robust state and fault estimation observer for discrete-time d-lpv systems with unmeasurable gain...
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ROBUST STATE AND FAULT ESTIMATION OBSERVERFOR DISCRETE-TIME D-LPV SYSTEMS
WITH UNMEASURABLE GAIN SCHEDULING FUNCTIONS. APPLICATION TO A BINARY DISTILLATION COLUMN
F. R. LÓPEZ ESTRADA (TecNM - Instituto Tecnológico de Tuxla Gutiérrez, Chiapas, México)
J.C. PONSART, D. THEILLIOL (CRAN – University of Lorraine, Nancy, France)
C. M. ASTORGA-ZARAGOZA, M. FLORES-MONTIEL (CENIDET, Cuernavaca, México)
frlopez@ittg.edu.mx
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OBSERVER DESIGN
Introduction
Fault detection and estimation problem Observer design
Sensor fault estimation
Actuator fault estimation
Application to a binary distillation column - Simulation results
Conclusions
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1
INTRODUCTION
2
INTRODUCTION: SYSTEMS REPRESENTATIONS
Nonlinear systems (ODE, DAE)
• Commonly approximate by LTI systems
2
Nonlinear approximation
INTRODUCTION: SYSTEMS REPRESENTATIONS
Nonlinear systems (ODE, DAE)
• Commonly approximate by LTI systems
2
Nonlinear approximation
LPV systems, Q-LPV systems (TS)
INTRODUCTION: SYSTEMS REPRESENTATIONS
Nonlinear systems (ODE, DAE)
• Commonly approximate by LTI systems
Continuous time
2
Nonlinear approximation
LPV systems, Q-LPV systems (TS)
INTRODUCTION: SYSTEMS REPRESENTATIONS
Nonlinear systems (ODE, DAE)
• Commonly approximate by LTI systems
Continuous time
*E is a singular matrix representing ODE (dynamic) and algebraic equations (non-dynamic)
2
Nonlinear approximation
LPV systems, Q-LPV systems (TS)
INTRODUCTION: SYSTEMS REPRESENTATIONS
Nonlinear systems (ODE, DAE)
• Commonly approximate by LTI systems
Continuous time
*E is a singular matrix representing ODE (dynamic) and algebraic equations (non-dynamic)
* Local models
2
Nonlinear approximation
LPV systems, Q-LPV systems (TS)
INTRODUCTION: SYSTEMS REPRESENTATIONS
Nonlinear systems (ODE, DAE)
• Commonly approximate by LTI systems
Continuous time
*E is a singular matrix representing ODE (dynamic) and algebraic equations (non-dynamic)
* Local models
* Gain scheduling functions depending on the state
Discrete-time D-LPV systems under noise and disturbances
where:
3
DISCRETE-TIME D-LPV SYSTEMS
Discrete-time D-LPV systems under noise and disturbances
where:
3
DISCRETE-TIME D-LPV SYSTEMS
The scheduling functions are defined through the following convex set
Note that the scheduling functions are depending on the state, which is considered unmeasurable
In addition the system can be affected by sensor faults
4
FAULT DETECTION AND ESTIMATION PROBLEM
Or actuator faults
In addition the system can be affected by sensor faults
4
FAULT DETECTION AND ESTIMATION PROBLEM
Or actuator faults
The challenge is to detect and estimate these faults, despite the problem of unknown gain scheduling functions depending on the system's states
Then, a suitable needs the estimation of the scheduling functions
5
OBSERVER DESIGN
In order to estimate the unmeasurable scheduling functions, the first challengeis to design a state observer by considering the system without faults
5
OBSERVER DESIGN
Then, for the discrete system
In order to estimate the unmeasurable scheduling functions, the first challengeis to design a state observer by considering the system without faults
5
OBSERVER DESIGN
Then, for the discrete system
The following observer is proposed
are unknown gain matrices to be computed
In order to estimate the unmeasurable scheduling functions, the first challengeis to design a state observer by considering the system without faults
5
OBSERVER DESIGN
Then, for the discrete system
are unknown gain matrices to be computed
In order to estimate the unmeasurable scheduling functions, the first challengeis to design a state observer by considering the system without faults
The following observer is proposed
To deal with the UGF, the D-LPV system is transformed into a perturbed system with estimated scheduling function as follows:
6
OBSERVER DESIGN
with:
To deal with the UGF, the D-LPV system is transformed into a perturbed system with estimated scheduling function as follows:
6
OBSERVER DESIGN
with:
Then, the estimation error is computed as
The error becomes
7
OBSERVER DESIGN
The error becomes
7
OBSERVER DESIGN
After some algebraic manipulations,the following error system is obtained
with
dk dkT k
T
T
The error becomes
7
OBSERVER DESIGN
After some algebraic manipulations,the following error system is obtained
with
Then, in order to guarantee asymptotic stability of (15) and robustness, the following criterion performance is considered
dk dkT k
T
T
Theorem 1: Robust state observer
8
OBSERVER DESIGN
then, the estimation error is quadratically stable with
Proof: Details in the paper.
If there exist matrices T1 and T2, a common matrix P = PT > 0, matrices i and a scalar , such that i [1, 2, …, h]
9
SENSOR FAULT ESTIMATION
The same observer design can be considering to estimate jointly the statesand sensor faults
9
SENSOR FAULT ESTIMATION
The same observer design can be considering to estimate jointly the statesand sensor faults
For instance, let us consider a D-LPV system under sensor fault as
9
SENSOR FAULT ESTIMATION
The same observer design can be considering to estimate jointly the statesand sensor faults
For instance, let us consider a D-LPV system under sensor fault as
In order to estimate sensor faults, the system (18) can be rewritten as an
augmented system with , such that the following augmented system is obtained
10
SENSOR FAULT ESTIMATION
where:
xk xkT fsk
T
T
10
SENSOR FAULT ESTIMATION
where:
The same observer is considered to estimate the augmented system
In order to estimate sensor faults, the system (18) can be rewritten as an
augmented system with , such that the following augmented system is obtained xk xkT fsk
T
T
11
SENSOR ESTIMATION ERROR
The error equation is computed as
with
dk dkT fsk
T kT
T
11
SENSOR ESTIMATION ERROR
The error equation is computed as
with
Note that the error equation has similar form that previous error equation,
then Theorem 1 can be considered to obtain a solution,
which guarantee convergence of the observer
and therefore, robust state and sensor fault estimation.
dk dkT fsk
T kT
T
12
ACTUATOR FAULT ESTIMATION
Under actuator faults and disturbance, the D-LPV system is represented by
12
ACTUATOR FAULT ESTIMATION
Under actuator faults and disturbance, the D-LPV system is represented by
We assume that the faults are slow variation
12
ACTUATOR FAULT ESTIMATION
Under actuator faults and disturbance, the D-LPV system is represented by
We assume that the faults are slow variation
A perturbed augmented system with
13
ACTUATOR ESTIMATION ERROR
The error equation is computed as
with
13
ACTUATOR ESTIMATION ERROR
The error equation is computed as
with
13
ACTUATOR ESTIMATION ERROR
The error equation is computed as
with
Note that the error equation has similar form that previous error equation,
then Theorem 1 can be considered to obtain a solution,
which guarantee convergence of the observer
and therefore, robust state and actuator fault estimation.
A 5 trays distillation column located at the Process Control Laboratory of CENIDET in Cuernavaca, is considered.
The distillation column was operated under liquid-vapor-(LV) configuration and without feed flow (F = 0).
The states variables are x = [x1 x2 x3 x4 x5], which represent the liquid compositions of the light component from the top tothe bottom, respectively.
14
APPLICATION TO A BINARY DISTILLATION COLUMN
For a mixture ethanol-water, the system inputs is u = [Vr Lr]T.
These inputs are functions of state x5, the reflux rv and the heating power on the boiler Qb such as:
are the vaporization enthalpy of ethanol and water
15
APPLICATION TO A BINARY DISTILLATION COLUMN
D-LPV system with 5 states, 4 local models, and 3 measured outputs
16
D-LPV MODEL
The gain scheduling functions are
Note that the scheduling functions depend on Vr and Lr that are
inputs depending on the state x5, which is unmeasurable.
Therefore a suitable observer design is required for the estimation of x5.
17
D-LPV MODEL
The observer gains for jointly state and sensor fault estimation are obtainedby solving Theorem 1 with the YALMIP toolbox. The following gain matrices are computed
18
OBSERVER GAIN COMPUTATION
19
SIMULATION RESULTS
The disturbance signal included in the system is a zero mean random signal bounded by 0.02
Simultaneous bias fault are considered on sensors 2 & 3
Simulation conditions
20
SIMULATION RESULTS
The disturbance signal included in the system is a zero mean random signal bounded by 0.02
Simultaneous bias fault are considered on sensors 2 & 3
Simulation conditions
State estimation errors and system inputs
- the observer converges fast and asymptotically- small deviation from zero of x4 related to changes in the system inputs which
consequently generate a change of the operation regions
21
SIMULATION RESULTS
The disturbance signal included in the system is a zero mean random signal bounded by 0.02
Simultaneous bias fault are considered on sensors 2 & 3
Simulation conditions
Estimated gain scheduling functions
- the evolutions of the estimated gain scheduling functions illustrate how the system and consequently the observer are constantly changed the operating region.
22
SIMULATION RESULTS
The disturbance signal included in the system is a zero mean random signal bounded by 0.02
Simultaneous bias fault are considered on sensors 2 & 3
Simulation conditions
Estimated simultaneous sensor faults
- the observer is able to detect and estimate simultaneous occurring faults, despite the small fault magnitudes.
- all simulation results show that the state and fault estimation are well performed despite the disturbance and the error provided by the unmeasurable gain scheduling functions.
23
CONCLUSIONS
A discrete-time state fault estimation (sensor or actuator) observer for D-LPV systems was proposed
Unmeasurable gain scheduling functions (UGF) are considered. This consideration increases the level of abstraction, but also the applicability
To solve the problem of UGF, the system was transformed into a perturbed D-LPV system with estimated gain scheduling functions
Robustness and asymptotic stability, of the estimation error are guaranteed by considering a quadratic criteria and a Lyapunov equation
Feasible LMIs are obtained to compute the observer gains
The method was extended to estimate jointly the state and the faults
The methodology was successfully applied to a realistic model of a binary distillation column.
ROBUST STATE AND FAULT ESTIMATION OBSERVERFOR DISCRETE-TIME D-LPV SYSTEMS
WITH UNMEASURABLE GAIN SCHEDULING FUNCTIONS. APPLICATION TO A BINARY DISTILLATION COLUMN
F. R. LÓPEZ ESTRADA (TecNM - Instituto Tecnológico de Tuxla Gutiérrez, Chiapas, México)
J.C. PONSART, D. THEILLIOL (CRAN – University of Lorraine, Nancy, France)
C. M. ASTORGA-ZARAGOZA, M. FLORES-MONTIEL (CENIDET, Cuernavaca, México)
Jean-Christophe.Ponsart@univ-lorraine.fr
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