CN105644810B - A kind of opened loop control reaction wheel rotation speed change and discharging method - Google Patents

Abstract

The invention provides a method for open-loop control of the speed change and unloading of the reaction wheel (flywheel for short), the specific steps are as follows: step 1, using four flywheels for control, and adjusting the control torque command of the reaction wheel of the fourth flywheel to the same size as The friction torque of the theoretical nominal speed is the same; step 2, limit the output control command of the controller to the maximum output torque, and distribute the control torque of each flywheel according to the flywheel distribution matrix, and limit the flywheel with the maximum output torque to the maximum output torque after distribution. torque, and scale the control torques of the other two flywheels proportionally; Step 3, calculate the synthetic angular momentum of the four flywheels, when the angular momentum of any axis reaches the unloading threshold range, and conforms to the relationship between the magnetic field strength and the angular momentum when unloading, Start the unloading of the magnetic torque device; Step 4, select the magnetic torque device in the direction with the largest unloading capacity to work, and use the switch control method to unload the flywheel.

Description

An open-loop control reaction wheel speed change and unloading method

technical field

The invention relates to the technical field of aerospace control, in particular to an open-loop control method for changing the rotational speed of a reaction wheel and unloading it.

Background technique

The reaction wheel is a common actuator for satellites. Due to the higher and higher requirements for satellite attitude accuracy and satellite life, the reaction wheel should be controlled to work near the optimum operating speed when performing attitude control to avoid excessive speed. Zero interference affects attitude accuracy while improving lifespan.

Using 4 flywheels for attitude control, the flywheels can be biased near the nominal speed to form zero momentum. For the torque control mode, the speed of the reaction flywheel will decrease under the action of friction torque. When the speed of the four reaction wheels decreases at the same time, It can also ensure stable attitude and zero momentum throughout the star, that is, it is impossible to maintain the flywheel speed through attitude closed-loop feedback. Therefore, to keep the flywheel near the nominal speed requires friction compensation for each flywheel, but because the friction torque of each flywheel is different , the compensation torque leads to the difference in the nominal speed of the flywheel, which affects the attitude control of the flywheel. In addition, the space environment disturbance torque will cause the flywheel to deviate from the nominal speed, and the disturbance is usually offset by unloading the magnetic torque device to ensure that the flywheel works near the nominal speed.

Contents of the invention

In order to solve the above problems, the present invention provides a method for open-loop control of reaction wheel speed variation and magnetic torque device unloading, comprising the following steps: Step 1, adopting a method comprising the first flywheel, the second flywheel, the third flywheel and the fourth flywheel The four flywheels are controlled, and the reaction wheel control torque command of the fourth flywheel is adjusted to be consistent with the friction torque of the theoretical nominal speed; step 2, the controller output control command is limited to the maximum output torque, and according to the first The flywheel allocation matrix composed of flywheel, second flywheel, and third flywheel in sequence distributes the control torque of each flywheel. After distribution, the flywheel with the largest output torque is limited to the maximum torque, and the control torque of the other two flywheels is scaled proportionally. Get three flywheel control torques; step 3, calculate the synthetic angular momentum of the four reaction wheels, and when the angular momentum of any shaft reaches the unloading threshold range, and conforms to the angular relationship between the magnetic field strength and the angular momentum during unloading, start the magnetic torquer unloading; step Fourth, select the magnetic torque device in the direction with the largest unloading capacity to work, and use the switch control method to unload the flywheel.

The advantage of the present invention is that only one flywheel is used for friction compensation in an open-loop manner, the flywheel does not participate in attitude control, and the other three flywheels perform attitude control. Due to the conservation of angular momentum, all flywheels are kept near the nominal speed. The method is simple to control, and the nominal rotational speed of the flywheel can also be controlled by adjusting the size of the compensation friction torque, which is flexible and convenient to use.

The accumulation of angular momentum generated by the disturbance torque of the space environment causes the flywheel speed to deviate from the nominal value, and the unloading of the magnetic torque device can offset the influence of the disturbance torque. The present invention adopts the internal source field as the reference magnetic field for magnetic unloading, and does not need to install a magnetometer, which simplifies the hardware configuration of the satellite; at the same time, the threshold value of the unloading controller is designed on the basis of fully analyzing the internal and external source fields to ensure the correctness of unloading control ; In addition, the switch control method is used to control the work of the magnetic torque device, which greatly simplifies the design of the drive control circuit.

Description of drawings

Accompanying drawing 1 is the judging logic diagram of the unloading judging condition of flywheel in the specific embodiment of the present invention;

Accompanying drawing 2 is the scheme of the specific embodiment of the present invention in the application example of the high-orbit satellite unloading strategy calculation magnetic torque device control instruction flow chart;

Accompanying drawing 3 is the scheme of the specific embodiment of the present invention in the application example of high orbit satellite;

Accompanying drawing 4 is the satellite attitude graph in the application example of the high-orbit satellite of the scheme of the specific embodiment of the present invention.

detailed description

The specific implementation of the method provided by the present invention will be described in detail below in conjunction with the accompanying drawings.

Step 1: Four flywheels including the first flywheel, the second flywheel, the third flywheel and the fourth flywheel are used for control, and the control torque command of the fourth flywheel is adjusted to be consistent with the friction torque of the theoretical nominal speed.

In this step, the friction torque T _f4 is obtained according to the nominal speed of the fourth flywheel, and the friction torque is compensated to obtain the reaction wheel control command T _wc4 :

T _wc4 = -T _f4

and the reaction wheel torque control voltage:

U _wc4 =T _wc4 /k _i4

Wherein, k _i4 is the fourth flywheel moment coefficient.

When in orbit, the friction torque can be increased or decreased according to the change of the speed of the fourth flywheel, and the nominal speed range of the flywheel can be adjusted.

Step 2: limit the output control command of the controller to the maximum output torque, and distribute the control torque of each flywheel according to the flywheel distribution matrix formed by the order of the first flywheel, the second flywheel and the third flywheel. The flywheel is limited at the maximum torque, and the control torques of the other two flywheels are scaled proportionally to obtain the control torques of the three flywheels.

In step 2, the installation matrix C _{u of the first flywheel, the second flywheel, and the third flywheel is inverted to the installation matrix C u of} the reaction wheel, and the corresponding distribution matrix C _P of the reaction wheel can be obtained.

First generate the reaction wheel control command T _wc . The command T _c is controlled by the reaction wheel controller, and the limit is within ±0.075Nm (the maximum output torque of the flywheel).

Through the distribution matrix C _P obtained in the previous step, the control distribution instructions of the three flywheels for instruction distribution can be obtained.

T _wc3 = C _P T _c

Limit the maximum value of the control command T _wc of the reaction wheel within ±0.075Nm,

Then calculate each flywheel torque control command according to the scaling, that is:

T _wci ＝T _wci *T _wcmax /T _wci(max)

Reaction wheel torque control voltage:

U _wci ＝ T _wci /k _ii

Among them, k _ii is the reaction flywheel moment coefficient.

Step 3: Calculate the synthetic angular momentum of the four reaction wheels. When the angular momentum of any axis reaches the unloading threshold range and conforms to the angular relationship between the magnetic field strength and the angular momentum during unloading, the magnetic torquer is started to unload.

In this step, after calculating the synthesized angular momentum of the four reaction flywheels, judge whether unloading is required according to the magnitude of the angular momentum, and the judging conditions, taking one of the axes as an example: h _x is the synthesized angular momentum of the X-axis of the flywheel, and the judging conditions for unloading are shown in Figure 1 shown.

a. Condition: |h _i -H _i |≥k ₁

Record: IsDump _i = on

b. Condition: IsDump _i = on and k ₁ >|h _i -H _i |≥k ₂

Record: IsDump _i = on

c. Condition: IsDimp _i =off and k ₁ >|h _i -H _i |≥k ₂

Record: IsDimp _i = off

d. Condition: |h _i -H _i |<k ₂

Record: IsDimp _i = off

Among them, the nominal angular momentum H _i of the reaction flywheel, the composite nominal angular momentum of the whole star zero momentum flywheel is 0Nms, k ₁ flywheel unloading angular momentum opening threshold, k ₂ flywheel unloading angular momentum closing threshold, IsDump _i , i=X, Y, Z flywheel unloading status.

Moreover, in this step, under the high-orbit weak magnetic environment, the magnetic field strength of the internal source field has decayed to about 100 nT, which is close to the magnetic field strength of the external source field. Due to the complex model of the external source field, which is greatly affected by the environment, the internal source field is used to calculate the magnetic field strength. In order to avoid the influence of the external source field, the unloading torque is reversed. with The included angle is greater than 45° and less than 135°, where with is the unit vector of ΔH and the local geomagnetic field strength B _b , unloading direction:

Otherwise, M _c =0, no unloading is performed.

Step 4, select the direction with the largest unloading capacity for the magnetic torque device to work, and use the switch control method to unload other flywheels.

In this step, the satellite installs magnetic torque devices in three directions. During the unloading process, each magnetic torque device will generate unloading torque, but the functions of the three axes are different. The main function accounts for more than 60%, and the minimum accounts for about 10%. Two magnetic torque devices are selected to play the main role. The torque T _mi generated by the magnetic torque device is projected on ΔH to generate the torque ΔT _mi

If |T _mi |≠0

Otherwise, ΔT _mi =0

Select the magnetic torque device with the largest unloading effect on the two axes among the three axes

By comparing |ΔT _m1 |, |ΔT _m2 |, |ΔT _m3 |, ΔT _mi maximum 2 axis unloading controller control command is M _ci , other axis control command is 0.

Provide the embodiment of above-mentioned scheme on a certain high-orbit satellite below.

The satellite adopts a three-orthogonal and one-oblique reaction flywheel with a maximum angular momentum of 45Nms, a speed range of ±6000rpm, a maximum output torque of 0.075Nm, and a control voltage of ±10V. The four reaction flywheel installation matrices are:

Step 1: Control the obliquely mounted reaction wheel 4 near the nominal speed, and the other orthogonal reaction wheels control the attitude. According to the principle of conservation of angular momentum, under the action of the obliquely mounted wheel, all four flywheels work near the nominal speed.

The optimum rotational speed of the reaction wheel on orbit is around 2000rpm, and the nominal angular momentums of 4 flywheels (code X, Y, Z, S1) are respectively 12Nms, 12Nms, 12Nms, 20.784Nms, corresponding to rotational speeds of 1596rpm, 1596rpm, 1596rpm, 2764rpm , the obliquely installed reaction flywheel S1 controls the work of the flywheel S1 according to the control voltage corresponding to the friction torque near 2764rpm. If the speed of the reaction wheel S1 is lower than 2764rpm, increase the control voltage; nearby. The other three reactions are converted into control voltage according to the output control torque of the controller to control the work of the reaction wheels X, Y, and Z. The specific calculation method:

The installation matrix C _u of the three reaction wheels installed orthogonally is inverted, and the corresponding distribution matrix C _P of the reaction wheels can be obtained.

The command T _c is controlled by the reaction wheel controller, and the limit is within ±0.075Nm.

Through the distribution matrix C _P obtained in the previous step, the control distribution instructions of the three flywheels for instruction distribution can be obtained.

T _wc ＝ C _P T _c

Limit the maximum value of the control command T _wc of the reaction wheel X/Y/Z within ±0.075Nm,

Then calculate each flywheel torque control command, namely: T _wci =T _wci *T _wcmax /T _wci(max)

Convert the reaction wheel X/Y/Z control command T _wc into the torque command form U _wc for driving the reaction flywheel:

U _wc ＝ T _wc /0.0075

The second step: Calculate the synthetic angular momentum of the reaction flywheel, calculate the control command of the magnetic torque device according to the unloading strategy, as shown in Figure 2, and drive the magnetic torque device to work.

According to the above scheme, the rotation speed curve of the satellite’s in-orbit reaction wheel is shown in Figure 3, the reaction wheel works within the nominal speed of ±500rpm, the satellite attitude curve is shown in Figure 4, the attitude control accuracy is 0.03 degrees, and the cumulative unloading time of one month is 29477s , under this control scheme, the entire satellite maintains zero momentum, and in the high-orbit space environment, the disturbance torque is small, and the flywheel speed can be well maintained under the unloading effect.

This embodiment has been successfully applied to model satellites. The in-orbit data show that the flywheel control strategy and unloading method are simple and effective, and can ensure that the reaction flywheel works near the nominal speed, and the attitude control accuracy is high, the unloading capacity is sufficient, and it can avoid Open the influence of the external source field.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be considered Be the protection scope of the present invention.

Claims (7)

1. an open-loop control reaction wheel speed variation and unloading method, it is characterized in that, the method comprises the steps: Step 1: Use four flywheels including the first flywheel, the second flywheel, the third flywheel and the fourth flywheel for control, and adjust the size of the flywheel torque control command of the fourth flywheel to be consistent with the friction torque corresponding to the theoretical nominal speed , where the flywheel is the reaction wheel; Step 2: limit the output control command of the controller to the maximum output torque, and distribute the control torque of each flywheel according to the flywheel distribution matrix formed by the order of the first flywheel, the second flywheel and the third flywheel. The flywheel is limited to the maximum output torque, and the control torque of the other two flywheels is scaled proportionally to obtain the control torque of the three flywheels; Step 3: Calculating the composite angular momentum of the four flywheels. When the angular momentum of any axis reaches the unloading threshold range and meets the angular relationship between the magnetic field strength and the angular momentum during unloading, the magnetic torquer is started to unload; Step 4, select the magnetic torque device in the direction with the largest unloading capacity to work, and use the switch control method to unload the flywheel. 2. The open-loop control reaction wheel speed change and unloading method according to claim 1, characterized in that: In step 1, the friction torque T _f4 is obtained according to the nominal speed of the fourth flywheel, and the friction torque is compensated to obtain the flywheel torque control command T _wc4 T _wc4 = -T _f4 and flywheel torque control voltage: U _wc4 =T _wc4 /k _i4 Wherein, k _i4 is the fourth flywheel moment coefficient. 3. The open-loop control reaction wheel speed change and unloading method according to claim 1, characterized in that: in step 2, the installation matrix C _u of the first flywheel, the second flywheel, and the third flywheel is inversely calculated The corresponding flywheel allocation matrix C _P can be obtained. 4. The open-loop control reaction wheel speed change and unloading method according to claim 1, characterized in that in step 3, after calculating the synthetic angular momentum of the four flywheels, it is judged whether unloading is required according to the angular momentum. 5. The open-loop control reaction wheel speed change and unloading method according to claim 1, characterized in that in step 3, the internal source field is used to calculate the magnetic field strength. 6. The open-loop control reaction wheel speed change and unloading method according to claim 1, characterized in that, in step 4, the magnetic torque device that plays a major role is selected to perform the unloading work. 7. The open-loop control reaction wheel speed change and unloading method according to claim 1, characterized in that the first flywheel, the second flywheel and the third flywheel are orthogonally mounted flywheels, and the fourth flywheel is a diagonally mounted flywheel.