Synthesis SP Skogestad And Postlethwaite(1996 .

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Topic #2416.31 Feedback Control Systems H SynthesisSP Skogestad and Postlethwaite(1996) Multivariable Feedback Control Wiley.JB Burl (2000). Linear Optimal Control Addison-Wesley.ZDG Zhou, Doyle, and Glover (1996). Robust and Optimal Control Prentice Hall.MAC Maciejowski (1989) Multivariable Feedback Design Addison Wesley.Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 200716.31 24–1Synthesis For the synthesis problem, typically define a generalized version ofthe system dynamics (SISO or MIMO)wz u Pzw (s) Pzu(s)Pyw (s) Pyu(s)Gc y Signals:Generalized plant: Pzw (s) Pzu(s)P (s) Pyw (s) Pyu(s)z – Performance outputw – Disturbance/ref inputscontains plant G(s) and all performance/uncertainty weightsy – Sensor outputsu – Actuator inputs With the loop closed (u Gcy), can show that z Pzw PzuGc(I PyuGc) 1Pyw w Fl (P, Gc)w– Called a (lower) Linear Fractional Transformation (LFT). Define the H norm for a TFM P (s) as P (s) sup σ[P (jω)]ω– Basically finds the peak amplification possible for the TFM overall frequencies (works for MIMO).December 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 200716.31 24–2 Design Objective: Find Gc(s) to stabilize the closed-loop system and minimize Fl (P, Gc) . Hard problem to solve, so typically consider suboptimal problem:– Find Gc(s) to satisfy Fl (P, Gc) γ– Then use bisection (called a γ iteration) to find the smallestvalue (γopt) for which Fl (P, Gc) γopt hopefully get that Gc approaches Goptc Consider the suboptimal H synthesis problem:1Find Gc(s) to satisfy Fl (P, Gc) γ A Bw BuPzw (s) Pzu(s): Cz 0 Dzu P (s) Pyw (s) Pyu(s)Cy Dyw 0where it is assumed that:1. (A, Bu, Cy ) is stabilizable/detectable (essential)2. (A, Bw , Cz) is stabilizable/detectable (essential)T3. Dzu[ Cz Dzu ] [ 0 I ] (simplify/essential) 0BwTDyw (simplify/essential)4.IDyw1 SP367December 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 200716.31 24–3 There exists a stabilizing Gc(s) such that Fl (P, Gc) γ iff(1) X 0 that solves the AREAT X XA CzT Cz X(γ 2Bw BwT BuBuT )X 0 and Rλi A (γ 2Bw BwT BuBuT )X 0 i(2) Y 0 that solves the AREAY Y AT BwT Bw Y (γ 2CzT Cz CyT Cy )Y 0 and Rλi A Y (γ 2CzT Cz CyT Cy ) 0 i(3) ρ(XY ) γ 2ρ is the spectral radius (ρ(A) maxi λi(A) ). Given these solutions, the central H controller is given by A (γ 2Bw BwT BuBuT )X ZY CyT Cy ZY CyTGc(s) : BuT X0where Z (I γ 2Y X) 1– Has as many states as the generalized plant. Note that this design does not decouple as well as the regulator/estimator for LQGDecember 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 200716.31 24–4Simple Design Example r–e z1Ws Gc(s)whereG uWuz2 ỹG(s) 200(0.05s 1)2(10s 1) Note there is 1 input (r) and two performance outputs - one thatpenalizes the sensitivity S(s) of the system, and the other thatpenalizes the control effort used. To achieve good low frequency tracking and a crossover frequencyof about 10 rad/sec, pickWs s/1.5 10s (10) · (0.0001)Wu 1– Typically treat Wu as a constant (similar role as ρ as the LQRcontrol control cost)December 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 200716.31 24–5 Generalized system in this case:Pwwsruz1zz2wuG eyGcFigure by MIT OpenCourseWare.Figure 1: Rearrangement of original picture in the generalized plant format. Easy to show that the closed-loop is: z1Ws S rWu Gc Sz2– Input r acts as “disturbance input” w to generalized system. Ws(s) Ws(s)G(s)z1 Ws(s)(r Gu) Wu(s)P (s) 0z 2 Wu u1 G(s) e r GuPzw (s) Pzu(s) u GcePyw (s) Pyu(s)PCL Fl (P, Gc) Ws WsGGc(I GGc) 11 Wu0 Ws WsGGcSWsS Wu G c SWu Gc SDecember 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 200716.31 24–6 In state space form, let A BG(s) : C 0ẋẋwz1z2e Ws(s) : Aw BwCw Dw Wu 1 Ax BuAw xw Bw e Aw xw Bw r Bw CxCw xw Dw e Cw xw Dw r Dw CxWu ur Cx A0 0 B B C A B0 www P (s) : Dw C Cw Dw 0 00 0 Wu C0 1 0 Now use the mu-tools code to solve for the controller. (Could alsohave used the robust control toolbox code).A [Ag zeros(n1,n2);-Bsw*Cg Asw];Bw [zeros(n1,1);Bsw];Bu [Bg;zeros(n2,1)];Cz [-Dsw*Cg Csw;zeros(1,n1 n2)];Cy [-Cg zeros(1,n2)];Dzw [Dsw;0];Dzu [0;1];Dyw [1];Dyu 0;P pck(A,[Bw Bu],[Cz;Cy],[Dzw Dzu;Dyw Dyu]);% call hinf to find Gc (mu toolbox)[Gc,G,gamma] hinfsyn(P,1,1,0.1,20,.001);December 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 200716.31 24–7 Results from the γ-iteration showing whether the various X, Y ,ρ(XY ) tests are passed/failed during the bisection searching overγ, starting at the initial bound of 20.Resetting value of Gamma min based on D 11, D 12, D 21 termsTest bounds: 461.3841.3651.3751.3701.3681.3661.3660.6667 hamx eig9.6e 0009.6e 0009.5e 0009.5e 0009.4e 0009.1e 0009.3e 0009.2e 0009.2e 0009.2e 0009.2e 0009.2e 0009.2e 0009.2e 0009.2e 0009.2e 000Gamma value achieved:gamma xinf eig hamy eig6.2e-008 1.0e-0036.3e-008 1.0e-0036.3e-008 1.0e-0036.5e-008 1.0e-0036.9e-008 1.0e-003-1.2e 004# 1.0e-0037.3e-008 1.0e-0037.6e-008 1.0e-003-6.4e 004# 1.0e-0037.7e-008 1.0e-003-1.9e 006# 1.0e-0037.7e-008 1.0e-0037.7e-008 1.0e-0037.7e-008 1.0e-0037.7e-008 1.0e-003-1.3e 007# 1.0e-00320.0000yinf eignrho xyp/f0.0e 0000.0000p0.0e 0000.0000p0.0e 0000.0000p0.0e 0000.0000p0.0e 0000.0000p-4.5e-0100.0000f0.0e 0000.0000p0.0e 0000.0000p0.0e 0000.0000f0.0e 0000.0000p0.0e 0000.0000f-4.5e-0100.0000p0.0e 0000.0000p0.0e 0000.0000p0.0e 0000.0000p0.0e 0000.0000f1.3664 Since γmin 1.3664, this indicates that the controller does notmeet the desired goal of S 1/ Ws (can only say that S 1.3664/ Ws ).– Confirmed by the plot, which that the blue line passes abovethe magenta But note that, even though this design fails the sensitivity weight- the controller still gets pretty good performance– For performance problems, can think of the objective of gettingγmin 1 as a “design goal” it is “not crucial”– Use Wu to tune the control designDecember 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 200716.31 24–8Figure 2: Visualization of the weighted sensitivity tests.Figure 3: Time response of controller that yields γmin 1.3664.December 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 200716.31 24–9Controller Interpretations Given these solutions, the central H controller is given by A (γ 2Bw BwT BuBuT )X ZY CyT Cy ZY CyTGc(s) : BuT X0where Z (I γ 2Y X) 1 Can develop a further interpretation of this controller if rewrite thedynamics as:x̂ Ax̂ γ 2Bw BwT X x̂ BuBuT X x̂ ZY CyT Cy x̂ ZY CyT yu BuT X x̂ x̂ Ax̂ Bw γ 2BwT X x̂ Bu BuT X x̂ ZY CyT [y Cy x̂] x̂ Ax̂ Bw γ 2BwT X x̂ Buu L [y Cy x̂]looks very similar to Kalman Filter developed for LQG controller. The difference is that there is an additional input ŵworst γ 2BwT X x̂that enters through Bw .– wworst is an estimate of worst-case disturbance to the system. Finally, note that a separation rule does exist for the H controller.But it is much more complicated than for LQG.December 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 200716.31 24–10Code: H Synthesis12345678% Hinf example% 16.31 MIT Fall 2007% Jon tSize’,20)91011121314151617clear allif exist(’yprev’)yprev [1 1]’;tprev [0 1]’;Sensprev [1 1];fprev [.1 100];Wu 1;end181920212223242526272829303132333435363738% define plant[Ag,Bg,Cg,Dg] tf2ss(200,conv(conv([0.05 1],[0.05 1]),[10 1]));Gol ss(Ag,Bg,Cg,Dg);% define sensitivity weightM 1.5;wB 10;A 1e-4;[Asw,Bsw,Csw,Dsw] tf2ss([1/M wB],[1 wB*A]);Ws ss(Asw,Bsw,Csw,Dsw);% form augmented P dynamicsn1 size(Ag,1);n2 size(Asw,1);A [Ag zeros(n1,n2);-Bsw*Cg Asw];Bw [zeros(n1,1);Bsw];Bu [Bg;zeros(n2,1)];Cz [-Dsw*Cg Csw;zeros(1,n1 n2)];Cy [-Cg zeros(1,n2)];Dzw [Dsw;0];Dzu [0;Wu];Dyw [1];Dyu 0;P pck(A,[Bw Bu],[Cz;Cy],[Dzw Dzu;Dyw Dyu]);3940414243% call hinf to find Gc (mu toolbox)diary hinf1 diary[Gc,G,gamma] hinfsyn(P,1,1,0.1,20,.001);diary off444546[ac,bc,cc,dc] unpck(Gc);ev max(real(eig(ac)/2/pi))474849505152535455PP ss(A,[Bw Bu],[Cz;Cy],[Dzw Dzu;Dyw Dyu]);GGc ss(ac,bc,cc,dc);CLsys feedback(PP,GGc,[2],[3],1);[acl,bcl,ccl,dcl] ssdata(CLsys);% reduce closed-loop system so that it only has% 1 input and 2 outputsbcl bcl(:,1);ccl ccl([1 2],:);dcl dcl([1 2],1);CLsys ss(acl,bcl,ccl,dcl);56575859606162636465666768f logspace(-1,2,400);Pcl freqresp(CLsys,f);CLWS squeeze(Pcl(1,1,:)); % closed loop weighted sensWS freqresp(Ws,f); % sens weightSensW squeeze(WS(1,1,:));Sens CLWS./SensW; % divide out weight to get closed-loop neWidth’,2)hold loglog(fprev,abs(Sensprev),’r.’)December 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Fall 2007697071727316.31 24–11legend(’S’,’1/W s’,’W sS’,’Location’,’SouthEast’)hold offxlabel(’Freq 9na size(Ag,1);nac size(ac,1);Acl [Ag Bg*cc;-bc*Cg ac];Bcl [zeros(na,1);bc];Ccl [Cg zeros(1,nac)];Dcl 0;Gcl ss(Acl,Bcl,Ccl,Dcl);[y,t] �LineWidth’,2.5)axis([0 1 0 1.1])hold old offxlabel(’Time sec’)ylabel(’Step response’)8788899091%yprev y;%tprev t;%Sensprev Sens;%fprev f;9293return949596print -dpng -r300 hinf1.pngprint -dpng -r300 hinf12.png97December 9, 2007Cite as: Jonathan How, course materials for 16.31 Feedback Control Systems, Fall 2007. MIT OpenCourseWare(http://ocw.mit.edu), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

16.31 Feedback Control Systems H Synthesis SP Skogestad and Postlethwaite(1996) Multivariable Feedback Control Wiley. JB Burl (2000). Linear Optimal Control Addison-Wesley. ZDG Zhou, Doyle, and Glover (1996). Robust and Optimal Control Prentice Hall. MAC Maciejowski (1989) Multivariable Feedback Design Addison Wesley.

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