Governor with dynamics: Gg(s)= 1 Turbine with dynamics: Gt(s) = 1 Load and machine with dynamics: Gp(s) = 1

Transcription

1 Load Frequency Control of Two Area Power System Using Conventional Controller 1 Rajendra Murmu, 2 Sohan Lal Hembram and 3 Ajay Oraon, 1 Assistant Professor, Electrical Engineering Department, BIT Sindri, Sindri, Dhanbad, Jharkhand, India 2 Reseach Scholar, Electrical Engineering Department, BIT Sindri, Sindri, Dhanbad, Jharkhand, India 3 Assistant Professor Chemical Engineering Department, BIT Sindri, Sindri, Dhanbad, Jharkhand, India Abstract: Currently as there has been an increase in the interconnected systems as far as power systems are concerned Load as well as power flow in tie-line are varying dynamically So there is a need of robust control of system frequency as well as tie-line power flow system This robust control could be achieved by the help of using I,PI and PID s This is due to the fact that gain constants in the case of conventional s remain same throughout, for changes in the load value But Load can t be the same throughout, load deviates from time to time Then simulation is done by using Matlab/Simulink software Keywords: Conventional Controllers, Two Area Power System, Load Frequency Control, MATLAB SIMULINK I INTRODUCTION For extensive level power systems which consist of interconnected control regions, load frequency; then it s paramount to hold into the frequency and entomb territory tie power close to the booked qualities The input mechanical power is utilized to control the frequency of the generators and the variation in the frequency and tie-line power are detected, which is the extent of the alteration in rotor angle A decently outlined power framework ought to have the capacity to give the satisfactory levels of power quality by keeping the frequency and voltage size inside middle of as far as possible Changes in the power system load influences chiefly the system frequency, while the reactive power is less delicate to changes in frequency and is fundamentally reliant on vacillations of voltage size So the control of the true and reactive power in the power system is managed independently As the loading in a power system is not constant so the s for the system must be aimed to provide quality service in the power system The power flow and frequency in an interconnected system is well regulated by AGC The main purpose of the AGC is to retain the system frequency constant and almost inert to any disturbances Generally two things are being controlled in AGC ie voltage and frequency Both have separate control loops and independent of each other In this paper, Matlab Simulation is carried out by using I, PI, PID s II TWO AREA POWER SYSTEM Generally, power systems obligate composite & multi-variable configurations and they have many non minimum and nonlinear phase systems Power networks are distributed by tie lines into regulator Areas Generators are expected to maintain synchronism with the tie line and connected Areas There are basically two types of control mechanism to control frequency in interconnected power systems ie first one is primary speed control & second one is secondary speed The first speed control creates the preliminary rough alteration of frequency For its activities, the variation in load is being tracked by the generators and share among them according to their ratings The inherent time lags of the system and the turbine itself is the major cause for the slow response of the system Liable on the turbine kind, the primary loop classically responds in 2 18 s The later speed control follows the well alteration of frequency by varying the frequency inaccuracy to zero by an integral control action The association among the load and speed is accustomed by varying a load set point input In exercise, the tuning of the load reference mark point is being done by functioning the speed changing motor This control is significantly sluggish and drives to action only when the job is done by the primary speed control Regulation of the frequency is done by the speed-governing system The isochronous governor changes the turbine valve/door to get the frequency once again to the ostensible or booked rate III MODEL OF TWO AREA POWER SYSTEM Each area is assumed to have only one equivalent generator and is equipped with governor- turbine system They are the control signals from the s we choose The plant for a power system with a non-reheated turbine consists of three parts: Governor with dynamics: Gg(s)= 1 1+Tgs Turbine with dynamics: Gt(s) = 1 1+Tts Load and machine with dynamics: Gp(s) = 1 Fig-31:Block diagram of two area power system 1+Tps Available Online@ 239

2 IV SYSTEM PARAMETERS The nominal parameters value of Two area power system model is given below in Table-1 Table -1: The nominal parameters value of Two area power system Parameters Nominal Value T g (Time constant of the generator) 008 T t (Time constant of the turbine) 03 R 1 and R 2 (Speed regulation constant) 24 b 1 and b 2 (Feedback bias cofficient) 0425 k p (Proportional gain constant) 120 T p (Power system time constant) 20 a 1 and a 2 (Synchronizing power coefficient) -1 The value of K i are following:- Table- 2:Integral Gain For I Controller Gain(for Value Gain(for Value area 1) area 2) K i K i V CONVENTIONAL CONTROLLERS A Controller The contribution from the integral term (sometimes called reset) is proportional to both the magnitude of the error and the duration of the error Summing the instantaneous error over time (integrating the error) gives the accumulated offset that should have been corrected previously 2 Mathematical expression I Transfer function of I is given in equation (1) and (2) e a =K i e(t)dt (1) C(s)= K i s T i s (2) K i =Integral gain, T i =Reset time= 1 K i 3 Simulink Model and results Fig-52:Output frequency response of area-1 of two area power Fig- 51: Simulink model of two area power system with I Fig-53:Output frequency response of area-2 of two area power According to output of I Controller, settling Time, Peak overshoot and steady state error are given below Table-3: Output Result Of I Controller B PI Controller Available Online@ 240 steady state erro The proportional gain provides stability and high frequency response The integral term insures that the average error is driven to zero Advantages of PI include that only two gains must be tuned, that there is no long-term error, and that the method normally provides highly responsive systems The speed of response, however, becomes much slower 2 Mathematical expression PI Transfer function of PI is given in equation (3) and (4)

3 e a = e(t)+k i e(t)dt (3) C(s) =K p + K i s = K p(1 + 1 T i s ) (4) Where: K p =Proportional gain, K i =Integral gain, T i =Reset time= K p K i 3 Simulink Model and results Fig-56:Output frequency response of area-2 of two area power According to output of PI Controller, settling Time, Peak overshoot and Steady state error are given below Table-5: Output Result of PI Controller steady state error Fig-54:Simulink model of two area power system with PI The value of K p and K i are following:- Table -4: Proportional and Integral Gain For Pi Controller Gain(for area Value Gain(for area Value 1) 2) K p K p K i K i C PID Controller A Conventional PID is most widely used in industry due to ease in design and inexpensive cost The PID formulas are simple and can be easily adopted to corresponding to different controlled plants but it can t yield a good control performance if controlled system is highly order and nonlinear The PID is a combination of the PI and PD s The PD control, as in the case of the lead compensator, improves the transient-response characteristics, improves system stability, and increases the system bandwidth, which implies fast rise time Fig-55:Output frequency response of area-1 of two area power Fig-57:General control structure of PID 2 Mathematical expression PID The actuating signal for the PID and the transfer function are given in (5) and (6) e a = e(t) +K i e(t)dt+k d de (t) dt (5) C(s) =K p + K i s +K ds = K p (1 + 1 T i s +T ds) (6) Available Online@ 241

4 Where: K p =Proportional gain, K i =Integral gain, T i =Reset time= K p K i, K d =Derivative gain, T d =Rate Time or derivative time= K d K p 3 Simulink Model and results Fig-510: Output frequency response of area-2 of two area power According to output of PID Controller settling Time,Peak overshoot and Steady state error are given below Table-7: Output Result of PID Controller steady state error Fig-58: Simulink model of two area power system with PID The valueof K p,k i andk d are following:- Table-6: Proportional, Integral and Derivative Gain For PID Controller Gain (for area Gain (for area value value 1) 2) K p K p K i K i K d K d CONCLUSIONS & SCOPE OF FUTURE WORK A Comparative Analysis The comparison among different methods in terms of various performance specifications such as settling time, overshoot and steady state error the conventional and intelligent methods has been shown in table 10 Table 10: Performance analysis of different types of Controller Settling Time Overshoot (Hz) steady state error I Controller PI Controller PID Controller Fig-59:Output frequency response of area-1 of two area power CONCLUSION AND FUTURE SCOPE The performance of all the s have been evaluated Performance evaluation scheme of has been done using time response analysis In time response analysis response of the respective has been presented and thereby Settling time, peak overshoot and steady state error have been founded The Performance of the each is shown table 10According to the result of PID it gives best settling time and minimum overshoot Finally it is concluded that by using of different conventional settling time and peak overshoot of the system is reduced and thus stability is improved As a further study, the proposed method can be applied to multi area power system load frequency control (ALFC) and also optimum values can be obtained by Genetic Algorithm and Neural networks Available Online@ 242

5 References [1] C Concordia, L K Kirchmayer, "Tie-Line Power & Frequency Control of ElectricPower Systems- Part II", AIEE Trans, vol 73, part III-A, 1954, pp [2] O IElgerd, Energy Systems Theory: an introduction, New York : McGraw-Hill,1982 [3] Kundur P Power system stability and control McGraw- Hill; 1994 [4] KOgata, Modern Control Engineering, New Jersey, Prentice Hall, 2008 [5] AdilUsman BP Divakar Simulation study of load frequency control of single and two area systems IEEE Global Humanitarian Technology Conference, pp , 2012 [6] E Cam and I Kocaarslan, Load frequency control in two area power systems using fuzzy logic, Energy Conversion and Management, vol 46, no 2, pp , 2005 [7] I J Nagrath and D P Kothari Modern power system analysis- TMH 1993 [8] T Kennedy, SM Hoyt and CF AbellVariable, nonlinear tie-line frequency bias for interconnected systems control, IEEE Trans Power Syst, 3 (3) (1988) [9] G Ray, A N Prasad, and G D Prasad, A new approach to the Design of robust load-frequency for large scale power systems, Elect Power Syst Res, vol 51, no 1, pp 13 22, 1999 [10] Nanda, J, and Kaul, BL, Automatic Generation Control of an Interconnected Power System, PROC IEE, Vol 125, No 5, PP , MAY, 1978 [11] Timothy J Ross 1995 Fuzzy logic with engineering application Mc-Graw Hill [12] IH Altas and AM Sharaf, A Generalized direct approach for designing fuzzy logic s in Matlab/Simulink GUI environment, International Journal of InformationTechnology and Intelligent Computing, Int J IT&IC, vol1,no4, 2007 Available Online@ 243