阅读说明：本技术 一种动量轮低转速下融合控制电压的高精度转速测量方法 (High-precision rotation speed measurement method for fusion control voltage of momentum wheel at low rotation speed ) 是由 王晋鹏 赵江涛 陈超 关宏 陆栋宁 雷拥军 施海燕 黄碳钢 于 2020-04-24 设计创作，主要内容包括：一种动量轮低转速下融合控制电压的高精度转速测量方法,通过动量轮控制电压信号和动量轮模型来预估动量轮的转速,并将预估转速与实际采集动量轮转速进行融合处理,同时通过优化算法,以提高动量轮低转速区的转速采集精度,解决了传统光电码盘测量动量轮转速在低转速情况下有较大误差和时延、容易导致动量轮摩擦力矩前馈补偿不准确的问题,方法流程清晰,测量精度高。(A high-precision rotation speed measuring method for fusion control voltage of a momentum wheel at low rotation speed includes predicting rotation speed of the momentum wheel through a momentum wheel control voltage signal and a momentum wheel model, fusing the predicted rotation speed and actual collected rotation speed of the momentum wheel, and improving rotation speed collection precision of a low rotation speed area of the momentum wheel through an optimization algorithm.)

1. A high-precision rotation speed measuring method for fusion control voltage under low rotation speed of a momentum wheel is characterized by comprising the following steps:

(1) acquiring initial parameters of a momentum wheel, wherein the initial parameters of the momentum wheel comprise: momentum wheel voltage-torque characteristic parameter C_{V_T}Characteristic parameter T of rotation speed and friction torque of momentum wheel_fricInitial rotation speed omega of momentum wheel_initMoment of inertia J of momentum wheel_mw；

(2) After the momentum wheel starts to rotate, acquiring the rotating speed of the momentum wheel in the current rotating period in real time;

(3) weighting the momentum wheel rotating speed obtained in the step (2) to obtain the weighted momentum wheel rotating speed of the current rotating period;

(4) and predicting the predicted rotation speed of the momentum wheel in the next rotation period according to the rotation speed of the momentum wheel weighted in the current rotation period and the control voltage of the momentum wheel.

2. The method for measuring the high-precision rotating speed of the fusion control voltage of the momentum wheel at the low rotating speed according to claim 1, wherein the method comprises the following steps: in the step (1), the momentum wheel rotating speed-friction torque characteristic parameter T_fricThe expression method specifically comprises the following steps:

in the formula, T_cIs the Coulomb friction torque, T_sIs the maximum static friction moment, omega_sFor boundary lubrication of critical speed, σ₂Is the viscous friction coefficient.

3. The method for measuring the high-precision rotating speed of the fusion control voltage of the momentum wheel at the low rotating speed according to claim 1, wherein the method comprises the following steps: in the step (2), the acquisition of the rotating speed of the momentum wheel in the current rotating period is influenced by the acquisition pulse number, and specifically comprises the following steps:

where M is the number of pulses generated by one revolution of the momentum wheel, ω_collectThe rotating speed of the momentum wheel in the current rotating period is shown, and delta T is the time length of the satellite-borne computer control rotating period.

4. The method for measuring the high-precision rotating speed of the fusion control voltage of the momentum wheel at the low rotating speed according to claim 1, wherein the method comprises the following steps: in the step (3), the method for acquiring the momentum wheel rotating speed after the current rotating period is weighted is as follows:

ω_weighting＝k(ω_collect)ω_collect+[1-k(ω_collect)]ω_est

in the formula, ω_weightingIs the momentum wheel speed, omega, weighted by the current rotation period_estIs the estimated rotation speed k (omega) of the momentum wheel of the current rotation period estimated by the previous rotation period_collect) Weighting factor, omega, for the rotational speed of the momentum wheel of the current rotation period_{low_lim}For weighting the lower limit speed, ω when the detected speed is lower than this speed_weightingIs directly equal to omega_est，ω_{high_lim}Is a weighting systemUpper limit of rotation speed, when the rotation speed is higher than the upper limit of rotation speed, omega_weightingIs directly equal to omega_collect。

5. The method for measuring the high-precision rotating speed of the fusion control voltage of the momentum wheel at the low rotating speed according to claim 1, wherein the method comprises the following steps: in the step (4), the estimated rotation speed omega of the momentum wheel in the next rotation period_estThe prediction method of' is as follows:

ω_est'＝ω_weighting+(V_outputC_{V_T}-T_fric)ΔT/J_mw

in the formula, V_outputThe control voltage of the momentum wheel is supplied to the spaceborne computer, wherein after the calculation is finished, the momentum wheel of the next rotation period of the current rotation period is used for estimating the rotation speed omega_est' Pair omega_estAnd updating to obtain the estimated rotation speed of the momentum wheel in the current rotation period in the next rotation period.

Technical Field

The invention relates to a high-precision rotation speed measurement method for fusion control voltage of a momentum wheel at low rotation speed, and belongs to the field of spacecraft attitude control.

Background

The momentum wheel is a key actuator of the satellite attitude control system. At present, most of momentum wheels at home and abroad adopt an electromagnetic torque control or current control mode, namely, a specific control voltage is input to obtain a control torque according to the voltage-torque characteristic of the momentum wheel. The momentum wheel controlled by the electromagnetic torque can not overcome the friction interference torque, and the interference torque in the flywheel is substantially introduced into the satellite attitude control system, so that the satellite attitude control precision is directly reduced. Therefore, the scheme can be optimized, and the influence on the satellite attitude control is reduced by acquiring the current rotating speed of the momentum wheel, then compensating the friction torque in a feedforward mode by utilizing the relation between the rotating speed of the momentum wheel and the friction torque.

The momentum wheel usually adopts a photoelectric coded disc to output rotating speed pulses for an on-board computer to collect, the momentum wheel rotates for one circle to generate a plurality of pulses, if the rotating speed of the momentum wheel and the collecting frequency of the on-board computer are fixed, the number of the momentum wheel pulses collected by the on-board computer in each period can be calculated, and under the condition of simultaneously collecting the rising/falling edges of the rotating speed pulses, the error of the number of the pulses in one period of the on-board computer can be obtained, so that the error of the rotating speed of the collected momentum wheel and the actual rotating speed is determined, if the collecting frequency of the rotating speed of the momentum wheel is changed, the calculated frequency of the rotating speed pulses can be changed, the rotating speed of the momentum wheel collected in each rotating period is easily caused to be 0, and also can be an accurate value.

Disclosure of Invention

The technical problem solved by the invention is as follows: aiming at the problems that the traditional photoelectric code disc has larger error and time delay when measuring the rotating speed of the momentum wheel under the condition of low rotating speed and the feedforward compensation of the friction torque of the momentum wheel is easy to cause inaccuracy in the prior art, the high-precision rotating speed measuring method fusing the control voltage under the low rotating speed of the momentum wheel is provided.

The technical scheme for solving the technical problems is as follows:

a high-precision rotation speed measuring method for fusion control voltage under low rotation speed of a momentum wheel comprises the following steps:

(1) acquiring initial parameters of a momentum wheel, wherein the initial parameters of the momentum wheel comprise: momentum wheel voltage-torque characteristic parameter C_{V_T}Characteristic parameter T of rotation speed and friction torque of momentum wheel_fricInitial rotation speed omega of momentum wheel_initMoment of inertia J of momentum wheel_mw；

(2) After the momentum wheel starts to rotate, acquiring the rotating speed of the momentum wheel in the current rotating period in real time;

(3) weighting the momentum wheel rotating speed obtained in the step (2) to obtain the weighted momentum wheel rotating speed of the current rotating period;

(4) and predicting the predicted rotation speed of the momentum wheel in the next rotation period according to the rotation speed of the momentum wheel weighted in the current rotation period and the control voltage of the momentum wheel.

In the step (1), the momentum wheel rotating speed-friction torque characteristic parameter T_fricThe expression method specifically comprises the following steps:

in the formula, T_cIs the Coulomb friction torque, T_sIs the maximum static friction moment, omega_sFor boundary lubrication of critical speed, σ₂Is the viscous friction coefficient.

In the step (2), the acquisition of the rotating speed of the momentum wheel in the current rotating period is influenced by the acquisition pulse number, and specifically comprises the following steps:

where M is the number of pulses generated by one revolution of the momentum wheel, ω_collectThe rotating speed of the momentum wheel in the current rotating period is shown, and delta T is the time length of the satellite-borne computer control rotating period.

In the step (3), the method for acquiring the momentum wheel rotating speed after the current rotating period is weighted is as follows:

ω_weighting＝k(ω_collect)ω_collect+[1-k(ω_collect)]ω_est

in the formula, ω_weightingIs the momentum wheel speed, omega, weighted by the current rotation period_estIs the estimated rotation speed k (omega) of the momentum wheel of the current rotation period estimated by the previous rotation period_collect) Weighting factor, omega, for the rotational speed of the momentum wheel of the current rotation period_{low_lim}For weighting the lower limit speed, ω when the detected speed is lower than this speed_weightingIs directly equal to omega_est，ω_{high_lim}For weighting the upper limit speed, ω is the speed at which the rotational speed is detected when the rotational speed is higher than this_weightingIs directly equal to omega_collect。

In the step (4), the estimated rotation speed omega of the momentum wheel in the next rotation period_estThe prediction method of' is as follows:

ω_est'＝ω_weighting+(V_outputC_{V_T}-T_fric)ΔT/J_mw

in the formula, V_outputThe control voltage of the momentum wheel is supplied to the spaceborne computer, wherein after the calculation is finished, the momentum wheel of the next rotation period of the current rotation period is used for estimating the rotation speed omega_est' Pair omega_estAnd updating to obtain the estimated rotation speed of the momentum wheel in the current rotation period in the next rotation period.

Compared with the prior art, the invention has the advantages that:

(1) the invention provides a high-precision rotation speed measuring method for fusion control voltage of a momentum wheel at low rotation speed, which predicts the rotation speed of the momentum wheel through a momentum wheel control voltage signal and a momentum wheel model, and fuses the predicted rotation speed and the actually acquired rotation speed of the momentum wheel to improve the rotation speed acquisition precision of a low rotation speed area of the momentum wheel, thereby solving the problems that the traditional photoelectric code disc has larger error and time delay when measuring the rotation speed of the momentum wheel at low rotation speed and the feedforward compensation of the friction torque of the momentum wheel is inaccurate easily caused;

(2) the high-precision rotation speed measuring method for the fusion control voltage of the momentum wheel at the low rotation speed can reduce the rotation speed measuring error of the momentum wheel at the low rotation speed, can improve the precision of the satellite feedforward torque compensation, reduces the interference torque when the momentum wheel passes through zero and improves the stability of the satellite through the optimized algorithm.

Drawings

FIG. 1 is a graph of the relationship between the friction torque and the rotation speed of the momentum wheel provided by the invention;

FIG. 2 is a schematic flow chart of a method for measuring a rotation speed according to the present invention;

FIG. 3 is a schematic diagram of the rotational speed and the rotational speed error of the momentum wheel provided by the present invention;

Detailed Description

A high-precision rotation speed measuring method for fusion control voltage of a momentum wheel at low rotation speed comprises the steps of firstly obtaining initial parameters of the momentum wheel, then actually measuring the rotation speed of the momentum wheel in the current period, carrying out weighting calculation on the rotation speed after actual measurement and estimating the estimated rotation speed of the next rotation period, and achieving the effect of predicting the rotation speed of the momentum wheel in each rotation period, wherein the specific steps are as follows as shown in figure 2:

(1) obtaining a voltage-torque characteristic parameter C of a measuring wheel_{V_T}Characteristic parameter T of rotation speed and friction torque of momentum wheel_fricInitial rotation speed omega of momentum wheel_initMoment of inertia J of momentum wheel_mwInitial parameters of the inner momentum wheel, wherein:

the characteristics of the momentum wheel rotating speed and the friction torque can be described by a fine LuGre model and also can be described by simplified piecewise linear fitting. Under the condition of precision allowance, on-board convenience can be realized if the piecewise fitting description is adopted, and only 4 static parameters including coulomb friction torque T are needed_cMaximum static friction moment T_sCritical speed omega of boundary lubrication_sViscous coefficient of friction sigma₂Describing the method;

momentum wheel rotating speed-friction torque characteristic parameter T_fricThe expression method specifically comprises the following steps:

in the formula, T_cIs the Coulomb friction torque, T_sIs the maximum static friction moment, omega_sFor boundary lubrication of critical speed, σ₂Is a viscous friction coefficient;

(2) after the momentum wheel starts to rotate, the rotating speed of the momentum wheel in the current rotation period is collected in real time, the collection of the rotating speed of the momentum wheel in the current rotation period is influenced by the number of collected pulses, and the specific relationship is as follows:

where M is the number of pulses generated by one revolution of the momentum wheel, ω_collectThe rotating speed of the momentum wheel in the current rotating period is shown, and delta T is the time length of the control rotating period of the satellite-borne computer;

(3) weighting the momentum wheel rotating speed obtained in the step (2) to obtain the weighted momentum wheel rotating speed of the current rotating period;

the method for acquiring the momentum wheel rotating speed after the current rotating period is weighted is as follows:

ω_weighting＝k(ω_collect)ω_collect+[1-k(ω_collect)]ω_est

in the formula, ω_weightingIs the momentum wheel speed, omega, weighted by the current rotation period_estIs the estimated rotation speed k (omega) of the momentum wheel of the current rotation period estimated by the previous rotation period_collect) Weighting factor, omega, for the rotational speed of the momentum wheel of the current rotation period_{low_lim}For weighting the lower limit speed, ω when the detected speed is lower than this speed_weightingIs directly equal to omega_est，ω_{high_lim}For weighting the upper limit speed, ω is the speed at which the rotational speed is detected when the rotational speed is higher than this_weightingIs directly equal to omega_collect. Wherein:

the method has the following characteristics in consideration of the acquisition error of the rotating speed of the momentum wheel: the error is small at high speed and large at low speed, so k (omega) in the above formula_collect) Can be designedProportional to the momentum wheel speed, i.e. the higher the momentum wheel speed, omega_collectThe higher the ratio, ω_theoryThe lower the occupancy ratio; otherwise omega_collectThe lower the duty ratio, ω_estThe higher the duty ratio. k (omega)_collect) Can be designed as a function related to the acquisition error of the rotating speed of the momentum wheel;

(4) predicting the predicted rotation speed of the momentum wheel in the next rotation period according to the weighted rotation speed of the momentum wheel in the current rotation period and the control voltage of the momentum wheel, wherein:

predicted rotation speed omega of momentum wheel in next rotation period_estThe prediction method of' is as follows:

ω_est'＝ω_weighting+(V_outputC_{V_T}-T_fric)ΔT/J_mw

in the formula, V_outputThe control voltage of the momentum wheel is supplied to the spaceborne computer, wherein after the calculation is finished, the momentum wheel of the next rotation period of the current rotation period is used for estimating the rotation speed omega_est' Pair omega_estUpdating to obtain the estimated rotation speed of the momentum wheel in the current rotation period in the next rotation period;

when the step (3) has been calculated to obtain ω_estThen, by ω for the next cycle_est' calculation can be made by using ω in the next cycle_est' alternative update omega_estLet ω be in each rotation period_estControl may be calculated.

The following is further illustrated with reference to specific examples:

as shown in fig. 1, the friction torque of the momentum wheel is not linear and varies more at low rotational speeds, especially when the rotational speed of the momentum wheel is zero. Therefore, the measurement of the rotating speed of the momentum wheel needs to be accurate, otherwise, new interference is introduced by the reverse feed-forward compensation when the measurement of the rotating speed is inaccurate. Especially, if the rotation speed measurement is delayed or inaccurate when the rotation speed of the momentum wheel passes through zero, 2 times of interference can be caused due to sign switching of friction torque.

The momentum wheel usually adopts a photoelectric code disc to output rotating speed pulses for the satellite-borne computer to collect, and n pulses are generated by one rotation of the momentum wheel (a)n is typically 24 or 36). Therefore, if the rotation speed of the momentum wheel is xRPM and the collection frequency of the satellite borne computer is yHz, the number of momentum wheel pulses collected by the satellite borne computer in each period is:

under the condition of simultaneously collecting the rising/falling edges of the rotating speed pulse, the maximum pulse number error in one control period of the spaceborne computer can be regarded as +/-1/2 pulse, namely the rotating speed pulse number of the momentum wheel is collectedThe momentum wheel speed thus collectedAnd the actual rotational speed x

And if the acquisition frequency of the rotating speed of the momentum wheel is 8Hz, the rotating speed pulse frequency is 4Hz when the rotating speed is 10RPM, which is easy to calculate, at the moment, the rotating speed of the momentum wheel acquired in each acquisition period may be 0RPM or 8RPM, and large fluctuation exists with actual large fluctuation, so that the moment compensation is definitely inaccurate.

In this embodiment, a momentum wheel within a time length of 1600 rotation control cycles is selected for measurement and calculation, and the measurement data of any cycle is as follows:

as shown in fig. 3, there are 3 curves, which are the theoretical rotation speed of the momentum wheel, the weighted rotation speed error and the collected rotation speed error from top to bottom. And after weighting, the rotating speed error is weighted rotating speed-theoretical rotating speed, and the collected rotating speed error is collected rotating speed-theoretical rotating speed. In the figure, the theoretical rotating speed of the momentum wheel starts to increase towards the positive direction from 0 at first, gradually decelerates to 0 after 2500RPM and then accelerates towards the reverse direction, and decelerates again after-2500 RPM. As can be seen from the figure, when the momentum wheel is at a high rotating speed, the weighted rotating speed error is equivalent to the collected rotating speed error; but when the momentum wheel is at a low rotating speed, the weighted acquisition error is obviously smaller than the acquisition rotating speed error.

Therefore, when the method is adopted for measurement, the rotating speed measurement error of the momentum wheel at low rotating speed can be reduced, the precision of satellite feedforward torque compensation is improved, the interference torque when the momentum wheel passes through zero is reduced, and the attitude stability of the satellite is improved.

Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.