Control System and Control Method for Controlling a Momentum Wheel Device for Stabilizing a Spacecraft

Abstract

A control system for a momentum wheel device is specified, wherein the momentum wheel device is a real momentum wheel device (1) and has a momentum wheel which is driven by a motor, and wherein a simulated momentum wheel device (2) is provided which simulates the behaviour of an ideal momentum wheel on the basis of an ideal physical model (12). The rotational speed of both the real momentum wheel device (1) and of the simulated momentum wheel device (2) can be changed by a torque command (6). A comparator device (11) is provided for comparing the real rotational angle (9) of the real momentum wheel device (1) and the simulated rotational angle (14) of the simulated momentum wheel device (2) and for generating a fault signal (15) corresponding to a deviation between the real rotational angle (9) and the simulated rotational angle (14). The fault signal (15) can be conducted to a control device (3), in order to actuate the motor on the basis of the fault signal (15), for the purpose of reducing the deviation.

Claims

1-11. (canceled)

12. A control system for a momentum wheel device that is a real momentum wheel device including a momentum wheel driven by a motor, the control system comprising: a simulated momentum wheel device configured to simulate a behavior of an ideal momentum wheel based on an ideal physical model; a control device configured to control the motor of the real momentum wheel device; a command device configured to specify a torque command to change a speed of both the real momentum wheel device and of the simulated momentum wheel device; a rotation angle detection device configured to detect a real rotation angle of the real momentum wheel device; an integration device configured to calculate a simulated rotation angle of the simulated momentum wheel device due to the given torque command; a comparator device configured to compare the real rotation angle and the simulated rotation angle, and to generate an error signal corresponding to a deviation between the real rotation angle and the simulated rotation angle, wherein the error signal can be fed to the control device to control the motor due to the error signal in order to reduce the deviation.

13. The control system of claim 12, wherein the command device is configured to transmit the torque command to the control device for the real momentum wheel device and to the simulated momentum wheel device.

14. The control system of claim 12, wherein the simulation of the behavior of the ideal momentum wheel is conducted based on the ideal physical model, without accounting for friction.

15. The control system of claim 12, wherein the ideal physical model corresponds to an equation of state of a rotational movement.

16. The control system of claim 15, wherein the equation of state has the following form:
φ=φ.sub.t0+ω.sub.t0×Δt.sub.1+0.5×α.sub.t0×Δt.sup.2 wherein φ is the rotation angle, ω is the rotational or angular speed, Δt is a time increment, and α is the torque inclusive of the moment of inertia.

17. The control system of claim 12, wherein the integration device is configured to calculate the simulated rotation angle by two-fold integration of the torque command.

18. The control system of claim 12, wherein a motor control is provided which can be controlled by the control device and, in turn, serves to operate the motor.

19. The control system of claim 12, further comprising a rotational speed detection device configured to detect the real rotational speed of the real momentum wheel device.

20. The control system of claim 12, wherein: an observer combining the rotation angle detection device and the rotational speed detection device is configured to determine the real rotational speed and/or the real rotation angle of the real momentum wheel device, and the observer is further configured to perform an error correction of the rotational speed and/or of the rotation angle of the real momentum wheel device.

21. The control system of claim 12, wherein the integration device is configured to calculate a simulated rotational speed of the simulated momentum wheel device by simple integration of the given torque command, the control system further comprising: a rotational speed comparator device configured to compare the real rotational speed and the simulated rotational speed, and to generate a rotational speed deviation signal corresponding to a deviation between the real rotational speed and the simulated rotational speed.

22. A control method for controlling a momentum wheel device for stabilizing a spacecraft, the method comprising: providing the momentum wheel device as a real momentum wheel device comprising a momentum wheel driven by a motor; providing a simulated momentum wheel device based on an ideal physical model; concurrent feeding of a torque command to the real momentum wheel device and to the simulated momentum wheel device to change a rotational speed of both the real momentum wheel device and the simulated momentum wheel device; controlling the motor to change the rotational speed dependent on the fed torque command; detecting a real rotation angle of the real momentum wheel device; calculating a simulated rotation angle of the simulated momentum wheel device by two-fold integration of the fed torque command; comparing the real rotation angle and the simulated rotation angle and generating an error signal corresponding to a deviation between the real rotation angle and the simulated rotation angle; and controlling the motor due to the error signal to reduce the deviation.

Description

[0045] These and additional advantages and features are explained in more detail in the following text, based on an example with the aid of the accompanying FIGURE. The only FIGURE shows, in a schematic form, the structure of a control system for a momentum wheel device for stabilizing a spacecraft.

[0046] The control system essentially consists of a real momentum wheel device 1 and a simulated momentum wheel device 2. The real momentum wheel device 1 is that momentum wheel device which is to be controlled by the control system within the actual meaning and which is used for the stabilization or alignment of the satellite. In principle, it is structured in a known manner and includes an actual momentum or reaction wheel not shown in the FIGURE, which is set in rotational motion by a motor which is also not illustrated. Due to the rotation of the momentum wheel and the gyroscopic effect arising in this process, the desired stabilizing effect is achieved. A similar flywheel device with regard to the mechanical structure of the real momentum wheel device 1 is known from DE 39 21 765 A1.

[0047] The real momentum wheel device 1 includes a control device 3 to control an actual motor control 4 which, in turn, includes the power electronics or current controller for the motor, etc.

[0048] The control device 3 can be elaborately designed and take appropriate control measures in a known manner such as accelerating or decelerating the momentum wheel, as well as corresponding start and stop functions. In addition, it is possible to store information (e.g. tables) in the control device 3 at which conditions (rotational speed, temperature, etc.) which bearing conditions (e.g. bearing friction) exist on the momentum wheel. If, for example, the satellite moves in a very cold area (shadow), the momentum wheel bearings will be cooled, whereby the bearing friction can increase. To compensate for this effect, the control device 3 can take corresponding control measures.

[0049] A command device 5 which, for example, can be part of the actual satellite control, is upstream of the control device 3. In this case, for example, a desired movement or alignment of the satellite is preset, which leads to a corresponding commanding of the momentum wheel device 1. Correspondingly, the command device 5 gives a torque command 6 to the control device 3. In this process, the torque is the physical basic command of the speed and underlies the change in the rotational speed of the momentum wheel.

[0050] The control device 3 can supply appropriate status information 7 to the superordinate satellite control from which, for example, information about the wheel status, the wheel speed or the wheel angle is obtained.

[0051] The motor controlled by the motor control 4 effects the rotational movement of the real momentum wheel. The rotational movement can be measured in a suitable manner. For example, it is known to provide Hall sensors (e.g. three Hall sensors) on the motor rotor in order to lock the rotational position of the rotating wheel.

[0052] Taking time into account, also the wheel rotational speed can be directly derived from the rotational position (the wheel rotation angle). For this purpose, an observer 8 is provided, which includes a rotation angle detection device and a speed or rotational speed detection device. In addition, the observer 8 can also provide further correction or estimation methods to detect the actual position of the wheel (the wheel rotation angle) or the wheel speed as precisely as possible. Due to the high rotational speed of the momentum wheel (e.g. 6000 revolutions per minute) on one hand and the extremely high requirements for the measurement accuracy on the other hand (e.g. an accuracy of 0.005 revolutions per minute is to be achieved for this high rotational speed of, e.g., 6000 min.sup.−1), the results of the observer 8 is usually never exact information, but best possible estimations at all times.

[0053] As a result of the observer 8, the real rotation angle 9 on one hand and the real rotational speed 10 (wheel speed) on the other hand is output.

[0054] The real rotation angle is delivered to a comparator device 11 to be explained later.

[0055] Parallel to the real momentum wheel device 1 thus described, the simulated momentum wheel device 2 is provided.

[0056] It is solely based on an ideal physical model 12, namely the equation of state for a rotational movement which, for example, can have the following form:

φ=φ.sub.t0+ω.sub.t0×Δt.sub.1+0.5×a.sub.t0×Δt.sub.1.sup.2  (2)

wherein φ is the rotation angle, ω the rotational speed (angular speed), Δt a time increment, and a the torque inclusive of the moment of inertia.

[0057] Thus, the simulated momentum wheel device 2 is solely realized with software, without requiring “real-world” mechanical momentum wheel components. The same torque command 6 from the command device 5, which is also fed to the control device 3, serves as an input variable for the physical model. The torque command 6 must naturally be fed to the real momentum wheel device 1 and to the simulated momentum wheel device 2 at the same time. In the physical model 12, a first integration 12a occurs initially, so that, as a result, a simulated speed or rotational speed 13 is obtained.

[0058] The simulated rotational speed 13 is subjected to a second integration 12b, whereby a simulated rotation angle 14 is obtained. This simulated rotation angle 14 is an ideal value due to the ideal physical model. Thus, it is a target value at the same time which is to be achieved by the real momentum wheel device 1.

[0059] For this purpose, the simulated rotation angle 14 is also fed to the comparator device 11, where a comparison between the simulated rotation angle 14 and the real rotation angle 9 is made. The difference identified in this process is fed back to the control device 3 as an error signal 15. The control device 3 is then, in turn, in a position to control the motor control 4 and thus the real momentum wheel in order to change the rotational speed of the real momentum wheel and reduce the error between the simulated rotation angle 14 and the real rotation angle 9.

[0060] The simulated rotational speed 13 can, together with the real rotational speed 10, be fed to a rotational speed comparator device 16. The rotational speed comparator device 16 determines a deviation between the values and can, accordingly, supply a rotational speed deviation signal 17 to the control device 3. This signal can be further processed as information by the control device 3. However, for the actual momentum wheel control it is subordinate since it is solely performed due to the determined rotation angles 9, 14 or their deviations from one another.