Device and method for protecting an LVDC network connected to equipment powered by an HVDC network

Abstract

A protection device (1) for mixed electrical equipment (M) configured to be electrically connected, on the one hand, to an LVDC network, and, on the other hand, to an HVDC network, the protection device (1) comprising a first connector (C1) configured to be connected to the LVDC network, a second connector (C2) configured to be connected to the mixed electrical equipment (M), the second connector (C2) being connected to the first connector (C1) by a power line, a third ground connector (C3) connected by a ground line to the power line at a connection point (CX), at least one first diode (D1), mounted in reverse on the ground line between the connection point (CX) and the third ground connector (C3), and at least one first fuse (F1), mounted on the power line, between the connection point (CX) and the second connector (C2). Figure 7

Description

Title of the invention: Device and method for protecting an LVDC network connected to equipment powered by an HVDC network Technical field

[0001] The present invention relates to the field of electrical architectures for aircraft with electric or hybrid propulsion. The electric motors and electrical equipment which contribute to the electric propulsion function, requiring significant electrical power of the order of magnitude from a hundred kilowatts to megawatts, are supplied by a high voltage direct current electrical network known as HVDC (High Voltage Direct Current) dedicated to the supply of power. Furthermore, the electrical equipment generally needs to be supplied by a low voltage direct current electrical network known as LVDC (Low Voltage Direct Current). The present invention relates more particularly to the electrical protection of the LVDC network with respect to the HVDC network.

[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various States. In particular, an ambitious standard applies both to new types of aircraft and those in circulation requiring the implementation of technological solutions in order to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0003] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work covers both new generations of aircraft engines and the lightening of aircraft, in particular through the materials used and the lighter on-board equipment, the development of the use of electric technologies to ensure propulsion, and, essential complements to technological progress, aeronautical biofuels.

[0006] With reference to [Fig. 1], an aircraft is known in the prior art comprising an LVDC network, for example 28Vdc, which makes it possible to power several pieces of equipment E1-E4 such as electric actuators, flight control, radio and navigation computers or other. The LVDC network comprises at least a first source SBt, in particular a low voltage source, which powers a voltage bus BUS in order to electrically power several pieces of equipment E1-E4. In a known manner, primary switches 2 are provided between the pieces of equipment E1-E4 and the voltage bus BUS in order to isolate a piece of equipment E1-E4 in the event of a short circuit.

[0007] Still with reference to [Fig.l], the aircraft comprises at least one HVDC network, for example having a voltage between 800Vdc and 1500Vdc, which makes it possible to power several high-voltage devices. The HVDC network comprises at least one second source SHt, in particular, an electric generator. In a known manner, the aircraft comprises so-called “mixed” electrical equipment, for example electric propulsion motors M, which are connected, on the one hand, to the LVDC network in order to receive, for example, control instructions and, on the other hand, to the HVDC network to receive the electrical power necessary for propulsion.

[0008] By way of example, with reference to [Fig. 2], a propulsion electric motor M comprises in a known manner a power part 90, connected to the HVDC network, the purpose of which is to modulate the electrical power using power converters, control inverters, etc. The propulsion electric motor M further comprises a control part 91 which is configured to exchange electrical signals (MLI, etc.) with the power part 90. In a known manner, the propulsion motor M comprises one or two galvanic isolation barriers 92 between the two LVDC, HVDC networks.

[0009] With reference to [Fig. 3], in the event of a short-circuit fault occurring within the power part 90, an electric arc A may appear. This is supplied transiently by electrical energy EHVDc from the HVDC network for a duration of a few milliseconds to a few hundred milliseconds. This duration allows the protections of the HVDC network to mitigate the fault, either by protections against short circuits or overloads. The electric arc A may also be supplied by the rotating kinetic energies ECin, or by wind effects. The orders of magnitude of the fault currents and voltages may be respectively several thousand amperes and up to thousands of volts. Under these conditions, the electric arc A produces a very wide plasma which may extend over several tens of centimeters. As a result, all the parts 90, 91 of the electric motor M are bathed in the arc. electric A.

[0010] In detail, with reference to [Fig.4], the HVDC network is then connected to the LVDC network by the electric arc A. If we consider the electric arc A as a sum of elementary voltages, an electrical potential difference can be created between two tracks of the LVDC network. In the example of [Fig.4], the electric arc A brings into contact an OVdc track and a 28Vdc track. A high value reverse voltage, which could reach several hundred volts, is thus applied between the two tracks and will create a fault in the control part 91. The fault, that is to say the negative voltage applied, will go up on the LVDC network and can potentially propagate to the other equipment E1-E4 which are not configured to withstand high voltage electrical faults. An example of a fault by application of a negative voltage has been presented but it goes without saying that a fault by application of a positive voltage could also occur.

[0011] The invention thus aims to eliminate at least some of these drawbacks. PRESENTATION OF THE INVENTION

[0012] The invention relates to a protection device for mixed electrical equipment configured to be electrically connected, on the one hand, to a first low voltage direct current electrical network, designated LVDC network, and, on the other hand, to a second high voltage direct current electrical network, designated HVDC network, the protection device comprising: • a first connector configured to be connected to the LVDC network, • a second connector configured to be connected to the mixed electrical equipment, the second connector being connected to the first connector by a power line, • a third ground connector connected by a ground line to the power line at a connection point, • at least a first diode, mounted in reverse on the ground line between the connection point and the third ground connector, and • at least one first fuse, mounted on the supply line, between the connection point and the second connector.

[0013] Advantageously, if an electrical fault of a first type induced by the HVDC network is present between the second connector and the third ground connector and injects a fault current through the third ground connector, the protection device makes it possible to conduct the fault current into the first diode and then into the first fuse so as to form a current loop. The protection device provides very fast and reactive protection, which protects the LVDC network. The flow of current in the current loop has the successive effect, i.e. secondly, to cause the first fuse to open. Thus, a high-voltage electrical fault can be dealt with reactively without damaging the LVDC network. The current loop initiated by the first diode thus ensures the protection of the upstream LVDC network.

[0014] According to one aspect, the first fuse is a high voltage fuse capable of withstanding a high voltage and an overcurrent induced by an electric arc fault originating from the HVDC network, for a determined duration of the order of one to a few milliseconds, for example two milliseconds.

[0015] According to one aspect, the protection device comprises a second diode mounted on the supply line between the second connector and the connection point. Preferably, the second diode is mounted in series on the supply line between the first fuse and the second connector.

[0016] The second diode is configured to allow current flow from the connection point to the second connector. According to one aspect, the second diode has a threshold voltage of at least 900V, preferably at least 1000V. This is particularly relevant when the HVDC network has a voltage of the order of 800Vdc.

[0017] If an electrical fault of a second type induced by the HVDC network is present, such a second diode can thus, in the event of a positive overvoltage induced on the second connector, block the power supply line as long as the electrical fault is present, i.e., block the passage of the fault current.

[0018] According to one aspect, the HVDC network having a maximum admissible voltage, the second diode has a threshold voltage higher than the maximum admissible voltage. Thus, the second diode only becomes blocking in the event of the appearance of an electrical fault in the manner of a controlled switch.

[0019] According to one aspect, the protection device comprises a second fuse, mounted on the power supply line, between the first connector and the connection point. Such a second fuse advantageously makes it possible to provide protection against a “low voltage” electrical fault originating from the LVDC network.

[0020] According to one aspect, the HVDC network having a maximum permissible voltage, the power line and the ground line of the protection device are configured to withstand the maximum voltage. Thus, the protection device can conduct high currents from the HVDC network without damage.

[0021] An electrical architecture is also presented comprising a first low voltage direct current electrical network, designated LVDC network, and, on the other hand, to a second high voltage direct current electrical network, designated HVDC network, at least one electrical equipment, designated mixed electrical equipment connected, on the one hand, to the HVDC network and, on the other hand, to the LVDC network via a device of protection as presented previously.

[0022] According to one aspect, the mixed electrical equipment is an electric propulsion motor.

[0023] An aircraft is also presented comprising at least one electrical architecture as presented previously.

[0024] Also presented is a method for protecting an electrical architecture as presented previously, an electrical fault, induced by the HVDC network being present, between the second connector and the third ground connector, and injecting a fault current into the third ground connector, the method comprising steps consisting of: • Conduct the fault current into the first diode then into the first fuse so as to form a current loop then • Open the first fuse under the effect of the fault current.

[0025] A method for protecting an electrical architecture as presented previously is also presented, an electrical fault induced by the HVDC network being present, between the third ground connector and the second connector, and applying a disturbing voltage to the second connector, the method comprising a step of blocking the power supply line by the second diode as long as the electrical fault is present. PRESENTATION OF FIGURES

[0026] The invention will be better understood on reading the description which follows, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0027] [Fig.l] is a schematic representation of an electrical architecture according to the prior art for powering a plurality of electrical devices.

[0028] [Fig.2] is a schematic representation of the power supply of an electric propulsion motor.

[0029] [Fig.3] is a schematic representation of the occurrence of an electric arc in the propulsion electric motor.

[0030] [Fig.4] is a schematic representation of the occurrence of an electrical fault in the LVDC network.

[0031] [Fig.5] is a schematic representation of an aircraft according to the invention with different electrical equipment powered by an electrical architecture.

[0032] [Fig.6] is a schematic representation of an electrical architecture comprising a protection device according to the invention for supplying a plurality of electrical equipment.

[0033] [Fig.7] is a detailed schematic representation of the protection device according to the invention.

[0034] [Fig.8] is a schematic representation of an example of use of the protection device during the occurrence of a first type of electrical fault.

[0035] [Fig.9] is a schematic representation of an example of use of the protection device when a second type of electrical fault occurs.

[0036] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0037] With reference to [Fig.5], the invention will be presented for an aircraft AE comprising an electrical architecture for powering various electrical equipment, in particular, electric actuators El, flight control computers E2, radio E3 and navigation E4, electric propulsion motors M or others.

[0038] With reference to [Fig. 6], the electrical architecture comprises a first low voltage direct current electrical network, designated an LVDC network for “Low Voltage Direct Current”. By definition, an LVDC network has a voltage lower than 120 Vdc and does not present an electrical risk. In this example, the LVDC network has a voltage of 28 Vdc. Such an LVDC network makes it possible to power primary electrical equipment, i.e. equipment connected to the first low voltage direct current electrical network, for example electric actuators E1, flight control computers E2, radio E3 and navigation E4. As illustrated in [Fig. 6], the LVDC network comprises in a known manner at least a first voltage source S bt, in particular a battery or a generator with a rectifier if necessary, which supplies a voltage bus BUS in order to electrically supply the primary electrical equipment E1-E4.In a known manner, a primary switch 2 is provided between each of the primary electrical equipment E1-E4 and the voltage bus BUS in order to isolate the corresponding primary electrical equipment in the event of a short circuit. In [Fig.7], the primary switches 2 are shown activated in the open state but they are by default in the closed state when in use.

[0039] The electrical architecture further comprises a second high voltage direct current electrical network, designated an HVDC network for “High Voltage Direct Current”. By definition, an HVDC network has a voltage greater than 120 Vdc and presents an electrical risk. In this example, the HVDC network has a voltage between 800 and 1500 Vdc which can power several high voltage devices. The HVDC network comprises at least one second SHt source, in particular, a high voltage battery, a fuel cell, an electric generator, etc. The HVDC network could also include a voltage bus.

[0040] In a known manner, the aircraft AE comprises mixed electrical equipment. Mixed electrical equipment is electrical equipment which comprises a control part powered by the LVDC network and a power part powered by the HVDC network. The power part makes it possible to ensure the functions of distributing electrical power or generating mechanical power (torque control). A propulsion electric motor M is mixed equipment since it comprises an electronic power module for supplying electrical power for driving the rotating motor.The electronic power module, which may or may not be integrated into the structure of the electric propulsion motor M, comprises a switching stage connected to the HVDC network controlled by a control part connected to the LVDC network which provides the electrical signals to control the switching of the high direct voltage supplied by the HVDC network, to generate the phase currents in the windings of the stator of the electric propulsion motor M making it possible to drive the propulsion rotor in rotation according to a torque command.

[0041] It goes without saying that the invention applies to any mixed electrical equipment, for example, an electric braking system by electric regeneration, a high voltage battery equipped with its charge controller system, a high voltage electrical distribution box equipped with its management system known by its English designation "Power Distribution Management Unit", an electrical air conditioning system comprising a high voltage compressor and its control electronics, an electrical defrosting system equipped with its control electronics, etc. In a known manner, a primary switch 2 is also provided between each mixed electrical equipment and the voltage bus BUS in order to isolate the mixed electrical equipment from a short-circuit fault in the LVDC network.

[0042] According to the invention, with reference to [Fig.6], the electrical architecture further comprises a protection device 1 connecting a mixed electrical equipment item which, in the example, is a propulsion electric motor M, to the LVDC network. As will be presented later, such a protection device 1 makes it possible to avoid any electrical disturbance, induced by the second electrical supply network R2, on the LVDC network. A protection device 1 is preferably associated with each mixed electrical equipment item.

[0043] In this example, with reference to [Fig. 3], the protection device 1 comprises: • a first connector C1 configured to be connected to the LVDC network, • a second connector C2 configured to be connected to the propulsion electric motor M, the second connector C2 being connected to the first connector C1 by a power supply line, • a third ground connector C3 connected by a ground line to the line power supply at a CX connection point, • a first diode Dl, mounted in reverse on the ground line between the connection point CX (cathode side of Dl) and the third ground connector C3 (anode side of Dl), and • a first fuse Fl, mounted on the supply line, between the connection point CX and the second connector C2.

[0044] Depending on the type of structure of the aircraft (metallic, carbon, fiber or other), the third ground connector C3 can be integrated into the first connector C1 or be in the form of a ground braid or other.

[0045] The first diode D1 is configured as a freewheeling diode, i.e. “normally blocked”, to allow current flow only from the third ground connector C3 to the connection point CX, i.e., in the event of a negative overvoltage.

[0046] In the example illustrated, the protection device 1 further comprises: • a second diode D2 on the power supply line, in series between the first fuse Fl and the connector C2; • a second fuse F2, mounted on the supply line, between the first connector Cl and the connection point CX.

[0047] Preferably, the second diode D2 is connected directly to the second connector C2.

[0048] In general, a primary switch 2 will be provided on the power supply line connecting the LVDC network to the first connector C1, making it possible to isolate the protection device 1 and the mixed electrical equipment from an electrical fault in the LVDC network.

[0049] In more detail, the first diode D1 advantageously makes it possible to circulate a fault current II from the third ground connector C3 to the first fuse F1 and the second connector C2 downstream, in order to prevent it from propagating upstream, to the LVDC network ([Fig.8]).

[0050] The first fuse F1 is a so-called “high voltage” fuse. By “high voltage”, it is indicated that it is chosen to be compatible with the HVDC voltage, for example 230 Vdc, 240 Vdc or 800 Vdc. Preferably, the first fuse F1 is of the FF or F type within the meaning of standard IEC 60127 and can cut off ten times the nominal current in less than 1 ms (FF type) or between 1 ms and 10 ms (F type). The second fuse F2, optional, is also a so-called “high voltage” fuse.

[0051] The second diode D2, which is optional, advantageously makes it possible to stop any fault current 12 originating from a positive arc voltage of the second connector C2 before it flows on the power supply line in order to prevent it from propagating to the LVDC network ([Fig.9]). Preferably, the second diode D2 has a threshold voltage of at least 900Vdc, preferably at least 1000Vdc.

[0052] Advantageously, the power supply line and the ground line of the protection device 1 are configured, in particular with a suitable cable gauge, to withstand the voltage of the HVDC network, i.e., more than 120 Vdc, preferably more than 1000 Vdc. Thus, although the protection device 1 is mounted in the LVDC network, the protection device 1 is adapted to conduct and process high voltage electrical faults originating from the HVDC network. The cables forming the power supply line and the ground line are not damaged in the event of a high voltage electric arc, which makes it possible to clarify the electrical fault without damaging the protection device 1.

[0053] First example of implementation ([Fig.8D

[0054] With reference to [Fig.8], a first type of electric arc fault A1, here a negative electric arc, induced by the HVDC network, appears between the second connector C2 and the third ground connector C3. A fault current II is injected into the third ground connector C3.

[0055] Thanks to the protection device 1, the method comprises steps consisting of conducting the fault current II successively in the first diode DI and in the first fuse F1 (and in the second diode D2 if present) so as to reach the second connector C2 in order to form a current loop. This advantageously makes it possible to avoid a circulation of the fault current II in the LVDC network, which could damage the primary equipment E1-E4.

[0056] In practice, the appearance of the electric arc fault A1 results in the appearance of a positive voltage across the terminals of the first diode DI which becomes conductive in a few microseconds. The first diode DI causes a voltage drop of a few volts across its terminals, which protects the upstream LVDC network from the high voltage coming from the HVDC network. The first diode DI allows the circulation of the fault current H in the current loop passing through the first fuse F1 to the second connector C2. The appearance of the electric arc fault A1 causes the LVDC network to be short-circuited by the propulsion electric motor M and the LVDC network then delivers a high current, which is added to the fault current H at the connection point CX.This is what causes the first fuse Fl to melt, typically in a few milliseconds, depending on the breaking characteristics of the first fuse FL. The electric arc fault Al is thus stopped by opening the power supply line. The propulsion electric motor M is then no longer powered by the LVDC network.

[0057] The presence of the first fuse F1 advantageously makes it possible to avoid oversizing the first diode D1. The components and electrical circuits of the protection device 1 are advantageously sized to withstand the melting time of the first fuse F1.

[0058] Second example of implementation ([Fig.9D

[0059] With reference to [Fig.9], a second type of electric arc fault A2, here a positive electric arc, induced by the HVDC network, appears between the third ground connector C3 and the second connector C2. The electric arc fault A2 results in a disturbing voltage V+ applied to the second connector C2.

[0060] Thanks to the protection device 1, the method comprises a step consisting of blocking the disturbing voltage V+ by preventing any circulation of a fault current 12 by the second diode D2. This advantageously makes it possible to isolate the LVDC network downstream of the power supply line, and therefore to protect the primary equipment E1-E4 while the electric arc fault A2 is clarified in the HVDC network.

[0061] When the electric arc fault A2 appears, the voltage applied to the terminals of the second diode D2 (anode-cathode voltage) becomes negative and the second diode D2 blocks, in a few microseconds, protecting the LVDC circuit, by isolating it from the propulsion electric motor M, from the high voltage coming from the HVDC network. This prevents any damage to the primary equipment E1-E4 connected to said voltage bus BUS while the electric arc fault A2 is being clarified. Once the electric arc fault A2 has been clarified, the second diode D2 becomes conductive again.

[0062] The protection device 1 thus advantageously fulfills a voltage-controlled switch function.

[0063] Thus, thanks to the invention, even if the control part of mixed equipment (powered by an LVDC network) is bathed in an electric arc coming from the power part (powered by the HVDC network), the LVDC network is advantageously protected.

Claims

Claims

1. Protective device (1) for mixed electrical equipment (M) configured to be electrically connected, on the one hand, to a first low-voltage direct current electrical network, designated LVDC network, and, on the other hand, to a second high-voltage direct current electrical network, designated HVDC network, the protective device (1) comprising: • a first connector (Cl) configured to be connected to the LVDC network, • a second connector (C2) configured to be connected to the mixed electrical equipment (M), the second connector (C2) being connected to the first connector (Cl) by a power supply line, • a third ground connector (C3) connected by a ground line to the power supply line at a connection point (CX), • at least one first diode (Dl), mounted in reverse on the ground line between the connection point (CX) and the third ground connector (C3), and • at least one first fuse (Fl),mounted on the supply line, between the connection point (CX) and the second connector (C2).,

2. Protective device (1) according to claim 1, comprising a second diode (D2) mounted on the supply line between the second connector (C2) and the connection point (CX).

3. Protection device (1) according to claim 2, wherein, the HVDC network having a maximum admissible voltage, the second diode (D2) has a threshold voltage higher than the maximum admissible voltage.

4. Protective device (1) according to one of claims 1 to 3, comprising a second fuse (F2), mounted on the supply line, between the first connector (Cl) and the connection point (CX).

5. Protection device (1) according to one of claims 1 to 4, wherein, the HVDC network having a maximum admissible voltage, the power supply line and the ground line of the protection device (1) are configured to support the maximum voltage of the HVDC network.

6. Electrical architecture comprising a first low voltage direct current electrical network, designated LVDC network, and, on the other hand, to a second high voltage direct current electrical network, designated HVDC network, at least one electrical equipment, designated mixed electrical equipment (M) connected, on the one hand, to the HVDC network and, on the other hand, to the LVDC network via a protection device (1) according to one of claims 1 to 5.

7. Electrical architecture according to claim 6, in which the mixed electrical equipment (M) is an electric propulsion motor.

8. Aircraft comprising at least one electrical architecture according to one of claims 1 to 7.

9. Method for protecting an electrical architecture according to one of claims 6 or 7, an electrical fault (Al), induced by the HVDC network being present, between the second connector (C2) and the third ground connector (C3), and injecting a fault current (II) into the third ground connector (C3), the method comprising steps consisting of: • Conducting the fault current (II) into the first diode (Dl) then into the first fuse (Fl) so as to form a current loop then • Opening the first fuse (Fl) under the effect of the fault current (H).

10. Method for protecting an electrical architecture according to one of claims 6 or 7 taken in combination with claim 2, an electrical fault (A2) induced by the HVDC network being present, between the third ground connector (C3) and the second connector (C2), and applying a disturbing voltage (V+) to the second connector (C2), the method comprising a step of blocking the power supply line by the second diode (D2) as long as the electrical fault (A2) is present.

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