Method and unit for controlling pumps arranged in series

Abstract

The invention relates to a method and an electronic control unit for controlling a set of rotodynamic pumps (1,2,3) arranged in series. This set comprises at least one upstream rotodynamic pump arranged directly upstream of a downstream rotodynamic pump. According to this method, a rotational speed of the upstream rotodynamic pump and a degree of opening of a regulating valve of the upstream rotodynamic pump are controlled as a function of a saturation margin of the downstream rotodynamic pump and of a flow rate coefficient of the upstream rotodynamic pump. The saturation margin of the downstream rotodynamic pump is a difference between the current pressure and the saturation pressure of the liquid at the inlet of the downstream rotodynamic pump. The flow rate coefficient of the upstream rotodynamic pump is the volumetric flow rate of the upstream rotodynamic pump divided by the rotational speed of the upstream rotodynamic pump.

Description

Description Title of the invention: Method and control unit for pumps arranged in series Technical Field

[0001] This presentation concerns a method for controlling a set of rotodynamic pumps arranged in series, as well as an electronic control unit adapted to the implementation of this method.

[0002] In particular, this process and electronic control unit can be used to supply a rocket engine propulsion chamber with propellants, especially cryogenic propellants. However, other applications are also conceivable, such as supplying fuel to another type of combustion engine, such as a gas turbine, or to a fuel cell. Previous technique

[0003] A rotodynamic pump is defined as a pump in which a rotor transfers kinetic energy to a fluid by increasing its flow velocity, and therefore its dynamic pressure. A subsequent reduction in this flow velocity without pressure loss will thus cause an increase in the fluid's static pressure. The most common type of rotodynamic pump is the centrifugal pump, in which the fluid is admitted near the rotor hub and exits through a volute located at the periphery, which converts the dynamic pressure into static pressure by reducing the flow velocity.

[0004] However, in such a rotodynamic pump, fluid acceleration and pressure losses at the inlet can lead to a local decrease in its static pressure. Under certain conditions, during liquid pumping, this local decrease in static pressure, along with heat inputs due, for example, to rotor drive, can cause a phase change, known as cavitation, with the formation of bubbles in the liquid near the rotor surface. In some applications, particularly in the fuel systems of cryogenic liquid propellant rocket engines, the liquid circulates under near-saturated conditions, which facilitates cavitation and therefore makes pumping more difficult.

[0005] To avoid cavitation, it is common practice to stagger the pressure increase by connecting several rotary pumps in series. In such a system, the pressure surge produced by an upstream rotary pump compensates for pressure losses and heat gains, thus limiting cavitation and its detrimental effects in another rotary pump located directly downstream. Furthermore, distributing the pressure across multiple rotary pumps allows for adaptation to the power limitations of individual pumps.

[0006] Furthermore, a rotodynamic pump typically has a limited optimal operating range, primarily characterized by the flow coefficient, which is the ratio of the volumetric flow rate to the rotational speed. When the volumetric flow rate is too high or the rotational speed is too low, the rotodynamic pump is operating at high flow rate. Conversely, when the volumetric flow rate is too low or the rotational speed is too high, the rotodynamic pump is operating at low flow rate. In both cases, instabilities, reduced efficiency, and a decrease in the pump's suction capacity can be observed.

[0007] To adjust the flow coefficient of a rotary pump to maintain optimal operating performance, the pump's rotational speed and / or volumetric flow rate can be varied. One way to adjust the volumetric flow rate of a rotary pump is to equip it with a regulating valve. Such a regulating valve can be installed on a bypass pipe connected to the pump outlet, leading either to an external outlet (load shedding) or upstream of the pump (recirculation). Opening such a valve therefore increases the volumetric flow rate of the pump, and closing it restricts it.

[0008] In a set of rotodynamic pumps arranged in series, however, controlling the flow coefficient of an upstream pump to stay within an optimal operating range of that upstream pump can degrade the operation of the pump or pumps located downstream of it, by reducing the saturation margin of the liquid and / or degrading their flow coefficient.

[0009] There is therefore a real need for a control method that is free, at least in part, from these drawbacks and that allows for the optimization of the operation of all the rotodynamic pumps arranged in series. Description of the invention

[0010] This description concerns a method for controlling a series of rotary pumps, comprising at least one upstream rotary pump located directly upstream of a downstream rotary pump, for pumping a liquid. In this description, the terms "upstream" and "downstream" are defined with respect to the flow of the liquid through the series of rotary pumps. "Directly upstream" means that no other pump is interposed between the upstream and downstream rotary pumps, although other components, particularly the connecting conduit, may be interposed between them.

[0011] According to this control method, in order to optimize the operation of the series-connected rotodynamic pumps, the rotational speed of the upstream rotodynamic pump and the opening angle of its regulating valve can be controlled based on a saturation margin of the downstream rotodynamic pump and a flow coefficient of the upstream rotodynamic pump. This makes it possible to maintain the upstream rotodynamic pump within its optimal operating range while preventing cavitation in the downstream rotodynamic pump.

[0012] In some embodiments, this process may include a step of comparing the saturation margin of the downstream rotodynamic pump with a saturation margin setpoint for the downstream rotodynamic pump, followed by a step of increasing the rotational speed of the upstream rotodynamic pump if the saturation margin of the downstream rotodynamic pump is less than the saturation margin setpoint for the downstream rotodynamic pump, or a step of decreasing the rotational speed of the upstream rotodynamic pump if the saturation margin of the downstream rotodynamic pump is greater than the saturation margin setpoint for the downstream rotodynamic pump. Thus, controlling the rotational speed of the upstream rotodynamic pump can help maintain the saturation margin setpoint for the downstream rotodynamic pump to prevent cavitation in the downstream rotodynamic pump.

[0013] Furthermore, in these embodiments, the process may include a step of increasing the saturation margin setpoint of the upstream rotodynamic pump if an upper limit of the upstream rotodynamic pump's rotational speed is reached, or a step of reducing the saturation margin setpoint of the upstream rotodynamic pump if a lower limit of the upstream rotodynamic pump's rotational speed is reached. The saturation margin setpoint of the upstream rotodynamic pump can thus be adapted to its operating constraints.

[0014] In some embodiments, the process may include a step of comparing the flow coefficient of the upstream rotary pump with a setpoint for the upstream rotary pump flow coefficient, followed by a step of opening the upstream rotary pump control valve if the upstream rotary pump flow coefficient is less than the setpoint for the upstream rotary pump flow coefficient, or a step of closing the upstream rotary pump control valve if the upstream rotary pump flow coefficient is greater than the setpoint for the upstream rotary pump flow coefficient. Thus, controlling the upstream rotary pump control valve can contribute to maintaining optimal operating conditions for the upstream rotary pump.

[0015] Furthermore, in these embodiments, the process may include a step of reducing the flow coefficient setpoint of the upstream rotary pump if an upper limit of the opening degree of the upstream rotary pump control valve is reached, or a step of reducing the flow coefficient setpoint of the upstream rotary pump if a lower limit of the opening degree of the upstream rotary pump control valve is reached. The flow coefficient setpoint of the upstream rotary pump can thus be adapted to the operating constraints of its control valve.

[0016] In some embodiments, a rotational speed of the downstream rotodynamic pump and a degree of opening of a control valve of the downstream rotodynamic pump can be controlled as a function of an outlet pressure of the downstream rotodynamic pump and a flow coefficient of the downstream rotodynamic pump, where the flow coefficient of the downstream rotodynamic pump is the volumetric flow rate of the downstream rotodynamic pump divided by the rotational speed of the downstream rotodynamic pump, in order to ensure the maintenance of an appropriate outlet pressure, in particular when the downstream rotodynamic pump is the last pump of the set of rotodynamic pumps arranged in series, while respecting the operating constraints of the downstream rotodynamic pump.

[0017] However, in some embodiments, the set of rotodynamic pumps arranged in series may include more than two rotodynamic pumps. Thus, one or more additional rotodynamic pumps may be arranged in series upstream and / or downstream of said upstream and downstream rotodynamic pumps, in order to distribute the pumping work among a larger number of rotor pumps.

[0018] In some embodiments, the liquid may be a cryogenic liquid, particularly liquid hydrogen. Such cryogenic liquids are often close to their saturation point and are therefore particularly prone to causing cavitation phenomena during pumping.

[0019] In some embodiments, the series of rotodynamic pumps can supply propellant to a rocket engine's propulsion chamber. Alternatively, however, it is possible for it to supply fuel to another type of combustion engine, such as a gas turbine or a fuel cell, for example, in an aircraft.

[0020] This presentation also relates to a computer program comprising instructions which, when the program is executed by a computer, cause the computer to implement the aforementioned control method, an electronic control unit adapted to implement this control method, a liquid supply system, in particular for an engine or fuel cell, comprising a set of rotodynamic pumps and the aforementioned electronic control unit for controlling the set of rotodynamic pumps, as well as a rocket engine comprising a propulsion chamber and the aforementioned supply system for supplying the propulsion chamber with liquid propellant, and an aircraft comprising the aforementioned supply system for supplying fuel to one or more engines and / or fuel cells of the aircraft.

[0021] The aforementioned features and advantages, as well as others, will become apparent upon reading the detailed description that follows, along with examples of implementations of the control process and the aforementioned devices. This detailed description refers to the attached drawings. Brief description of the drawings

[0022] The attached drawings are schematic and are primarily intended to illustrate the principles of the presentation.

[0023] In these drawings, identical elements (or parts of elements) are identified by the same reference symbols from one figure to the next. Furthermore, elements (or parts of elements) belonging to different embodiments but having a similar function are identified in the figures by numerical references incremented by 100, 200, etc.

[0024] [Fig. 1] Figure 1 is a schematic view of a cryogenic liquid propellant rocket engine,

[0025] [Fig. 2] Figure 2 is a schematic view of a set of rotodynamic pumps arranged in series in a fuel supply circuit for the rocket engine of Figure 1,

[0026] [Fig. 3] Figure 3 is a flowchart illustrating a control routine for the first rotodynamic pump of the set of rotodynamic pumps in Figure 2,

[0027] [Fig. 4] Figure 4 is a flowchart illustrating a control routine for an intermediate rotodynamic pump of the rotodynamic pump assembly in Figure 2,

[0028] [Fig. 5] Figure 5 is a flowchart illustrating a control routine for the last rotodynamic pump in the set of rotodynamic pumps in Figure 2, and

[0029] [Fig. 6] Figure 6 is a flowchart illustrating a control subroutine of a regulating valve of a rotodynamic pump of the rotodynamic pump assembly of Figure 2. Description of the implementation methods

[0030] To make the explanation more concrete, an example of a method for controlling a set of rotodynamic pumps is described in detail below, with reference to the attached drawings. It should be noted that the invention is not limited to this example.

[0031] Figure 1 represents an example of a liquid-propellant rocket engine 100. This rocket engine 100 includes propellant tanks 200, 300, a propulsion chamber 400 with an injection head 500 and a convergent-divergent nozzle 600, and a feed circuit 700, 800 connecting each of the tanks 200, 300 to the injection head 500 of the propulsion chamber 400.

[0032] Tanks 200 and 300 can contain liquid propellants, and in particular cryogenic liquid propellants such as liquid hydrogen and liquid oxygen. Other liquid propellants, such as liquid methane, are also possible. To deliver each propellant to the propulsion chamber 400 through the injection head 500, even against very high combustion pressures in the propulsion chamber 400, each of the supply circuits 700 and 800 can include a plurality of rotodynamic pumps arranged in series.These rotodynamic pumps can be centrifugal pumps, although axial pumps are also conceivable as alternatives or complements to centrifugal pumps, and can comprise one or more electrically driven pumps and / or one or more turbopumps, i.e., rotodynamic pumps driven by the expansion of a fluid in one or more turbines mechanically coupled to the rotodynamic pumps. These turbines can be driven, for example, by hot gases resulting from the complete or partial combustion of propellants, or by propellant heated in a regenerative cooling circuit. They can be directly coupled to the rotodynamic pumps, or via a transmission, such as a gear train.

[0033] The 700 power supply circuit illustrated in Figure 2 comprises a set of three rotodynamic pumps 1, 2, and 3 arranged in series. However, it is also possible to include only two rotodynamic pumps in series in this set, or conversely, to include more than three.

[0034] Each of these rotary pumps 1, 2, 3 can be associated with a corresponding control valve 11, 21, 31. In the illustrated assembly, the control valve 11 of the first rotary pump 1 is a relief valve located on a bypass pipe 12 connected directly downstream of the first rotary pump 1 and opening to the outside, while the control valves 21, 31 are recirculation valves located on respective bypass pipes 22, 32, each connected directly downstream of the corresponding rotary pump 2, 3 and each opening directly upstream of the same rotary pump 2, 3. Alternative configurations of each of the bypass pipes 12, 22, 32 are, however, conceivable.For example, the bypass conduits 22, 32 can alternatively open upstream of a rotodynamic valve located further upstream than the one to which each is associated, or even outside so that the control valves 21, 31 are relief valves, while the bypass conduit 12 can open upstream of the control valve 11, to make it a recirculation valve.

[0035] Each of the rotodynamic pumps 1, 2, 3 can also be equipped with a set of sensors. Thus, each of the rotodynamic pumps 1, 2, 3 can be equipped with a rotational speed sensor 13, 23, 33 and a volumetric flow rate sensor 14, 24, 34. In addition, rotodynamic pumps 2 and 3 can be equipped with inlet pressure sensors 25, 35 and inlet temperature sensors 26, 36, and the last rotodynamic pump 30 is also equipped with an outlet pressure sensor 37. All these sensors can be connected to an electronic control unit 900 which is connected to the rotodynamic pumps 1, 2, 3 and their respective control valves 11, 21, 31 to form a supply system and is configured to control their operation according to the method described below. However, it is also conceivable that at least one parameter among the rotational speeds, volumetric flow rates, inlet pressures and temperatures, and outlet pressures and temperatures of the rotodynamic pumps 1, 2, 3 could be obtained by a means other than direct measurement by a sensor. Thus, for example, the rotational speed of each of the rotodynamic pumps 1, 2, 3 could be estimated using a corresponding control signal, while the pressures, temperatures, and flow rates could also be estimated using other physical parameters.

[0036] As illustrated in Figure 3, to control the first rotodynamic pump 1, in a first step S101, a saturation margin NPSP20 of the rotodynamic pump directly downstream, i.e., of the rotodynamic pump 2, is calculated according to the formula:

[0037] [Math. 1] NPSP2 = P2 - P sat (T2 where P2 and T2 correspond respectively to the current pressure and temperature at the inlet of the rotodynamic pump directly downstream, i.e. of the rotodynamic pump 2, as they can in particular be measured by the inlet pressure sensor 25 and the inlet temperature sensor 26, and Psat(T2) corresponds to the saturation pressure corresponding, for the liquid circulating through this set of rotodynamic pumps arranged in series, to the temperature T2.

[0038] In a second step S102, a flow coefficient T>1 of the first rotodynamic pump 1 is calculated according to the formula:

[0039] [Math. 2] where Qi and ooi correspond, respectively, to the volumetric flow rate and rotational speed of the first rotodynamic pump 1 currents, as they can in particular be measured, respectively, by the volumetric flow rate sensor 14 and the rotational speed sensor 13 of this first rotodynamic pump 1, or otherwise estimated.

[0040] In a third step S103, the saturation margin NPSP2 of the directly downstream rotodynamic pump, i.e., rotodynamic pump 2, is compared to a saturation margin setpoint NPSP2,c for this rotodynamic pump 2. In a subsequent step S104 or S105, the flow coefficient $>i of the first rotodynamic pump 1 is compared to a flow coefficient setpoint i,c for this first rotodynamic pump 1.

[0041] If the saturation margin NPSP2 of the rotodynamic pump 2 is less than the corresponding saturation margin setpoint NPSP2,c, but the flow coefficient T>1 of the first rotodynamic pump 1 reaches the corresponding flow coefficient setpoint i,c, an increase in the rotational speed œi of the first rotodynamic pump 1 is commanded in step S106 to increase the saturation margin NPSP2 of the rotodynamic pump 2 and decrease the flow coefficient i,c of the first rotodynamic pump 1. This rotational speed œi of the first rotodynamic pump 1 is then compared to a corresponding upper limit œi,max in step S107. As long as this upper limit œi,max is not reached, this control routine for the first rotodynamic pump 1 can then return to step S101.However, if the upper limit œi,max is reached, the routine is interrupted because the operating range of the rotodynamic pump assembly is exceeded. The system may then enter a degraded operating mode, which is not the subject of this disclosure.

[0042] If the saturation margin NPSP2 of rotary pump 2 and the flow coefficient T>1 of the first rotary pump 1 are both lower than the corresponding setpoints NPSP2,c and i,c, then, in step S108, it is checked whether the degree of opening Ai of the control valve 11 of the first rotary pump 1 has reached a maximum limit Ai.max. If this maximum limit Ai.max is not reached, an increase in the rotational speed œi of the first rotary pump 1 is also commanded in step S109, followed by a subroutine to control this control valve 11 in step S110 to increase the degree of opening Ai before returning to step S101. Conversely, if the maximum limit Ai.max opening of the regulating valve 11 is reached, a decrease in the rotation speed oei of the first rotodynamic pump 1 is commanded in a step S111, to try to maintain this rotodynamic pump 1 in an operating regime with a flow coefficient. optimal, even if it means not strictly adhering to the saturation margin setpoint NPSP2,c of the rotodynamic pump 2 directly downstream. In a subsequent step S112, it is verified that the rotational speed œi of the first rotodynamic pump 1 or the saturation margin NPSP2 of the rotodynamic pump 2 is not below the corresponding lower limits cüi.min or NPSP2,min before returning to the first step S101. If the rotational speed œi of the first rotodynamic pump 10 is below its lower limit cüi.min or if the saturation margin NPSP2 of the second rotodynamic pump 2 is below its lower limit NPSP2,min, the routine is interrupted, because the operating range of the entire rotodynamic pump system is then exceeded. The system may then enter a degraded operating mode, which is not the subject of this disclosure.

[0043] If the saturation margin NPSP2 of the rotodynamic pump 2 is not less than the corresponding saturation margin setpoint NPSP2,c, but the flow coefficient <t>i of the first rotodynamic pump 1 is less than the set flow coefficient In a corresponding step, a reduction in the rotational speed œi of the first rotodynamic pump 1 is commanded in step S113, and this rotational speed œi of the first rotodynamic pump 1 is then compared to the corresponding lower limit ooi.min in step S114. As long as the rotational speed œi remains above this lower limit coi.min, this control routine for the first rotodynamic pump 1 can return to step S101. However, if the rotational speed œi is no longer above this lower limit coi.min, the routine stops, because the operating range of the rotodynamic pump assembly is then exceeded. The system may then enter a degraded operating mode, which is not the subject of this disclosure.

[0044] If neither the NPSP2 saturation margin of the rotodynamic pump 2 nor the flow coefficient <t>i of the first rotodynamic pump 1 are less than the corresponding setpoints NPSP2,c and <t>In step S115, it is checked whether the degree of opening Ai of the control valve 11 of the first rotary pump 1 has reached a lower limit Ai.min. If the degree of opening Ai remains above this lower limit Ai.min, a reduction in the rotational speed œi of the first rotary pump 1 is also commanded in step S116, followed by a subroutine controlling this control valve 1 in step S117 to reduce the degree of opening Ai before returning to step S101. Conversely, if the degree of opening Ai is no longer above this lower limit Ai.min, an increase in the rotational speed œi of the first rotary pump 1 is commanded in step S118, to try to maintain this first rotary pump 1 in an operating regime with a flow coefficient <t>i optimal, even if it means not strictly adhering to the saturation margin setpoint NPSP2,c of the rotodynamic pump 2. In a subsequent step S119, it is verified that the rotational speed œi of the first rotodynamic pump 1 does not reach a corresponding upper limit coi, max with a flow coefficient <t>i less than a corresponding lower limit <t>i,min before returning to the first step S101. If the rotational speed 001 of the first rotodynamic pump 1 reaches its upper limit C l,max and the flow coefficient t>i is less than the corresponding lower limit <t>At i,min, the routine is interrupted because the operating range of the rotodynamic pump assembly is exceeded. The system may then enter a degraded operating mode, which is not the subject of this disclosure.

[0045] As illustrated in Figure 4, to control the rotodynamic pump 2, which is an intermediate rotodynamic pump between the first rotodynamic pump 1 and the last rotodynamic pump 3, in a first step S201, a saturation margin NPSP3 of the rotodynamic pump directly downstream, i.e. in this case of the rotodynamic pump 3, is calculated according to the formula:

[0046] [Math. 3] NPSP3 = P3 - P sat (T where P3 and T3 correspond respectively to the current pressure and temperature at the inlet of the rotodynamic pump directly downstream, i.e. in this case of the rotodynamic pump 3, as they can in particular be measured by the inlet pressure sensor 35 and the inlet temperature sensor 36, and Psat(T3) corresponds to the saturation pressure corresponding, for the liquid circulating through this set of rotodynamic pumps arranged in series, to the temperature T3.

[0047] In a second step S202, the saturation margin NPSP3 of the rotodynamic pump directly downstream, i.e. in this case the third rotodynamic pump 3, is compared to a saturation margin setpoint NPSP3,c for this rotodynamic pump 3.

[0048] If the saturation margin NPSP3 of the directly downstream rotary pump 3 is lower than the corresponding saturation margin setpoint NPSPs.c, the rotational speed 002 of the rotary pump 2 is compared to a corresponding upper limit 002, max in a step S203. If this upper limit 002, max is not reached, an increase in the rotational speed 002 of the rotary pump 2 is then commanded in a step S204 to increase the saturation margin NPSP3 of the rotary pump 3. However, if the upper limit 002, max is reached, the saturation margin setpoint NPSP2,c of the rotary pump 2 is increased in a step S205, so as to transfer part of the overall pumping effort to the directly upstream rotary pump.

[0049] After steps S204 or S205, a flow coefficient $>2 of the rotodynamic pump 2 is calculated, in a step S206, according to the formula:

[0050] [Math. 4] < where Q2 and 002 correspond, respectively, to the volumetric flow rate and the rotational speed of the current rotodynamic pump 2, as they can in particular be measured, respectively, by the volumetric flow rate sensor 24 and the rotational speed sensor 23 of this rotodynamic pump 2.

[0051] The flow coefficient d>2 of the rotodynamic pump 2 is compared to a setpoint flow coefficient <t>2,c corresponding in a step S207. If the flow coefficient d>2 of the second rotodynamic pump 2 is greater than the flow coefficient setpoint <t>2,c corresponding, the control routine of this rotodynamic pump 2 then returns to its first step S201. However, if the flow coefficient d>2 of the rotodynamic pump 2 is not greater than the flow coefficient setpoint <t>In step S208, a corresponding check is performed to verify whether the degree of opening A2 of the control valve 21 of the rotary pump 2 is still below an upper limit A2,max. If the degree of opening A2 of the control valve 21 of the rotary pump 2 is still below the upper limit A2,max, a subroutine controlling this control valve 21 is executed in step S209 to increase the flow coefficient $>2 of the rotary pump 2 before returning to step S101.On the other hand, if the degree of opening A2 of the control valve 21 of the rotodynamic pump 2 is no longer less than the upper limit A2,max, a decrease in the rotation speed 002 of the rotodynamic pump 2 is commanded in a step S210, to try to maintain this rotodynamic pump 2 in an operating regime with an optimal flow coefficient $>2, and the saturation margin setpoint NPSP2,c of the rotodynamic pump 2 is increased in a step S211, so as to transfer part of the overall pumping effort to the rotodynamic pump directly upstream, before returning to the first step S201.

[0052] If the saturation margin NPSP3 of the directly downstream rotary pump 3 is not less than the corresponding saturation margin setpoint NPSPs.c, the rotational speed 002 of the second rotary pump 2 is compared to a corresponding lower limit 002,min in a step S212. If the rotational speed 002 of rotary pump 2 remains above this lower limit 002,min, a decrease in the rotational speed 002 of rotary pump 2 is then commanded in a step S213. However, if the rotational speed 002 of rotary pump 2 is no longer above this lower limit 002,min, the saturation margin setpoint NPSP2,c of rotary pump 2 is decreased in a step S214, so as to transfer part of the overall pumping effort to this rotary pump 2.

[0053] After steps S213 or S214, the flow coefficient $>2 of the rotary pump 2 is calculated, according to the aforementioned formula, in a step S215, and compared to a corresponding flow coefficient setpoint 2, c in a step S216. If the flow coefficient $>2 of the rotary pump 2 is not greater than the corresponding flow coefficient setpoint 02, c, the control routine for this rotary pump 2 then returns to its first step S201. However, if the flow coefficient $>2 of the rotary pump 2 is greater than the corresponding flow coefficient setpoint 02, c, it is checked in a step S217 whether a degree of opening A2 of the control valve 21 of the rotary pump 2 is still greater than a lower limit A2,min.If the degree of opening A2 of the control valve 21 of the rotodynamic pump 2 is still below the upper limit A2,max, the subroutine controlling this control valve 21 is executed in step S218 to reduce the flow coefficient $>2 of the second rotodynamic pump 2 before returning to step S201. Conversely, if the degree of opening A2 of the control valve 21 of the rotodynamic pump 2 is no longer above the lower limit A2,min, an increase in the rotational speed 002 of the rotodynamic pump 2 is commanded in step S219, to try to maintain this rotodynamic pump 2 in an operating regime with a flow coefficient. <t>2 optimal, and the saturation margin setpoint NPSP2,c of the rotodynamic pump 2 is decreased in a step S220, so as to transfer part of the overall pumping effort to this rotodynamic pump 2.

[0054] It should be noted that, although in the illustrated embodiment the series-connected rotodynamic pump assembly comprises only one rotodynamic pump 2 interposed between the first rotodynamic pump 1 and the last rotodynamic pump 3, it is also possible to have a plurality of rotodynamic pumps interposed in series between the first rotodynamic pump 1 and the last rotodynamic pump 3. In this case, each of these intermediate rotodynamic pumps could be controlled in a manner analogous to this rotodynamic pump 2, based on its own flow coefficient and the saturation margin of the rotodynamic pump located directly downstream. Furthermore, it is also possible to have no rotodynamic pump interposed between the first rotodynamic pump and the last rotodynamic pump.

[0055] As illustrated in Figure 5, to control the last rotodynamic pump 3, in a first step S301, the outlet pressure Po of this last rotodynamic pump 3 is compared to an outlet pressure setpoint Po,c for this last rotodynamic pump 3.

[0056] If the outlet pressure Po of the last rotary pump 3 is lower than the outlet pressure setpoint Po,c, the rotational speed 003 of rotary pump 3 is compared to a corresponding upper limit 003,max in a step S302. If this upper limit 003,max is not reached, an increase in the rotational speed 003 of rotary pump 3 is then commanded in a step S303. However, if the upper limit 003,max is reached, the saturation margin setpoint NPSPs.c of rotary pump 3 is increased in a step S304, so as to transfer part of the overall pumping effort to the rotary pump directly upstream.

[0057] After steps S303 or S304, a flow coefficient d>3 of this last rotodynamic pump 3 is calculated, in a step S305, according to the formula:

[0058] [Math. 6] where Û3 and 003 correspond, respectively, to the volumetric flow rate and the rotational speed of the rotodynamic pump 3, as measured, respectively, by the volumetric flow rate sensor 34 and the rotational speed sensor 33 of this rotodynamic pump 3.

[0059] This flow coefficient d>3 of the rotodynamic pump 3 is then compared to a setpoint flow coefficient <t>3,c corresponding in a step S306. If the flow coefficient d>3 of the rotodynamic pump 3 is greater than the flow coefficient setpoint <t>3,c corresponding, the control routine of this rotodynamic pump 3 then returns to its first step S301. However, if the flow coefficient d>3 of the rotodynamic pump 3 is not greater than the flow coefficient setpoint <t>3,c corresponding, we proceed to check, in a step S307, whether a degree of opening A3 of the control valve 31 of the rotodynamic pump 3 is still less than an upper limit A3, max. If the degree of opening A3 of the control valve 31 of the rotodynamic pump 3 is still less than the upper limit A3, max, we proceed to a subroutine controlling this control valve 31 in a step S308 to increase the flow coefficient d>3 of the rotodynamic pump 3 before returning to step S301. On the other hand, if the degree of opening A3 of the control valve 31 of the rotodynamic pump 3 is no longer less than the upper limit A3, max, a decrease in the rotation speed 003 of the rotodynamic pump 3 is commanded in a step S309, to try to maintain this rotodynamic pump 3 in an operating regime with an optimal flow coefficient d>3, and the saturation margin setpoint NPSPs.c of the rotodynamic pump 3 is increased in a step S310, so as to transfer part of the overall pumping effort to the rotodynamic pump directly upstream, in order to meet the outlet pressure setpoint Po,c, before returning to the first step S301.

[0060] If the outlet pressure Po of the rotary pump 3 is not lower than the corresponding outlet pressure setpoint Po, the rotational speed 003 of the rotary pump 3 is compared to a corresponding lower limit 003, min in a step S311. If the rotational speed 003 of the rotary pump 3 remains above this lower limit 003, min, a decrease in the rotational speed 003 of the rotary pump 3 is then commanded in a step S312. However, if the rotational speed 003 of the rotary pump 3 is no longer above this lower limit 003, min, the saturation margin setpoint NPSPs.c of the rotary pump 3 is decreased in a step S313, so as to transfer part of the overall pumping effort to this rotary pump 3 to maintain the outlet pressure setpoint Po,c.

[0061] After steps S312 or S313, the flow coefficient d>3 of the rotary pump 3 is calculated, according to the aforementioned formula, in a step S314, and compared to a corresponding flow coefficient setpoint 03, c in a step S315. If the flow coefficient d>3 of the rotary pump 3 is not greater than the corresponding flow coefficient setpoint 03, c, the control routine of this last rotary pump 3 then returns to its first step S301. However, if the flow coefficient d>3 of the rotary pump 3 is greater than the corresponding flow coefficient setpoint 03, c, it is checked, in a step S316, whether a degree of opening A3 of the control valve 31 of the rotary pump 3 is still greater than a lower limit A3, min.If the degree of opening A3 of the control valve 31 of the rotodynamic pump 3 is still greater than the lower limit A3,min, the subroutine controlling this control valve 31 is executed to reduce the flow coefficient d>3 of the rotodynamic pump 3 in a step S317 before returning to step S301. Conversely, if the degree of opening A3 of the control valve 31 of the rotodynamic pump 3 is no longer greater than the lower limit A3,min, an increase in the rotational speed 003 of the rotodynamic pump 3 is commanded in a step S317, to try to maintain this rotodynamic pump 3 in an operating regime with a flow coefficient. <t>3 optimal, and the saturation margin setpoint NPSPs.c of the rotodynamic pump 3 is decreased in a step S319, so as to transfer, to this rotodynamic pump 3, part of the overall pumping effort to respect the outlet pressure setpoint Po,c.

[0062] The subroutine for controlling the control valves 11, 21 or 31 of each of the rotodynamic pumps 1, 2 and 3, as carried out in steps S110, S117, S209, S217, S308 or S316 of the routines previously described, is illustrated in Figure 6. In a first step S501, the flow coefficient 0, where i is the integer corresponding to the position of the respective rotodynamic pump, is compared to its respective setpoint 0i,c.

[0063] If the flow coefficient T>i is less than its setpoint, the corresponding control valve opening degree Ai is then compared in step S502 to its upper limit Ai, max. If the opening degree Ai is still less than its upper limit Ai, max, an increase in the opening degree Ai is commanded in step S503 before concluding the subroutine. However, if the opening degree Ai has reached its upper limit Ai, max, in step S504 the flow coefficient T>i is compared to a corresponding lower limit. <t>i,min. If the flow coefficient T>i is still greater than its lower limit <t>i,min, the respective instruction <t>i,c is reduced in step S505 before concluding the subroutine. However, if the flow coefficient T>i is no longer greater than its lower limit <t>At time i,min, the subroutine terminates because the operating range of the rotodynamic pump assembly is exceeded. The system may then enter a degraded operating mode, which is not the subject of this disclosure.

[0064] If the flow coefficient T>i is not less than its setpoint <t>In step S506, the degree of opening Ai of the corresponding control valve is then compared to its lower limit Ai, min. If the degree of opening Ai is still greater than its lower limit Ai, min, a reduction in the degree of opening Ai is commanded in step S507 before concluding the subroutine. However, if the degree of opening Ai is no longer greater than its upper limit Ai, min, in step S508 the flow coefficient T>i is compared to a corresponding upper limit. <t>i,max. If the flow coefficient T>i is still less than its upper limit <t>i,max, the respective setpoint d>i, c is increased in step S509 before concluding the subroutine. However, if the flow coefficient T>i is no longer below its lower limit <t>At the maximum value of i, the subroutine terminates because the operating range of the rotodynamic pump assembly is exceeded. The system may then enter a degraded operating mode, which is not the subject of this disclosure.

[0065] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. For example, the rotodynamic pumps could be integrated into a fuel supply circuit connecting a fuel tank to a combustion chamber of an internal combustion engine, particularly an aircraft engine, and / or to a fuel cell. Individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered illustrative rather than restrictive.

[0066] It is also evident that all the characteristics described with reference to a process are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a process.< / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t> < / t>

Claims

Demands

1. A method for controlling a set of rotodynamic pumps (1, 2, 3) arranged in series, comprising at least one upstream rotodynamic pump disposed directly upstream of a downstream rotodynamic pump, for pumping a liquid, wherein: The rotational speed of the upstream rotodynamic pump and the degree of opening of a control valve of the upstream rotodynamic pump are controlled as a function of a saturation margin of the downstream rotodynamic pump and a flow coefficient of the upstream rotodynamic pump, where the saturation margin of the downstream rotodynamic pump is a difference between current pressure and saturation pressure of the liquid inlet of the downstream rotodynamic pump and the flow coefficient of the upstream rotodynamic pump is the volumetric flow rate of the upstream rotodynamic pump divided by the rotational speed of the upstream rotodynamic pump.

2. A control method according to claim 1, comprising a step (S101, S210) of comparing the saturation margin of the downstream rotodynamic pump with a saturation margin setpoint of the downstream rotodynamic pump, followed by a step (S106, S205) of increasing the rotational speed of the upstream rotodynamic pump if the saturation margin of the downstream rotodynamic pump is less than the saturation margin setpoint of the downstream rotodynamic pump, or a step (S113, S213) of decreasing the rotational speed of the upstream rotodynamic pump if the saturation margin of the downstream rotodynamic pump is greater than the saturation margin setpoint of the downstream rotodynamic pump.

3. A control method according to claim 2, comprising a step (S206, S305) of increasing a saturation margin setpoint of the upstream rotodynamic pump if an upper limit of the rotational speed of the upstream rotodynamic pump is reached.

4. A control method according to claim 2, comprising a step (S214, S313) of reducing a saturation margin setpoint of the upstream rotodynamic pump if a lower limit of the rotational speed of the upstream rotodynamic pump is reached.

5. A control method according to any one of the preceding claims, comprising a step (S501) of comparing the flow coefficient of the upstream rotary pump with a setpoint for the flow coefficient of the upstream rotary pump, followed by a step (S503) of opening the control valve of the upstream rotary pump if the flow coefficient of the upstream rotary pump is less than the setpoint for the flow coefficient of the upstream rotary pump, or a step (S507) of closing the control valve of the upstream rotary pump if the flow coefficient of the upstream rotary pump is greater than the setpoint for the flow coefficient of the upstream rotary pump.

6. Control method according to claim 5, comprising a step (S505) of reducing the flow coefficient setpoint if an upper limit of the degree of opening of the upstream rotodynamic pump control valve is reached.

7. Control method according to claim 5, comprising a step (S509) of increasing the flow coefficient setpoint if a lower limit of the degree of opening of the upstream rotodynamic pump control valve is reached.

8. A control method according to any one of the preceding claims, wherein: a rotational speed of the downstream rotodynamic pump and a degree of opening of a control valve of the downstream rotodynamic pump are controlled as a function of an outlet pressure of the downstream rotodynamic pump and a flow coefficient of the downstream rotodynamic pump, where the flow coefficient of the downstream rotodynamic pump is the volumetric flow rate of the downstream rotodynamic pump divided by the rotational speed of the downstream rotodynamic pump.

9. A control method according to any one of the preceding claims, wherein the set of rotodynamic pumps (1, 2, 3) arranged in series comprises more than two rotodynamic pumps.

10. A control method according to any one of the preceding claims, wherein the liquid is a cryogenic liquid.

11. A control method according to any one of the preceding claims, wherein the set of rotodynamic pumps (1, 2, 3) arranged in series supplies propellant to a propulsion chamber (400) of a rocket engine (100).

12. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to implement the control method according to any one of the preceding claims.

13. Electronic control unit (900) adapted to implement the control method according to any one of claims 1 to 11.

14. Liquid supply system, in particular for engine or fuel cell, comprising a set of rotodynamic pumps (1,2,3) and the electronic control unit (900) according to claim 13 for controlling the set of rotodynamic pumps (1,2,3).

15. Rocket engine (100) comprising a propulsion chamber (400) and the liquid supply system according to claim 14 for supplying the propulsion chamber (400) with liquid propellant.

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