 Open Access
 Total Downloads : 978
 Authors : Dewashri Pansari, Deepali Chandrakar, Balram Timande
 Paper ID : IJERTV1IS7456
 Volume & Issue : Volume 01, Issue 07 (September 2012)
 Published (First Online): 26092012
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
A Robust PID Controller Design For Network Control System
Dewashri Pansari1, Deepali chandrakar 2 balram Timande3
Department of Electrical and Electronics Engineering, DIMAT Raipur
C.G. Swami Vivekananda Technical University, Raipur, Chhattisgarh, India
ABSTRACT We propose a robust PID controller for controlling the delay induced in the Network control system (NCS) .With regard to the problems brought by the network induced delay in NCS, this paper design a robust PID controller to overcome the influence of network induce delays on control system performance by using gain phase margin method. The controller gains are directly selected from parameter region and a design controller can guarantee the system at least a prespecified safety margin to compensate for instability induced by time delays. The paper presents optimization in tuning controllers for varying time delay system using simulation. The simulation results show the effectiveness of these compensation methods.
Index Terms Nonminimum phase system, network control system, delays Compensation, gain margin, phase margin, PID controller, Distributed system.

INTRODUCTION
The robust PID controller is the modified form of PID controller in which the parameters of system are tuned to compensate for instability induce by time delays for nonminimum phase system and endows the system with robust safety margins in terms of gain and phase. According to modern control theory, the information (signals) are transmitted along perfect communication channels, which involve network communication. New controllers, algorithms and demonstration must be developed in which the basic input/output are data packets that may arrive at variable times not necessarily in orders and sometimes not at all. When PID controllers receive the sensor information or transmit its output through a communication network, its parameters are difficult to tune using classical tuning methods; this is due to the delays introduced by the network. This paper presents the ZieglerNichols closed loop cycling methods for tuning the various parameter of a system. Now a day there is a trend in the research of control theory to investigate control loop that are stretched over a network.
simple and fast implementation, and powerful system diagnosis and maintenance utilities. The disadvantage is that the analysis and design of an distributed system becomes complex Distributed system is shown in fig.1.
Dewashri pansari is currently Perusing Masters Deegre in Electrical Devices and Power System engineering in DIMAT, Raipur, India, ph09770145207. Email:
pansaridewashri@gmail.com.

DISTRIBUTED SYSTEM
In distributed systems the controller and the process are physically separated and connected with a network. Their sensors, actuators, estimator units, and control units are connected through communication networks. This type of system provides several advantages such as modular and flexible system design,
Figure 1. Distributed System
Fig (2) shows the timing diagram of network delay propagation. Delay in an NCS can be divided into different types on the basis of data transfers i.e.,

sensor to controller delay

controller to actuator delay.
Control
KP
KI
KD
P
0.5 KC
PI
0.45 KC
1.2TC
PID
0.33 KC
2 TC
0.33 TC
Figure2. Timing diagram of Network delay propagations


PID CONROLLER IN NCS
The PD controller could add damping to a system, but steady state response is not affected. The PI controller could improves the relative stability and improves the steady state error at the same time, but the rise time is increased .This leads to the motivation of using PID controller so that the best features of each of PI and PD controllers are utilized. The PID Control is one of the most popular control strategies for process control because of its simple control structure and easy tune
.The transfer function of PID controller is
GC (s) =KP + KDS +
Where,
KP = proportional gain constant, KI = Integral gain constant,
KD = Derivative gain constant,
The PID controller is traditionally suitable for second and lower order systems. It can also be used for higher order plants with dominant second order behaviour. In this paper we used Ziegler Nichols closed loop cycling method and gain margin, phase margin tester methods for PID controller tuning.
Ziegler Nichols closed loop cycling methods: Procedure for tuning

Select proportional control alone.

Increase the value of the proportional gain until the point of instability is reached, the critical value of gain KC is reached.

Measure the period of oscillation to obtain the critical time constant, Tc.
Once the values for KC and TC are obtained, the PID parameters Can be calculated, according to the
Design specification given in Table1.
Table 1
Figure3. Simulink Model for ZN Tuning PID Controller
1.5
1
Referenc
SystemR
R(s)
+=
D(s)
GP(s)
GC(s)
0.5
Amplitude
0
0.5
1
1.5
0 100 200 300 400 500 600 700 800
Simulation Time
Figure 4. PID controller response with ZN tuning and no delay
The PID Controller is suitable for second and lower order system and when delays is introduce in the system, performance of the system is degraded and also destabilized the system by reducing the system stability margin, thus a Robust PID Controller design is introduced in this paper for higher order nonminimum system which contains the time delay element

A ROBUST PID CONTROLLER DESIGN:
Whenever there is a delay between the commanded response and the start of the output response time delay occurs in the control system which decreases the phase margin and lowers the damping ratio and hence increases the oscillatory response for the closed loop system. Time delay also decreases the gain margin, thus moves the system closer to the instability.
Figure 5. Block Diagram of a Typical PID Control System
An erroractuated PID controller has the general transfer function
GC (s) =KP + KDS + (2)
The forward openloop transfer function of the control system shown in Fig. 5 is
G0(S) = GC(S) .GP(S) (3)
By letting S= , and Re [G0 ( )] and Imaginary [G0( )] be the real part and imaginary part of the G0( ), respectively, one has
G0 ( )
(4)
Where,
(6)
Substituting (4) and (3), one obtains
(7)
Let
A = (8)
In this paper, suitable algorithms are introduced for the instability induced by the time delays. For a high order non minimum phase system which contains the time delay element, whose transfer function is as shown.
Transfer function = (1)
Where, T is the delay time of the system.
=+180. (9)
When =0, A is the gain margin of the system, and when A=1, is the corresponding phase margin. Now we define the gainphase margin tester function as,
F ) = D ( ) + N ) (10)
(7), (8), (9) and (10) imply that the function F ( ) should always be equal to zero. This indicates that the gain margin and the phase margin of the PID control system can be determined rom the characteristic equation.
Imaginary parts:
The open loop transfer function defined as
B2=
putting s= Noting that =A – A ,
N ( ) =
Let us define
(24) C2=
(25) D2=
Then we can write from (10), (23), (24), (25), and (26):
B2+C2+D2=0 (27)
Solving the equations (22) and (27), we can find: AND
(28)

SIMULATION RESULTS
Let us define
Define:
Then we can write from (10), (18), (19), (20), and (21) as
The simulation is carried out in MATLAB and SIMULINK .With the help of robust PID controller system stability is achieved and the system with delay gets stable and gives high degree of performance as shown in fig (6)
B1+C1+D1=0 (22)
Figure6. Frequency and phase response of a system

CONCLUSION
The robust PID controller with certain variation in algorithms has made the system stabilized though various types of delays are present in the system. The advantage of this method is the guaranteed robustness with respect to plant variation and external disturbances. It promises the control system with good tracking and disturbance rejection behaviour. This method of achieving stability and good performance can be applied to the wide range of industrial applications.
REFERENCES

YING J. HUANG AND YUANJAY WANG. ROBUST PID CONTROLLER DESIGN FOR NONMINIMUM PHASE TIME DELAY SYSTEMS, ISA TRANSACTIONS 40(2001)3139

A.M. DE PAOR AND M. O'MALLY, CONTROLLERS OF ZIEGLERNICHOLS TYPE FOR UNSTABLE PROCESS WITH TIME DELAY. INT. J. OF CONTROL 49 4 (1989), PP. 1273 1284.

A.T. SHENTON AND Z. SHAFIEI, RELATIVE STABILITY FOR CONTROL SYSTEMS WITH ADJUSTABLE PARAMETERS. J. OF GUIDANCE, CONTROL AND DYNAMICS 17 (1994), PP. 304310.

W.K. HO AND W. XU, PID TUNING FOR UNSTABLE PROCESSES BASED ON GAIN AND PHASEMARGIN SPECIFICATIONS. IEE PROC. CONTROL THEORY AND APPL 145 5 (1998), PP. 392396.

C.H. CHANG AND K.W. HAN, GAIN MARGINS AND PHASE MARGINS FOR CONTROL SYSTEMS WITH ADJUSTABLE PARAMETERS. J. OF GUIDANCE, CONTROL, AND DYNAMICS 13 3 (1990), PP. 404408.

K.W. HAN, C.C. LIU, Y.T. WU, DESIGN OF CONTROLLERS BY PARAMETERSPACE METHOD AND GAINPHASE MARGIN TESTER METHOD. PROC. OF 1999 ROC AUTO. CONTROL CONF. YUNLIN, 1999, PP. 145 150.

G.H. LII, C.H. CHANG AND K.W. HAN, ANALYSIS OF ROBUST CONTROL SYSTEMS USING STABILITY EQUATIONS. J. OF CONTROL SYSTEMS AND TECHNOLOGY 1 1 (1993), PP. 8389.

K.W. HAN AND G.J. THALER, CONTROL SYSTEM ANALYSIS AND DESIGN USING A PARAMETER SPACE METHOD. IEEE TRANS. ON AUTOMATIC CONTROL, AC11 (3) (1966), PP. 560563.

D.D. ILJAK, PARAMETER SPACE METHODS FOR ROBUST CONTROL DESIGN: A GUIDED TOUR. IEEE TRANS. ON AUTOMATIC CONTROL34 7 (1989), PP. 674 688.

D.D. ILJAK, GENERATION OF THE PARAMETER PLANE METHOD. IEEE TRANS. ON AUTOMATIC CONTROL 11 7 (1997), PP. 674688.

C.T. HUANG, M.Y. LIN AND M.C. HUANG, TUNING PID CONTROLLERS FOR PROCESSES WITH INVERSE RESPONSE USING ARTIFICAL NEURAL NETWORKS. J. CHIN. INST. CHEM. ENGRS 30 3 (1999), PP. 223232.

D.D. ILJAK, NONLINEAR SYSTEMS: THE PARAMETER ANALYSIS AND DESIGN. , JOHN WILEY & SONS INC, NEW YORK (1969).

N.S. NISE, CONTROL SYSTEMS ENGINEERING. (2ND ED.

ED.),, ADDISONWILEY PUBLISHING COMPANY,