Series arc detection in a DC / AC power converter

Abstract

Power supply device (23) comprising: a DC / AC power converter (24) arranged to produce at least one AC output voltage (Va) from a DC input voltage (Ve); a monitoring circuit (35) comprising: an AC / DC converter (36) arranged to produce a monitoring voltage (Vsur) from at least one AC output voltage; a detection circuit (37) arranged to detect the occurrence of a series electrical arc in the DC / AC power converter from the monitoring voltage. Figure 8

Description

Title of the invention: Detection of series electric arcs in a DC / AC power converter

[0001] The invention relates to the field of monitoring DC / AC power converters.

[0002] BACKGROUND

[0003] 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 various states. In particular, an ambitious standard applies both to new types of aircraft and to 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. 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 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 aircraft energy efficiency. Consequently, the Applicant continuously works to reduce its negative climate impact by employing methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible, thereby reducing the environmental footprint of its activities.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 onboard equipment, the development of the use of electric technologies for propulsion, and, as essential complements to technological progress, aviation biofuels.

[0004] Increasingly, aircraft manufacturers are thus offering architectures for aircraft with electric or hybrid-electric propulsion. Indeed, these architectures seem promising for reducing the carbon footprint of aircraft, particularly on commuter or regional aircraft with low passenger capacity (typically less than 30 passengers).

[0005] With reference to [Fig.1], the propulsion system 1 of an electrically or hybrid-electrically propelled aircraft classically comprises a plurality of electric motors 2, each of which drives a propeller 3 in rotation.

[0006] The power supply chain 4 of the motors 2 includes an energy storage device, comprising batteries 5 and a BMS 6 (for Battery Management System) intended for managing the charging and discharging of the battery cells 5.

[0007] The power supply chain 4 further comprises, for each electric motor 2: - a distribution device, including for example a contactor 7 allowing the electric current to be cut off or allowed to pass to the motor 2; - a protective device 8, for example of type I2t; - a filtering stage (for example a capacitor or a device " DC-link") 9; - a DC / AC power converter 10 (DC for Direct Current, and AC for Alternating Current). The DC / AC power converter 10 is usually three-phase (like motor 2).

[0008] It is possible to have cases of series electrical arc failure at the DC / AC power converter 10.

[0009] Series electric arcs can occur at several levels between the DC / AC power converter 10 and the electric motor 2.

[0010] With reference to [Fig.2], we see that: - a series 1 electric arc may occur at the input interface of the DC / AC power converter 10; - a series 11b electric arc may occur in a switching element of the converter; - a series 1 electric arc may occur between the switching element and the output interface of converter 10; - a series 1 Id electric arc may occur at the output interface of converter 10.

[0011] These failure modes are difficult to identify in operation and can lead to a fire which is extremely detrimental to the operational safety of the aircraft.

[0012] Methods are known which make it possible to detect the occurrence of a series electric arc in a circuit.

[0013] Thus, document FR3102892A1 describes a method for detecting an electric arc in an electrical network. The method uses reflectometry. However, This method is not very effective in the case of a power converter, because the converter components prevent injected Fonde from propagating.

[0014] Document FR3133452A1 describes a method that uses a Bragg grating. This method requires adapting the monitored power supply device. It cannot be implemented on a pre-existing power supply device, thus necessitating the redevelopment and requalification of the power supply device. However, these development and qualification activities are governed by a number of standards, notably DO-254 (for hardware) and DO-178 (for software), and are complex and costly.

[0015] Moreover, this method requires instrumenting the monitored power supply device with a relatively high number of instrumentation components, and therefore has a significant impact in terms of size and mass.

[0016] OBJECT

[0017] The invention relates to a means of detecting the occurrence of a series electric arc in a DC / AC power converter, which is efficient, simple, inexpensive, compact, and which can be used to monitor a pre-existing power supply device.

[0018] SUMMARY

[0019] To achieve this goal, a power supply device is proposed, arranged to electrically supply a load and comprising: • a DC / AC power converter arranged to produce at least one alternating output voltage from a direct input voltage, at least one alternating output voltage being intended to be applied between terminals of the load; • a monitoring circuit comprising: • an AC / DC converter arranged to produce a monitoring voltage from at least one alternating output voltage; • a detection circuit arranged to detect the occurrence of a series electric arc in the DC / AC power converter from the monitoring voltage.

[0020] The monitoring circuit enables the highly effective detection of a series electrical arc in a DC / AC power converter. A series electrical arc generates a voltage drop in the relevant AC output voltage of the DC / AC power converter, which is reliably and accurately detected by the AC / DC converter. The monitoring circuit can be implemented with a pre-existing DC / AC power converter without requiring any modification. The monitoring circuit uses simple and few components. and has a small footprint and low weight. It is also relatively simple to design and qualify.

[0021] The invention will be better understood in the light of the following description of a particular, non-limiting embodiment of the invention. Brief description of the drawings

[0022] Reference will be made to the attached drawings, among which:

[0023] [Fig-1] [Fig.1] represents a power supply chain of a propulsion system aircraft;

[0024] [Fig.2] [Fig.2] represents a DC / AC power converter and the locations where a series electric arc may occur;

[0025] [Fig.3] [Fig.3] represents a DC / AC power converter, and the AC / DC converter of the monitoring circuit;

[0026] [Fig.4] [Fig.4] represents the DC / AC power converter;

[0027] [Fig. 5] [Fig. 5] represents a graph comprising voltage curves arc length depending on the arc length, for a copper cable and for an aluminium cable;

[0028] [Fig.6] [Fig.6] represents a graph including the output waveform of the AC / DC converter in the absence of a series electrical arc fault in the DC / AC power converter;

[0029] [Fig.7] [Fig.7] is a figure similar to [Fig.6], in the presence of an arc defect series electrical in the DC / AC power converter;

[0030] [Fig.8] [Fig.8] represents the DC / AC power converter and the monitoring circuit;

[0031] [Fig.9] [Fig.9] is a figure similar to [Fig.8], but slightly more detailed;

[0032] [Fig. 10] [Fig. 10] represents two graphs, one representing the output of the detection circuit in the presence of a series electric arc in the DC / AC power converter, and the other representing the output of the detection circuit in the absence of said fault. DETAILED DESCRIPTION

[0033] With reference to Figures 3 and 4, an aircraft 20 comprises an electrical propulsion system 21 which includes a plurality of electric motors 22 and, for each motor 22, a power supply 23. The power supply 23 includes a DC / AC power converter 24 and a power source 25. The power source 25 produces a DC input voltage Ve. The power supply 23 supplies power to the electric motor 22.

[0034] The DC / AC power converter 24 produces at least one alternating output voltage from the DC input voltage Ve, at least one alternating output voltage being intended to be applied between the terminals of the motor 22.

[0035] The DC / AC power converter 24 is here a three-phase converter, just like the electric motor 22. The DC / AC power converter 24 therefore produces three alternating output voltages Vaa, Vab, Vac, one for each phase of the motor 22.

[0036] The DC / AC power converter 24 is an inverter comprising three branches 26a, 26b, 26c, each comprising an upper inverter arm 27 and a lower inverter arm 28. Each arm comprises a switching element, and each branch therefore comprises two switching elements. The switching elements are, for example, MOSFET transistors 29. In each branch 26a, 26b, 26c, the drain of transistor 29 in the upper arm 27 is connected to the positive terminal of the power supply 25, the source of transistor 29 in the lower arm 28 is connected to the negative terminal of the power supply 25, and the source of transistor 29 in the upper arm 27 is connected to the drain of transistor 29 in the lower arm 28.

[0037] The inverter 24 therefore generates an alternating output voltage Va (Va = Vaa, Vab or Vac) at each midpoint 30 of each branch, said midpoint 30 being connected to the source of the transistor in the upper arm 27 and to the drain of the transistor in the lower arm 28 of said branch. The transistors are driven here using the PWM (Pulse Width Modulation) technique.

[0038] With reference to [Fig.5], when a series electric arc occurs, it causes a voltage drop which depends in particular on the arc length and the material of the conductor on which the arc occurs.

[0039] Curve Cl corresponds to an aluminium conductor and curve C2 corresponds to a copper conductor.

[0040] The voltage drop, or "arc voltage", is similar to a back electromotive force. The value of this back electromotive force is typically greater than 17Vdc.

[0041] With reference to [Fig. 6], the alternating output voltage Va of each branch of the inverter normally has, in the absence of a series arc fault, a waveform similar to curve C3. The voltage waveform varies between a low level of OVdc and a high level, in the example of 800Vdc, which corresponds to the DC input voltage Ve.

[0042] With further reference to [Fig. 4], a series electric arc present in the upper inverter arm 27 of branch 26a can be modeled by a DC voltage Varc equal here, for example, to 20 Vdc. The waveform of the AC output voltage Vaa of branch 26a then has a shape similar to the curve C4 shown. on [Fig.7]. The voltage Vaa evolves between a low level of OVdc and a high level of 800Vdc, then between a low level of 20Vdc and a high level of 800Vdc, then again between a low level of OVdc and a high level of 800Vdc, etc.

[0043] The same waveform is observed when the series electric arc is present in a lower arm 28.

[0044] With reference to figures 8 and 9, the power supply device 23 therefore includes a monitoring circuit 35 whose role is to detect the occurrence of a series electric arc in the DC / AC power converter 24. The PWM control module 34 of the DC / AC power converter 24 is shown schematically in [Fig.9].

[0045] The monitoring circuit 35 aims to detect the presence of a voltage at one of the midpoints 30 of the DC / AC power converter 24, which is between a minimum voltage threshold Vmin (minimum arc voltage) and a maximum voltage threshold Vmax (maximum arc voltage), and which is therefore significant of the occurrence of a series arc fault.

[0046] The minimum arc voltage is for example equal to 12Vdc and the maximum arc voltage is for example equal to 40Vdc.

[0047] The monitoring circuit 35 includes an AC / DC converter 36 and a detection circuit 37.

[0048] The AC / DC converter 36 is here a three-phase full-wave rectifier (here with diodes), which includes an input Ea connected to the midpoint 30 of branch 26a, an input Eb connected to the midpoint 30 of branch 26b, and an input Ec connected to the midpoint 30 of branch 26c.

[0049] The alternating output voltage Vaa of the DC / AC converter 36 is therefore applied to the input Ea, the alternating output voltage Vab is applied to the input Eb, and the alternating output voltage Vac is applied to the input Ec of the AC / DC converter 36.

[0050] The AC / DC converter 36 therefore produces on its output a monitoring voltage Vsur from at least one alternating output voltage Va, here from the three alternating output voltages Vaa, Vab, Vac.

[0051] The voltage Vsur has the same waveform as each voltage Va. In the absence of a series arc, the monitoring voltage Vsur therefore has the same waveform as the alternating output voltage Va shown in [Fig. 6]. In the presence of a series arc, the monitoring voltage Vsur therefore has the same waveform as the alternating output voltage Vaa shown in [Fig. 7].

[0052] The detection circuit 37 detects the occurrence of a series electric arc in the DC / AC power converter 24 from the monitoring voltage Vsur.

[0053] The detection circuit 37 includes an isolation transformer 38 (not shown in [Fig.8]), a two-threshold comparator 39, and a logic circuit comprising at least one "AND" gate 40 and an "RS" flip-flop 41.

[0054] The isolation transformer 38 comprises a positive input and a negative input, respectively connected to a positive output and a negative output of the AC / DC converter 36. The monitoring voltage Vsur is therefore applied to the input of the isolation transformer 38, and reproduced at the output of the isolation transformer 38.

[0055] The two-threshold comparator 39 comprises a first operational amplifier 42a forming a first comparator, and a second operational amplifier 42b forming a second comparator.

[0056] The first comparator 42a compares the monitoring voltage Vsur with the maximum voltage threshold. The second comparator 42b compares the monitoring voltage with the minimum voltage threshold, which is lower than the maximum voltage threshold.

[0057] The maximum arc voltage Vmax (maximum voltage threshold) is applied to the non-inverting input of the first operational amplifier 42a. The output of the isolation transformer 38, and therefore the monitoring voltage Vsur, is applied to the inverting input of the first operational amplifier 42a.

[0058] The minimum arc voltage Vmin (minimum voltage threshold) is applied to the inverting input of the second operational amplifier 42b. The monitoring voltage Vsur is applied to the non-inverting input of the second operational amplifier 42b.

[0059] The output of the first operational amplifier 42a and the output of the second operational amplifier 42b are connected respectively to a first input and a second input of the AND gate 40 of the logic circuit.

[0060] The output of the AND gate 40 is applied to the input S of the RS flip-flop 4L. The input R of the RS flip-flop 41 is grounded. The output Q of the RS flip-flop 41 produces a detection voltage Vd.

[0061] The detection circuit 37 further includes a processing unit 44 which is an electronic and software unit. The processing unit 44 includes at least one processing component 45, which is for example a "general-purpose" processor, a processor specializing in signal processing (or DSP, for Digital Signal Processor), a processor specializing in artificial intelligence algorithms (of the NPU type, for Neural Processing Unit), a microcontroller, or a programmable logic circuit such as an FPGA (for Field Programmable Gate Arrays) or an ASIC (for Application Specified Integrated Circuit).

[0062] The processing unit also includes one or more memories 46, connected to or integrated into the processing component(s) 45. At least one of these memories 46 forms a computer-readable recording medium on which is recorded at least one computer program comprising instructions which lead the processing unit 44 to execute the steps of the detection process which will be described.

[0063] It is noted that the processing unit 44 is not necessarily dedicated solely to this serial arc detection function.

[0064] The first comparator formed by the first operational amplifier 42a therefore compares the monitoring voltage Vsur with the maximum arc voltage Vmax and the second comparator formed by the second operational amplifier 42b therefore compares the monitoring voltage Vsur with the minimum arc voltage Vmin.

[0065] The output of the first comparator goes to the "true" logic stage when Vsur < Vmax. The output of the second comparator goes to the "true" logic stage when Vsur > Vmin.

[0066] Thus, when the monitoring voltage Vsur has a waveform not passing through zero but shifted from the series arc voltage (for example 20Vdc), and when it reaches this value, the output of the first comparator and the output of the second comparator simultaneously go to the "true" state, and therefore the output of the AND gate 40 also goes to the "true" state and then controls the RS flip-flop 41 which will memorize the fault.

[0067] The processing unit 44 continuously acquires and monitors the detection voltage Vd on the output Q of the RS flip-flop 4L. The processing unit 44 detects the occurrence of a series electric arc from this detection voltage Vd.

[0068] The graph on the left of [Fig. 10] shows the curve C5 of the detection voltage Vd in the presence of a series electric arc, and the graph on the right shows the curve C6 of the detection voltage Vd in the absence of a series electric arc.

[0069] It can therefore be seen that the monitoring circuit 35 is very effective at detecting a series electric arc and thus at preventing any thermal runaway or fire. The components of the monitoring circuit (small signals) are simple, few in number, and small in size. The added mass is very low. The monitoring is robust and free from false detections.

[0070] The monitoring circuit 35 can be integrated into a pre-existing power supply device to monitor the DC / AC power converter without modifying the power converter itself. Simply connecting the monitoring circuit to the DC / AC power converter is sufficient; no requalification of the DC / AC converter or the rest of the power supply device is required.

[0071] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0072] The power supply device is not necessarily integrated into an aircraft. The load powered by the power supply device is not necessarily an electric motor.

[0073] The DC / AC power converter and the AC / DC converter could be single-phase or polyphase converters with a number of phases other than three.

[0074] The AC / DC converter could use a different technology, for example based on operational amplifiers.

Claims

Demands

1. Power supply device (23) arranged to electrically supply a load (22) and comprising: • a DC / AC power converter (24) arranged to produce at least one alternating output voltage (Va) from a direct input voltage (Ve), the at least one alternating output voltage being intended to be applied between terminals of the load; • a monitoring circuit (35) comprising: • an AC / DC converter (36) arranged to produce a monitoring voltage (Vsur) from the at least one alternating output voltage; • a detection circuit (37) arranged to detect the occurrence of a series electric arc in the DC / AC power converter from the monitoring voltage.

2. Power supply device according to claim 1, wherein the load (22) is a polyphase load, the DC / AC power converter (34) being arranged to produce several alternating output voltages (Vaa, Vab, Vac), which are applied to the input of the AC / DC converter (36) of the monitoring circuit to produce the monitoring voltage.

3. Power supply device according to claim 2, wherein the load (22) is a three-phase load, and the DC / AC power converter (24) and the AC / DC converter (36) are three-phase converters.

4. Power supply device according to any one of the preceding claims, the AC / DC converter (36) being a full-wave rectifier.

5. Power supply device according to any one of the preceding claims, the detection circuit (37) comprising: - a first comparator (42a) arranged to compare the monitoring voltage (Vsur) with a maximum voltage threshold (Vmax); - a second comparator (42b) arranged to compare the monitoring voltage with a minimum voltage threshold (Vmin) lower than the maximum voltage threshold;

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10. - an AND gate (40) comprising a first input connected to an output of the first comparator and a second input connected to an output of the second comparator; - an RS flip-flop (41) comprising an input connected to an output of the "AND" gate. Electrical system (21) comprising a power supply device (23) according to any one of the preceding claims and the load (22) which is supplied by said power supply device. Electrical system (21) according to claim 6, the load being an electric motor. Electrical system (21) according to claim 7, the electric motor being a three-phase motor. Electrical system (21) according to any one of claims 6 to 8, the electrical system being an aircraft propulsion system. Aircraft (20), incorporating an electrical system according to claim 9.

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