Device and method for detecting an isolation fault in an electrical hybridisation system

Abstract

The invention relates to a device for detecting an isolation fault in an aircraft hybridisation system, the hybridisation system comprising an electric machine connected to a power converter configured to be powered by a voltage source, the device comprising: - a divider bridge connected between the two potentials of the power supply bus of the power converter, a midpoint of the divider bridge being configured to be coupled to a general mechanical ground, and - a supervisor connected to the divider bridge and configured to compare values of the voltages at the terminals of the divider bridge with a reference voltage value for detecting an isolation fault in the hybridisation system.

Description

[0001] DESCRIPTION

[0002] TITLE: Device and method for detecting insulation faults in an electrical hybridization system

[0003] technical field

[0004] The invention relates to the technical field of detecting insulation faults in an electrical hybridization system coupled to a turbomachine of an aircraft.

[0005] Previous techniques

[0006] An electric hybridization system is a hybrid electrical power source that provides power to a connected load and includes one or more electric generators driven by internal combustion engines or gas turbine engines.

[0007] When alternating current (AC) motors are used to propel an aircraft, the electrical energy typically supplied by a direct current (DC) power source is converted to alternating current. For example, a DC-to-AC converter is connected to a high-voltage direct current (HVDC) power bus, which itself may be powered by one or more HVDC voltage sources. The term "high voltage" here refers to any direct current voltage above 500 VDC.

[0008] A hybrid-powered aircraft can take various forms. For example, an electric aircraft can be an airplane, a rotorcraft, a helicopter, a quadcopter, an unmanned aerial vehicle, or any other type of aircraft.

[0009] Electric propulsion systems require protection against short circuits. The term "short circuit" refers to an electrical circuit with zero or very low electrical resistance.

[0010] A short circuit typically occurs when the positive and negative terminals of an electrical voltage source are short-circuited. Short-circuit protection involves using monitoring devices to detect insulation faults.

[0011] In the state of the art, insulation monitoring devices, such as devices designated by the acronym CBIT (for "Continuous Built In Test"), monitor the loss of insulation between a phase and a structure of the turbomachine.

[0012] The electrical systems currently installed on an aircraft turbomachine are designed to ensure starting and / or the generation of electrical power to the aircraft. Such systems include, for example, IDGs (Integrated Drive Generators) or VFGs (Variable Frequency Generators).

[0013] The generators are controlled by an SGCU (for "Starter Generator Control Unit") either by applying torque to ensure the starting function, or by regulating the Electromotive Force (EMF) in generator mode.

[0014] In the state of the art, the neutral of the IDG and VFG generators is connected to the mechanical mass constituted by the structure of the aircraft's turbomachine.

[0015] In aeronautics, the commonly used neutral system is the so-called "TN" system, in which:

[0016] - T designates the neutral of the installation connected directly to earth, - N designates the mass of the installation connected to the neutral conductor.

[0017] This TN neutral system allows the 0 V reference potential to be referenced to the mechanical ground. Insulation loss detection with an electrical system referenced to the aircraft structure is performed by the differential protection of an SGCU control unit. This protection measures the difference between the current delivered by an aircraft's electrical generator and the current supplied to the primary electrical distribution boxes.

[0018] If there is a difference between the measured current values, an insulation fault is present on the power distribution bus between the two current measurements. The insulation loss is detected only on the current path between two current measurements and not on the entire electrical network.

[0019] The loss of insulation in this case consists of a short circuit between a phase and the structure of the turbomachine, which is comparable to the contacting of two different potentials.

[0020] Insulation faults can be internal to loads, sources, or wiring between electrical system components. Existing insulation monitoring devices are effective in TN systems (neutral connected to the mechanical ground) but ineffective with systems where the neutral is not connected to the aircraft's mechanical ground (systems operating in "floating" mode). However, some electrical architectures being considered for hybridizing combustion engines or gas turbines include such new architectures with the neutral isolated from the mechanical ground. This architectural choice therefore necessitates new methods for detecting insulation losses (or short circuits).

[0021] Failure to detect insulation loss would be unacceptable not only for the safety of maintenance personnel, but could also lead to the gradual degradation of electrical equipment. This would then result in operational delays on airport runways.

[0022] Furthermore, climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by different countries. In particular, an ambitious standard applies to both new types of aircraft and those already in service, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0023] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental consequences, with the aim of improving the energy efficiency of aircraft.

[0024] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0025] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as essential complements to technological progress, aviation biofuels.

[0026] To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft.

[0027] Description of the invention

[0028] In view of the foregoing, the invention aims to eliminate at least some of the aforementioned disadvantages by proposing a device for detecting insulation faults in an aircraft electrical machine that is simple and inexpensive, and that allows insulation faults to be anticipated as early as possible, particularly in electrical architecture configurations where the neutral is not connected to the mechanical mass of the aircraft.

[0029] The invention relates to a device for detecting insulation faults in an aircraft hybrid system, the hybrid system comprising an electric machine connected to a power converter supplied by a voltage source. The device includes a voltage divider connected between two potentials of the power converter's supply bus. The midpoint of this voltage divider is configured to be connected to the general mechanical ground. The device also includes a supervisor connected to the voltage divider and configured to compare voltage values ​​across the voltage divider with a reference voltage value for detecting an insulation fault in the hybrid system.

[0030] According to another feature of the detection device, the divider bridge includes a first resistor and a second resistor connected in series between the two potentials (e.g., HVDC potentials).

[0031] In one embodiment, the supervisor is configured to determine a first voltage across the first resistor and to determine a second voltage across the second resistor.

[0032] According to another characteristic, the first resistor has a first resistance value and the second resistor has a second resistance value, and the first resistance value is equal to the second resistance value. In other words, the voltage divider is balanced.

[0033] Preferably, the voltage source includes a positive terminal and a negative terminal, the negative terminal being impedance-agnostic to earth, i.e., isolated from the general mechanical mass.

[0034] In one embodiment, the threshold value for detecting an insulation fault is equal to a sum of a tolerance margin and the voltage generated by the voltage source divided by two.

[0035] Advantageously, the voltage generated by the power supply is between 500 and 1000 V and / or the resistance values ​​are between 10 kOhm and 1 MOhm.

[0036] Preferably, the voltage divider is connected between the HVDC supply and the DC / AC converter. The converter also preferably includes a plurality of switches configured to switchably connect and disconnect the voltage divider to the PhA, PhB, and PhC power supply buses so as to detect insulation loss upstream and downstream of the voltage divider.

[0037] The invention also relates to a method for detecting an insulation fault in an aircraft hybrid system intended to be implemented by an insulation fault detection device as defined above. The hybrid system comprises an electrical machine connected to a power converter. The method comprises the steps of:

[0038] - powering the power converter from a voltage source via two power buses;

[0039] - comparison, by a supervisor, of the voltage values ​​across a voltage divider with a reference voltage value for detecting an insulation fault, the voltage divider being connected between said two power buses, the voltage divider including a midpoint connected to a general mechanical ground.

[0040] Preferably, the method includes a step of determining whether an insulation fault is present in the hybridization system based on the comparison of voltage values ​​and of emitting a warning signal if an insulation fault is present in the hybridization system.

[0041] The invention also relates to an aircraft comprising a hybridization system including an insulation fault detection device as defined above.

[0042] Brief description of the drawings

[0043] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example and made with reference to the accompanying drawings in which:

[0044] - Figure [Fig 1] schematically illustrates the architecture of an insulation fault detection device in a hybridization system according to an embodiment of the invention, in a power supply network of an electric machine coupled to a turbomachine of an aircraft;

[0045] - Figure [Fig 2] is a flowchart illustrating a method for detecting an insulation fault;

[0046] - Figure [Fig 3] illustrates the evolution of characteristic voltages of the voltage divider bridge of a device similar to that of Figure 1 during the detection of an insulation fault.

[0047] Detailed description

[0048] Figure 1 shows an electric machine 1 of an electrical hybrid system coupled to a turbomachine of an aircraft. The electric machine constitutes a generator or motor 1 connected to a three-phase DC / AC power converter 2 supplied by a high-voltage direct current (HVDC) voltage source 3, in particular between 500 and 1000 V, for example 800 V. The electric machine 1 is configured to operate both in motor mode (injecting mechanical torque, for example onto a shaft of the turbomachine to which machine 1 is coupled) and in generator mode (removing mechanical torque, for example again from a shaft of the turbomachine to which machine 1 is coupled).

[0049] The HVDC voltage source 3 includes a positive terminal 4 and a negative terminal 5 to which two parallel power buses 6, 7 are respectively connected. Thus, the first power bus 6 delivers a positive voltage between the power source 3 and the power converter 2 with a reference to earth and the second power bus 7 delivers a negative voltage between the power source 3 and the power converter 2 with a reference to earth.

[0050] The hybrid system is equipped with an insulation fault detection device comprising a voltage divider 10 connected between the two power supply buses 6 and 7 of the power converter 2, and a supervisor 12 configured to compare the difference between the voltage values ​​Vs1 and Vs2 (generally zero) across the voltage divider 10 with a reference voltage value REF. The reference voltage REF compensates for differences in acquisition between the two chains VS1 and VS2. The voltage divider comprises a first resistor 8 and a second resistor 9 connected in series and divides the input voltage generated by the voltage source 3 between the two power supply buses 6 and 7.

[0051] For example, the two resistance values ​​RI and R2 are between 10 kΩ and 1 MOhm. The first resistance value RI is, for example, equal to the second resistance value R2 and could be, for example, 50 kΩ.

[0052] The divider bridge 10 includes a midpoint 11 connected to the mechanical ground, according to an IT type neutral configuration, for example connected to the impedance neutral through the resistances RI, R2 which have for example a resistance value of 5kOhm.

[0053] In an IT configuration, the neutral is isolated ("I"), and the mechanical assembly is connected to earth ("T"). The only reference to the electrical machine is made at the voltage divider 10 via the midpoint 11. In other words, the midpoint 11 is a neutral connected to the mechanical assembly via a high resistance; therefore, the midpoint 11 is impedance-bearing. In an IT neutral system, the installation's neutral is isolated from earth or is impedance-bearing with respect to earth, and the mechanical assembly is connected to earth.

[0054] The IT configuration allows the fault current between the mechanical mass and a hot spot, such as the positive terminal 4 of the HVDC voltage source 3 or one of the alternating phases PhA, PhB or PhC output of the converter 2. The limited fault current or short-circuit current on the hot spot greatly reduces the risk of fire.

[0055] Indeed, the short-circuit current at the hot point is limited by the high resistances 8 and 9, particularly those exceeding 10 kΩ. Furthermore, the potential of the aircraft's mechanical mass is limited by the low current flowing through the aircraft's metallic structure.

[0056] The IT neutral system also has the advantage of allowing continued use of the electrical supply network even after an initial insulation fault has occurred. In this case, the current flowing through the mechanical mass then flows into the neutral impedance. The resistance of the neutral impedance significantly limits the leakage current, and the electrical network is not immediately shut down.

[0057] In a TN type electrical network, the negative terminal of the power source is referenced with respect to the mechanical mass of an aircraft, constituted by its metallic structure.

[0058] As illustrated in Figure 1, the negative terminal 5 is impedance-dependent with respect to the general mechanical mass, i.e. isolated from the earth, and the neutral of the electric machine is "floating", i.e. without reference to the general mechanical mass.

[0059] The electric machine casing and the DC / AC power converter casing, the voltage source 3, and the supervisor 12 are referenced to the turbomachine structure. Phases PhA, PhB, and PhC are isolated from the turbomachine structure. Finally, the internal star neutral point of electric machine 1 is floating.

[0060] As previously stated, the insulation loss in the IT neutral system is monitored by monitoring the two voltages across the two resistors 8, 9 of the divider bridge 10. A voltage Vsl across the first resistor 8 between the first supply bus 6 and the midpoint 11 and a voltage Vs2 across the second resistor 9 between the second supply bus 7 and the midpoint 11 are measured by the supervisor 12.

[0061] Each power bus 6, 7 includes at least one switch 13, 14 connected between the voltage divider 10 and the voltage source 3 and controlled by the supervisor 12. A switch is an electromechanical component configured to switch or alternate between an on or closed state and an off or open state. In one embodiment, the switches 13, 14 are double-pole contactors.

[0062] The supervisor 12 is specifically programmed to measure the voltages Vsl and Vs2 across the voltage divider 10 or to acquire the values ​​of these voltages Vsl and Vs2. The supervisor 12 may be equipped with an analog-to-digital converter 15 configured to convert an analog value of the voltages Vsl and Vs2 into a digital value. The supervisor 12 includes a comparator 16 that compares the digital values ​​of the voltages Vsl and Vs2 with a reference voltage value REF for fault detection.

[0063] Based on this comparison, the supervisor 12 determines whether an insulation fault is present in the hybrid system. In one embodiment, the reference voltage value REF for detecting an insulation fault is stored in a memory of the supervisor.

[0064] In one example, the reference voltage value REF for detecting an insulation fault is equal to the sum of the voltage VS generated by the voltage source 3 divided by two and a tolerance margin VT. The tolerance margin VT is generally the difference between the maximum and minimum permissible values ​​of the voltage measurements. The tolerance margin VT may also include a margin of error between the measured voltage value and the actual voltage value. This tolerance margin VT can be defined by the user in the supervisor software 12 and can take positive or negative values.

[0065] Supervisor 12 is also configured to monitor the operating status of switches 13 and 14 and power buses 6 and 7, preferably to determine whether or not there is a control or status fault. Therefore, the proper condition of switches 13 and 14 is also monitored before their use in the hybrid system.

[0066] A logic diagram of a method for detecting an insulation fault is illustrated in Fig. 2. In the initial operating state of the hybridization system, the voltage source 3 is off and all switches 13, 14 are open.

[0067] The process begins at the first step 100, during which the voltage source 3 supplies the power converter 2 via the two power buses 6, 7 with the voltage VS, switches 13 and 14 are closed. This step is carried out continuously.

[0068] In a subsequent step 105, the supervisor 12 commands the closure of internal switches in the power converter 2 for a duration between 1 and 100 ms. This very short closure ensures that there is no insulation loss on phases PhA, PhB, and PhC. In the following step 110, the voltage Vsl across the first resistor 8 and the voltage Vs2 across the second resistor 9 are transmitted to the supervisor 12.

[0069] In a subsequent step 115, the analog-to-digital converter 15 receives the voltages Vsl, Vs2 and converts them into a digital value of the voltages. Then, the comparator 16 compares the digital values ​​of the voltages Vsl, Vs2 with the reference voltage value REF for detecting an insulation fault.

[0070] The supervisor 12 then determines whether an insulation fault is present in the hybridization system by comparing the voltages Vsl and Vs2 with the reference voltage value REF (step 120). If one of the phases PhA, PhB, or PhC is short-circuited, the voltage divider 10 is unbalanced, and the voltages Vsl and Vs2 are no longer balanced. This means that the voltages Vsl and Vs2 are not equivalent to the sum of the voltage Vs generated by the voltage source 3 divided by two and the tolerance margin VT. Therefore, a short circuit is considered to be present in the hybridization system at one of the phases PhA, PhB, or PhC, and a warning signal is issued by the supervisor 12 (step 125).

[0071] If, during step 120, the supervisor 12 detects that the voltage values ​​Vsl and Vs2 do not exceed the reference voltage value REF for detecting an insulation fault, it is considered that the short circuit is not present in the hybrid system. A control signal is then emitted, informing the maintenance team or the driver that the short circuit was not detected during the operation of the hybrid system (step 130).

[0072] Figure 3 illustrates an example of monitoring the voltages Vsl and Vs2 as a function of time when an insulation fault occurs in the hybridization system. In this example, the voltage generated Vs by voltage source 3 has been reduced to 50 V.

[0073] Line 20 represents the voltage evolution across the negative terminal 5, and line 21 represents the voltage evolution across the positive terminal 4. The transition from "0" to "1" indicates an insulation fault, leading to an imbalance between the voltages Vsl and Vs2. Initially, the voltage source 3 is off for between 1 and 5 seconds. After 5 seconds, the voltage Vs is generated by the voltage source 3. Within a time interval of between 5 and 10 seconds, the voltages Vsl and Vs2 are balanced and have an approximate value of 25 V. After 10 seconds of operation, an insulation fault has appeared in the hybrid system, creating an imbalance between the voltages Vsl and Vs2. This insulation defect results in a difference between the value of Vsl shown on line 20 and the value of Vs2 shown on line 21. In this example, the value of Vsl is 35 V and the value of Vs2 is 15 V.This difference determined by supervisor 12 allows us to conclude that an insulation fault is present in the hybridization system.

Claims

DEMANDS 1. Device for detecting an insulation fault in an aircraft hybridization system, the hybridization system comprising an electrical machine (1) connected to a power converter (2) configured to be powered by a voltage source (3), characterized in that the device comprises: - a voltage divider (10) connected between two potentials of the power supply bus (6, 7) of the power converter (2), a midpoint (11) of the voltage divider (10) being configured to be connected to a general mechanical ground, and - a supervisor (12) connected to the divider bridge (10) and configured to compare voltage values ​​(Vsl, Vs2) across the divider bridge (10) with a reference voltage value (REF) for detecting an insulation fault in the hybridization system.

2. A device for detecting an insulation fault according to claim 1, in which the divider bridge (10) comprises a first resistor (8) and a second resistor (9) connected in series between the two potentials, the two potentials preferably being HVDC potentials.

3. A device for detecting an insulation fault according to claim 2, wherein the supervisor (12) is further configured to determine a first voltage (Vsl) across the first resistor (8), and to determine a second voltage (Vs2) across the second resistor (9).

4. A device for detecting an insulation fault according to any one of claims 2 and 3, wherein the first resistor (8) has a first resistance value (RI) and the second resistance (9) has a second resistance value (R2), and in which the first resistance value (RI) is equal to the second resistance value (R2).

5. Device for detecting an insulation fault according to any one of claims 1 to 4, wherein the voltage source (3) comprises a positive terminal (4) and a negative terminal (5), the negative terminal (5) being impedance-dependent with respect to the general mechanical mass.

6. A device for detecting an insulation fault according to any one of claims 1 to 5, wherein the reference voltage value (REF) for detecting an insulation fault is equal to a sum of a tolerance margin (VT) and the voltage (VS) generated by the voltage source (3) divided by two.

7. Device for detecting an insulation fault according to any one of claims 1 to 6, wherein the voltage (VS) generated by the power supply (3) is between 500 and 1000 V and / or the resistance values ​​(RI, R2) are between 10 kOhm and 1 MOhm.

8. A method for detecting an insulation fault in an aircraft hybrid system being intended to be implemented by an insulation fault detection device according to any one of claims 1 to 7, the hybrid system comprising an electric machine (1) connected to a power converter (2), the method comprising the steps of: - power supply of the power converter (2) by a voltage source (3) via two power buses (6, 7); - comparison, by a supervisor (12), of the voltage values ​​(Vsl, Vs2) across a voltage divider (10) with a reference voltage value (REF) for detection of a insulation fault, the divider bridge (10) being connected between said two power buses (6, 7), the divider bridge comprising a midpoint (11) connected to a general mechanical ground.

9. Method for detecting an insulation fault according to claim 8, further comprising a step of determining whether an insulation fault is present in the hybridization system based on the comparison of voltage values ​​(Vsl, Vs2) and of emitting a warning signal if an insulation fault is present in the hybridization system.

10. Aircraft comprising a hybridization system including an insulation fault detection device according to any one of claims 1 to 7.

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