Power supply circuit for turbine engine, turbine engine and aircraft comprising such turbine engine

Abstract

The invention relates to a power supply circuit for a turbine engine, comprising a high-voltage DC circuit powered by a high-voltage DC source, the high-voltage DC circuit being connected to at least one DC / AC converter (3), the at least one DC / AC converter being respectively connected to at least one rotary electric machine (2), the at least one rotary electric machine being respectively coupled to at least one propeller of the turbine engine, the at least one DC / AC converter (3) is arranged to rotate the at least one propeller or to generate electricity by rotation of the at least one propeller, the circuit comprising: at least one step-up stage (3 ') connected between the high voltage source and the at least one DC / AC converter (3), the at least one step-up stage being able to increase the voltage supplied to the at least one rotating electric machine when the rotating electric machine rotates the at least one propeller.

Description

Field of the Invention

[0001] The present invention relates to the field of turbomachines, and more particularly to a power supply circuit for a turbomachine integrated with a rotating electric machine, a turbomachine including such a circuit, and an aircraft including such a turbomachine. Background Art

[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. In fact, various states have adopted, are adopting, or will adopt various restrictions on carbon emissions. In particular, strict standards apply not only to new aircraft, but also to those currently in circulation that require the implementation of technical solutions to bring such technical solutions into compliance with current regulations. Civil aviation has been taking action for many years to contribute to the fight against climate change.

[0003] Technological research results have made it possible to significantly improve the environmental performance of aircraft. The applicant takes into account influencing factors at all design and development stages in order to obtain aviation components and products with lower energy consumption, more environmentally friendly, and with a moderate impact on the environment during integration and use in civil aviation, with the aim of improving the energy efficiency of aircraft.

[0004] Therefore, the applicant is constantly working to reduce the negative impact of greenhouse gas emissions on the climate by using methods, running benign development and manufacturing methods, and reducing greenhouse gas emissions to the lowest possible level, in order to reduce the environmental footprint of activities that emit greenhouse gases.

[0005] This ongoing research and development work includes new generation aircraft engines, reducing the weight of aircraft (especially through the materials used and lighter on-board equipment), using electrical technologies to ensure the development of propulsion, and aviation biofuels as a necessary complement to technological progress.

[0006] The document FR 3 116 303 filed by Safran Helicopter Engines describes the possibility of equipping an aircraft with a turbomachine (such as a turboprop engine) that integrates a gas turbine in the thermal components and a rotating electric machine in the electrical components. The thermal components and the electrical components enable the turbomachine to operate in hybrid mode. The rotating electric machine makes it possible to provide a power generation function in generator mode to supply power to the aircraft, and a propulsion function in the case of ground movement of the aircraft (especially taxiing).

[0007] However, there are situations where transient additional power is required related to the power limits that the turbomachine can provide. In fact, the thermal components of the turbomachine can be limited in terms of engine speed or acceleration, and the electrical components also have power limits.

[0008] For example, especially under high altitude conditions with high temperatures, a Full Authority Digital Engine Control (FADEC) can detect the attainment of the inherent limits of a gas turbine (i.e., the limits of the power delivered). In such a case, the need for additional power is identified. SUMMARY OF THE INVENTION

[0009] An object of the present invention is to solve the above problems of the prior art by providing a power supply circuit for a turbine engine, the power supply circuit including a high - voltage DC circuit powered by a high - voltage DC source, the high - voltage DC circuit being connected to at least one DC / AC converter of the power supply circuit, each of the at least one DC / AC converters being respectively connected to at least one rotating electrical machine, and the at least one rotating electrical machine being respectively coupled to at least one propeller of the turbine engine to rotate at least one propeller or generate electricity by the rotation of at least one propeller.

[0010] The power supply circuit includes at least one boost stage connected between the high - voltage source and the at least one DC / AC converter, and the at least one boost stage is capable of increasing the voltage supplied to the at least one rotating electrical machine when the rotating electrical machine rotates the at least one propeller.

[0011] Thanks to the present invention, additional power can be obtained in a transient or stable manner with respect to the power limit that the turbine engine can provide when necessary.

[0012] This additional power or "electric boost" can exist throughout the entire speed range of a turboprop engine. Compared with the case where additional power is provided by increasing the speed of a gas turbine (which will cause wear on the gas turbine), this additional power or "electric boost" does not cause any wear.

[0013] The turbine engine circuit according to the present invention is particularly suitable for providing transient or stable electric boost in a turbine engine with an electric hybrid architecture in the case of detecting a power demand, especially for the electric taxiing function of an aircraft.

[0014] According to an alternative preferred feature, at least one boost stage includes a boost - type converter, or an interleaved boost - type converter, or a DAB - type converter, or a quasi - Z - source type converter.

[0015] According to a preferred feature, the power supply circuit of the turbine engine further includes a low - voltage DC circuit, and the low - voltage DC circuit is connected to the high - voltage DC circuit through a converter of the power supply circuit.

[0016] According to a preferred feature, the power supply circuit of the turbine engine further includes a contactor connected in parallel with the boost stage.

[0017] The present invention also relates to a turbine engine including the power supply circuit as described above.

[0018] The present invention also relates to an aircraft comprising a turbomachine as described above.

[0019] The present invention also relates to a method for controlling at least one boost stage in a power supply circuit of a turbomachine as described above, characterized in that the method comprises the following steps:

[0020] - Detecting a power demand greater than the power that the turbomachine is capable of delivering,

[0021] - When a power demand greater than the power that the turbomachine is capable of delivering is detected, controlling the activation of the boost stage such that the boost stage delivers a high voltage to the rotating electrical machine during a transient period, and

[0022] - Controlling the end of the activation of the boost stage at the end of the transient period.

[0023] The turbomachine, the aircraft and the method have advantages similar to those described above.

[0024] In a particular embodiment, the steps of the method according to the invention are implemented by computer program instructions.

[0025] Thus, the present invention also relates to a computer program on an information medium, which program may be implemented in a computer, the program comprising instructions suitable for implementing the steps of the method as described above.

[0026] The present invention also relates to a computer-readable information medium, the computer-readable information medium comprising computer program instructions suitable for implementing the steps of the method as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further features and advantages will become apparent by reading the following description of preferred embodiments given by way of non-limiting example and with reference to the accompanying drawings, in which:

[0028] Figure 1 A turbomachine according to an embodiment of the invention is shown, here a turboprop engine.

[0029] Figure 2 The electrical architecture of a turbomachine according to an embodiment of the invention is shown.

[0030] Figure 3 A part of the high-voltage DC sub-circuit of the circuit of a turbomachine according to an embodiment of the invention is shown.

[0031] Figure 4 A first variant of a boost stage included in the high-voltage DC sub-circuit of the circuit of a turbomachine according to an embodiment of the invention is shown.

[0032] Figure 5 Shows a second variant of a boost stage included in a high - voltage DC sub - circuit of a circuit of a turbomachine according to an embodiment of the present invention.

[0033] Figure 6 Shows a third variant of a boost stage included in a high - voltage DC sub - circuit of a circuit of a turbomachine according to an embodiment of the present invention.

[0034] Figure 7 Shows a fourth variant of a boost stage included in a high - voltage DC sub - circuit of a circuit of a turbomachine according to an embodiment of the present invention.

[0035] Figure 8 Shows a method for controlling a boost stage according to an embodiment of the present invention.

[0036] Identical, similar or equivalent components in the various figures have the same reference numerals in order to facilitate the transition from one figure to another.

[0037] For the sake of readability of the figures, the various components shown in the figures are not necessarily shown to scale.

[0038] Each possibility (variant and embodiment) must be understood as not being mutually exclusive and can be combined with one another. Detailed description

[0039] According to Figure 1 The preferred embodiment shown, the turbomachine (here a turboprop engine 10) includes a rotating electrical machine 2 capable of providing an electric - power generation function and a propulsion function. The propulsion function can be provided when the gas turbine is operating or stopped.

[0040] When the gas turbine is operating, the electrical machine can provide additional power. When the gas turbine is stopped, the electrical machine can provide the power required for taxiing.

[0041] Alternatively, the architecture can be fully electric instead of thermo - electric hybrid.

[0042] The turbomachine 10 is a free - turbine turboprop engine. The turboprop engine 10 includes a gas turbine 11, a propeller 12, a propeller - carrying shaft 13, the propeller - carrying shaft 13 extending towards the gas turbine 11 and being coupled to the free turbine 111 via a gearing as described below.

[0043] Thus, the gas turbine 11 includes a high - pressure turbine (not shown) that rotates a turbine shaft 14, a compressor (not shown), and a free turbine 111 that drives a secondary shaft (not shown) of the gas turbine that is concentric with the turbine shaft 14.

[0044] The free turbine 111 can be rotatably mounted about the turbine shaft 14 of the high-pressure turbine. The propeller-bearing shaft 13 is surrounded by a protective housing 15. The propeller-bearing shaft 13 is supported in the housing 15 by bearings 16 and 17. One of the bearings 16 is close to the propeller 12, and the other bearing 17 is adjacent to a gear 18 for driving the propeller shaft 13, and the gear 18 meshes with the above-mentioned transmission. In this example of the present invention, the rotary electric machine 19 is arranged concentrically about the transmission shaft 13 between the first bearing 16 and the gear 18 by being surrounded by the housing 15.

[0045] Thus, in this embodiment, the turboprop engine is a "conventional" turboprop engine. Alternatively, the turboprop engine can be a tiltrotor turboprop engine, more commonly referred to as a proprotor, and the tiltrotor turboprop engine is intended to equip a vertical takeoff aircraft called a tiltrotor. Thus, the turboprop engine can be a turboprop engine or a turboprop engine. A person skilled in the art can of course generalize the presented information described for a "conventional" turboprop engine to these other types of turboprop engines.

[0046] It should be noted that since the gas turbine 11 is of the free turbine type, the gas turbine 11 provides two means for driving the elements of the turboprop engine, the high-pressure turbine and its turbine shaft 14, and the free turbine 111 and its secondary shaft.

[0047] It should also be noted that if the rotary electric machine 2 is a simple rotary electric machine capable of providing a power generation function and an electric propulsion function, the rotary electric machine 2 can have additional functions, such as the function of powering a circuit for de-icing the blades of the propeller.

[0048] Preferably, the rotary electric machine 2 is a brushless rotary electric machine, which limits the risk of wear and maintenance of the turboprop engine 10. Therefore, the rotary electric machine 2 can be a synchronous rotary electric machine with permanent magnets and a synchronous rotary electric machine with variable reluctance, or an asynchronous rotary electric machine.

[0049] The propeller 12 is a single-acting variable pitch propeller. The propeller is driven by the gas turbine 11 and / or the rotary electric machine 2, as described in FR3116303. The gas turbine 11 and the rotary electric machine 2 are capable of driving an engine oil pump 21, and the engine oil pump 21 enables the oil to circulate, and the oil supplies hydraulic pressure especially to the propeller control unit. The propeller control unit includes an additional oil pump, and the additional oil pump is designed to increase the oil pressure provided by the engine oil pump so as to enable hydraulic control of the pitch of the propeller.

[0050] Therefore, in the case where there is no oil pressure when the gas turbine is shut down and the rotary electric machine stops, the propeller is in the feather position. When oil pressure is generated by the gas turbine and / or the rotary electric machine, the pitch of the propeller decreases, which generates traction.

[0051] Particular attention is now paid to the electrical components of the turbomachine. Figure 2 The electrical architecture of a turbomachine according to an embodiment of the present invention is schematically shown.

[0052] It should be noted that the present invention can be implemented on multiple turboprop engines (for example, two turboprop engines as Figure 2 shown).

[0053] Thus, the two propellers 12a and 12b can be rotated by two gas turbines and two rotating electrical machines 2a and 2b respectively.

[0054] The circuit of the turbomachine includes a first high-voltage direct current (HVDC) sub-circuit.

[0055] The HVDC sub-circuit includes an HVDC battery 1, preferably of the power type, which forms a voltage source capable of generating a power of, for example, several tens of kilowatts to several hundreds of kilowatts at a voltage of, for example, approximately several hundreds of volts for several seconds or several minutes.

[0056] The HVDC battery 1 is connected to a DC converter 4. The input voltage of the converter 4 is determined by the state of charge of the battery, and the output voltage of the converter 4 is an adjustable DC voltage. The converter 4 is optional. The converter 4 can be a series buck type to reduce the voltage, or a parallel boost type to increase the voltage, or a buck-boost type to reduce or increase the voltage.

[0057] The DC converter 4 is connected to an HVDC bus 7, which is in turn connected to DC / AC converters 3a and 3b. Each of the DC / AC converters 3a, 3b is connected to an electrical machine 2a, 2b respectively. To ensure the electrical propulsion of the aircraft, direct current is supplied to the converters 3a and 3b via the HVDC bus 7. The converters 3a and 3b operate as inverters to convert DC into AC and supply the AC to the electrical machines 2a and 2b to rotate the propellers 12a and 12b. Conversely, the converters 3a and 3b operate as rectifiers to convert the AC supplied by the electrical machines 2a and 2b operating as generators into direct current supplied to the battery 1 via the HVDC bus 7.

[0058] The structure of the converters 3a and 3b is described in detail below.

[0059] Preferably, the circuit of the turbomachine includes a second low-voltage DC sub-circuit, typically 28V. The low-voltage DC sub-circuit includes a DC generator 5 and a battery capable of supplying power to various devices of the aircraft.

[0060] For example, as described in FR 3 116 303, the first high-voltage DC sub-circuit and the second low-voltage DC sub-circuit are connected by a converter 6.

[0061] Figure 3 Schematically shows a part of the high-voltage DC sub-circuit of the circuit of the previously described turbomachine, and more particularly details the converter 3.

[0062] Thus, the HVDC bus 7, the converter 3, and the rotating electrical machine 2 are found. It should be understood that the rotating electrical machine 2 and the converter 3 respectively correspond to Figure 2 each of the rotating electrical machines 2a and 2b and each of the converters 3a and 3b of

[0063] The converter 3 includes a boost stage 3'. Preferably, the boost stage 3' is integrated into the converter 3. Alternatively, the boost stage 3' can be a separate component of the converter 3. The boost stage 3' is of the boost DC type.

[0064] Preferably, the contactor 8 is connected in parallel with the boost stage 3'.

[0065] The boost stage 3' is capable of transiently increasing the voltage supplied from the HVDC bus 7 to the rotating electrical machine 2 to apply an overvoltage to the machine so that the machine generates additional transient power.

[0066] The contactor 8 is used to short-circuit the boost stage 3' when the contactor 8 is closed.

[0067] For example, especially under high-altitude conditions with high temperatures, the FADEC can detect the reaching of the inherent limits of the gas turbine (that is, the limits of the power delivered). In this case, the need for additional power is identified.

[0068] The boost stage 3' enables a higher voltage to be supplied to the rotating electrical machine 2. Thus, an electric boost is generated and applied to the shaft of the propeller.

[0069] This electric boost can increase the maximum power received by the propeller during the steady state when operating within the static limits of the internal combustion engine (i.e., the limits of the stop N1 or T4 corresponding to the maximum engine speed), or temporarily increase the transient power received by the propeller when the internal combustion engine is operating under its acceleration limits.

[0070] When it is recognized that the electric boost is not required, the boost stage 3' is made inactive by closing the contactor 8, which prevents any energy dissipation.

[0071] According to a variant, the structure of the boost stage 3' can be of the "boost" type as Figure 4 shown.

[0072] In Figure 4In an embodiment, the boost stage 3' includes an input terminal where a DC voltage V1 exists at the terminal of the input. Starting from the first terminal of the input, the boost stage 3' includes a resistor R in series with an inductor L, which enables energy storage.

[0073] The inductor L is connected to a first transistor T1, and the first transistor T1 is also connected to the second input terminal of the boost stage 3'.

[0074] The inductor L is also connected to a second transistor T2, and the second transistor T2 is connected to the first output terminal of the boost stage 3' and a capacitor C. The capacitor C is also connected to the second output terminal of the boost stage 3', and the second output terminal of the boost stage 3' is connected to the second input terminal of the boost stage 3'.

[0075] The first transistor T1 has a switching function such that energy can be accumulated in the inductor L when the first transistor T1 is closed, and the energy can be transferred to the capacitor C when the first transistor T1 is opened. Therefore, the output voltage V2 at the output terminal of the boost stage 3' is higher than the input voltage V1.

[0076] This variant is particularly applicable when the amplification ratio between the input voltage V1 and the output voltage V2 does not exceed 3.

[0077] According to another variant, the structure of the boost stage 3' can be as Figure 5 shown in the "interleaved boost" type.

[0078] In this case, the first input terminal is connected to a plurality of parallel branches (three parallel branches in the shown example), and each branch includes a resistor R1, R2, and R3 in series with inductors L1, L2, and L3. Each of the inductors L is connected to a corresponding transistor T11, T12, and T13, and the transistors T11, T12, and T13 are in turn connected to the second input terminal of the boost stage 3'. Each of the inductors L is also connected to a corresponding diode D1, D2, and D3, and the diodes D1, D2, and D3 are connected to the first output terminal of the boost stage 3' and the capacitor C. The capacitor C is also connected to the second output terminal of the boost stage 3', and the second output terminal of the boost stage 3' is connected to the second input terminal of the boost stage 3'.

[0079] This variant enables optimal operation to be maintained even in the case of transistor failure and limits the current ripple at the input terminal of the converter 3.

[0080] According to another variant, the structure of the boost stage 3' can be as Figure 6of the Dual Active Bridge (DAB) type as shown. This variant is suitable for voltage amplification that can be up to 3. This configuration is also of interest because it enables galvanic isolation between the HVDC bus 7 and the converter 3. This configuration also enables bidirectional current, that is to say, this type of converter can also be used for the propeller braking function. This function of returning energy to the grid is of particular interest, for example, in cases where it is desired to rapidly brake the propeller for reasons such as avoiding obstacles such as birds or power lines.

[0081] The boost stage 3' from the HVDC bus 7 to the converter 3 includes:

[0082] - A first low-pass filter stage 551, which is particularly suitable for at least partially filtering frequencies, for example, greater than or equal to 1 kHz.

[0083] - A second reversible DC / AC converter stage 552, which is capable of providing an inverter function for energy transfer from the HVDC bus 7 to the converter 3 and a rectifier function for energy transfer from the converter 3 to the HVDC bus 7. The second stage is capable of providing a high-frequency AC voltage, for example, greater than or equal to 1 kHz.

[0084] - A transformer 553, which is configured to step up the AC voltage provided by the second stage. Preferably, the transformer is a resonant transformer, that is to say, preferably, the resonant frequency of the primary side circuit of the transformer 553 is equal to the resonant frequency of the secondary side circuit of the transformer 553. Preferably, the second DC / AC converter stage 552 is configured to provide an AC voltage at a frequency that is substantially equal to the resonant frequency of the circuits on the primary and secondary sides of the transformer 553.

[0085] - A third reversible DC / AC converter stage 554, which is capable of providing a rectifier function for energy transfer from the HVDC bus 7 to the converter 3 and an inverter function for energy transfer from the converter 3 to the HVDC bus 7. The third stage is capable of providing a high-frequency AC voltage, for example, greater than or equal to 1 kHz. In the case where the transformer 553 is a resonant transformer, preferably, the third reversible AC / DC converter stage 554 is configured to provide an AC voltage at a frequency that is substantially equal to the resonant frequency of the circuits on the primary and secondary sides of the transformer 553.

[0086] - A fourth low-pass filter stage 555, which is particularly suitable for at least partially filtering frequencies greater than or equal to 1 kHz.

[0087] It should be noted that the first filtering stage 551 and the fourth filtering stage 555 are not necessary. In a simplified configuration, it is possible to consider not providing the first filtering stage 551 and the fourth filtering stage 555, or advantageously only providing the first filtering stage 551 to protect the HVDC bus 7.

[0088] According to another variant, the structure of the boost stage 3' can be of the quasi-Z-source type as Figure 7 shown. This variant optimizes the weight of the converter. In fact, the inductors of the circuit can be coupled, which limits the weight and the occupied space of the inductors, and which also makes it possible to limit the EMC suppression in differential mode at the input of the converter 3.

[0089] The boost stage 3' from the HVDC bus 7 to the converter 3 includes two input terminals. Starting from the first input terminal, the boost stage 3' includes a first resistor R41, a first inductor L41, a transistor T4, a second resistor R42, and a second inductor L42 connected in series. The second inductor L42 is connected to the first output terminal of the boost stage 3'.

[0090] A first capacitor C41 is connected in parallel with the transistor T, the second resistor R42, and the second inductor L42.

[0091] A second capacitor C42 is connected between the midpoint between the transistor T4 and the second resistor R42 and the second input terminal of the boost stage 3'. The second input terminal of the boost stage 3' is directly connected to the second output terminal of the boost stage 3'.

[0092] Figure 8 An embodiment of a method for controlling the boost stage 3' is shown and includes steps E1 to E3.

[0093] The first step E1 is to detect that the power provided by the turbomachine to properly ensure the regulation objective of the turbomachine is greater than the maximum power allowed by the inherent limits of the turbomachine. The regulation objective generally depends on the control of the propeller speed. For example, the inherent limits of the turbomachine correspond to the engine limits of the engine speed or acceleration. For example, this detection is performed by the FADEC of the aircraft.

[0094] When this detection is performed, step E1 is followed by step E2, in which information is provided to a monitor that controls the activation of the electric boost on the rotating machine. For example, the monitor is a monitor of the thermal and electrical components of the turbomachine.

[0095] The activation of the electric boost includes opening the contactor 8 and powering the boost stage 3' via the HVDC bus 7.

[0096] As already mentioned, the electrical supercharging conferred by the boost stage can increase, for example, the maximum power received by the propeller during the steady state phase in the case of operation under the static limits of an internal combustion engine, or can temporarily increase the transient power received by the propeller, for example, in the case of operation of the internal combustion engine under its acceleration limits.

[0097] Here, preferably, the electrical supercharging is transient. At the end of the transient period, step E2 is followed by step E3, in which the monitor controls the end of the electrical supercharging by controlling the closing of the contactor 8, thus short-circuiting the boost stage.

Claims

1. An aircraft, the aircraft comprising a turbomotor, the turbomotor comprising a power supply circuit of the turbomotor, the power supply circuit comprising a high-voltage DC circuit powered by a high-voltage DC source (1), the high-voltage DC circuit being connected to at least one DC / AC converter (3, 3a, 3b) of the power supply circuit, the at least one DC / AC converter being respectively connected to at least one rotary electric machine (2, 2a, 2b) of the turbomotor, the at least one rotary electric machine being respectively coupled to at least one propeller (12a, 12b) of the turbomotor to rotate the at least one propeller or generate electricity by the rotation of the at least one propeller, the power supply circuit comprising at least one boost stage (3') connected between the high-voltage source (1) and the at least one DC / AC converter (3), the at least one boost stage (3') being capable of raising the voltage supplied to the at least one rotary electric machine (2, 2a, 2b) when the rotary electric machine rotates the at least one propeller (12a, 12b), It is characterized in that, the aircraft comprising a FADEC: - capable of detecting a power demand greater than the power that the turbomotor can deliver, - capable of controlling the activation of the boost stage when detecting a power demand greater than the power that the turbomotor can deliver, such that the boost stage delivers a high voltage to the rotary electric machine during a transient period, and - capable of controlling the end of the activation of the boost stage at the end of the transient period.

2. The aircraft according to claim 1, wherein, The at least one boost stage (3') comprises a boost-type converter.

3. The aircraft according to claim 1, wherein, The at least one boost stage (3') comprises an interleaved boost-type converter.

4. The aircraft according to claim 1, wherein, The at least one boost stage (3') comprises a DAB-type converter.

5. The aircraft according to claim 1, wherein, The at least one boost stage (3') comprises a quasi-Z-source type converter.

6. The aircraft according to any one of claims 1 to 5, further comprising a low-voltage DC circuit, the low-voltage DC circuit being connected to the high-voltage DC circuit through a converter (6) of the power supply circuit.

7. The aircraft according to any one of claims 1 to 6, further comprising a contactor (8) connected in parallel with the boost stage (3').

8. A turbomotor, the turbomotor comprising a power supply circuit of the turbomotor, the power supply circuit being adapted to equip an aircraft according to any one of claims 1 to 7.

9. A power supply circuit of a turbomotor, the power supply circuit being adapted to equip an aircraft, the turbomotor being the turbomotor according to claim 8.

10. A method for controlling at least one boost stage in a power supply circuit of a turbomachine of an aircraft according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: - detecting (E1) a power demand greater than the power that the turbomotor can deliver, - when detecting a power demand greater than the power that the turbomotor can deliver, controlling (E2) the activation of the boost stage to deliver a high voltage to the rotary electric machine during a transient period, and - controlling (E3) the end of the activation of the boost stage at the end of the transient period.

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