Feedback stabilization of diagonal infinite-dimensional systems in the presence of delays IFAC World Congress 2020 Workshop: Input-to-state stability and control of infinite-dimensional systems Hugo Lhachemi Joint works: Christophe Prieur, Robert Shorten, Emmanuel Tr´ elat 11 July 2020 H. Lhachemi Stabilization of delayed PDEs 11 July 2020 1 / 93
Delay boundary control of PDEs Topic: stability and stabilization of PDEs in the presence of a delay in the boundary conditions. [Nicaise and Valein, 2007], [Nicaise and Pignotti, 2008] [Krstic, 2009], [Nicaise, Valein, and Fridman, 2009] [Fridman, Nicaise, and Valein, 2010], [Prieur and Tr´ elat, 2018]. Objective: boundary stabilization and regulation control of open-loop unstable PDEs in the presence of a long input delay. Example: reaction-diffusion equation y t = y xx + cy y ( t , 0) = 0 , y ( t , L ) = u ( t − D ) y (0 , x ) = y 0 ( x ) [Krstic, 2009] - backstepping design. [Prieur and Tr´ elat, 2018] - spectral reduction and predictor feedback. H. Lhachemi Stabilization of delayed PDEs 11 July 2020 2 / 93
Boundary control of PDEs in the presence of a state-delay Topic: stability and stabilization of PDEs in the presence of a state-delay. [Fridman and Orlov, 2009], [Solomon and Fridman, 2015], [Hashimoto and Krstic, 2016], [Kang and Fridman, 2017], [Kang and Fridman, 2018]. Objective: boundary stabilization of open-loop unstable PDEs in the presence of a state-delay delay. Example: reaction-diffusion equation y t ( t , x ) = y xx ( t , x ) + a ( x ) y ( t , x ) + by ( t − h , x ) y ( t , 0) = 0 , y ( t , L ) = u ( t ) y (0 , x ) = y 0 ( x ) [Hashimoto and Krstic, 2016] - backstepping design. [Kang and Fridman, 2017] - Dirichlet/Neumann boundary conditions and time-varying delay - backstepping design. H. Lhachemi Stabilization of delayed PDEs 11 July 2020 3 / 93
Spectral reduction methods for control of PDEs Spectral reduction and finite-dimensional feedback: 1 Spectral reduction. 2 Keep a finite number of modes to build a finite-dimensional truncated model capturing the unstable dynamics of the original PDE. 3 Design a controller for the truncated model. 4 Check that the proposed controller successfully stabilizes the original infinite-dimensional systems. Early occurrences of this control design method: [Russell, 1978], [Coron and Tr´ elat, 2004], [Coron and Tr´ elat, 2006], etc. Extension to delay boundary control of a reaction-diffusion equation: [Prieur and Tr´ elat, 2018] by using a predictor feedback [Artstein, 1982] H. Lhachemi Stabilization of delayed PDEs 11 July 2020 4 / 93
Outline Generalities on spectral reduction methods for boundary stabilization 1 Stabilization with delayed boundary control 2 Boundary stabilization in the presence of a state-delay 3 PI regulation with delayed boundary control 4 Conclusion 5 H. Lhachemi Stabilization of delayed PDEs 11 July 2020 5 / 93
Generalities on spectral reduction methods for boundary stabilization 1 Stabilization with delayed boundary control 2 Boundary stabilization in the presence of a state-delay 3 PI regulation with delayed boundary control 4 Conclusion 5 H. Lhachemi Stabilization of delayed PDEs 11 July 2020 6 / 93
Abstract boundary control system H is a separable Hilbert space on K , which is either R or C . d X d t ( t ) = A X ( t ) + p ( t ) , t ≥ 0 B X ( t ) = u ( t ) , t ≥ 0 X (0) = X 0 A : D ( A ) ⊂ H → H a linear (unbounded) operator; B : D ( B ) ⊂ H → K m with D ( A ) ⊂ D ( B ) a linear boundary operator; p : R + → H a distributed disturbance; u : R + → K m the boundary control. H. Lhachemi Stabilization of delayed PDEs 11 July 2020 7 / 93
Abstract boundary control system H is a separable Hilbert space on K , which is either R or C . d X d t ( t ) = A X ( t ) + p ( t ) , t ≥ 0 B X ( t ) = u ( t ) , t ≥ 0 X (0) = X 0 We assume that ( A , B ) is a boundary control system [Curtain and Zwart, 1995]: 1 the disturbance-free operator A 0 , defined on the domain D ( A 0 ) � D ( A ) ∩ ker ( B ) by A 0 � A| D ( A 0 ) , is the generator of a C 0 -semigroup S on H ; 2 there exists a bounded operator L ∈ L ( K m , H ), called a lifting operator, such that R ( L ) ⊂ D ( A ), A L ∈ L ( K m , H ), and B L = I K m . H. Lhachemi Stabilization of delayed PDEs 11 July 2020 7 / 93
Assumed diagonal structure for A 0 A1) A 0 is a Riesz-spectral operator, i.e. it has simple eigenvalues λ n with corresponding eigenvectors φ n ∈ D ( A 0 ), n ∈ N ∗ that satisfy: 1 { φ n , n ∈ N ∗ } is a Riesz basis: span K n ∈ N ∗ φ n = H ; 1 + such that for all N ∈ N ∗ and all there exist constants m R , M R ∈ R ∗ 2 α 1 , . . . , α N ∈ K , 2 N � N � N | α n | 2 ≤ � � � � � | α n | 2 . α n φ n ≤ M R m R � � � � n =1 � n =1 � n =1 H 2 The closure of { λ n , n ∈ N ∗ } is totally disconnected, i.e. for any distinct a , b ∈ { λ n , n ∈ N ∗ } , [ a , b ] �⊂ { λ n , n ∈ N ∗ } . A2) There exist N 0 ∈ N ∗ and α ∈ R ∗ + such that Re λ n ≤ − α for all n ≥ N 0 + 1. H. Lhachemi Stabilization of delayed PDEs 11 July 2020 8 / 93
Spectral reduction Let { ψ n , n ∈ N ∗ } be the dual Riesz-basis of { φ n , n ∈ N ∗ } , i.e., � φ k , ψ l � H = δ k , l for all k , l ≥ 1. We define x n ( t ) � � X ( t ) , ψ n � H the coefficients of the projection of X ( t ) into the Riesz basis { φ n , n ∈ N ∗ } . � X ( t ) = x n ( t ) φ n n ≥ 1 | x n ( t ) | 2 ≤ � X ( t ) � 2 ≤ M R � � | x n ( t ) | 2 m R H n ≥ 1 n ≥ 1 Dynamics of the coefficients of projection: x n ( t ) = λ n x n ( t ) + � ( A − λ n I H ) Lu ( t ) , ψ n � H + � p ( t ) , ψ n � H ˙ H. Lhachemi Stabilization of delayed PDEs 11 July 2020 9 / 93
Finite dimensional truncated model ˙ Y ( t ) = AY ( t ) + Bu ( t ) + P ( t ) , where A = diag ( λ 1 , . . . , λ N 0 ) ∈ K N 0 × N 0 B = ( b n , k ) 1 ≤ n ≤ N 0 , 1 ≤ k ≤ m ∈ K N 0 × m with b n , k = � ( A − λ n I H ) Le k , ψ n � H and ( e 1 , e 2 , . . . , e m ) the canonical basis of K m , x 1 ( t ) � X ( t ) , ψ 1 � H � p ( t ) , ψ 1 � H . . . . . . Y ( t ) = = , P ( t ) = . . . x N 0 ( t ) � X ( t ) , ψ N 0 � H � p ( t ) , ψ N 0 � H A3) We assume that ( A , B ) is stabilizable. H. Lhachemi Stabilization of delayed PDEs 11 July 2020 10 / 93
Closed-loop dynamics and stability result Closed-loop system dynamics with predictor feedback synthesized based on the truncated model: d X d t ( t ) = A X ( t ) + p ( t ) , B X ( t ) = KY ( t ) , X (0) = X 0 with gain K ∈ K m × N 0 such that A cl � A + BK is Hurwitz. Stability result There exist constants κ, C 1 , C 2 > 0 such that � X ( t ) � H + � u ( t ) � ≤ C 1 e − κ t � X 0 � H + C 2 sup � p ( τ ) � H τ ∈ [0 , t ] H. Lhachemi Stabilization of delayed PDEs 11 July 2020 11 / 93
Generalities on spectral reduction methods for boundary stabilization 1 Stabilization with delayed boundary control 2 Case of a constant and known input delay Case of an uncertain and time-varying input delay Extensions Boundary stabilization in the presence of a state-delay 3 PI regulation with delayed boundary control 4 Conclusion 5 H. Lhachemi Stabilization of delayed PDEs 11 July 2020 12 / 93
Sharp introduction to the concept of predictor feedback Objective: stabilization of LTI plants in the presence of an input delay D > 0: x ( t ) = Ax ( t ) + Bu ( t − D ) , ˙ t ≥ 0 , for a stabilizable pair ( A , B ). Idea: setting u ( t − D ) = Kx ( t ) we have: x ( t ) = A cl x ( t ) ˙ where K is selected such that A cl = A + BK is Hurwitz. Predictor component: the control input at time t takes the form of u ( t ) = Kx ( t + D ); we need to predict x ( t + D ) from x ( t ): � t � � x ( t + D ) = e DA e ( t − D − s ) A Bu ( s ) d s x ( t ) + . t − D Reference: seminal work [Artstein, 1982]. H. Lhachemi Stabilization of delayed PDEs 11 July 2020 13 / 93
Extension to diagonal infinite-dimensional systems? Positive answer for the reaction-diffusion system: y t = y xx + c ( x ) y y ( t , 0) = 0 , y ( t , L ) = u ( t − D ) y (0 , x ) = y 0 ( x ) reported in [Prieur and Tr´ elat, 2018] for a constant and known input delay D > 0. Possible extension to: General Sturm-Liouville operator? Dirichlet/Neumann/Robin boundary condition and boundary control? Robustness issues: Uncertain and time-varying input delay D ( t )? Boundary and distributed perturbations? Extension to diagonal infinite-dimensional systems? H. Lhachemi Stabilization of delayed PDEs 11 July 2020 14 / 93
Stabilization with delayed boundary control 2 Case of a constant and known input delay Case of an uncertain and time-varying input delay Extensions H. Lhachemi Stabilization of delayed PDEs 11 July 2020 15 / 93
Problem setting H is a separable Hilbert space on K , which is either R or C . d X d t ( t ) = A X ( t ) + p ( t ) , t ≥ 0 B X ( t ) = u ( t − D ) , t ≥ 0 X (0) = X 0 Assumptions: ( A , B ) is a boundary control system. Assumption A1 holds: the disturbance free operator A 0 is diagonal in a Riesz basis. Assumption A2 holds: A 0 admits a finite number of unstable modes while the real part of the stable ones do not accumulate at 0. The control input u ( t ) ∈ K m is subject to a constant and known delay D > 0. H. Lhachemi Stabilization of delayed PDEs 11 July 2020 16 / 93
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