Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2001-02-28
2002-01-08
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S132000, C310S315000, C361S025000
Reexamination Certificate
active
06338026
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for limiting an electric current through an electrical component, in particular an electrical winding, and a limiting apparatus by means of which an electric current through an electrical component can be limited.
Johncock (U.S. Pat. No. 5,321,308) is based on control of the field current through the rotor winding of a generator. The temperature of the rotor is calculated with the aid of the field current and the electrical resistance of the rotor winding. In this case, a known resistance/temperature relationship for copper is used as the basis. The field current is reduced if the rotor overheats.
Kohl, et al. (U.S. Pat. No. 5,198,744) describes a generator, in particular a starter for a motor vehicle. A field current through a field winding of the generator is controlled as a function of a measured temperature in the generator. Temperatures at specific points in the generator are preferably calculated from the measured temperature. The use of the generator temperature to control the field current allows the generator to be operated in a state where it is overexcited at times, or in high ambient temperature.
A generator, in particular for supplying power in a motor vehicle, is known from German Published, Non-Prosecuted Patent Application DE 41 41 837 A1, in which a field current through a field winding of the generator is likewise controlled as a function of a temperature, to be precise on or in a voltage regulator. The invention in this case envisages that, when a critical temperature value is exceeded, any further temperature rise owing to an excessively high field current is prevented. To this end, the field current is reduced in a suitable manner.
Busick et al. (U.S. Pat. No. 5,373,205) discloses a mathematical model for determining the temperature of an electronic switching component, for example a transistor, for engine or motor control. The temperature model is based on an exponential time function. The temperature is calculated periodically, using the model, with the calculated temperature values being compared with a maximum permissible temperature value. The calculated temperature value is in this case a function of both the instantaneous current through the component and the current in the previous period.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for limiting an electric current through an electrical component, and a limiting apparatus that overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and that limits an electric current through an electrical component, in which overheating of the electrical component is reliably avoided but in which, at the same time, a sufficiently high electric current can be passed through the electrical component.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for limiting an electric current through an electrical component. The first step of the method is determining a time temperature profile for an electrical component. The next step is calculating a thermal load for the electrical component from the time temperature profile. The next step is limiting an electric current through the electrical component by maintaining the thermal load below a predetermined load maximum value.
With the objects of the invention in view, there is also provided a limiting apparatus for limiting an electric current through an electrical component. The electrical component receives a current and has a temperature. The integration unit integrates a time profile of the component temperature to determine a thermal load of the electrical component. The thermal load measures a material stress on the electrical component resulting from sustained high temperatures. A limiting unit connected to the integration unit limiting the current as a function of the thermal load outputted by the integration unit.
In accordance with another feature of the invention, a limiting apparatus for an electric current through an electrical component is to be provided that achieves a high exhaustion level of the magnitude of the electric current, with high operational reliability at the same time.
In accordance with another feature of the invention, a method provides for limiting an electric current through an electrical component in which a time temperature profile is determined for the electrical component and a thermal load for the electrical component is obtained from this, with the electric current being limited such that the thermal load remains below a load maximum value which can be predetermined.
The thermal load on the electrical component is a measure of the material stress in the component arising from high temperatures being present over a period of time. Because the electric current is limited on the basis of the thermal load, this on the one hand indicates that the electrical component is not thermally loaded beyond a permissible extent. On the other hand, the electric current is fully exhausted in terms of its magnitude and duration, since, using the thermal load, the magnitude and direction of the electric current can be set to be sufficiently high and for sufficiently long that there is just no longer any danger to the electrical component. In other words, the electric current can assume a maximum value and/or can be applied for a maximum maintenance period while reliably avoiding damage caused by thermal overloading. Control just on the basis of the temperature of the electrical component does not guarantee that the electric current is completely exhausted because the thermal load on the electrical component resulting from short-term high temperatures needs to be assessed differently to the load from temperatures which are raised over a lengthy time period.
A temperature limit for the electrical component is preferably defined on the basis that the electrical component is damaged after a certain time above the temperature limit, with the thermal load being calculated by summation or integration of the proportion of the time temperature profile in which the temperature is above the temperature limit.
The temperature limit is that temperature above which thermal damage will occur to the electrical component after a time that is significant in the scale of the average life. In other words, the definition of the temperature limit provides a parameter above which a significant thermal load occurs on the electrical component. The thermal load is obtained by summation and/or by integration of the temperatures in that time interval or in those time intervals in which the temperature is above the temperature limit.
The thermal load is preferably calculated using a thermal time constant of the electrical component, which thermal time constant indicates a characteristic warming-up or cooling-down time for the electrical component. The thermal time constant is used to take account of the thermal inertia of the electrical component in the calculation of the thermal load. If, for example, the electric current is switched off at a temperature above the temperature limit, then this results in the temperature of the electrical component decaying—generally exponentially. Despite the electric current being switched off, the temperature of the electrical component will thus still be above the temperature limit for a certain period of time. This results in a thermal load on the electrical component, which is used for controlling the limiting of an electric current that is connected once again.
The thermal load is preferably obtained from the following formula:
b
(
t
0
)
=
1
A
∫
0
t
0
T
(
t
)
-
T
G
ⅆ
t
,
where
b(t
0
): is the thermal load over the time t
0
,
T(t): is the temperature of the electrical component as a function of time,
T
G
: is the temperature limit, and
A: is an integration time constant.
The integration constant A reflects the thermal inertia of the electrical componen
Hofmann Hermann
Kutzner Rüdiger
Steinbrink Jörn
Assouad Patrick
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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