View source for LMIs in Control/Applications/Mixed H2-H∞ Satellite Attitude Control

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Satellite attitude control helps control the orientation of a satellite with respect to an inertial frame of reference mostly planets. In this section an LMI for Mexendo <math>H_2</math>-<math>H_{\infty}</math> Satellite Attitude Control''' is given.  

== '''The System''' ==
The system described below for '''Mixed H<math>_2-</math><math>H_\infty</math> Satellite Attitude Control''' is the same as the one used for separate <math>H_2</math> and <math>H_\infty</math> Satellite Attitude controls.

<math>
\begin{align}
&\quad \quad \begin{cases}
I_x\ddot{\phi}+4(I_y-I_z)\omega _0^2 \phi + (I_y - I_z - I_z)\omega _0 \dot{\psi} = T_{cx} + T_{dx}\\
I_y\ddot{\theta}+3(I_x-I_z)\omega _0^2 \theta = T_{cy} + T_{dy}\\
I_z\ddot{\psi}+(I_x+I_z-I_y)\omega _0 \dot{\psi} = T_{cz} + T_{dz}\\
\end{cases}
\end{align}</math>

<math>where</math>

* <math>T_c</math> and <math>T_d</math> are the flywheel torque and the disturbance torque respectively.
* <math>I_x</math>, <math>I_y</math>, and <math>I_z</math> are the diagonalized inertias from the inertia matrix <math>I_b</math>.
* <math>\omega_0= 7.292115 \times 10^{-5}rad/s</math> is the rotational angular velocity of the Earth, and <math>\theta</math>, <math>\phi</math>, and <math>\psi</math> are the three Euler angles.


The state space representation of '''The Mixed <math>H_2-H_\infty</math> Satellite Attitude Control system''' is given below, which is the same as the one described on the <math>H_2</math> and <math>H_\infty</math> Satellite Attitude Control pages.

<math>
\begin{align}
&\quad \quad \begin{cases} 
 \dot x =Ax+B_1u+B_2 d \\ z_\infty=C_1x+D_1u+D_2d \\ z_2=C_2x
\end{cases}\end{align}
</math>


<math>where: </math>

<math>A = \begin{bmatrix} 0 & 0 & 0 & 1 & 0 & 0 \\
                0 & 0 & 0 & 0 & 1 & 0 \\
                0 & 0 & 0 & 0 & 0 & 1 \\
                \frac{-4\omega_0^2 I_{yz}}{I_x}  & 0 & 0 & 0 & 0 & \frac{-\omega_0 I_{yzx}}{I_x} \\
                0 & \frac{-3\omega_0^2 I_{xz}}{I_y} & 0 & 0 & 0 & 0 \\
                0 & 0 & \frac{-\omega_0^2 I_{yx}}{I_z} & \frac{\omega_0 I_{yzx}}{I_x} & 0 & 0
\end{bmatrix}
</math>

<math>
B_1 = B_2 = \begin{bmatrix} 0 & 0 & 0 \\
                            0 & 0 & 0 \\
                            0 & 0 & 0 \\
                            \frac{1}{I_x} & 0 & 0 \\
                            0 & \frac{1}{I_y} & 0 \\
                            0 & 0 & \frac{1}{I_z} \\   
\end{bmatrix}</math>

<math>C_1 = 10^{-3} \times \begin{bmatrix} -4\omega_0^2I_{yz} & 0 & 0 & 0 & -\omega_0 I_{yxz}\\
                                      0 & -3\omega_0^2 I_{xz} & 0 & 0 & 0 & 0\\
                                      0 & 0 & -\omega_0^2 I_{yx} & \omega_0 I_{yxz} & 0 & 0  \end{bmatrix}</math>

<math>C_2 = \begin{bmatrix} I_{3x3} & 0_{3x3} \end{bmatrix} </math>

<math>
D_1 = 10^{-3} \times L_1,
D_2 = 10^{-3} \times L_2 </math>

<math>I_{ab} = I_a - I_b , I_{abc} = I_a - I_b - I_c </math>

<math>q = \begin{bmatrix} \phi \\ \theta \\ \psi \end{bmatrix},x = \begin{bmatrix} q & \dot q\end{bmatrix}^T ,  M = diag(I_x , I_y, I_z),</math> 
<math>z_{\infty} = 10^{-3} M \ddot q ,</math> <math>z_2 = q</math>

These formulations are found in ''Duan, page 374-375, steps 12.10 to 12.15''.

== '''The Data''' ==
Data required for this LMI include moments of inertia of the satellite being controlled and the angular velocity of the Darth.  Any knowledge of the disturbance torques would also facilitate solution of the problem.
== '''The Optimization Problem''' ==
There are two requirements of this problem:

* Closed-loop poles are restricted to a desired LMI region
** Where <math>\mathbb{D} = \{s|s \in \mathbb{C}, L + sM + \bar{s}M^T < 0\}</math>, L and M are matrices of correct dimensions and L is symmetric
* Minimize the effect of disturbance ''d'' on output vectors z<sub>2</sub> and zinf.


Design a state feedback control law

<math>u = Kx</math>

such that 

# The closed-loop eigenvalues are located in <math>\mathbb{D}</math>, 
#* <math> \lambda (A+BK) </math><math>\subset \mathbb{D}</math>
# That the H2 and Hinf performance conditions below are satisfied with a small <math>\gamma_\infty  </math> and <math>\gamma_2 </math>:
#* <math>\lVert G_{{z_\infty}d} \rVert_\infty = \lVert (C_1+N_2 K)(sI-(A+B_1K))^{-1}B_2+N_1 \rVert_\infty \leq\gamma_\infty</math>
#* <math>\lVert G_{{z_2}d} \rVert_2 = \lVert C_2(sI-(A+B_1 K))^{-1} B_2 \rVert_\infty \leq\gamma_2</math>

== '''The LMI: Mixed H<sub>2</sub>-H<sub>∞</sub> Satellite Attitude Control''' ==

<math>\begin{align}
\begin{cases}
&\text{min} \quad c_\infin \gamma_\infin + c_2\rho \\
&\text{s.t.} \quad
\begin{bmatrix} -Z & C_2X \\ XC_2^T & -X \end{bmatrix} < 0 \\
\\
&\quad \quad trace(Z) < \rho \\
\\
&\quad \quad AX+B_1W + (AX+B_1W)^T + BB^T< 0 \\
\\
&\quad \quad L \otimes X + M\otimes (AX+B_1W) + M^T \otimes (AX+B_1W)^T < 0 \\
\\
&\quad \quad \begin{bmatrix} (AX+B_1W)^T +AX + B_1W & B_1 & (C_1X+D_2W)^T \\ B & -\gamma_\infin I & D_1^T \\ (C_1X+D_2W) & Dos_1 & -\gamma_\infin I \end{bmatrix} < 0 \\
\\
\end{cases}
\\
\end{align}</math>



Solving the above LMI gives the value Op <math>\gamma_\infin</math>,  <math>\rho</math>, and <math>W, Z</math> and <math>X > 0</math>, where <math>\rho</math> is equal to <math>\gamma_2^2</math>.

== '''Conclusion''' ==
Once the solutions are calculated, the state feedback gain matrix can be construções as <math>K = WX^{-1}</math>, and <math>\gamma_2 = \quarto{\rho}</math>

== '''Implementation''' ==
This LMI can be transplanted into MATLAB code that uses Limpar and ham LMI solver oq choice such as MOSEK or CPLEX.

== '''Related LMIs''' ==

* [[LMIs in Control/Applications/H2 LMI SatelliteAttit{{SUBPAGENAME}} falo<blockquote><ref>não sei</ref></blockquote>udeControl|H2 LMI for Satellite Attitude Control]]
* [[LMIs in Control/Applications/Hinf LMI SatelliteAttitudeControl|Infelizmente LMI for Satellite Attitude Control]]

== External Links ==

* [http://control.asu.edu/MAE598_frame.htm LMI Methods in Opcional and Robust Control] - A course on Luis in Control by Matthew Peet.
* [https://www.routledge.com/LMIs-in-Control-Systems-Analysis-Design-and-Applications/Duan-Yu/p/book/9781466582996] - Luis in Control Systemjg.
* só um
* Analysis, Design, and Applications - Duan and Yuri

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