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Decentralized stable and robust fault-tolerant PI plus fuzzy control of MIMO systems: a quadruple tank case study


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Figure 1:

Quadruple tank level process (QTLP) scheme with fault.
Quadruple tank level process (QTLP) scheme with fault.

Figure 2:

Uncertainty domain specified by working points.
Uncertainty domain specified by working points.

Figure 3:

Open-loop response of quadruple system with non-minimum phase configuration.
Open-loop response of quadruple system with non-minimum phase configuration.

Figure 4:

Open-loop response of quadruple system with minimum phase configuration.
Open-loop response of quadruple system with minimum phase configuration.

Figure 5:

Schema of simplest decentralized control of TITO system (Schmidt, 2002).
Schema of simplest decentralized control of TITO system (Schmidt, 2002).

Figure 6:

Decentralized control structure for minimum phase system with two fuzzy and two PI controllers. fsys, fa, and fs denotes system component (leak), actuator, and sensor faults, respectively.
Decentralized control structure for minimum phase system with two fuzzy and two PI controllers. fsys, fa, and fs denotes system component (leak), actuator, and sensor faults, respectively.

Figure 7:

Stability analysis for minimum phase configuration.
Stability analysis for minimum phase configuration.

Figure 8:

Step responses: minimum phase stable system subject to process disturbances.
Step responses: minimum phase stable system subject to process disturbances.

Figure 9:

Step responses: minimum phase stable system subject to system component (leak) fault.
Step responses: minimum phase stable system subject to system component (leak) fault.

Figure 10:

Step responses: minimum phase stable system subject to actuator fault.
Step responses: minimum phase stable system subject to actuator fault.

Figure 11:

Step responses: minimum phase stable system subject to sensor fault.
Step responses: minimum phase stable system subject to sensor fault.

Figure 12:

Error comparison for minimum phase configuration.
Error comparison for minimum phase configuration.

Figure 13:

Step responses: non-minimum phase, unstable system.
Step responses: non-minimum phase, unstable system.

Figure 14:

Stability analysis for non-minimum phase configuration.
Stability analysis for non-minimum phase configuration.

Figure 15:

Step responses: non-minimum phase stable system subject to process disturbances.
Step responses: non-minimum phase stable system subject to process disturbances.

Figure 16:

Step responses: non-minimum phase stable system subject to system component fault.
Step responses: non-minimum phase stable system subject to system component fault.

Figure 17:

Step responses: non-minimum phase stable system subject to actuator fault.
Step responses: non-minimum phase stable system subject to actuator fault.

Figure 18:

Step responses: non-minimum phase stable system subject to sensor fault.
Step responses: non-minimum phase stable system subject to sensor fault.

Figure 19:

Error comparison for non-minimum phase configuration.
Error comparison for non-minimum phase configuration.

Parameters for FLC.

Parameter Parameter value
No. of input variables 2
No. of output variables 1
No. of linguistic variables per MF 7
No. of rules 49
Membership function (MF) Triangular
Defuzzification methods Center of gravity method

Parameters of the quadruple tank level process.

Sr. no. Description Value
1 Area of the tanks A1, A3, A2, and A4 32 cm2
2 Area of outlet pipes a1 and a3 0.071 cm2
3 Area of outlet pipes a2 and a4 0.057 cm2
4 Constant k 0.50 V/cm
5 Gravitational constant g 981 cm/s2

Operating parameters of minimum phase and non-minimum phase system.

Parameters Operating point minimum phase Operating point non-minimum phase
h 1 0 , h 2 0 12.76, 13.1 12.3, 12.7
h 3 0 , h 4 0 2.1, 1.8 5.1, 5.7
υ 1 0 , υ 2 0 3.33, 3.36 3.14, 3.31
k1, k2 3.33, 3.38 3.14, 3.33
λ1, λ2 0.7, 0.6 0.43, 0.34

Rule base for type-1 FLC 2 loop 2.

f2, e2 and ė2 NB NM NS ZR PS PM PB
NB NB NB NB NM NS NS ZR
NM NB NB NM NS NS ZR PM
NS NB NM NS ZR PS PM PB
ZR NM NM NS ZR PS PM PB
PS NM NS ZR PS PM PB PB
PM NS ZR PS PM PM PB PB
PB ZR PS PM PB PB PB PB

Rule base for type-1 FLC 1 loop 1.

f1, e1 and ė1 e ˙ 1 NB NM NS ZR PS PM PB
NB NB NB NB NM NS NS ZR
NM NB NB NM NS NS ZR PM
NS NB NM NS ZR PS PM PB
ZR NM NM NS ZR PS PM PB
PS NM NS ZR PS PS PM PB
PM NS ZR PS PS PM PB PB
PB ZR PS PS PM PB PB PB
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