Method for optimising the electrical drive chain of an aircraft fuel pump powered by a high-voltage network and associated electrical drive chain

Abstract

The invention relates to a method for controlling an electrical drive chain (1) of an aircraft fuel pump, the method comprising receiving (202) a pair of speed and mechanical torque setpoints for the electric motor (2), receiving (204) a maximum voltage setpoint delivered by a DC high-voltage source (3), calculating (206) the minimum voltage required at the input of the electrical inverter (5) for the setpoint torque, calculating (208) the losses in the electrical drive chain (1) for a range of voltages between the minimum voltage and a maximum voltage corresponding to, at most, the maximum voltage setpoint, selecting (210) an optimal voltage to be applied at the input of the electrical inverter (5), the optimal voltage corresponding to the voltage for which the losses in the electrical drive chain (1) are the lowest, and calculating (212) the duty cycle to be applied to the step-down converter (6) on the basis of the selected optimal voltage.

Description

[0001] Description

[0002] Title of the invention: Method for optimizing the electric drive chain of an aircraft fuel pump powered by a high-voltage network and associated electric drive chain

[0003] Technical Field

[0004] The invention relates to the optimization of an electric drive chain and more particularly to a method for controlling an electric drive chain of an aircraft fuel pump powered by a high voltage network.

[0005] Prior art

[0006] The present invention is used on high voltage avionics networks typically for voltages of 540V or more. More specifically, it is a converter assembly provided with a "buck" type voltage reducer, an electrical inverter and an electric motor for the variable speed drive of an aircraft fuel pump.

[0007] Operating a system such as a drive chain at high voltage causes problems with the insulation of cables and electrical components, and can lead to "partial discharges" or even insulation breakdown. Two solutions for the design of electrical equipment can then be considered to resolve this problem.

[0008] A first solution consists of developing new solutions capable of operating directly at high voltages (540 V) in a safe and reliable manner over time.

[0009] A second solution consists of reducing the operating voltage at the electrical equipment level to voltages below the voltage threshold at which partial discharges appear by inserting a voltage step-down converter (buck converter) between the high-voltage avionics network (540 V) and the electrical inverter supplying the three-phase electric motor.

[0010] The main disadvantage of the second solution is the addition of a potentially bulky converter, which has an impact on cost. The first solution seems more attractive but may require more complex (multi-level) architectures or rugged components, which are therefore more expensive.

[0011] The general problem is therefore to find a solution for optimal and reliable operation of a fuel pump on a high voltage network (typically 400 V to 900 V) while guaranteeing operational safety, reduced cost and sufficient efficiency.

[0012] Statement of the invention

[0013] The invention aims to overcome the drawbacks mentioned above and to provide an electrical drive chain for an aircraft fuel pump making it possible to reduce the losses of the inverter and the motor and therefore to improve the energy efficiency of the overall chain.

[0014] This aim is achieved firstly by means of a method for controlling an electric drive chain of an aircraft fuel pump, the electric drive chain comprising a three-phase electric motor, a direct high voltage source, and a converter assembly electrically connected between the input of the three-phase electric motor and the high voltage source and comprising an electric inverter and a voltage step-down converter.

[0015] According to a general characteristic of the invention, the control method comprises the following steps:

[0016] - reception of a pair of instructions relating to the speed and mechanical torque desired for the operation of the motor,

[0017] - reception of a maximum continuous voltage setpoint delivered by the high voltage source at the input of the converter assembly,

[0018] - a calculation of the minimum voltage required at the input of the electrical inverter for the operation of the motor at the said torque of speed and mechanical torque instructions,

[0019] - a calculation of the losses of the electric drive chain for a voltage range between said calculated minimum voltage and a maximum voltage corresponding at most to said maximum continuous voltage setpoint,

[0020] - a selection of an optimal voltage to be applied to the input of the electrical inverter, the optimal voltage being selected from said voltage range and corresponding to the voltage for which the losses of the electrical drive chain are the lowest,

[0021] - a calculation of the duty cycle to be applied to the voltage step-down converter from the ratio between the value of the selected optimal voltage and the value of the continuous high voltage delivered by the high voltage source, and

[0022] - a control of the voltage step-down converter based on the calculated duty cycle.

[0023] At low speed and / or low torque of the electric motor, an electric inverter has a better efficiency at low voltage than at high voltage. Switching losses in the inverter increase if its input voltage increases.

[0024] For the step-down converter, losses come from conduction and switching losses in the semiconductors (MOSFET or IGBT) and from copper and iron losses in the inductor. As the voltage difference between the output and input increases, the current ripple in the inductor increases, and consequently, the losses in the magnetic circuit and in the copper of the inductor increase.

[0025] For the motor, we consider the copper losses in the three-phase winding as well as the iron losses in the magnetic circuit. To reduce these losses, it is necessary to reduce the excess current consumed by adopting the voltage at a level sufficient to reduce the current and the excess current consumption due to the defluxing mode.

[0026] However, the voltage delivered by the electric inverter must still be higher than a certain minimum to avoid entering a defluxing mode of the electric motor.

[0027] The method for controlling the electric drive chain according to the invention makes it possible to determine the optimal voltage to have at the input of the inverter and therefore the duty cycle with which to control the voltage step-down converter to drive the fuel pump at the optimal efficiency point of the electric drive chain and this whatever the engine speed.

[0028] According to a first embodiment of the control method, the maximum voltage of the voltage range is preferably lower than a voltage threshold at which partial discharges appear, said voltage threshold (V PD ) varying depending on the altitude of the aircraft.

[0029] Thus, in addition to lowering the high voltage delivered by the DC high voltage source to minimize losses, the step-down converter also has the role of lowering the high voltage delivered by the DC high voltage source to a voltage below a voltage threshold so that the association of the electric inverter with the electric motor is free from partial discharges.

[0030] The method for controlling the electric drive chain according to the invention thus makes it possible to determine the optimal voltage to have at the input of the inverter and therefore the duty cycle with which to control the voltage step-down converter to drive the fuel pump not only at the point of optimal efficiency of the electric drive chain and whatever the engine speed, but also below a voltage threshold making it possible to avoid partial discharges between the electric inverter and the electric motor.

[0031] In a second mode of implementation of the control method, the voltage threshold (V PD ) from which partial discharges can occur is calculated during operation of the electric drive chain depending in particular on the altitude at which the aircraft is located, and an aging factor of the drive chain.

[0032] In a variant, the voltage threshold (V PD ) from which partial discharges can occur can be determined from the signals delivered by a partial discharge sensor mounted on said electric drive chain.

[0033] In a third embodiment of the control method, the method may further comprise a determination of the altitude of the aircraft, a comparison of the measured altitude with a low altitude threshold, and a bypass of the voltage reducer when the measured altitude is lower than the low altitude threshold.

[0034] At low altitude (2000 m or less for example), partial discharges are significantly lower than at high altitude (15000 m for example). Not using the step-down converter allows to avoid the losses it can generate. The control process can thus bypass the step-down converter at low altitude and reactivate it from an altitude threshold to adapt the voltage at the input of the electrical inverter to a safe voltage level to avoid partial discharges and an amplitude allowing to have the minimum of losses on the electric drive chain.

[0035] In a fourth embodiment of the control method, the determination of the altitude of the aircraft can be carried out from a pressure measurement of the environment in which the aircraft is located.

[0036] According to another object of the invention, there is provided an electric drive chain for a fuel pump of an aircraft, the electric drive chain comprising a three-phase electric motor, a direct high voltage source, and a converter assembly electrically connected between the input of the three-phase electric motor and the high voltage source, and an electronic control unit controlling the converter assembly, the converter assembly comprising an electric inverter and a voltage step-down converter.

[0037] According to a general characteristic of the invention, the electronic control unit is configured to select the optimal voltage to be applied at the input of the electrical inverter and to control the voltage step-down converter with a duty cycle equal to the ratio between the value of the optimal voltage to be applied and the value of the high DC voltage delivered by the high DC voltage source, the optimal voltage being selected in a voltage range between a minimum voltage necessary at the input of the electrical inverter for the operation of the motor at said pair of speed and mechanical torque setpoints and a maximum voltage corresponding at most to said maximum DC voltage setpoint, and the selected optimal voltage corresponding to the voltage in said voltage range for which the losses of the electrical drive chain are the lowest.

[0038] In a first embodiment of the electric drive chain, the voltage step-down converter can be connected between the high DC voltage source and the electric inverter.

[0039] In a second embodiment of the electric drive chain, the converter assembly may further comprise a filter (LC) electrically connected between the electric inverter and the three-phase electric motor. In a third embodiment of the electric drive chain, the step-down converter may be integrated into the inverter, the converter assembly comprising three electrical output branches each coupled to a phase of the three-phase electric motor, each branch comprising an inductor and a capacitor serving both for voltage step-down and as an output filter.

[0040] The integration of the step-down converter with the electrical inverter allows for a reduction in size, particularly because the inductors and capacitors serve both for the step-down converter and as an output filter for the electrical inverter. Each arm of the converter assembly represents a structure of a "buck-boost" type DC / DC converter allowing it to work in step-down or step-up voltage mode depending on the duty cycle. The output voltage is continuous but follows a sinusoidal shape dictated by the control applied to the switches, such as the sine-triangle control (SPWM).

[0041] In a fourth embodiment of the electric drive chain, the electric drive chain may further comprise a partial discharge sensor configured to detect partial discharges between the converter assembly and the electric motor, the electronic control unit being further configured to limit said voltage range so that the maximum voltage is lower than a voltage threshold corresponding to the lowest voltage at which partial discharges have been detected by the partial discharge sensor.

[0042] In a fifth embodiment of the electric drive chain, the electric drive chain may further comprise a pressure sensor configured to measure the pressure of the environment in which the aircraft on which the electric drive chain is mounted is located, the electronic control unit comprising a module for determining the altitude of the aircraft configured to determine the altitude of the aircraft from the pressure measured by the pressure sensor.

[0043] Brief description of the drawings [Fig. 1] Figure 1 schematically illustrates an electrical architecture of an electric drive chain of an aircraft fuel pump according to one embodiment of the invention.

[0044] [Fig. 2] Figure 2 shows a flowchart of a method for controlling the electric drive chain of Figure 1 according to one implementation mode.

[0045] [Fig. 3] Figure 3 schematically presents an electrical architecture of a converter assembly of an electric drive chain according to another embodiment of the invention.

[0046] Description of the embodiments

[0047] In Figure 1 is schematically represented an electric drive chain 1 of a fuel pump of an aircraft according to an embodiment of the invention.

[0048] The electric drive chain 1 comprises a three-phase electric motor 2, a DC high voltage source 3, and a converter assembly 4 electrically connected between the input of the three-phase electric motor 2 and the DC high voltage source 3.

[0049] The electric drive chain 1 further comprises an electronic control unit 10 controlling the converter assembly 4.

[0050] In the embodiment illustrated in Figure 1, the converter assembly 4 comprises an electrical inverter 5, a voltage step-down converter 6 connected between the high DC voltage source 3 and the electrical inverter 5, and a filter (LC) 8 electrically connected between the electrical inverter 5 and the three-phase electric motor 2.

[0051] Subsequently, each controlled switch comprises a diode and a controlled transistor connected in parallel.

[0052] The voltage step-down converter 6 comprises a first input terminal 61 and a second input terminal 62 connected between the terminals of the DC high voltage source 3, and a first output terminal 63 and a second output terminal 64 connected to the input terminals of the electrical inverter 5. The second input terminal 62 is coupled to the ground of the DC high voltage source 3. The voltage step-down converter 6 comprises two input capacitors 65 and 66 coupled in series between the first input terminal 61 and the second input terminal

[0053] 62, two controlled switches 67 and 68, two inductors 69 and 70, and an output capacitor 60 coupled between the first output terminal 63 and the second output terminal of the step-down converter 6.

[0054] The first controlled switch 67 and the first inductor 69 are coupled together in series between the first input terminal 61 and the first output terminal

[0055] 63. The second controlled switch 68 and the second inductor 70 are coupled together in series between the second input terminal 62 and the second output terminal 64.

[0056] Furthermore, the voltage step-down converter 6 comprises two diodes 71 and 72 coupled in series in the same direction passing between a first electrical node 73 connecting the first controlled switch 67 to the first inductance 69 and a second electrical node 74 connecting the second controlled switch 68 to the second inductance 70.

[0057] Further, a third electrical node 75 connecting the two input capacitors 65 and 66 together is electrically coupled to a fourth electrical node 76 connecting the two diodes 71 and 72 together.

[0058] The electrical inverter 5 comprises three branches 50, each intended to be connected to a phase of the electric motor 2. Each branch 50 of the electrical inverter 5 is connected between the first output terminal 63 of the voltage step-down converter 6 and the second output terminal 64 of the voltage step-down converter. Each branch 50 of the electrical inverter 5 comprises two controlled switches 52 and 54 coupled in series and an output terminal coupling an electrical connection node 56 between the two controlled switches 52 and 54 to a phase of the electric motor 2.

[0059] The filter 8 comprises, for each of the three branches of the electric inverter 5 coupled to a phase of the electric motor 2, a filtering inductance 80 coupled in series between the electric inverter 5 and the electric motor 2 and a filtering capacitor 82 coupled in parallel with the electric motor 2 between the filtering inductance 80 and the electric motor 2. The electric drive chain 1 further comprises a partial discharge sensor 90 configured to detect the presence of partial discharges on the converter assembly 4 and the electric motor 2.

[0060] The electric drive chain 1 also comprises a pressure sensor 92 configured to measure the pressure of the environment in which the aircraft on which the electric drive chain 1 is mounted is located.

[0061] The electronic control unit 10 is configured to select an optimal voltage to be applied at the input of the electrical inverter 5 and to control the voltage step-down converter 6 with a duty cycle equal to the ratio between the value of the optimal voltage to be applied and the value of the high DC voltage delivered by the high DC voltage source 3. The optimal voltage is selected in a voltage range between a minimum voltage necessary at the input of the electrical inverter 5 to operate the electric motor 2 according to a pair of speed and mechanical torque setpoints and a maximum voltage corresponding at most to a maximum DC voltage setpoint. The optimal voltage selected corresponds to the voltage in the voltage range for which the losses of the electric drive chain 1 are the lowest.

[0062] The electronic control unit 10 is further configured to limit the voltage range so that the maximum voltage is less than a voltage threshold corresponding to the lowest voltage at which partial discharges have been detected by the partial discharge sensor 90.

[0063] The electronic control unit comprises an aircraft altitude determination module configured to determine the aircraft altitude from the pressure measured by the pressure sensor 92.

[0064] Figure 2 shows a flowchart of a method for controlling the electric drive chain of Figure 1 according to one implementation mode.

[0065] The control method comprises a first step 200 of initializing the electric drive chain 1, then a second step 202 of receiving a pair of instructions relating to the speed and mechanical torque desired for the operation of the electric motor 2, and a third step 204 of receiving a maximum DC voltage instruction delivered by the DC high voltage source 3 at the input of the converter assembly 4. The method then comprises a fourth step 206 of calculating the minimum voltage required at the input of the electric inverter 5 for the operation of the electric motor 2 at the pair of speed and mechanical torque instructions, and a fifth step 208 of calculating the losses of the electric drive chain 1 for a voltage range between the calculated minimum voltage and a maximum voltage corresponding at most to the maximum DC voltage instruction.

[0066] In a sixth step 210, the electronic control unit 10 selects an optimal voltage to be applied to the input of the electrical inverter 5, the optimal voltage being selected from the voltage range and corresponding to the voltage for which the losses calculated for the electrical drive chain 1 are the lowest.

[0067] In a seventh step 212, the electronic control unit 10 performs a calculation of the duty cycle to be applied to the voltage step-down converter 6 from the ratio between the value of the selected optimal voltage and the value of the high DC voltage delivered by the high DC voltage source 3, then, in an eighth step 214, it performs a control of the voltage step-down converter 6 from the calculated duty cycle.

[0068] The method further comprises a ninth step 216 for preventing partial discharges. This ninth step 216 can be carried out between the sixth step 210 and the seventh step 212 or at another time in the method. The selected optimal voltage is compared to a voltage threshold corresponding to a voltage value from which partial discharges generally appear in flight conditions, namely for a given altitude and a given aging of the electric drive chain 1. In a variant or in addition, a partial discharge sensor can be used to detect the occurrence of partial discharges on the electric inverter 5 and the electric motor 2.

[0069] Following this ninth step 216, if the value of the voltage threshold for partial discharges is lower than the value of the maximum voltage of the voltage range, the maximum voltage of the range is modified to have the value of the voltage threshold and thus limit the number of calculations to be made and the calculation time.

[0070] Furthermore, the control method further comprises a tenth step 218 of determining the altitude of the aircraft, in particular from a measurement of environmental pressure using the pressure sensor 92. The tenth step 218 can be carried out before the fourth step 206 of calculating the minimum voltage Vmin. It comprises a measurement of the pressure of the environment in which the aircraft on which the electric drive chain 1 is mounted is located, a determination of the altitude from the pressure measurement, and a comparison of the measured altitude with a low altitude threshold.

[0071] In the case where the altitude is lower than the low altitude threshold, the electronic control unit 10 controls a bypass of the voltage step-down converter 6, the voltage step-down converter 6 directly transmitting the voltage delivered by the high DC voltage source 3 to the input of the electrical inverter 5. In this case, the method goes directly from the tenth step 218 to the eighth step 214 of controlling the voltage step-down converter 6 with a duty cycle equal to one.

[0072] Figure 3 shows a converter assembly 40 according to a second embodiment of the invention, in which the voltage step-down converter is integrated into the inverter.

[0073] In the second embodiment, the converter assembly 40 comprises three electrical branches 41 each comprising a first controlled switch 42, a second controlled switch 43, an inductance 44 and a capacitor 45.

[0074] Further, the converter assembly 40 includes an input capacitor 46 coupled between a first input terminal 47 and a second input terminal 48 of the converter assembly 40.

[0075] On each electrical branch 41, the first controlled switch 42 is coupled between the first input terminal 47 and the inductor 44 which is coupled on its other end to the second input terminal 48. The first controlled switch 42 and the inductor 44 are connected via a branch electrical node 424.

[0076] The second controlled switch 43 is coupled between the electrical branch node 424 and the capacitor 45 which is coupled, on its other end, to the second input terminal 48. The second controlled switch 43 and the capacitor 45 are connected via an output terminal 49 forming an electrical node and further connected to a phase of the electric motor 2. Each electrical branch 42 of the converter assembly 40 thus comprises an inductor 44 and a capacitor 46 serving both for voltage reduction and as an output filter.

[0077] The invention thus provides an electrical drive chain for an aircraft fuel pump making it possible to reduce the losses of the inverter and the motor and therefore to improve the energy efficiency of the overall chain.

Claims

Claims

1. A method of controlling an electric drive chain (1) of a fuel pump of an aircraft, the electric drive chain (1) comprising a three-phase electric motor (2), a high DC voltage source (3), and a converter assembly (4) electrically connected between the input of the three-phase electric motor (2) and the high DC voltage source (3) and comprising an electric inverter (5) and a voltage step-down converter (6), the control method comprising: - a reception (202) of a pair of instructions relating to the speed and mechanical torque desired for the operation of the electric motor (2), - a reception (204) of a maximum direct voltage setpoint delivered by the direct high voltage source (3) at the input of the converter assembly (4), - a calculation (206) of the minimum voltage required at the input of the electrical inverter (5) for the operation of the electric motor (2) at said setpoint speed and mechanical torque, - a calculation (208) of the losses of the electric drive chain (1) for a voltage range between said calculated minimum voltage and a maximum voltage corresponding at most to said maximum continuous voltage setpoint, - a selection (210) of an optimal voltage to be applied to the input of the electrical inverter (5), the optimal voltage being selected in said voltage range and corresponding to the voltage for which the losses of the electrical drive chain (1) are the lowest, - a calculation (212) of the duty cycle to be applied to the voltage step-down converter (6) from the ratio between the value of the selected optimal voltage and the value of the high DC voltage delivered by the high DC voltage source (3), and - a control (214) of the voltage step-down converter (6) from the calculated duty cycle.

2. A control method according to claim 1, wherein the maximum voltage of the voltage range is lower than a voltage threshold at which partial discharges occur, said voltage threshold (V PD ) varying depending on the altitude of the aircraft.

3. The method of claim 2, wherein said voltage threshold (V PD) from which partial discharges can occur is calculated during operation of the electric drive chain (1) depending in particular on the altitude at which the aircraft is located, and an aging factor of the electric drive chain (1).

4. The method of claim 2, wherein said voltage threshold (V PD ) from which partial discharges can occur is determined from the signals delivered by a partial discharge sensor mounted on said electric drive chain (1).

5. Control method according to one of claims 2 or 3, further comprising a determination (218) of the altitude of the aircraft, a comparison of the measured altitude with a low altitude threshold, and a bypass of the voltage step-down converter (6) when the measured altitude is lower than the low altitude threshold.

6. Control method according to claim 4, in which the determination of the altitude of the aircraft is carried out from a pressure measurement of the environment in which the aircraft is located.

7. An electric drive chain (1) for a fuel pump of an aircraft, the electric drive chain (1) comprising a three-phase electric motor (2), a DC high voltage source (3), and a converter assembly (4, 40) electrically connected between the input of the electric motor (2) and the DC high voltage source (3), and an electronic control unit (10) controlling the converter assembly (4, 40), the converter assembly (4) comprising an electric inverter (5) and a voltage step-down converter (6), characterized in that the electronic control unit (10) is configured to select the optimal voltage to be applied to the input of the electric inverter (5) and control the voltage step-down converter (6) with a duty cycle equal to the ratio between the value of the optimal voltage to be applied and the value of the high DC voltage delivered by the high DC voltage source (3), the optimal voltage being selected in a voltage range between a minimum voltage necessary at the input of the electric inverter for the operation of the electric motor (2) to said pair of speed and mechanical torque setpoints and a maximum voltage corresponding at most to said maximum DC voltage setpoint, and the optimal voltage selected corresponding to the voltage in said voltage range for which the losses of the electric drive chain (1) are the lowest.

8. An electric drive chain (1) according to claim 7, wherein the voltage step-down converter (6) is connected between the DC high voltage source (3) and the electric inverter (5).

9. An electric drive chain (1) according to claim 8, the converter assembly further comprises a filter (8) electrically connected between the electric inverter (5) and the electric motor (2).

10. An electric drive chain (1) according to claim 7, wherein the voltage step-down converter is integrated into the inverter, the converter assembly (40) comprising three electrical branches (41) each coupled to a phase of the electric motor (2), each branch (41) comprising an inductance (44) and a capacitor (45) serving both for voltage step-down and as an output filter.

11. An electric drive chain (1) according to one of claims 7 to 10, further comprising a partial discharge sensor (90) configured to detect partial discharges between the converter assembly (4, 40) and the electric motor (3), the electronic control unit (10) being further configured to limit said voltage range so that the maximum voltage is lower than a voltage threshold corresponding to the lowest voltage at which partial discharges have been detected by the partial discharge sensor (90).

12. Electric drive chain (1) according to one of claims 7 to 10, further comprising a pressure sensor (92) configured to measure the pressure of the environment in which the aircraft on which the electric drive chain (1) is mounted is located, the electronic control unit (10) comprising a module for determining the altitude of the aircraft configured to determine the altitude of the aircraft from the pressure measured by the pressure sensor (92).

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