Patent Application
20090228117
The invention lies in the field of controlling the operation of a complex system.
It applies particularly, but not exclusively, to controlling an engine.
In general, regulated complex systems respond to external setpoints, with a regulation relationship adjusting internal operating variables that tend to bring the system to the operating point that complies with the setpoint, and to keep it there.
For example, with an engine, an increasing thrust setpoint has as its first effect an increase in the variable that is representative of pressure in the combustion chamber of the engine.
In order to regulate a complex system, it is known to use a setpoint that is filtered by a first order filter, as shown in
In this example, the filtered setpoint C* is obtained from the setpoint C by applying equation (1) below, in which the gain K represents the dynamic speed of the filter and C*n-1 is a preceding value of the filtered setpoint:
C*=K×(C−C*n-1)+C*n-1 (1)
In
Furthermore, complex systems usually include subsystems having internal parameters that need to be kept below respective operating limits, regardless of the operating conditions desired of the system.
For example, in an engine, the speed of rotation of a turbine must never exceed a predetermined limit value.
Conflicts can therefore arise between the need to comply with the operating limits of a subsystem and the objective of responding to the setpoints.
These conflicts can arise in particular due to poor knowledge of the utilization ranges while designing the system, or to drift over time in certain characteristics of the system.
In an attempt to mitigate this problem, the prior art proposes systems such as that shown in
A saturator SAT concerning the rate at which a setpoint can change is applied to the parameter K×(C−C*n-1), where the value of the filtered setpoint C* is obtained using equation (2) below:
C*=SAT(K×(C−C*n-1))+C*n-1 (2)
It is also possible to use a second saturator concerning the rate at which a setpoint can change, with the value of the filtered setpoint C* then being obtained by equation (3):
C*=SAT(SAT(K×(C−C*n-1))+C*n-1) (3)
However, that solution is unsatisfactory since although it enables the rate of change of operating points to be slowed down while tending towards the setpoint, and although it enables the setpoint to be limited, it does not in any way guarantee that critical parameters of the subsystems are kept within their own operating limits.
The invention provides a device for controlling a regulated system enabling it to tend towards a desired setpoint while giving priority to complying with operating limits for internal parameters of the system.
More precisely, the invention provides a control device for controlling at least one operating variable V of a regulated system, the device comprising:
In general, the gain of the filter module, in other words the speed of the filter, is adjusted so that the above-mentioned parameter complies with its operating limit.
In accordance with the invention, this constraint has priority over complying with the setpoint.
In a particular embodiment of the invention, the control module obtains the factor α by a relationship of the type α=f(δ), where δ is the difference between the parameter P and the operating limit LFP, and f is a saturated affine function.
The person skilled in the art will understand that the normal passband of the filter is obtained when α=1.
Advantageously, the gain control factor α can take negative values, serving to define the rate at which the critical parameter returns to below its operating limit in the event of exceeding it.
In accordance with the invention, a plurality of constraints may be implemented simultaneously.
In this particular embodiment of the invention, the control module takes account of a plurality of system parameters and selects the gain control factor as being the minimum value of the values αi, where αi=f(δi), δi being the difference between a parameter Pi and its operating limit LFPi, and f being a saturated affine function.
In a preferred embodiment of the invention, the difference between the protected parameter and its operating limit is taken into account only when the residue between the setpoint and its filtered value is positive (an instruction to raise the operating point), the gain of the filter not being weighted when the residue is negative (an instruction to lower the operating point).
Advantageously, this characteristic makes it possible to brake the rate of change of operating points when the protected parameter approaches its operating limit, while applying a normal speed (α not applied) when instructing a lowering of the setpoint, in other words movement away from the operating limit.
In a particular embodiment of the invention, the control module sets the gain control factor to a constant on detecting at least one predetermined event.
It is thus possible to short circuit or inhibit the function of calculating the gain control factor and to return it to its initial value or to some other predetermined value.
In a particular embodiment of the invention, the correction module applies a multivariable command relationship of the Predictive Internal Model (PIM) type. This multivariable command makes it possible to obtain a large stability margin. It is also very robust in systems that have a parameter that varies moderately.
The invention also provides an engine including two pumps feeding a combustion chamber with two propellant components, the flow rate of each of the components being adjustable by means of respective valves, the engine including a control device as specified above, in which:
Other characteristics and advantages of the present invention appear from the following description, with reference to the accompanying drawings that show an embodiment having no limiting character. In the figures:
In the example described below, the control device 10 controls an operating variable V of a regulated system 40.
It is assumed that the control device 10 has an input receiving a setpoint C, this setpoint C being filtered by a filter module 20, the filtered setpoint being written C*. The difference ε between the setpoint C and its filtered value C* is referred to below as the “residue”:
ε=C−C* (4)
The filtered setpoint C* is one input to a module 30 for correcting the variable V of the regulated system 40 by servo-control.
This correction module 30 generates a command U that is applied to the regulated system 40. As in the prior art, the filter module 20 includes a subtracter 21, an adder 24, and a delay 25. In the example described here, it also includes two optional saturators 26 and 27 having effects that are identical to those described with reference to
However, in accordance with the invention, the gain K of the filter module 20 can be weighted as a function of the residue ε and of a weighting factor α, α1 so as to guarantee that a critical parameter P of the regulated system 40 complies with a operating limit LFP.
For this purpose, the control device in accordance with the invention has a module 50 that receives as input the value of the parameter P of the regulated system 40.
In the embodiment described, the control module 50 comprises a processor 51 suitable for determining whether a predetermined event is occurring.
If so, the processor 51 sets the weighting factor to be equal to a constant α1.
Otherwise, if no predetermined event is detected, then the processor 51 generates a gain control factor α by applying a relationship α=f(δ), where δ is the difference between the value of the parameter P and the operating limit LFP for this parameter, the limit LFP being stored in the control module 50.
An example of a profile for the factor α is described below with reference to
There follows a detailed description of how the weighting is calculated for the gain K of the filter module in the embodiment described.
In this example, two situations can arise as a function of the sign of the residue ε.
When the residue is positive (ε+), the filtered setpoint C* is obtained at the output from the multiplier 29 in application of equation (5) if the control module 50 has detected an event EV, or otherwise in application of equation (6):
C*=C*
n-1
+K·ε
+·α1 (5)
C=C*
n-1
+K·ε
+·α (6)
In the embodiment described, when the residue ε is negative (ε−), gain weighting is not implemented.
Under such circumstances, the filtered setpoint C* is obtained by equation (7):
C=C*
n-1
+K·ε
− (7)
In the embodiment described, the correction module 30 includes means 32 for generating the command U in application of a command relationship of the Predictive Internal Model type, said module 32 having as inputs: firstly the filtered setpoint C*, and secondly the operating variable V of the system 40.
The regulated system 40 has two ports 41 and 42 enabling the control module 50 and the correction module 30 respectively to obtain the value of the critical parameter P that needs to be monitored and the value of the operating variable V of the system.
In
This factor α is obtained by a relationship of the type α=f(δ), where δ is the difference between the parameter P and its operating limits LFP, and f is a saturated affine function.
In the example described, two values δMIN and δMAX are defined such that:
This profile thus defines a range in which the tracking speed is slowed down when δ lies in the range δMIN to δMAX, and two stages in which this speed varies fast when the parameter P departs from its operating limit LFP.
The engine has two propellant component tanks referenced 131 and 132, each of which is upstream from a respective pump 111 or 112. The delivery rate of each of these propellant components can be regulated by a respective valve 121, 122.
In the embodiment described, the engine includes a controller 105 adapted to obtain:
The controller 105 is adapted to generate commands VR1 and VR2 for controlling the extent to which each of the valves 121 and 122 is opened.
In this example, the controller 105 receives two setpoints, namely a setpoint PCC for pressure in the combustion chamber 100, and a setpoint RMC for the ratio of the mass flow rates of the two propellant components delivered to the combustion chamber 100.
The controller 105 thus continuously monitors the values of the regulated parameters, i.e. the pressure PC in the combustion chamber 100 and the ratio RM of the flow rates DE1 and DE2 upstream from the pumps 111 and 112.
The controller 105 constitutes a controller device in the meaning of the invention, in which:
Thus, the invention serves to adjust the positioning of the valves 121 and 122 so as to cause the regulated variables PC and RM to converge on the setpoint vector (PCC, RMC), this regulation being constrained to comply with the functional limit in terms of speed of rotation of the pumps 111 and 112.
The invention is particularly advantageous when certain internal members of the engine deteriorate, where such deterioration leads to the pumps operating at excessive speeds of rotation RT1 and RT2.
Under such circumstances, the invention makes it possible to limit the speeds of rotation of the pumps to below their operating limits, at the expense of failing to comply with the pressure and propellant component ratio setpoints PCC and RMC.
In
In the bottom portion of
It can be seen in the top portion of
This is made possible by regulating the tracking speed of the setpoint filter, this setpoint being slowed or braked once the speed of rotation of a pump reaches a predetermined value RT0. The person skilled in the art will understand, with reference to
d
MAX
=RTL1−RT0 (8)
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 0851485 | Mar 2008 | FR | national |
