Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2000-12-22
2001-12-11
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
C363S091000, C363S124000, C323S329000, C323S330000, C323S362000
Reexamination Certificate
active
06330171
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to control circuits with chopping means used in particular in automotive vehicles, for example to power window lifters, windscreen wipers, robotized gearboxes or steering column adjustment systems.
2. Description of the Related Art
Represented in
FIG. 1
is such a circuit, here a pulse width modulation (PWM) circuit which conventionally includes a source
5
delivering a supply voltage V
bat
, followed by a low-pass filter
10
and then a chopping circuit
15
with two outputs A and B, and filtering circuits F
1
, F
2
installed at these two outputs A and B. A load CH has its terminals connected at the output of the filters F
1
and F
2
.
The chopping circuit
15
(or converter), typically a bridge of circuit breakers forming a chopping type bidirectional voltage source (here an H bridge), delivers two signals with variable pulse width on the two outputs A and B.
The role of the filtering circuits F
1
and F
2
is to reduce the electromagnetic disturbances (EMC) generated by the chopping (chopping noise), especially when the load CH is far from the chopping circuit
15
(this same type of filter is also used at the input of converters).
The load CH is traversed by a current I (load current) which is substantially continuous although it can change direction in certain applications, as a function of the sign of a control voltage.
According to a first conventional example, F
1
and F
2
are both formed by an LC circuit (such as that represented in
FIG. 2
with reference to F
1
), whose coil L
1
links an output of the power circuit
15
to a terminal of the load CH, and whose capacitor C
1
links this same terminal of the load CH to ground.
These known circuits remain rather unsatisfactory, in particular when the load CH is to be supplied in both directions, such as for example for electric motors of certain applications, since the load current I may reach a high enough value to saturate the coil L
1
, which then exhibits decreased inductance, denying the LC circuit its role as filter. Particularly significant electromagnetic disturbances are then obtained at the terminals of the load CH.
Moreover, the capacitor C
1
is then linked directly to the output of the circuit
15
, reducing the efficiency of the latter, and, because the chopped voltage exhibits high spans and low spans of different durations, the capacitor C
1
can charge up to its maximum capacitance.
For this reason, it is often necessary to limit the capacitance of the capacitor C
1
. However, in this case the filter exhibits a high impedance, and, because it is in series with the load CH, it forms a voltage divider. Consequently, here again the converter
15
generates electromagnetic disturbances at the terminals of the load CH.
It has indeed been proposed that coils having a higher inductance be installed, but they are expensive and bulky and dissipate heat.
The inductance can reasonably reach 10 &mgr;H with a saturation current of 15 to 20 A and the capacitance may reach a value of 20 &mgr;F maximum.
It has been proposed (
FIG. 3
) that an LC circuit be arranged at the output of each of the two branches of such a chopping circuit and that the coils of the two circuits be wound around the same core.
Each coil is traversed by a current whose average is substantially the load current. The coils therefore induce average magnetic fields having opposite directions and substantially equal values, regardless of the direction of the load current.
The magnetic fields therefore compensate one another, thereby giving a zero mean flux and protecting the coil from saturation. This type of circuit applies in particular when the load is inductive, and the common core used is for example a toroidal core. In such a device, a capacitor is necessarily installed on each side of the load.
Such a device requires complex adaptations and a large number of components. It is therefore still fairly expensive.
SUMMARY OF THE INVENTION
The main aim of the present invention is to solve the aforesaid drawbacks, that is to say to propose a chopping type control circuit, and upstream or downstream filtering, which is inexpensive and produces effective filtering.
Such a circuit is a control circuit, in particular for a load in an automotive vehicle, comprising a chopping circuit, at least one LC filter, means opposing the saturation of the inductor of this LC circuit, wherein these latter means are provided so as to prebias the inductor in a chosen direction.
Other characteristics, aims and advantages of the invention will become apparent on reading the detailed description which follows, given with reference to the appended drawings in which:
REFERENCES:
patent: 3671810 (1972-06-01), Barnes et al.
patent: 4230955 (1980-10-01), Johannessen
patent: 4985819 (1991-01-01), Mori et al.
patent: 5773969 (1998-06-01), Nakayama et al.
patent: 5889373 (1999-03-01), Fisher et al.
patent: 6166931 (2000-12-01), Mueller
patent: 628421 (1963-08-01), None
Patent Abstract of Japan, Pub. No. 62048257, Pub. Date Mar., 1987.
Liniak Berenato Longacre & White
Sterrett Jeffrey
Valeo Electronique
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