AUTOMATIC LOAD FREQUENCY CONTROL OF MULTI AREA POWER SYSTEMS

Transcription

1 AUTOMATIC LOAD FREQUENCY CONTROL OF MULTI AREA POWER SYSTEMS A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF TECHNOLOGY IN POWER ELECTRONICS AND DRIVES BY SUSHMITA EKKA ROLL: 22EE4243 DEPARTMENT OF ELECTRICAL ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA ROURKELA , ODISHA, INDIA

2 AUTOMATIC LOAD FREQUENCY CONTROL OF MULTI AREA POWER SYSTEMS A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF TECHNOLOGY IN POWER ELECTRONICS AND DRIVES BY SUSHMITA EKKA ROLL: 22EE4243 UNDER THE GUIDANCE OF PROF.PRAVAT KUMAR RAY DEPARTMENT OF ELECTRICAL ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA ROURKELA , ODISHA, INDIA

3 Department of Electrical Engineering National Intitute of Technology, Rourkela C E R T I F I C A T E Thi i to certify that the thei entitled " AUTOMATIC LOAD FREQUENCY CONTROL OF MULTI-AREA POWER SYSTEMS" being ubmitted by Mi. Suhmita Ekka, to the National Intitute of Technology, Rourkela (Deemed Univerity) for the award of degree of Mater of Technology in Electrical Engineering with pecialization in "Power Electronic and Drive", i a bonafide reearch work carried out by her in the Department of Electrical Engineering, under my uperviion and guidance. I believe that thi thei fulfil a part of the requirement for the award of degree of Mater of Technology. The reearch report and the reult embodied in thi thei have not been ubmitted in part or full to any other Univerity or Intitute for the award of any other degree or diploma. Prof. Pravat Kumar Ray Dept. of Electrical Engineering National Intitute of Technology Place: N.I.T., Rourkela Rourkela, Odiha, Date: INDIA

4 ACKNOWLEDGEMENTS Firt and foremot, I am truly indebted and wih to expre my gratitude to my upervior Profeor Pravat Kumar Ray for hi inpiration, excellent guidance, continuing encouragement and unwavering confidence and upport during every tage of thi endeavour without which, it would not have been poible for me to complete thi undertaking uccefully. I alo thank him for hi inightful comment and uggetion which continually helped me to improve my undertanding. I expre my deep gratitude to the member of Mater Scrutiny Committee, Profeor Bidyadhar Subudhi, A.K.Panda, Somnath Maithy, K.B.Mohanty, P.C.Panda, Monaliha Pattnaik, for their loving advice and upport. I am alo very much obliged to the Head of the Department of Electrical Engineering, NIT Rourkela for providing all poible facilitie toward thi work. Thank to all other faculty member in the department. I would alo like to expre my heartfelt gratitude to my friend who have alway inpired me and particularly helped me in my work. My whole hearted gratitude to my parent for their contant encouragement, love, wihe and upport. Above all, I thank Almighty who betowed hi bleing upon u. Suhmita Ekka Rourkela, May 204

5 ABSTRACT Variation in load bring about drift in frequency and voltage which in turn lead to generation lo owing to the line tripping and alo blackout. Thee drift might be reduced to the mallet poible value by automatic generation control (AGC) which contitute of two ection viz load frequency control (LFC) along with automatic voltage regulation (AVR). Here imulation evaluation i done to know the working of LFC by building model in SIMULINK which help u to comprehend the principle behind LFC including the challenge. The three area ytem i alo being taken into conideration together with ingle area in addition to two area ytem. Several important parameter of ALFC like integral controller gain (KIi), parameter for governor peed regulation (Ri) a well a parameter for frequency bia (Bi) are being optimized by uing an optimization technique that i Bacteria Foraging Optimization Algorithm (BFOA) becaue uing the general hit and trial method in the imulation ha ome demerit which ha inited on uing BFOA for obtaining the deired value of the different parameter. Simultaneou optimization of certain parameter like KIi, Ri and Bi ha been done which grant not only the bet dynamic repone for the ytem but alo permit u to ue quiet larger value of Ri than put into practice. Thi will help the indutrie concerning power for impler a well a cheaper realization of the governor. The performance of BFOA i alo invetigated through the convergence characteritic which reveal that that the Bacteria Foraging Algorithm i relatively fater in optimization uch that there i drop in the computational load and alo minimum ue of computer reource utilization. i

6 TITLE TABLE OF CONTENTS PAGE ABSTRACT..... (i) TABLE OF CONTENTS... (ii) LIST OF SYMBOLS.... (iv) LIST OF FIGURES.... (v) LIST OF TABLES (vii) CHAPTER. INTRODUCTION Characteritic of properly deigned power ytem Reaon for limiting frequency deviation Concept of control area Objective relating to control area Major objective of ALFC in a power ytem Advantage of ALFC in multi area ytem Type of control Need for the inter-connection of area Advantage Diadvantage Literature review Motivation Problem tatement Load frequency problem Tie-line problem How etimation problem become optimization problem Why to go for BFOA DYNAMICS OF THE POWER SYSTEM Turbine Generator... ii

7 2.3. Governor Load Tie-line Area control error Parallel operation of generator Modeling of ALFC DESIGN MODEL FOR VARIOUS SYSTEMS Single area ytem Two area ytem Three area ytem SIMULATION RESULTS OF AUTOMATIC LOAD FREQUENCY CONTROL Single area ytem without uing econdary loop Single area ytem by uing econdary loop Two area ytem without uing econdary loop Two area ytem by uing econdary loop Three area ytem without uing econdary loop Three area ytem by uing econdary loop Obervation Concluion BACTERIA FORAGING OPTIMIZATION ALGORITHM (BFOA) Introduction Decription BFO algorithm Application of BFOA to three area ytem Sytem invetigated Simulation reult uing BFOA Reult and dicuion CONCLUSION AND FUTURE SCOPE Concluion of the thei Scope for future work REFERENCES. 64 iii

8 LIST OF SYMBOLS = incremental peed reference etting = drift in frequency for tep change in load or teady tate frequency deviation = turbine output = power due to tie line = power change in tie line = deviation of frequency in area = deviation of frequency in area 2 = turbine output of area = turbine output of area 2 = Increae of load in area = Increae of load in area 2 = Active power generation = Active power demand and = compoite frequency repone characteritic of area along with area 2 = the input to the turbine =the output from the turbine = the output from the generator = the input to the generator = time contant of the generator iv

9 LIST OF FIGURES FIGURE PAGE Fig. 2.: Block diagram of Automatic load frequency control 0 Fig. 2.2: Block diagram for parallel operation of generator Fig. 2.3: Automatic load frequency control loop Fig.2. 4: Power tranfer through tie line Fig. 3.: Model of ingle area ALFC without uing econdary control Fig. 3.2: Model of ingle area ALFC by uing econdary control... 2 Fig. 3.3: Model of two area ALFC without uing econdary control Fig. 3.4: Model of two area ALFC by uing econdary control Fig. 3.5: Model of three area ALFC by uing econdary control Fig. 4.: Simulink model of ingle area ytem without uing econdary loop Fig. 4.2: Plot of variation in frequency v. time for ingle area ytem without uing econdary loop. 29 Fig. 4.3: Simulink model of ingle area ytem by uing econdary loop Fig. 4.4: Plot of change in turbine output v. time for ingle area ytem by uing econdary loop Fig. 4.5: Plot of change in frequency v. time for ingle area ytem by uing econdary loop... 3 Fig. 4.6: Plot of incremental peed reference ignal v. time for ingle area ytem by uing econdary loop... 3 Fig. 4.7: Simulink model of two area ytem without uing econdary loop Fig. 4.8: Plot of change in frequency v. time for two area ytem without uing econdary loop 33 Fig. 4.9: Plot of change in power output v. time for two area ytem without uing econdary loop v

10 Fig. 4.0: Simulink model of two area ytem by uing econdary loop Fig. 4.: Plot of change in frequency v. time for two area ytem by uing econdary loop Fig. 4.2: Plot of change in power output v. time for two area ytem by uing econdary loop. 36 Fig. 4.3: Simulink model of three area ytem without uing econdary loop...37 Fig. 4.4: Plot of change in frequency v. time for three area ytem without uing econdary loop Fig. 4.5: Plot of change in tie line power output v. time for two area ytem without uing econdary loop.. 38 Fig. 4.6: Simulink model of three area ytem by uing econdary loop Fig. 4.7: Plot of change in frequency v. time for three area ytem by uing econdary loop Fig. 4.8: Plot of change in tie line power output v. time for two area ytem by uing econdary loop Fig. 5.: Bacteria Foraging Algorithm Flow chart Fig. 5.2: Model of three area thermal ytem Fig. 5.3: Plot of deviation in frequency in area v. time Fig. 5.4: Plot of deviation in frequency in area 2 v. time Fig. 5.5: Plot of deviation in frequency in area 3 v. time Fig. 5.6: Plot of deviation of tie line power involving area and Fig. 5.7: Plot of deviation of tie line power involving area 2 and Fig. 5.8: Plot of deviation of tie line power involving area and Fig. 5.9: Plot of convergence characteritic of BF algorithm 60 vi

11 LIST OF TABLES TABLE PAGE TABLE 4.: Sytem parameter for ingle area ytem without uing econdary control loop TABLE 4.2: Sytem parameter for ingle area ytem by uing econdary control loop TABLE 4.3: Sytem parameter for two area ytem without uing econdary control loop TABLE 4.4: Sytem parameter for two area ytem by uing econdary control loop. 34 TABLE 4.5: Sytem parameter for three area ytem without uing econdary control loop TABLE 4.6: Sytem parameter for three area ytem by uing econdary control loop vii

12 CHAPTER CHAPTER. INTRODUCTION Power ytem are very large and complex electrical network coniting of generation network, tranmiion network and ditribution network along with load which are being ditributed throughout the network over a large geographical area []. In the power ytem, the ytem load keep changing from time to time according to the need of the conumer. So properly deigned controller are required for the regulation of the ytem variation in order to maintain the tability of the power ytem a well a guarantee it reliable operation. The rapid growth of the indutrie ha further lead to the increaed complexity of the power ytem. Frequency i greatly depend on active power and the voltage greatly depend on the reactive power. So the control difficulty in the power ytem may be divided into two part. One i related to the control of the active power along with the frequency wherea the other i related to the reactive power along with the regulation of voltage [2]. The active power control and the frequency control are generally known a the Automatic Load Frequency Control (ALFC). Baically the Automatic Load Frequency Control (ALFC) deal with the regulation of the real power output of the generator and it frequency (peed). The primary loop i relatively fat where change occur in one to everal econd. The primary control loop react to frequency change through the peed governor and the team (or hydro) flow i managed accordingly to counterpart the real power generation to relatively fat load variation. Thu maintain a megawatt balance and thi primary loop perform a coure peed or frequency control. The econdary loop i lower compared to the primary loop. The econdary loop maintain the excellent regulation of the frequency, furthermore maintain appropriate real power exchange among the ret of the pool member. Thi loop being inenitive to quick change in load a well a frequency although it focue on wift change which occur over period of minute. Load diturbance due to the occurrence of continuou and frequent variation of load having maller value alway create problem for ALFC. Becaue of the change in the active power demand/load in an area, tie-line power flow from the interconnected area and the

13 CHAPTER frequency of the ytem change and thu the ytem become untable. So we need Automatic Load Frequency Control to keep up the tability at the time of the load deviation. Thi i done by minimizing tranient deviation of frequency in addition to tie-line power exchange and alo making the teady tate error to zero [3]. Inequality involving generation with demand caue frequency deviation. If the frequency i not maintained within the cheduled value then it may lead on the way to tripping of the line, ytem collape a well a blackout... CHARACTERISTICS OF A PROPERLY DESIGNED POWER SYSTEM It hould upply power everywhere the cutomer demand practically. It hould alway upply power. It hould alway upply the ever changing load demand. The upplied power hould be of good quality. The upplied power hould be economical. The neceary afety requirement hould be atified. The power delivered mut atify certain minimal neceitie with regard to the upply quality. The uperiority of the power upply can be decided a follow: a) The ytem frequency mut be kept around the pecified value i.e. 50 Hz. b) The magnitude of the bu voltage i maintained within precribed limit around the normal value. Voltage and frequency control are the neceary requirement for the effective operation of the power ytem..2. REASONS FOR LIMITING FREQUENCY DEVIATIONS There are few reaon a to why there hould be trict limitation on frequency deviation and keeping the ytem frequency contant. They are a follow: 2

14 CHAPTER The three phae a.c. motor running peed are directly proportional to the frequency. So the variation of ytem frequency will directly affect the motor performance. The blade of the team turbine and the water turbine are deigned to operate at a particular peed and the frequency variation will caue change in the peed. Thi will lead to exceive vibration and caue damage to the turbine blade. The frequency error may produce havoc in the digital torage and retrieval proce..3. CONCEPT OF CONTROL AREA A control i interpreted a a ytem where we can apply the common generation control or the load frequency control cheme. Uually a elf-governing area i made reference to a a control area. Electrical interconnection i very trong in every control area when compared to the tie in the midt of the adjoining area. Within a control area all the generator move back and forth in logical and conitent manner which i depicted by a particular frequency. Automatic Load frequency Control difficulty of a bulky interrelated power ytem have been invetigated by dividing the whole ytem into number of control area and termed a multi-area [4]. In the common teady tate proce, power ytem every control area mut try to counterbalance for the demand in power by the flow of tie-line power through the interconnected line. Generally the control area encompa only retricted right to ue to the information of the total grid: they are able to manage their own repective bue however they cannot alter the parameter at the unknown bue directly. But an area i alert of the dominance of it nearby area by determining the flow in and flow out of power by the ide of it boundarie which i commonly known a the tie-line power. In every area the power equilibrium equation are computed at the boundarie, taking into conideration the extra load enuing from the power that i being exported. Later on, the area work out the optimization problem in accordance to their objective function which i local..4. OBJECTIVES RELATING TO CONTROL AREAS The major objective relating to control area are a follow:- 3

15 CHAPTER Each control area hould accomplih it individual load demand in addition to the power tranfer all the way through tie line on the bai of communal agreement. Every control area mut have adjutable frequency according to the control..5. MAJOR OBJECTIVES OF ALFC IN A POWER SYSTEM To take care of the required megawatt power output of a generator matching with the changing load. To take care of the appropriate value of exchange of power linking control area. To facilitate control of the frequency for larger interconnection..6. ADVANTAGES OF ALFC IN MULTI AREA SYSTEM The ALFC help to diminih the tranient deviation in addition to making the teady tate error to zero. It alo hold ytem frequency at a pecified value. The ALFC alo collaborate in keeping the net power interchange between the pool member at the predetermined value..7. TYPES OF CONTROL ) Primary Control: Thi type of control i endeavored locally to keep the balance involving generation along with demand within the network. It i apprehended by peed of turbine governor that adjut the generator output a a repone to the frequency divergence in the area. If there i a major diturbance then the primary control permit the balance of generated a well a utilized power at a frequency ditinguihable from the et-point quantity in order to make the network table. 2) Secondary Control: Thi type of control i exerted by mean of an automatic centralized procedure in the control building block. It ha two purpoe: 4

16 CHAPTER It keep the interchange power connecting the control block and it adjoining block according to the planned value. In cae of major frequency drop, it bring back the et point value of the frequency..8. NEED FOR THE INTER-CONNECTION OF AREAS Earlier electric power ytem were uually operated a individual unit. But a need for the interconnection wa realized due to the following reaon: There wa a demand for larger bulk of power with increaed reliability o there wa interconnection of neighboring plant. It i alo beneficial economically ince fever machine are neceary a reerve for action at peak load (reerve capacity) and alo le machine are needed to be run without load to take care of udden rie and fall in load(pinning reerve). For that reaon, everal generating unit are connected with each other forming tate, regional and national grid repectively. Alo for the control of power flow in thee grid the Load dipatch center are needed..8.. ADVANTAGES OF HAVING INTERCONNECTED SYSTEM Reerve capacity i reduced and thu there i reduction in the intalled capacity. For larger unit the capital cot/kw i reduced. (in India a particular unit can hold up >500MW due to interconnection) Generator are ued effectively. Generation i optimized o there i reduction in the intalled capacity. The reliability of the ytem i increaed. 5

17 CHAPTER.8.2. DISADVANTAGES OF HAVING INTERCONNECTED SYSTEM Fault get propagated which i reponible for fater witchgear operation. Circuit breaker rating increae. Proper management i required..9. LITERATURE REVIEW A lot of work ha been done related to automatic load frequency control in power ytem. Load variation give rie to drift in frequency along with voltage conequential in reduction of generation becaue of line tripping a well a blackout. Thee variation are reduced by AGC that contitute of two ection namely LFC and AVR. In the paper [5] imulation analyi i dipened to comprehend operation of LFC by riing model in SIMULINK that help to know the principle and variou challenge relating to LFC. The PI controller parameter derived from conventional or trial-and-error method can t have enible dynamical act for a large variety of operating circumtance and change in load in multi-area power ytem. To olve thi difficulty, decentralized LFC combination i developed a an H- control problem plu worked out by mean of iterative linear matrix inequalitie algorithmic rule to tyle turdy PI controller in multi-area power ytem a hown in [6]. In the paper [7] a unified PID tuning technique dependent on two-degree-of-freedom for LFC of power ytem i dicued. Alo time domain act in addition to robutne of conequential PID controller i aociated to two regulation contraint a well a it robutne i dicued. Simulation reult how improvement in damping of power ytem. The additional degree-offreedom cancel the impact of unwanted pole of the diturbance, improving the diturbance reduction performance of ytem having cloed-loop. FA i ued in control of the frequency in CCGT plant for controller gain optimization in the paper [8]. Alo Performance of traditional controller I, PI, PID a well a ID are alo compared. Invetigation of differential evolution algorithmic program baed on PI controller deigned for AGC of interrelated power ytem i hown in the paper [9] by U.K.Rout and the outcome are made a comparion by mean of BFOA and GA on the bai of PI controller. 6

18 CHAPTER In the paper [0] tuning method i ued to model PID load frequency controller meant for power ytem along with relay baed recognition technique i conidered for etimation of dynamic of the power ytem. Robutne invetigation on tability a well a performance are given in relation to uncertaintie in parameter of the plant and it i een that on the whole the ytem remain aymptotically teady for all encloed uncertaintie in addition to ocillation in the ytem..0. MOTIVATION There are numerou work pertaining to ALFC of interconnected area of the power ytem by uing variou control method like claical, optimal, uboptimal and adaptive control etc. to obtain better dynamic repone characteritic but there are a very mall number of work concerned to primary control/governor control characteritic i.e. uitable choice of peed regulation contraint R. Alo the work are concerned with the election of the peed regulation contraint R more willingly than the optimized value. Alo few work ha been preented about the tudy of the ignificance of the tie line power alteration and it impact on the ytem dynamic repone. The change in the ytem repone due to imbalanced tie which are preent in actual operation in a multi area ytem have not been invetigated properly. Through imulation, the objective i to maintain contant frequency and fulfill the load demand and alo minimize the overall generated teady tate error but it poe ome demerit. The general hit and trial method eem very tireome for finding the uitable parameter o we are uing an optimization tool i.e. BFOA for tuning of the parameter uch a KIi, Ri and Bi. Along with the optimized parameter the teady tate error i to be minimized. Convergence characteritic can enure reduction in computational burden a it i fater. 7

19 CHAPTER.. PROBLEM STATEMENT... LOAD FREQUENCY PROBLEM In a ytem a the load change, the frequency of the ytem alo change. No regulation control would be required if it wa not important to keep the frequency of the ytem contant. Normally the frequency would vary by 5% approx. from light load to full load condition...2. TIE LINE POWER PROBLEM In cae of a two machine ytem having two load, the change in load i to be taken care of by both the machine uch that there i equal participation by both the machine in haring the tie-line power and alo maintaining the ytem tability by reducing the error to zero value..2. HOW ESTIMATION PROBLEM BECOMES OPTIMIZATION PROBLEM Etimation problem i baed on the empirical or meaured data o a to approximate the value of the unknown parameter ued from among the group of meaured data. Optimization problem i baed on the proce of finding the bet olution from among the feaible olution with repect to a particular goal, obtained through the proce of everal tep. The bet olution i known a the optimal value. Here the optimization technique i being utilized to find the value of the controllable factor that determine the ytem behavior and minimize the objective function contituting the error which occur due to variation in load. 8

20 CHAPTER.3. WHY TO GO FOR BFOA An effort ha been done to initiate a new-fangled optimization method called a Bacteria Foraging Optimization Technique (BFOA) intended for optimization of the parameter of the Automatic Load Frequency Control (ALFC) which would otherwie have been very difficult. BFOA technique give u a chance to optimize everal parameter imultaneouly. Simultaneou optimization of the parameter control the relative effect of the variation of the parameter. The mot vital achievement of uing thi method i the optimization of R together with the controller gain parameter. 9

21 CHAPTER 2 CHAPTER 2 2. DYNAMICS OF THE POWER SYSTEM The automatic load frequency control loop i mainly aociated with the large ize generator. The main aim of the automatic load frequency control (ALFC) can be to maintain the deired unvarying frequency, o a to divide load among generator in addition to managing the exchange of tie line power in accordance to the cheduled value. Variou component of the automatic load frequency control loop are a given away in the Fig. 2. Governor Turbine Load and Power ytem Droop Fig.2.: Block diagram of Automatic load frequency control 2.. TURBINES Turbine are ued in power ytem for the converion of the natural energy, like the energy obtained from the team or water, into mechanical power (P m ) which can be conveniently upplied to the generator. There are three categorie of turbine uually ued in power ytem: non-reheat, reheat in addition to hydraulic turbine, each and every one of which may be modeled and deigned by tranfer function. We have non-reheat turbine which are repreented a firt-order unit where the delay in time known a time delay (T ch ) take place between the interval during witching of the valve and producing the torque in the turbine. Deign of reheat turbine i done by uing econd-order unit a there are different tage becaue of oaring and low down of the preure of the team. Becaue of the inertia of the water hydraulic turbine are treated a non-minimum phae unit. The turbine model repreent change in the team turbine power output to variation in 0

22 CHAPTER 2 the opening of the team valve. Here we have conidered a non-reheat turbine with a ingle gain factor and ingle time contant. In the model the repreentation of the turbine i, Where = the input to the turbine =the output from the turbine 2.2. GENERATORS Generator receive mechanical power from the turbine and then convert it to electrical power. However our interet concern the peed of the rotor rather than the power tranformation. The peed of the rotor i proportional to the frequency of the power ytem. We need to maintain the balance amid the power generated and the power demand of the load becaue the electrical power cannot be tored in bulk amount. When there i a variation in load, the mechanical power given out by the turbine doe not counterpart the electrical power generated by the generator which reult in an error which i being integrated into the rotor peed deviation ( ). Frequency bia. The load of the power can be divided into reitive load (P L ), which may be fixed when there i a change in the rotor peed due to the motor load which change with the peed of the load. If the mechanical power doe not change then the motor load hall compenate the change in the load at a rotor peed which i completely diimilar from the planned value. Mathematically, 2 Where = the output from the generator = the input to the generator = time contant of the generator

23 CHAPTER GOVERNORS Governor are employed in power ytem for ening the bia in frequency which i the reult of the modification in load and eliminate it by changing the turbine input uch a the characteritic for peed regulation (R) and the governor time contant (T g ). If the change in load occur without the load reference, then ome part of the alteration can be compenated by adjuting the valve/gate and the remaining portion of the alteration can be depicted in the form of deviation in frequency. LFC aim to limit the deviation in frequency in the preence of changing active power load. Conequently, the load reference et point can be utilized for adjuting the valve/gate poition o a to cancel all the variation in load by controlling the generation of power rather than enuing deviation in frequency. Mathematically, 3 Where = governor output 2.4. LOAD = the reference ignal R = regulation contant or droop = frequency deviation due to peed The power ytem load contitute of a diverity of electrical device. The load that are reitive, for example lighting and alo heating load are not dependent on frequency, but the motor load are reponive to frequency depending on the peed-load characteritic a hown below: 5 Where = non frequency reponive load change = frequency reponive load change 2

24 CHAPTER TIE-LINES Variou area can be connected with one another by one or more tranmiion line in an interconnected power grid through the tie-line. When two area are having totally different frequencie, then there an exchange of power between the two area that are linked by the tie line. The power due to tie-line trade in area i and area j (ΔPij) and the tie-line ynchronizing torque coefficient (Tij). Thu we can alo ay that the integral of the divergence in frequency among the two area i an error in the power due to tie-line. The objective of tie-line i to trade power with the ytem or area in the neighborhood whoe cot for operation create uch tranaction cot-effective. Moreover, even though no power i being tranmitted through the tie-line to the neighborhood ytem/area and it o happen that uddenly there i a lo of a generating unit in one of the ytem. During uch type of ituation all the unit in the interconnection experience a alteration in frequency and becaue of which the deired frequency i regained. Let there be two control area and power i to be exchanged from area to area 2. Mathematically, 6 Where tand for control area and 2 tand for control area 2 = erie reactance involving area and 2 and = magnitude of voltage of area plu area AREA CONTROL ERROR The aim of LFC i not jut to terminate frequency error in all area, but a well to enable the exchange of the power due to tie-line a cheduled. In view of the fact that the error due to tie-line power will be the integral of the diimilarity in frequency among every pair of area, but 3

25 CHAPTER 2 when we direct frequency error back to zero, all teady tate error preent in the ytem frequency will give rie to in tie-line power error. For thi reaon it i neceary to conider the control input in the variation in the tie-line power. Conequently, an area control error (ACE) i tated. Each of the power generating area conider ACE ignal to be ued a the output of the plant. By making the ACE zero in all area make all the frequency along with error in the tieline power in the ytem a zero. In order to take care of the total interchange of power among it area within the neighborhood, ALFC utilize real power flow determination of all tie line a emanating through the area and there after ubtract the predetermined interchange to compute an error value. The total power exchange, jointly with a gain, B (MW/0.Hz), known a the bia in frequency, a a multiplier with the divergence in frequency i known a the Area Control Error (ACE) pecified by, MW 7 Where, = power in the tie line (if out of the area then +ve) = planned power exchange f 0 = bae frequency f act = actual frequency Poitive (+ve) ACE how that the flow i out of the area PARALLEL OPERATION OF GENERATORS If there are a number of unit for power generation to be operational in parallel in that particular area, a counterpart generator may be created for eae. The correponding generator inertia contant (M eq ), damping contant of load (D eq ) and characteritic for frequency repone (B eq ) may be hown. Tie line flow a well a frequency droop repreented for interconnecting power area may be combined characteritic derived from parallel action of generator. Each 4

26 CHAPTER 2 one of the area could retain it peed, then a load general to both area; by uperpoition include the voltage at the terminal. Two generator paralleled include completely divere governor-peed-droop characteritic. Since they may be in parallel, power exchange linking them init them to ynchronize at a general frequency. G Tie line G2 Bu Bu Load Load Fig.2.2: Block diagram for parallel operation of generator 2.8. MODELING OF ALFC A. Modeling for the change in frequency Let u conider an automatic load frequency control loop of a ytem which i iolated intended for the examination of the teady tate and dynamic repone. The figure i a hown below in the Fig. 2.. [] Steady tate analyi Let be the etting for the peed changer and be the alteration in demand of the load. Conidering a imple ituation where the peed changer might have contant etting i.e. a well a there i change in the load demand. Thi may be known to be free governor operation. 5

27 CHAPTER 2 () P ref P g () P D () P v () K T K p TH TT T P () P () T G p F() / R Fig.2.3: Automatic load frequency control loop For uch a proce the teady modification in the ytem frequency for a tep change in load i.e. i obtained a follow: 8 Thi implie that, 9 After implification we get, 0 Where β i the area frequency repone characteritic 6

28 CHAPTER 2 [2] Dynamic analyi For a tep change in load, Auming amplifier and turbine repone to be intantaneou i.e. T T =T H =0 and K T =, we have 2 After implification we get, 3 B. Modeling of the Tie-Line Let u conider that area i having urplu power and it tranfer power to the area 2 by the tie-line. Control area Tie line Control area 2 Fig.2.4: Power tranfer through tie line P 2 = power exchanged from area toward area 2 via tie line. Then the power tranfer equation the tie-line i pecified a follow: 7

29 CHAPTER 2 4 Where and = power angle of end voltage and of correponding machine of the two area. = reactance of the tie line. and = magnitude of voltage of area and area 2 The equence of the ubcript depict that the flow of power due to the tie line i poitive in the direction from to 2. For little deviation in the angle and change by and, the tie line power change a follow: i.e. 5 6 i.e. 7 Where, = Torque produced In a control area which i iolated, the incremental power (ΔP G ΔP D ) i the rate of rie of preerved kinetic energy due to rie in the load followed by a rie in the frequency. The power due to the tie-line for each area i a below:

30 CHAPTER 2 Control of tie line bia i utilized to get rid of the teady tate error becaue of frequency plu the exchange of the power due to tie-line. Thi how that all of the control area hould put in their hare in frequency control, beide dealing with their own particular total interchange of power. Let, ACE = area control error of area ACE 2 = area control error of area 2 ACE 3 = area control error of area 3 ACE, ACE 2 and ACE 3 are hown a linear arrangement of frequency along with tie-line power error a follow: Where are known a bia in area frequency of area, area 2 and area 3 repectively. Area control error (ACE) i negative when the net power flow output from an area i very mall or ele when the frequency ha dropped or both. During uch ituation we need to increae the generation. 9

31 CHAPTER 3 CHAPTER 3 3. DESIGN MODEL FOR VARIOUS SYSTEMS 3.. SINGLE AREA SYSTEM Fig.3. how the Automatic Load Frequency Control (ALFC) loop. The frequency which change with load i contrated with reference peed etting. The frequency can be et to the deired value by making generation and demand equal with the help of team valve controller which regulate team valve and increae power output from generator. It erve the primary/baic purpoe of balancing the real power by regulating turbine output ( ) according to the variation in load demand ( ). ( 0 ) () ref Kg Kt Tg () v () Tt g m () 2H D () R Fig. 3.: Model of ingle area ALFC without uing econdary control The tranfer function of the model of the ingle area ytem a hown in Fig. 3. i a below:

32 CHAPTER 3 For the cae with load which i not enitive to frequency load (D=0): 27 From the above equation we can get the teady tate value of new ytem frequency which i le than the initial value. But we have to make the frequency drift ( ) to zero or to an acceptable value with the help of econdary loop for table operation. Thi i hown above in Fig.3.. Due to change in load there i change in the teady tate frequency ( ) o we need another loop apart from primary loop to convey the frequency to the initial value, before the load diturbance occur. The integral controller which i reponible in making the frequency deviation zero i put in the econdary loop a hown in Fig.3.2. Therefore the ignal from i being fed back all the way through an integrator block (/) to regulate to get the frequency value to teady tate. Thu. Thu integral action i reponible for automatic adjutment of making. So thi act i known a Automatic Load Frequency Control tranfer function with integral group i hown below by repreenting it in the form of equation. ( 0 ) () ref ref () K g Kt T T g t 2H D m () () g () v () R K Fig. 3.2: Model of ingle area ALFC by uing econdary control 2

33 28 CHAPTER TWO AREA SYSTEM Two area interconnected ytem which i joined by mean of tie-line for the flow of tie-line power i given in Fig Let the additional input be, be the load change in area and the repective frequencie of the two area be 29 Let be the reactance of the tie line, then power delivered from area to area 2 i 30 When and Equation can be linearized a: 3 The tie-line power deviation: 32 Let. For area, For area 2,

34 CHAPTER 3 B R ( 0 ) K g t K T g K T t ( m ) 2H D ( ) ( m2 ) P K 2 2g 2g K T 2g K T 2g () m2 2H D ( ) ( 02 ) R 2 B 2 Fig. 3.3: Model of two area ytem without uing econdary loop or uing only primary loop control Thu rie in load in area reduce the frequency of both the area and lead to the flow of tie-line power. If i negative then power flow from area 2 to area. Correpondingly for alteration in load in area 2 ( ),

35 CHAPTER 3 K B R ( 0 ) K g t K T g K T t ( m ) 2H D ( ) ( m2 ) P K 2 2g 2g K T 2g K T 2g () m2 2H D ( ) ( 02 ) R 2 B 2 K 2 Fig. 3.4: Model of two area ytem by uing econdary loop The econdary control baically retore balance linking all area load generation which i poible by maintaining the frequency at cheduled value. Thi i hown in Fig.3.4. Suppoe there i a variation in load in area then the econdary control i in area and not in area 2 o area control error (ACE) i being brought to ue [5]. The ACE contituting two area i repreented a follow In cae of area : In cae of area 2: ACE = ACE2 =

36 CHAPTER 3 For an entire load change of the teady tate frequency deviation in two area i 42 There can be one ALFC for every control area in an interrelated multi area ytem. ACE are the actuating ignal that timulate modification in reference power et point uch that and become zero a oon a teady-tate i attained. Each area ACE i a combination of frequency a well a tie-line error THREE AREA SYSTEM The control in three area ytem i like the two area ytem and i hown in Fig The integral control loop which i ued in the ingle area ytem and two area ytem can alo be related to the three area ytem. Due to change in load there i change in the teady tate frequency ( ) o we need another loop apart from primary loop to make the frequency to the initial value, before the load diturbance occur. The integral controller which i reponible in making the frequency deviation zero i put in the econdary loop. Three area interconnected ytem conit of three interconnected control area. There i flow of tie line power a per the change in the load demand due to the interconnection made between the control area. Thu the overall tability of the ytem i maintained at a balanced condition in pite of the contant variation in the load and load change. 25

37 CHAPTER 3 K B R ( 0 ) K g T t T K g K t ( m ) 2H D 2T 3 K B R ( 0 ) 2T 2 K g t K T g K T t ( m ) 2H D a 2 2 T 23 K B R ( 0 ) a 23 K g T t T K g K t ( m ) 2H D a 3 Fig. 3.5: Model of three area ytem by uing econdary loop Change in frequency for the three area i a follow:

38 CHAPTER 3 The tie-line power flow among three area i a below:

39 CHAPTER 4 CHAPTER 4 4. SIMULATION RESULTS OF AUTOMATIC LOAD FREQUENCY CONTROL By uing imulation model we can obtain the performance characteritic of the ytem very eaily and quickly for analyi purpoe. Below are the variou ytem imulink model with their repective repone plotted againt time. Here we conidered ingle area, two area and three area ytem. 4.. SINGLE AREA SYSTEM WITHOUT USING SECONDARY LOOP t To Workpace Step Tranfer Fcn Scope Tranfer Fcn 0.5+ Tranfer Fcn Gain -30 Fig. 4.: Simulink model of ingle area ytem without uing econdary loop TABLE 4.: Sytem parameter for ingle area ytem without uing econdary control Name Kg Tg() Kt Tt() H() D(puMW /Hz) /R Value

40 frequency deviation (del f) in Hz CHAPTER time (t) in ec Fig. 4.2: Frequency deviation v. time for ingle area ytem without econdary loop The plot in Fig. 4.2 which i obtained by imulating the model a hown in Fig.4. how that the change in load caue alteration in peed and that caue deviation in frequency. From the plot we are able to comprehend that the frequency ocillation will gradually tay down to a limited value. The new-fangled operating frequency i uppoed to be leer than the nominal value. We have taken the value of the different parameter a hown in table 4. for modeling the imulink model and it ucceful operation to obtain the deired reult SINGLE AREA SYSTEM BY USING SECONDARY LOOP In Fig. 4.3 an integral controller by mean of a gain i.e. Ki i ued to regulate the ignal of peed reference i.e. (a given away in Fig. 4.6) o that proceed to zero (a hown in Fig. 4.5). Fig. 4.4 how the variation in turbine output with time. The drift in frequency ha been brought to zero becaue of the integral loop. We have taken the value of the different 29

41 turbine output (del Pm) in p.u. CHAPTER 4 parameter a hown in table 2 for modeling the imulink model and it ucceful operation to obtain the deired reult Tranfer Fcn 0.5+ Tranfer Fcn Tranfer Fcn2 Scope Step Gain 20 Gain 7 Integrator Fig. 4.3: Simulink model for ingle area ytem by uing econdary loop time (t) in ec Fig. 4.4: Change in turbine output v. time for ingle area ytem by uing econdary loop 30

42 increamental peed reference ignal (del Pref) frequency deviation (del f) in Hz CHAPTER 4 TABLE 4.2: Sytem parameter for ingle area ytem by uing econdary control Name Kg Tg() Kt Tt() H() D(p.u.MW/Hz) /R K Value time (t) in ec Fig. 4.5: Change in frequency v. time for ingle area ytem by uing econdary loop ref del Pref time (t) in ec Fig. 4.6: Incremental peed reference ignal v. time for ingle area by uing econdary loop 3

43 CHAPTER TWO AREA SYSTEM WITHOUT USING SECONDARY LOOP Fig. 4.7 preent that the two ytem are being interrelated o the drift in the frequency of the two are liable to ettle down to imilar value oon after a few ocillation. The two mechanical input change to minimize the inequality power connecting electrical load in area a well a the mechanical input. Area 2 i capable to generate exceive power to ditribute the variation in load in area. We have taken the value of the different parameter a hown in table 4.3 for modeling the imulink model and it ucceful operation to obtain the deired reult. Gain2 -K- Gain Gain Integrator 0.2+ Tranfer Fcn 0.5+ Tranfer Fcn2 Step Tranfer Fcn5 Scope Gain6 2 Integrator2 0.3 Gain Integrator Scope 0.3+ Tranfer Fcn 0.6+ Tranfer Fcn Tranfer Fcn4 Gain4 6 Gain5 -K- Fig. 4.7: Simulink model of two area ytem without econdary loop 32

44 change in power output (del P) in p.u. frequency deviation (del f) in Hz CHAPTER 4 TABLE 4.3: Sytem parameter for two area ytem without uing econdary control Name Kg Tg() Kt Tt() H() D(p.u.MW/Hz) /R ΔPL(p.u) Area Area del f del f time (t) in ec Fig. 4.8: Frequency deviation v. time for two area ytem without uing econdary loop del Pm del P2 del Pm time (t) in ec Fig. 4.9: Change in power output v. time for two area without uing econdary loop 33

45 CHAPTER 4 Change in flow of tie-line power might be oberved with change in diturbance by load in area a given away in Fig Fig. 4.8 prove that the frequency can be reolved to a limited value which i le than the actual frequency. Although we get ame reult a area but tability i improved with interconnection TWO AREA SYSTEM BY USING SECONDARY LOOP Two area ytem by uing econdary loop are hown in Fig The econdary loop i reponible for the minimization of drift in frequency to zero a hown in Fig. 4.. By changing the econdary loop gain we can ee the variation in the ytem dynamic repone characteritic through tie line power a given away in Fig We have taken the value of the different parameter a hown in table 4.4 for modeling the imulink model and it ucceful operation to obtain the deired reult. TABLE 4.4: Sytem parameter for two area ytem by uing econdary control Name Kg Tg() Kt Tt() H() D(p.u.MW/Hz) /R ΔPL(p.u) K Area Area

46 CHAPTER 4 Gain2 Gain8 7 Integrator4 -K- -K- Gain Gain Integrator 0.2+ Tranfer Fcn 0.5+ Tranfer Fcn2 Step Tranfer Fcn5 t Scope To Workpace Gain6 2 Integrator2 t2 To Workpace2 0.3 Gain Integrator Scope 0.3+ Tranfer Fcn 0.6+ Tranfer Fcn Tranfer Fcn4 Gain4 Gain5 6 Gain7 7 Integrator3 Fig. 4.0: Simulink model for two area ytem by uing econdary loop 35

47 change in power output (del P) in p.u. frequency deviation (del f) in Hz CHAPTER del f del f time (t) in ec Fig. 4.: Frequency deviation v. time for two area by uing econdary loop del Pm del P2 del Pm time (t) in ec Fig. 4.2: Change in power output v. time for two area by uing econdary loop 4.5. THREE AREA SYSTEM WITHOUT USING SECONDARY LOOP Three area interconnected ytem without uing econdary loop i given in Fig Fig. 4.4 preent the ettling down of frequency to a finite value which i le than the actual frequency. Fig. 4.5 how the power change due to tie-line on account of the deviation in the 36

48 CHAPTER 4 load. Here tability i improved with interconnection. We have taken the value of the different parameter a hown in table 4.5 for modeling the imulink model and it ucceful operation to obtain the deired reult. T3 Block Controller AREA 5 gain 0.8+ Governor 0.3+ Turbine SLP 20+ p Add4 a2 -K- T2 Block T23 Block t To Workpace -Kgain2 0.3 Controller 2 AREA 2 20 gain 0.2+ Governor Turbine 2 SLP p 2 Add -Ka23 Scope -K- a Governor Turbine p 3 Scope2 -Kgain4 Controller 3 6 gain3 SLP3 t AREA 3 To Workpace2 Fig.4.3: Simulink model of three area ytem without uing econdary loop 37

49 tie line power deviation (del Ptie) in p.u. frequency deviation (del f) in Hz CHAPTER del f del f2 del f time (t) in ec Fig.4.4: Frequency deviation v. time for three area ytem without uing econdary loop del P2 del P23 del P time (t) in ec Fig. 4.5: Tie line power deviation v. time for three area ytem without uing econdary loop TABLE 4.5: Sytem parameter for three area ytem without uing econdary control Name Kg Tg () Kt Tt () H() D(p.u.MW/Hz) /R ΔPL(p.u) Area

50 CHAPTER 4 Area Area THREE AREA SYSTEM BY USING SECONDARY LOOP The model for the three area ytem including the econdary control i given away in Fig.4.6. The reult of the variation in frequency a well a tie line power output with repect to time are being hown in Fig. 4.7 and Fig The ytem operate in a imilar way to that of the two area ytem, taking into conideration the change in the load. We have taken the value of the different parameter a hown in table 4.6 for modeling the imulink model and it ucceful operation to obtain the deired reult. TABLE 4.6: Sytem parameter for three area ytem by uing econdary control Name Kg Tg() Kt Tt() Tp () H() D (p.u.mw/hz) Ki /R ΔPL (p.u.) Area Area Area

51 CHAPTER 4 Gain2 Integrator2 5 T3 Block Controller AREA 5 gain 0.8+ Governor 0.3+ Turbine SLP 20+ p Add4 a2 -K- T2 Block T23 Block t To Workpace 0.3 Controller Governor Turbine p 2 -Kgain2 AREA 2 20 gain Gain 5 Integrator SLP Add -Ka23 Scope -K- 0.3 Controller Governor Turbine p 3 a3 Scope2 -Kgain4 AREA 3 6 gain3 SLP3 t2 Gain7 Integrator3 To Workpace2 5 Fig. 4.6: Simulink model of three area ytem by uing econdary loop 40

52 tie line power deviation (del Ptie) in p.u. frequency deviation (del f) in Hz CHAPTER del f del f2 del f time (t) in ec Fig.4.7: Frequency deviation v. time for three area ytem by uing econdary loop del P2 del P23 del P time (t) in ec Fig.4.8: Tie line power deviation v. time for three area ytem by uing econdary loop 4

53 CHAPTER OBSERVATION By conidering the above-tated imulation graph it could be een that the ytem encounter drift in the frequency ucceeding a diturbance in the load and it i primarily becaue of the mimatch involving the electrical load a well a the mechanical input which i given to the prime mover/turbine. Fluctuation in the ytem i more in the ingle area ytem than two area ytem for the reaon that all the variation in the load are to be handled by one area only. Moreover variation in frequency i made to be zero by uing a econdary loop in both ingle area in addition to two area ytem. we alo ee that the three area ytem alo operate in a imilar manner like that of two area ytem CONCLUSION Thu we ee that developing model in SIMULINK help u to undertand the principle behind LFC including challenge. In cae A load change o peed change and thu drift in frequency i ettled down near to a limited value and o new working frequency i le a compared to the uppoed value. In cae B frequency drift i made zero by integral loop. In cae C there i tability improvement with interconnection. In cae D econdary loop i reponible for making the frequency drift to zero value and by changing gain dynamic repone i oberved. In cae E the ytem operate imilar to that of cae D although it conit of three control area. Thu the advantage of interconnection i undertood and we ee that the dynamic repone i chiefly adminitered by mean of the econdary loop. But in cae of three area ytem tuning of the parameter i quiet a tireome work by uing imple hit and trial method. Therefore we have opted for Bacteria Foraging Optimization Technique (BFOA) intended for tuning the variou parameter of the ytem imultaneouly by taking into conideration all the effect related to it. 42