Electricity: battery or capacitor charging or discharging – Battery or cell charging – With thermal condition detection
Reexamination Certificate
2002-11-20
2004-01-13
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
With thermal condition detection
Reexamination Certificate
active
06677731
ABSTRACT:
FIELD OF THE INVENTION AND PRIOR ART
The present invention is related to a method and device for charging a battery and, more particularly, to a method and device for dynamically varying a current limit value for battery charging current.
First of all, it is pointed out that “the alternating current source” herein is to be given a very broad sense and may for instance be an alternating current net, but also be formed by converting electric energy from a direct current supplying arrangement, such as a direct voltage net, into an alternating voltage, so that the “alternating current source” is used as a summary for all types of configurations, which are adapted to supply an alternating current on the input of said rectifier.
A device of this kind may be used for charging all kinds of batteries, but to clearly illustrate the problems the invention tries to solve, such a device for charging a battery onboard a railway vehicle for electrified railway traffic will be explained hereinafter, but thus not at all for the purpose of limiting the invention. Such a battery onboard a railway vehicle is in most cases used especially to give an extra energy addition when starting the vehicle, but also to feed for example computers and lighting equipment in the vehicle. The alternating current consumer, which is fed in parallel with the battery, may be for instance fans, main compressors, lighting equipment etc in the vehicle or cars connected thereto. The electric energy is normally obtained by the vehicle taking, from a contact line
1
(see FIG.
1
), electric energy, for instance in the form of an alternating voltage, which in Sweden normally is a single phase alternating voltage with a frequency of 16⅔ Hz, and that this via a rectifier not shown is converted into a direct voltage, of for instance about 750 V, which is then brought to a converter in the form of an inverter
2
, where it is converted into an alternating voltage. The level of this alternating voltage is then changed by a transformer
3
, from which the alternating voltage is fed further to consumers
4
of the kind mentioned. At the same time, a part of the alternating voltage is taken into a converter in the form of a rectifier
5
, which rectifies the voltage and, at a higher voltage on its output
6
than the voltage of a battery
7
, sends a charging current thereto for charging thereof. Said converters are preferably formed by current valves connected in series, each having at least one switch in the form of a semiconductor element and a rectifying diode connected in anti-parallel therewith controlled in a conventional manner according to a pulse width modulation pattern as in the embodiment shown in
FIG. 2
or as non-controlled rectifiers, e.g. diode rectifiers, as in the embodiment according to FIG.
1
.
From the contact line
1
, the engine of the vehicle obtains electric energy also in parallel with the shown device, preferably by a not shown converter.
The charging current to the battery can be measured by schematically indicated members
8
, whereas the voltage of the battery can be measured by members
9
. The measurement values obtained in this manner are used for controlling the output voltage of the rectifier
5
and thereby the charging current to the battery
7
. When the output voltage on the output
6
exceeds the voltage of the battery, the battery will be charged by the coil
10
. The device also has an arrangement
11
adapted to control the voltage on the output of the rectifier based on information about a comparison of the measured charging current with a current limit value and decrease it if the measured current exceeds the current limit value for reduction of the charging current. This takes place at a device of the kind shown in
FIG. 1
by controlling the inverter
2
so that a suitable voltage level is obtained on its output. However, this has the disadvantage that when the voltage to the rectifier
5
has to be decreased, the level of the voltage to the consumers
4
will then be reduced automatically.
FIG. 2
shows a variant of the device according to
FIG. 1
, at which said arrangement
11
controls the rectifier instead, so that the feed to the battery and that to the consumers practically become independent of each other.
In
FIG. 3
it is shown somewhat more in detail how the arrangement
11
of a device of this kind may function. The value of the measured charging current arrives at
12
and its negative value is added in an addition member
13
to a current limit value arriving at
14
. If the addition in
13
, which in practice is a comparison of the charging current with a current limit value, which the charging current should not exceed to prevent triggering of overcurrent protection and stopping the operation of the entire device according to
FIGS. 1 and 2
with interruption of the feed of electric energy to said consumers
4
as well as to the battery as a result, gives a negative value on the input
15
to a member
16
, a reference voltage value for the voltage on the output
6
of the rectifier is output on the output of said member, and is then made lower than a predetermined voltage value input to the member
16
at
17
. However, should the value of the charging current be lower than said current limit value, then the reference voltage input at
17
would also be output at
18
. At
19
, the battery voltage multiplied by −1 is input to an addition member
20
, which inputs the result of the addition to a member
21
, which at a lower reference voltage than battery voltage sends signals to a control unit
22
, which in the device according to
FIG. 1
controls the inverter
2
as concerns voltage peak value and in the device according to
FIG. 2
controls the rectifier
5
as concerns voltage peak value. If the battery voltage is higher than the reference voltage at
18
, said voltage peak value and thereby the voltage out of the rectifier and thereby finally the charging current to the battery are reduced.
In
FIG. 4
it is schematically shown what could happen if the level of the voltage into the rectifier suddenly decreases, for instance due to a large power output from a consumer when starting the same. It is schematically illustrated how the output voltage U
6
varies over time, U
B
being the battery voltage. Furthermore, the charging current I
B
is drawn and said current limit value I
B
,lim is drawn with a broken line over time. It is apparent that when the output voltage from the rectifier decreases below the battery voltage, the charging current is lowered to 0, but when said output voltage then rises again above the battery voltage, the result due to the low internal resistance in the battery will be a very steep rise of the charging current, which often leads to a very large overshoot of the charging current. This implies that the charging current passes the current limit value and the arrangement
11
performs a control in the manner shown in
FIG. 3
to lower the charging current below this value. However, the current overshoot is at times so large that over-current protection manages to trigger to prevent damages to transformers and diodes, so that the entire device is shut off with significant problems as a result. It is pointed out that voltage drops with corresponding problems as a result also can arise on the load side of the battery, where also large loads may occur.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a device and a method of the initially defined kind, which find a remedy for the above mentioned problems with risk for triggering over-current protection upon suddenly rising output voltage from the rectifier. This object is obtained according to the invention by providing such a device with a unit adapted to form said current limit value by comparing a current value formed by the value of said measured charging current with a restriction on its positive rise speed with a predetermined maximum current limit value, and to determine the lowest of the so obtained current value and said maximum current limi
Bombardier Transportation GmbH
Howrey Simon Arnold & White
Tso Edward H.
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