controlled in accordance with the command generated from
the signal generator 32E thus bringing the converter 22A
15 into the forward conversion operation. As a result of the
forward conversion operation, the ac power~converted to a dc
power and the secondary battery 10 is charged. This period
of operation corresponds to the interval between the times
t20 and t2l. During this interval, the battery voltage of
20 the secondary battery lO is compared with the desired
charged voltage value by the comparing means 32G. The
difference between the battery voltage and the desired
charged voltage value is amplified by the battery voltage
controlling amplifier 32B and it is then applied to the
25 comparing means 32H. The comparing means 32H compares the
applied difference signal with the detection signal from the
battery current detecting circuit 30. The difference
between the battery voltage and the detection signal from
- 21 -
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the battery current detecting circuit 30 is amplified by the
battery current controlling amplifier 32c and then applied
to the gate controller 32D. The applied difference signal
controls the phase of a gate signal generated from the gate
5 controller 32D. This control is effected so that the
battery voltage of the secondary battery 10 attains the
desired charged voltage value.
Thus, as shown in the interval from t20 to t21 in Fig. 6,
the secondary battery 10 is charged with a constant charging
10 voltage and constant charging current.
Then, at the time t21, the signal generator 32F applies
an open-circuit command or the converter 22A to the gate
controller 32D. This stops the application of the gate
signal to he converter 22A by the gate controller 32D. As
15 a result, the operation of the converter 22A is stopped.
Then, at the time t22, the signal generator 32E applies an
inverse conversion operation command or the converter 22B
to the gate controller 32D. Thus, the gate controller 32D
applies a gate signal to the converter 22B. When this
20 occurs, the converter 22B starts its inverse conversion
operation and the dc power from the secondary battery 10 is
converted to an ac power. The converted ac power is sent
back to the power source.
Then, at the time t23, the signal generator 32E applies
25 an open-circuit command for the converter 22B ,to the gate
controller 32D. This stops the application of the gate
signal to the converter 22B by the gate controller 32D. As
a result, the operation of the converter 22B is stopped.
- 22 -
3~3g~
Then, at the time t24, the signal generator 32E applies a
forward conversion operation command for the converter 22B
to the gate controller 32D~ Thus, the gate controller 32D
applies a gate signal to the converter 22Bo
5 This gate signal differs in phase from the gate signal
generated during the interval from t22 to t23. In other
words, during the interval from t22 to t23 the control angle
is a lead angle and the converter 22B iS controlled
correspondingly. On the other hand, during the interval
10 from t24 and on, the control angle is a lag angle thus
correspondingly controiling the converter 22B~ As a result
of the forward conversion operation of the converter 22B~
the reversed charge of the secondary ba-ttery 10 is effected.
Then, when the battery voltage of the secondary battery
15 10 becomes -e2 at the time t26, the signal generator 32E
applies an open-circuit command for the converter 22B to the
gate controller 32D~ At this time, the signal generator 32E
also applies an operation command for the converter 22A to
the gate controller 32D~ Consequently, the operation of the
20 converter 22B is stopped and at the same time the operation
of the converter 22A is started thus starting the reversed
discharge of the second battery 10. Then, as the time t28
is reached, the operation of the converter 22A is stopped
in response to the command from the signal generator 32E~
25 Note that the above-mentioned operations are repeated on and
after the time t29.
23
Fig. 8 shows another detailed example o the embodiment
shown in Fig. 5. In Fig. 8, the ac-dc converter circuit 22
comprises a thyristor Ward-Leonard section 220, a step-up
circuit 222 and a change-over switch section 224. The
S thyristor Ward-Leonard section 220 includes converters 220A
and 220B arranged in an inverse parallel connection. In
this apparatus, the converter 220B operates in a different
manner from that of the apparatus shown in Fig. 7. More
specifically, the converter 220B performs only the inverse
10 conversion operation and no forward conversion operation is
performed. During the reversed charging of the secondary
battery 10, the polarity change-over by the change-over
switch section 224 is efected and therefore the forward
conversion operation of the converter 220B is not required.
lS The change-over switch section 224 is controlled by a
switching controller 34.
The step-up circuit 222 is of the known type disclosed
in Japanese Patent No. Publication No. 55-49519. Now
beginning with a description of the step-up circuit 222, a
20 thyristor 222B which is in inverse parallel connection with
a diode 222A is connected in series between dc reactors 220C
and 222C. The thyristor 222B is connected with a polarity
such that a current flows to the secondary battery 10 from
the converters 220A and 220B, respectively. Connected to
25 the cathode of the thyristor 222B is a thyristor 222E which
is in inverse parallel connection with a diode 222D. The
- 24 -
~3~g,~7
thyrlstor 222E is connected such that its anode is connected
to the cathode of the thyristor 222B. The step-up circuit
~22 is controlled by a step-up controller 36.
The construction of the step-up controller 36 is
5 substantially the same with the construction of the control
circuit 32 shown in F.ig. 7. The step-up controller 36
includes setting means 36A, a voltage controlling amplifier
36B, a current controlling amplifier 36C, a gate controller
36D and a signal generator 36E. A suitable voltage is
10 applied to the setting means 36A from a terminal 36F. The
step-up controller 36 also includes comparing means 36G and
36H, a voltage detector 36I and a current detector 36J. The
voltage detector 36I and the current detector 36~
respectively detect the battery voltage and the battery
15 current ox the secondary battery 10.
The control of the step-up circuit 222 by the step-up
controller 36 will now be described briefly. This control
is effected by controlling the duration in each of the
alternately interchanging ON period and OFF period of gate
20 signals which are applied to the thyristors 222B and 222E
from the gate controller 36D in accordance with the command
of said signal generator 36E.
Specifically, with the thyristor 222B ON, the current
flows through the converter 220A, the dc reactor 220C, the
25 thyristor 222B, the dc reactor 222C and the secondary
battery 10 sequentially. Under this condition, when the
thyristor 222B is turned OFF, and ON gate signal is applied
to the thyristor 222E (even in this case, the thyristor 222E
- 25 -
~38~7 -- -
remains in OFF state, as will be described later), a high
voltage of reverse polarity against the polarity shown in
Fig. 8 is generated across both ends of dc reactor 222C due
to the fact that the current flowing into the dc reactor
5 222C tends to keep flowing in the same direction. This
reverse voltage causes the current to flow through a loop
formed with the dc reactor 222C, the secondary battery 10
and the diode 222D. At this moment, a voltage drop occurs
across both ends of said diode 222D. Since this dropped
10 voltage has a reverse polarity in relation to the thyristor
222E, the thyristor 222E remains in OFF state no matter
whether ON gate signal is applied thereto.
Next, the current slowing through the diode 222D will
not be vanlshed rapidly, but will be reduced gradually to
lS zero as time passes, depending on the amoun-t ox energy
stored in the dc reactor 222C ,and the terminal voltage of
the secondary battery 10. At the zero level, the current
will then flow reversely through a loop formed with the
secondary battery 10, the dc reactor 222C and the thyristor
20 222E.
Then, when the thyristor 222E is turned OFF and ON gate
signal is applied to the thyristor 222B (even in this case,
the thyristor 222B remains in OFF state), the current
flowing through the thyristor 222E is cut off, with the
25 result that, similarly as mentioned above a high voltage of
same polarity against the polarity shown in Fig. 8 is
generated across both ends of the dc reactor 222C ,and
causes the current to flow through a loop formed with the dc
- 26 -
~L~3~
reactor 222C, the diode 222A, the dc reactor 220C, the
converter 220B and the secondary battery 10. This current
is reduced gradually to zero as time passes, and when the
thyristor 222B is turned ON, the current flows in the
5 reverse direction.
In this manner, the thyristors 222B and 222E will
repeat their respective ON-OFF operation alternately.
During this ON-OFF repetitious operation, if the ON or OFF
period of the thyristor 222B, for instance, is equal to the
10 OFF period of the thyristor 222E, the mean value of the
current (id) flowing through the dc reactor 222C is null,
but if the ON period of the thyristor 222E is longer than
that oE the thyristor 222B, the mean value of the current
(id) becomes a negative value, in which case the current
lS flows from the secondary battery side to the diode 222A
side. Accordingly, in the case of the negative mean value
of current rid), the electric power is transferred from the
secondary battery side to the converter 220B side, whereby
the power regeneration is effected to the AC power source
20 by means of the converter 220B.
.
The following Table 2 shows the ON states of the
converters 220A and 220B, the diodes 222A and 222D, the
thyristors 222B and 222~ and the change-over switch section
25 224 during the respective operating modes shown in Fig. 6.
- 27 -
~3~3g'~'
As described hereinabove, in accordance with the
second embodiment the ac-dc converter circuit 22 is controlled
such that after the normal discharge of the secondary battery
has been effected, the reversed charge of the secondary
battery 10 is effected. Thus, the zinc remaining on each
negative electrode of the battery stack of secondary cells 10
after the normal discharge is completely dissolved into the
electrolyte by virtue of the reversed charge.
It is to be noted that in accordance with the second
embodiment the use of the open-circuit condition during the
interval from t28 to t2g is arbitrary. Also, in the case of an
electrolyte circulation-type battery stack of secondary cells,
electrolyte circulating pumps are also stopped as previously
during the reversed charge and the reversed discharge. In the
second embodiment, the reversed charge and discharge operations
may be performed for every charge and discharge cycle of the
secondary battery 10 or at intervals of several cycles.
Then, enumerated below are the results ox the tests
made by applying the operating method oE the above-mentioned
second embodiment to zinc-bromine battery (battery stack of 24
bipolar secondary cells having each effective electrode area of
750 cm2 and subjected to an 8-hour charge with a charging
current of 15A and average charging voltage of 46.5V and then
to a discharge with a discharge current of 13A until the
battery voltage decreasing to 24V) and the satisfactory results
were obtained in all the cases. It is to be noted that in the
tests, the voltage of the ac power
- 29 -
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. . .
N N
N O b
m
q N
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S q N N
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: 5 N N
h
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-- 28
source 26 was 200V and the ac-dc converter circuit 22
comprised an inverse-parallel connected circuit of a step-up
circuit and a thyristor rheonade as disclosed in Japanese
Patent Publication No. 55-49519. Also, the battery current
S detecting circuit 30 detects the currents corresponding to
the charging and discharging dc current values in the form
of alternating currents.
(1) After the discharge, the reversed charge was
started with the battery current of 5A so that upon the
10 battery voltage reaching-24v at the expiration of about 120
minutes the secondary battery was disassembled and the
negative electrode surfaces were observed showing that the
zinc on the whole surfaces was completely dissolved.
~2) After the discharge, the reversed charge was started
15 with the battery current of SA and the reversed discharge
was effected with the battery current of SA upon the battery
voltage reaching -24V. Then, after the battery voltage had
reached +24V, the normal charge was effected with the
, .
battery current of 15A for 8 hours and the secondary battery
20 was disassembled. The observation of the electrodeposited
zinc on the whole negative electrode surfaces showed that
the electrodeposition was uniform and that there was no
abnormal electrodeposition.
(3) The measurement of the amounts of electric power in
25 terms of ac current in the reversed charge mode and the
reversed discharge mode showed the results as shown in Table
3 and ultimately the power of 25.4 Wh was regenerated by
both of the reversed charge and discharge modes.
_ 39 _
~Z3~39~'7
Table 3
Regeneration Driving
5 Reversed charge mode 71 Wh 42 Wh
Reversed discharge mode ~.4 Wh 6 Wh
From the foregoing it will be seen that in accordance
with the second embodiment the energy stored in the
secondary battery is regenerated or returned to the ac power
source even in the reversed charge and discharge modes and
efective utilizatlon of the energy is ensured.
As described hereinabove, the secondary battery
operating method o this invention has the effect of
satisfactorily preventing the occurrence of abnormal
electrodeposition of zinc and increasing the charge and
discharge cycle life of secondary batteries.
As Malay apparently widely different embodiments of this
invention may be made without departing from the spirit and
scope thereof, it is to be understood that the present
invention is not limited to the specifl~ embodiments
thereof except as defined in the appended claims.
- 3~ -
