JPS6147760B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a three-axis satellite attitude control device for driving a reaction wheel without using a yaw angle signal in a bias moment time satellite having a reaction wheel.

A three-axis satellite has three coordinate axes fixed to the satellite.
An artificial satellite that is controlled so that its (roll axis), Y (pitch axis), and Z (yaw axis) are aligned with the direction of travel, the direction perpendicular to the orbital plane, and the direction toward the center of the earth, respectively. The rotation angles around the respective axes X, Y, and Z are called attitude angles, and are called roll angles, pitch angles, and yaw angles, respectively.

Usually, a three-axis satellite attitude control system is configured as shown in FIG.

In the figure, 1 is an earth sensor that detects the roll angle and pitch angle, 2 is a momentum wheel, and 3 is a momentum wheel.
is a reaction wheel, and 4 is a control device that drives these two wheels 2 and 3. In the figure, the X, Y, and Z coordinate axes indicate the roll axis, pitch axis, and yaw axis, respectively.

In FIG. 1, the momentum wheel 2 has the function of giving a large angular momentum to the pitch axis to reduce posture fluctuations due to disturbance torque, and at the same time, the momentum wheel 2 is designed to reduce the pitch angle error detected by the earth sensor 1 to zero. The rotation is controlled. Similarly, the reaction wheel 3 is configured such that the rotation of the wheel is controlled so as to make the roll angle error detected by the earth sensor 1 zero. FIG. 2 shows the above configuration as an operation. In particular, in a bias momentum three-axis satellite, the roll motion and yaw motion are strongly coupled due to the angular motion of the momentum wheel, so if the roll angle is controlled, the yaw angle, which is difficult to observe, will not be detected. The advantage is that the yaw angle can be controlled indirectly.

In a three-axis satellite having such a configuration, the control device 4 operates to change the phase of the detected pitch angle and roll angle signals through a filter, and rotate each wheel with a torque proportional to the output from the filter. Here, the pitch control circuit is a normal phase advance circuit and there is no particular problem, but the roll control circuit is a non-minimum circuit in order to stabilize the system. A non-minimum phase circuit is a type of filter that has the characteristic that the output phase lags the input phase by 180 degrees or more. Conventionally, the transfer function of this circuit has been expressed in the form, for example, K1- _T2S /1+ _T1S , and has a positive real number pole.

However, in the case of such a circuit, it is difficult to stably increase the attenuation rate of the system, and the second
As shown in the figure, since the control method only takes as input the difference between the roll angle setting value and the roll angle signal, it has undesirable characteristics such as an excessively reverse response when the setting value is changed. .

This invention was made in order to eliminate the drawbacks of the conventional systems as described above, and consists of an observation device that estimates the yaw angular velocity from the roll angle signal and the drive torque signal of the reaction wheel, taking into account the dynamics of the satellite. However, by feeding back the estimated yaw angular velocity together with the roll angle signal to the reaction wheel, the purpose is to improve the damping characteristics of the satellite and the transient response characteristics to set value input.

A block diagram of such a roll angle control device is shown in FIG. In this figure, the yaw angular velocity estimation observation device 5 is an artificial satellite 10 output from the earth sensor 1.
This is for estimating the yaw angular velocity by inputting the roll angle signal of and the reaction wheel drive signal of the reaction wheel 3. The estimated yaw angular velocity is fed back to the reaction wheel drive circuit 41 as a suitable linear combination of the roll angle and the roll angle set value error signal. Here, it is known that the output from the observer 5 does not change the feedback characteristic root of the system, so the values of the amplifiers 1 and 6 and the amplifiers 2 and 7 are determined when the yaw angular velocity is directly known. You can use the same amplifier that is specified. Here, gain 1 and gain 2 are written to distinguish the amplification rates in Fig. 4,
It means an amplification device, but it does not indicate an amplification rate.

Observer 5 receives the driving torque μ which is the input of the artificial satellite.
This is to obtain an estimated rate of change Ψ of the unobservable yaw angle Ψ by electrically processing the output roll angle Ψ using the mechanical characteristics of the artificial satellite.

Approximately, the short-period motion characteristics of the satellite are described by a third-order differential equation, but this observation device is also a differential equation of at least second order, and can be expressed by equation (1).

Here, φ and Ψ are roll angular velocities, estimated values of yaw angular velocities Z ₁ and Z ₂ are state variables of the observer, and l ₁ and l ₂ are parameters used to obtain the eigenvalues of the observer.

In addition, in equation (1), the nutrition period of the satellite is 1.
It is assumed to be in radians per second. Note that here, Ψ indicates the output of the observation device and is the estimated value of the yaw angular velocity. Also, φ, Ψ, μ are Laplace transformed values,
The values that do not exist are used without distinction. The eigenvalue of the observation device 5 should normally be selected to be a negative real number about twice the nutrition angular velocity. In this way, by appropriately providing the amplifiers 1 and 6 and the amplifiers 2 and 7, it is possible to considerably widen the range of the damping rate and characteristic frequency of the satellite. Furthermore, as shown in FIG. 3, since the roll angle setting value input is directly applied as a control input, unnatural characteristics such as reverse response can be eliminated. With the above-mentioned observation device 5, the yaw angular velocity can be accurately estimated for the first time using the dynamics of the satellite. By controlling the drive torque of the reaction wheel using this estimated yaw angular velocity, the damping characteristics and transient response characteristics of the satellite can be improved.

In the above embodiment, the reaction wheel rotation axis is parallel to the yaw axis, but as shown in FIG. In the case of wheels, a similar effect can be obtained by simply changing the parameters of the observation device. The reaction wheel axis may be mounted in any direction as long as it is not parallel to the pitch axis. The reaction wheel drive circuit is also installed inside the satellite. In addition, as shown in Fig. 5, the wheel has a wheel configuration in which the two wheel rotation axes are tilted from the pitch axis Y to the positive and negative directions of the yaw axis Z, with an offset angle β, and the momentum wheel function is determined by the sum of the two rotation vectors. There are also satellites with a composite momentum wheel that functions as a reaction wheel, but satellites with this type of system are essentially equivalent to the one in Figure 1, so they are exactly the same. Observers can be applied.

As described above, according to the present invention, since the yaw angular velocity estimation and observation device is used in the reaction wheel drive circuit, it is possible to significantly improve the motion characteristics of a satellite having the same wheel configuration.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a control system for a normal bias momentum three-axis satellite, Figure 2 is a block diagram of a conventional control system, and Figure 3 is a diagram of a satellite attitude control system using a yaw angular velocity estimation observation device according to the present invention. The block diagrams, FIGS. 4 and 5, are configuration diagrams of three-axis satellite control devices of different types. In the figure, 1 is an earth sensor, 2 is a momentum wheel, 3 is a reaction wheel, 4 is a wheel drive control device, 41 is a reaction wheel drive circuit, 5 is a yaw angular velocity estimation observation device, 6 is an amplifier 1, 7 The amplifiers 2 and 8 are composite momentum wheels. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1 In a three-axis satellite attitude control system in which the roll axis, pitch axis, and yaw axis fixed to the satellite are controlled so that they coincide with the direction of travel of the satellite, the direction perpendicular to the orbital plane, and the direction of the center of the earth, respectively. ,
an earth sensor that detects a roll angle indicating the attitude around the roll axis and the pitch axis; a reaction wheel whose driving torque is controlled so that the detected roll angle becomes a set value; and the driving torque and the roll angle. A yaw angular velocity observation device that estimates the yaw angular velocity around the yaw axis from the yaw angular velocity, and a signal that is the sum of the estimated yaw angular velocity signal and an error signal between the roll angle and the set value drives the reaction wheel. A three-axis satellite attitude control system equipped with a reaction wheel drive circuit that controls torque.