Device for providing protection against short circuits upstream from a power module

The protection device for providing protection against short-circuits upstream from an electrical power supply module having an inlet filter with at least one capacitor and an inductor and having a converter with components associated with a plurality of freewheel diodes includes at least one auxiliary winding and a dissipator element associated with the inlet filter, thereby making it possible to provide an inlet filter of small size without over dimensioning the freewheel diodes.

TECHNICAL FIELD AND PRIOR ART

The invention lies in the field of electrical power supply modules, in particular for electrical power distribution racks used in aircraft.

An electrical power supply module, referred to more simply as a “power module”, is powered from a direct current (DC) electrical energy source, possibly obtained by rectification and via an alternating current (AC) transformer, and including an inlet filter having at least one capacitor. The power module comprises at least one converter, which itself includes in particular inductors and freewheel diodes, possibly incorporated in switch components.

Usually, a plurality of optionally identical power modules are operated from a common electricity source and they may be associated in parallel in a power distribution rack in order to power a common load.

When the volume of an inlet filter is minimized, a converter is found to be particularly vulnerable to short-circuit at its inlet, where such a short-circuit constitutes a common mode of failure in power distribution racks. A short-circuit can cause excessive current to flow in the power module, and in particular in the freewheel diodes of the converter.

In order to remedy that problem, it is general practice to add cut-off members such as fuses, contactors, or circuit breakers. In addition to the complexity due to those additional members, that leads to operation being interrupted, which can be inconvenient and might even affect safety.

The extent to which the size of an inlet filter can be reduced, as is necessary to enable it to be incorporated in a power distribution rack, is limited for the capacitor C, since it needs to be dimensioned to be capable at least of supplying the current required by the converter, and is limited for the inlet inductor L by the minimum inductance authorized in particular because of constraints on emitting interference in the electromagnetic compatibility (EMC) sense. Under such circumstances, the current produced by a short-circuit at the inlet is given by:
−U/√{square root over (L/C)}

A small value for L contributes to reducing the volume of the inlet filter, thereby increasing the current produced by a short-circuit.

This current flows through the freewheel diodes for a considerable length of time, which means that the diodes need to be over dimensioned.

There thus exists a need to provide an inlet filter that is of small size, while ensuring that, in the event of a short-circuit at the inlet of the filter, the current that flows through the freewheel diodes of a converter of a power module is not too great, and that it does not flow for too long.

OBJECT AND DEFINITION OF THE INVENTION

The invention seeks to remedy the above-mentioned drawbacks and to make it possible in particular to protect power modules against inlet short circuits in a manner that is simple and reliable, and without leading to an untimely interruption of the operation of the power module.

In order to resolve the above-mentioned problems, there is provided a protection device for providing protection against short-circuits upstream from an electrical power supply module having an inlet filter with at least one capacitor and an inductor, and having a converter with a plurality of freewheel diodes, the device being characterized in that it comprises at least one auxiliary winding coupled to said at least one inductor of the inlet filter and a dissipator element connected to said at least one auxiliary winding, said dissipator element being adapted to dissipate the energy stored in said at least one capacitor of the inlet filter in the event of a short-circuit occurring at the inlet of said inlet filter.

More particularly, the dissipator element may be constituted by a resistor of the braking resistance type.

In a particular embodiment, a switch member, such as an active component or a magnetic amplifier, is configured to allow the current to flow in said auxiliary winding only when the switch member has detected a malfunction due to the short-circuit, such as a sudden drop in the voltage across the terminals of the capacitor of the inlet filter or an overcurrent within the converter.

The invention is particularly applicable to power modules for providing an electrical power supply in aircraft.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1is a diagram of a device of the invention for providing protection against short-circuits upstream from power modules160,160′ that are designed for electrically powering equipment, in particular within an aircraft where electrical power supply devices need to be capable of powering more and more equipment at ever higher powers.

InFIG. 1, there can be seen a diagram of two power modules160,160′, each comprising in particular at least one converter120,120′ including amongst other components inductors and switch components associated with freewheel diodes118,118′ that may optionally be integrated with the switch components. Each power module160,160′ is powered from a DC source via lines101,102;101′,102′ and via an inlet filter comprising inductors104,105;104′,105′ that are optionally coupled with capacitors106to108;106′ to108′ that are optionally connected to the frame109,110;109′,110′.

FIG. 1also shows an auxiliary winding131that is connected to a dissipator element132and a diode133, and that is coupled to one of the inductors105′ of the inlet filter.

The dissipator element132may be constituted by a resistor of the braking resistance type or by some other dissipator device that is capable of dissipating the energy stored in a capacitor of the inlet filter by means of the auxiliary winding131, which comes into action when a short-circuit103arises at the inlet of the filter, e.g. a short-circuit between the lines101and102as shown by way of example inFIG. 1.

FIG. 3Ashows how the voltage across the terminals of the capacitor106or106′ varies in the event of the short-circuit103appearing at an instant t1, firstly when the auxiliary winding131and the dissipator element132are not used (curve141), which constitutes the prior art, and secondly in the presence of the auxiliary winding131, the dissipator element132, and the diode133in accordance with the invention (curve142).

Furthermore,FIG. 3Ashows instants t2, t3that correspond to the beginning of conduction by the freewheel diodes of the converter120,120′, respectively without and with the auxiliary winding and the dissipator element. It can be seen that the drop in the voltage across the terminals of the capacitor106or106′ is much slower with the protection device of the invention (curve142) than without the device (curve141).

FIG. 3Bshows how the current to the power module160,160′ varies in the event of a short-circuit103appearing at an instant t1, firstly when the auxiliary winding131and the dissipator element132are not used (curve151), which constitutes the prior art, and secondly in the presence of the auxiliary winding131, the dissipator element132, and the diode133of the invention (curve152).FIG. 3Balso shows the instants t2, t3that correspond to the beginning of conduction by the freewheel diodes of the converter120,120′ respectively without and with the auxiliary winding of the dissipator element. It can be seen that the short-circuit current is much more limited with the protection device of the invention (curve152) than without the device (curve151).

In more particular manner, the short-circuit current without the auxiliary winding131(curve151) presents a value equal to:
−U/√{square root over (L/C)}
where L is the inductance of the inductor104,105;104′,105′ of the inlet filter, and where C is the capacitance of the capacitor106,106′ of the inlet filter.

In contrast, the short-circuit current with an auxiliary winding131having a turns ratio of n relative to the number of turns of the inductor105;105′, and with a dissipator element132having a resistance R, (curve152) presents a value equal to:
−U/(R/n2)
that, with suitably selected values for R and n, can be very significantly less than the current without the protection device131to133, assuming that there exist constraints on selecting the values L and C for the inlet filter, which values are associated with the operation of the converters120,120′ of the power modules160,160′, which constraints do not apply for the auxiliary protection circuit131to133.

FIG. 1shows two power modules160,160′, but naturally the invention applies to a greater number of power modules powered from parallel power supplies from a common DC voltage source.

FIG. 2shows a particular embodiment of a protection device of the invention with measurement means for characterizing the effect of the protection device of the invention.

InFIG. 2, the primary15aof a transformer15is powered using switches13controlled by a control circuit14for alternating between connection to the power supply11,12and operating with an upstream short-circuit; the power supply is made up of DC voltage sources11,12(e.g. each at 300 volts (V)).

The secondary15bof a transformer15is connected to a series of elements contributing to limiting current, such as inductors21,25, resistors22,23, and a Zener diode24.

In accordance with the invention, a secondary constituting an auxiliary winding15bis associated with the primary15aof the transformer15. A power module with its inlet filter and its converter are represented symbolically by a capacitor17, a diode18, and a load resistance19that form a parallel connection with one of its ends connected to the terminal of an inductor16that is not connected to the primary15aof the transformer15, and with its other end connected to the switches13.

In order to take measurements, a current probe31is connected in series with the DC voltage sources11,12in order to measure a current Idc, a current probe32is connected between the inductor16and the capacitor17to measure a current Is1, and a current probe33is connected between the capacitor17and the resistance19in order to measure a current Isd.

The secondary15bof the transformer15having a primary15ato secondary15btransformation ratio of 1:n, the resistor22of resistance R, and the diode24perform the same functions as the elements131to132respectively ofFIG. 1.

The diode18represents the freewheel diodes118,118′ included in the converters120and120′ ofFIG. 1.

FIGS. 4A and 4Bplot curves showing how the current and the voltage measured at various points of theFIG. 2circuit vary over time, with a short-circuit being simulated at instant t1, for a resistor22having a resistance of 40 ohms and corresponding to a peak value for Isd of 200 amps (A).

FIGS. 5A and 5Bplot curves showing how the current and the voltage measured at various points of theFIG. 2circuit vary over time, with a short-circuit being simulated at instant t1, for a resistor22having a resistance of 4 ohms and corresponding to a peak value for Isd of 1600 A.

The curves211and221inFIGS. 4A and 5Ashow the current Is1measured using the probe32.

The curves212and222ofFIGS. 4A and 5Ashow the current Isd measured using the probe33.

The curves213and223ofFIGS. 4A and 5Ashow the current Isecondary measured at the secondary of the transformer15.

The curves214and224ofFIGS. 4B and 5Bshow the voltage Vcapa across the terminals of the capacitor17.

The curves215and225ofFIGS. 4B and 5Bshow the voltage Vcrowbar applied to the inlet of the power module.

In the event of a short-circuit at the inlet filter formed by the primary15aof the transformer and the capacitor17, it can be seen that by virtue of the measures recommended by the present invention (namely adding a single auxiliary winding15band a dissipator resistor22, associated with a diode24, to the primary15aof the transformer15) the repercussion on the current Isd passing through the diode18is greatly attenuated.

FIG. 6shows an example of a protection device of the invention, as described above with reference toFIG. 2, including detection of overcurrent for the current Is1as measured by the probe32and switching of the elements15band21to25as performed by a magnetic amplifier40. Elements in common in the circuits ofFIGS. 2 and 6are given the same reference numbers.

FIG. 7shows another example of a protection device of the invention, as described above with reference toFIG. 2, including detection of overcurrent for the current Is1measured by the probe32, or of under-voltage across the terminals of the capacitor17by logic components52to54including an OR gate52. The elements15band21to25are switched by an active component51, which may for example be a thyristor having its gate connected to the output of the OR gate52. Once more, elements in common in the circuits ofFIGS. 2 and 7are given the same reference numbers.

The invention is not limited to the embodiments described, but extends to any variant coming within the ambit of the claims.

In particular, although the dissipator element is advantageously constituted by a braking resistance, it is possible to use other dissipator devices.