IJEET Number 2, May - July (2011), pp I A E M E IAEME,

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1 Internationa Journa of of Eectrica Engineering and Technoogy (IJEET), ISSN (Print), and ISSN Technoogy (Onine) (IJEET), Voume ISSN 2, 0976 Number 6545(Print) 2, May - Juy (2011), IAEME ISSN (Onine), Voume 2 IJEET Number 2, May - Juy (2011), pp I A E M E IAEME, CASCADED UZZY CONTROLLER SCHEME OR COMBUSTION CONTROL O A UTILITY BOILER USING CONTROL BALANCE MODEL A.Sewin Mich Priyadharson 1 & Dr.T.R.Rangaswamy 2 1. Assistant Prof, EIE Dept, Vetech Dr. RR & Dr. SR Technica University, Avadi, Chennai , TamiNadu India. Emai: sewin_priyadharson@yahoo.co.in 2. Professor & Dean (Academics), B.S. Abdur Rahman University, Vandaur, Chennai , TamiNadu, India, Emai: ramy49@bsauniv.ac.in ABSTRACT An innovative design for combustion contro of utiity boier using contro baance mode based cascaded fuzzy controer scheme is proposed. The existing contro schemes have difficuty to cope up with inherent time deay, noninearity due to uncertainty of the combustion process and frequent oad changes, caorific vaue of the fue etc. This paper presents the contro baance mode with uzzy controer to reguate fue, cascaded with another uzzy controer to reguate air for combustion process. An experimenta setup is fabricated in the aboratory for fue and air contro and simuation studies were carried out using conventiona PID, cascaded PID controer scheme based on contro baance mode and proposed cascaded fuzzy controer scheme based on contro baance mode. The performance of proposed scheme is evauated by simuation and the resuts are compared with conventiona controers using rea time data obtained from the therma power pant. The advantages of the proposed scheme over the existing controers are highighted. Key words: contro baance mode, utiity boier, cascaded PID controer, cascaded uzzy controer, combustion contro 1. INTRODUCTION The utiity boiers are arge capacity steam generators used purey for the eectrica power generation. The main object of combustion contro is to reguate the heat input to the boier in terms of fue and air suppied in reation of steam pressure is detected and suppy of air and fue is adjusted accordingy. The steam pressure decreases with increasing oad and vice versa. The variation system consist of airfow and the fue fow contro oops that are driven by the firing rate demand signa through master steam pressure controer. Conventiona PID (Proportiona Integra Derivative) controer used for combustion contro is simpe in structure, reiabe in operation and robust to certain extent in performance. But they are not generay suitabe for non-inear, higher order, time deayed and compex systems that have no precise mathematica modes. urther it needs frequent tuning, which is not an easy task and is aso time consuming. 42

2 Horn,M et a [1] demonstrated an inteigent concepts superior to a standard PI controer with a setting found by cassic tuning rues through siding-mode controer. Widd et a [2] proposed predictive controers based on inearization of the mode. A-Awami et a [3] proposed Coordinated trading of wind and therma energy to mitigate risks due to those uncertainties and they obtained the optima trade-off bidding strategy that maximizes the tota expected profits whie controing trading risks. Bezerra et a [4] deveoped a stochastic optimization mode for the creation of a bidding strategy for a generator in an energy ca option auction. ang et a [5] described accuratey the status of boier furnace combustion in simuation, anaysis and optimization of power generation process and to improve the accuracy of simuation.huan Zhao et a[6] in order to improve boier efficiency and to reduce the NOx emission of a coa-fired utiity boier using combustion optimization, a hybrid mode, by combining support vector regression (SVR) with simpified boier efficiency mode, was proposed to express the reation between operationa parameters of the utiity boier and both NOx emission and boier efficiency. arshad et a [7] anayzed reiabiity indices for a parts of generation unit (Therma Power Pants) by using new method of modeing. Hou Guoian et a [8] proposed a kind of method of fuzzy identification based on improved T-S (Takagi -Sugeno) mode for coordinated contro system in power pants buit with weighted recursive east-square agorithm. Han Zhongxu et a [9] demonstrated inherence reation and compatibiity of fuzzy contro and state feedback contro. uzzy contro has been appied in automatic contro fied of therma power pants, at the same time the appication of state feedback contro system in therma contro fied which based on observer has aso obtained some practica resuts. Xiangjie et a [10] presented two aternative methods of expoiting the noninear predictive contro. One is the input-output feedback inearization technique based on a suitaby chosen approximated inear mode. The other is based on neurofuzzy networks to represent a noninear dynamic process using a set of oca modes. Peng et a [11] proposed to sove the time-deay and time-varying probem, a fuzzy immune adaptive Smith-PID controer aso presented. The controer combines bioogica immune system and fuzzy inference with Smith prediction controer. Duan et a [12] brings forward the concept of initia risk evauation about constructive projects in therma power pant, puts forward and buids the evauation index system for the first time. Besides deveoping traditiona anaytic hierarchy process (AHP) using trianguar fuzzy numbers according to the subjective fuzziness of experts' judging, so to sove the weight of index in each eve. Yinsong et a [13] first introduced a noninear mode combining boier-turbine-generator dynamic characteristics for a therma-power-generation unit. Based on the noninear mode, a new coordinated contro design is proposed using the backstepping method incorporating the coordinated passivation approach that considers the entire boierturbine-generator system as a whoe. Qingi et a [14] through the study of the boierturbine coordination and contro network, anaysed the difficuties of the inverse system anaytica method in practica use Lee et a [15] investigated a arge-scae once-through-type utra supercritica boier power pant for the deveopment of an anayzabe mode for use in deveoping an inteigent contro system. In order to utiize the robustness and advantages of the fuzzy controer, a contro baance mode based cascaded fuzzy controer is proposed. 43

3 The present paper is organized as foows: Section 2 deas with the conventiona scheme for combustion process. Section 3 deas with contro baance mode based cascaded PID controer scheme. Section 4 deas with contro baance mode based cascaded fuzzy controer scheme. Section 5 deas ab scae experimenta setup. Section 6 describes the simuation studies of conventiona & contro mode based cascaded fuzzy controer for combustion process. Section 7 gives the summary & concusions. 2. CONVENTIONAL COMBUSTION CONTROL SCHEME The oad controer generates the demand to the steam throtte vave from the unit oad demand and the measured generated power. The throtte pressure controer generates heat rate to the combustion controer from the measured throtte pressure and the turbine inet pressure set point. inay combustion controer activates the fue vave and air dampers. Bock diagram for combustion contro of boier is shown in ig.1. Throtte Pressure Controer Heat Rate PID Combustion Controer Steam D Boier O 2 Load Controer T eed Water G Legends T-Turbine G-Generator O 2 -Oxygen ue ue The arrangement for conventiona PID controer scheme for air and fue contro is shown in ig.2. PID contro signa ig.1. Bock diagram for PID Combustion Controer for a Utiity Boier 1 U ( s) = K p (1 + + TD s) E( s) T s Where K p, T I, T D are proportiona gain, integra time and derivative time. E(s) error signa U(s) contro signa. I 44

4 rom Pressure Controer Set vaue Set Vaue ue + - Actua fue fow - + PID Actua fow PID ue Vave Damper B O I L E R ig.2. Conventiona PID Scheme for air and fue In order to test and compare the performance of the proposed contro baance mode based PID controer with conventiona controer it is required to obtain PID parameters. The optimum PID controer parameters obtained by tria and error from the simuation test conducted in the ab scae experimenta setup for various oad conditions with respect to rea time data coected from therma power pant are presented in Tabe 1. Tabe 1 PID Parameters Contro oop PID parameters K P K I K D ue Controer Controer CONTROL BALANCE MODEL BASED CASCADED PID CONTROLLER SCHEME The necessity for the boier to maintain energy baance not ony under steady state conditions but aso under changing oad demand. To maintain the energy baance between boier energy suppied and energy required under changing oad, accounting for the energy storage characteristics of the boier is a necessity. It is necessary to baance the contro action fue and air to equaize the energy demand and suppy. The contro baance based cascaded scheme is shown in ig.3. 45

5 Input Energy Demand + - Energy Suppy Error proportiona to ue (e f ) ue PID Controer ue vave Dynamic change Manipuator PID Controer Damper ig.3 Contro Baance based cascaded scheme ony. Assumption1: The turbo generator is not on automatic oad dispatch contro. Assumption2: The steam demand variation is due to oad (MW) disturbance Assumption3: The unit contro is under boier foow mode. With the above assumptions a contro mode has been deveoped to get variabe fue error. Contro Baance Mode measuring scheme is shown in ig 4 P D DRUM P T U RN AC E TURBINE G P 1 ig.4. Measuring System for Contro Baance Mode P Turbine first stage steam pressure (1) P t - Throtte steam pressure (Turbine inet pressure)... (2) d- Drum pressure differentia (3) P s - is the set point for the throtte pressure... (4) Contro baance error is proportiona to (Required Pressure) - (appied pressure)... (5) 46

6 This is proportiona to the fue error at any oad varying condition. This wi track a desired trajectory within the boundary region. ue error = (P / P t ) P s - (appied pressure)... (6) ue error = (P / P t ) P s - (P 1 ± d )... (7) When oad increases, the steam demand increases, throtte pressure decreases. The difference between the set-point & throtte pressure wi produce the error signa to the combustion controer which wi increase the airfow first & then the fue fow to bring back the throtte pressure to the desired vaue. There wi be a time deay between the appication of the input to the combustion controer and the resuting effect on it, which wi degrade the tota performance. To improve the performance, a contro baance mode has been deveoped to give the variabe fue error to the PID controer for fue. A contro mode for air has been deveoped which is proportiona to variabe fue error is presented beow. or combustion contro, if ony the theoretica air required for compete combustion of fue is suppied, substantia amount of soot and Carbon Monoxide wi be observed in the fue gases. or achieving compete combustion excess air over and above the theoreticay required quantity wi have to be suppied to the boier. To maintain excess air, the set vaue for the air controer is proposed with respect to the fue error derived from equation (7). Set vaue for air controer = e f Mode + (e f Mode * Weight factor)... (8) Where Weight factor = (W/100) * e f Mode... (9) W=12 for ess than 30% of oad or steam fow... (10) W = 15 for 30 % to 50% of oad or steam fow... (11) W = 20 for 51 % to 75% of oad or steam fow... (12) W = 25 for 76 % to 100% of oad or steam fow (13) The proposed vaue of the weight factor W for air is arrived after considering severa dynamics of the boier and aso the knowedge obtained from the experts of therma power station. This wi aso satisfy the contro baance derived by practicing engineers and researchers. The above contro baance mode based air set vaue wi change the airfow immediatey after dynamic or programmed oad disturbance, which wi aways be in excess to the theoretica vaue. 47

7 Contro Mode for ue e f = (P / P t ) P s - (P 1 ± P d ) e f ue PID controer ue contro vave Set point = e f + (e f * Weight factor) + e a - Damper Contro Mode for PID controer Actua fow Boier ig.5.contro Baance Mode Based Cascaded PID Contro for ue and The cascaded controer diagram is shown in fig. 5. ue error derived from the fue mode is cascaded to air mode. When there is dynamic change due to grid disturbance the contro baance mode is proposed by considering turbine first stage pressure change, which is the first and immediate response, due to oad disturbance and considered as feed forward information. In order to test the performance of the contro baance mode based PID controer, it is required to obtain PID parameters. The optimum PID controer parameters obtained by tria and error from the simuation test conducted in the ab scae experimenta setup for various oad conditions with respect to rea time data coected from therma power pant are presented in Tabe 2. These vaues are considered as optimum because of satisfactory agreement with the rea time response obtained from therma power pant. Tabe 2 The controer parameters for Contro baance mode based cascaded PID controer scheme Contro scheme Contro baance mode cascaded PID Contro oop KP KI KD ue PROPOSED CONTROL BALANCE MODEL BASED CASCADED UZZY CONTROLLER SCHEME The proposed Contro Baance Mode Based fuzzy controer system for fue and air contro is shown in the ig.6. 48

8 (P 1 /P t ) x Ps + P 1 + d ue contro unction vave of ue Error (e f ) from mode - e f uzzy ue controer To Boier fow manipuator Desired fow - + e Actua e a uzzy ow transmitter Damper B O I L E R ig.6. Contro baance mode based Cascaded uzzy controer scheme There are two fuzzy controers separatey for fue and air. Input to the uzzy controer for fue is derived from the contro baance mode. Input to the uzzy controer for air is derived with respect to fue error deveoped from mode equation (7). fow manipuator gives input to the fuzzy contro as per the equation (9-13). The fuzzy ogic controer impemented for combustion process has two inputs and one output for fue and air respectivey. The inputs are error and change in error and the output is the controer position. The universes of discourse of the controer variabes are E, E and U respectivey. The trianguar membership functions are used to represent the inguistic terms (VS=Very sma; S=sma; M= medium; L= arge; VL= Very arge). Rue base is deveoped and an inference mechanism is designed using Mamdani (min-max) method that gives the output signa to the fina contro eements. The output of the inference mechanism is a fuzzy vaue and is converted into crisp vaue using center of area method for defuzzification. The parameters of the LC system designed for the combustion contro of utiity boier are presented in Tabe.3. Tabe 3 LC parameters for fue and air controer Parameters ue Contro Contro Input variabes 2 2 uzzy sets 5 5 Rues Membership function Trianguar Trianguar Defuzzyfication method Center of area Center of area 5. IMPLEMENTATION O LAB SCALE EXPERIMENTAL SET UP or the present work, the manipuated variabes are air and fue fow to the boier with respect to the set vaue. There are two distinct contro oops, for air and fue contro. In the fabricated set-up, the fue pumped from the fue tank wi return back to the tank via contro vave, rotameter and fow transmitter (In practice, the fue fow wi be admitted to the boier for combustion). The pressurized air from the compressor is reguated and fed to the contro vave positioner and current to pressure (I/P) converter. One more tapping from air compressor is used as combustion air, which is aowed to go to atmosphere via air contro vave and airfow transmitter. (In practice, the airfow wi be admitted to the boier for combustion). 49

9 ig.7 Experimenta Set Up These anaog signas are interfaced with the computer through I/O card. The processed signas from computer through I/O card are given to I/P converters as manipuated vaue to operate air and fue vaves. The actua fabricated ab scae experimenta set-up is shown in ig SIMULATION STUDIES Severa experiments were conducted on the experimenta set-up and the performances for both changes in the set point as we as in the oad perturbation were studied. The responses obtained for change in oad are shown in ig A I r o w t /h PID K P=1.5, K I=0.8, K D= 0.2 Set point t/hr CB Mode based Cascaded uzzy CB Mode based Cascaded PID K P=1.5, K I=1.2, K D= Time In Seconds ig.8. ow Response Load 21MW-42MW 50

10 u e o w t/hr PID ue K P =1.75, K I =1, K D = 0.2 ue fow set point 5-12 t/hr CB Mode based Cascaded PID ue K P =1.5, K I =2, K D = 0.5 CB Mode based Cascaded uzzy ue Time in Seconds ig.9. ue fow response Load 21MW-42MW u e o w t/hr CB Mode based Cascaded uzzy ue PID ue K P =1.75, K I =1, K D = 0.2 ue fow set point t/hr CB Mode based Cascaded PID ue K P =1.5, K I =2, K D = Time in Seconds ig.10. ue fow response Load 110MW-63MW u e o w t/hr CB Mode based Cascaded PID K P =1.5, K I =1.2, K D = 0.5 PID K P =1.5, K I =0.8, K D = 0.2 fow set point t/hr CB Mode based Cascaded uzzy Time in Seconds ig.11. fow response Load 110MW-63MW 51

11 Comparisons of time domain specifications and the performance criteria Integra Square Error (ISE) and Integra Absoute Error (IAE) for various step changes in oad are presented in Tabe 4 & 5. Tabe 4 Percentage Improvement in performance criteria (ISE and IAE) Contro scheme PID to Cascaded PID Contro oop Load 21MW-42MW Load 110MW-63MW ISE IAE ISE IAE ue fow fow PID to Cascaded uzzy ue fow fow Tabe.5. Percentage Improvement in performance criteria (Time domain specifications) Contro scheme Contro oop Load 21MW-42MW Load 110MW- 63MW Rise time Peak time Set time Under shoot PID ue ow fow ue ow fow Contro baance mode cascaded PID Contro baance mode cascaded uzzy 7. CONCLUSION Set time ue ow fow The resuts of this paper highights the robustness of the contro baance mode based cascaded uzzy controer scheme for step changes in oads. The cosed oop response of the contro baance mode based cascaded uzzy controer scheme shows satisfactory transient response without much overshoot and settes down after about 38 and 33 steps of increment for air and fue respectivey. This shows 36% improvement over conventiona schemes in setting time for both air and fue. The proposed contro baance mode based cascaded uzzy controer scheme resuts in east ISE and IAE vaues for the step changes in oad showing 17% improvement for air and 22% improvement for fue contro when compared to conventiona schemes. The quaitative and quantitative comparisons of the performance of the various contro schemes revea the superiority of the contro baance mode based cascaded uzzy controer scheme over the conventiona schemes. 52

12 REERENCES 1. Horn, M. Reichhartinger, M. (08 eb 2010), Mode-free contro of a therma pant IEEE Internationa Conference on Contro and Automation, New Zeaand, pp: Widd, A. Ekhom, K. Tunesta, P. Johansson, R, (15 Apr 2011), Mode Predictive Contro of HCCI Combustion Phasing Using ast Therma Management and Physics-Based VVA IEEE Transactions on Contro Systems Technoogy, Issue: 99, pp A-Awami, A.T., E-Sharkawi, M., (Juy 2011), A Coordinated Trading of Wind and Therma Energy, IEEE Transactions on Sustainabe Energy, Vo 2, Issue 3, pp Bezerra, B., Barroso, L.A., Pereira, M.V., (May 2011), Bidding Strategies with ue Suppy Uncertainty in Auctions of Long-Term Energy Ca Options, IEEE Transactions on Power Systems, Vo 26, Issue: 2, pp ang ang Sun Lii, (20 Sep 2010), Joint modeing and simuation of furnace combustion 29th Chinese Contro Conference, China, pp Huan Zhao, Pei-hong Wang, (12 May 2009), Modeing and Optimization of Efficiency and NOx Emission at a Coa-ired Utiity Boier 2009 Aciapacific Power and Energy Engineering Conference, China, pp arshad Khosravi, Naziha Ahmad Azi, Ebrahim Babaei, (Dec 2010), A New Modeing Method for Reiabiity Evauation of Therma Power Pants, IEEE Internationa conference on power and Energy,Kuaa Lumpur,Maaysia, pp Hou Guoian, Zeng anchun, Hou Qian,Zhang Jianhua (June 2010), uzzy Identification Based on Improved T-S uzzy Mode and Its Appication in Power Pants pp ,5th IEEE Conference on Industria Eectronics and Appications,China,pp , Han Zhongxu Zhu Zeei Yan Cuihui, (07 Apri 2010) Compatibiity Anaysis of uzzy Contro and State eedback Internationa Conference on Inteigent System Design and Engineering Appication, China, Vo 1, pp Xiangjie Liu Ping Guan Chan, C.W (23 Sep 2010) Noninear Mutivariabe Power Pant Coordinate Contro by Constrained Predictive Scheme IEEE Transactions on Contro Systems Technoogy, Vo 18, Issue: 5, pp Peng Shu-Hua Hao Cui Li Deng-Hua, (27May2010) uzzy Immune Adaptive Smith- PID Contro for Water Quaity Adjusting System of Therma Power Pant 2nd Internationa Workshop on Inteigent Systems and Appications (ISA),China,pp Duan Lidong Niu Dongxiao Lv Haitao Kou Bingen, (02 eb 2010) Risk Assessment of Therma Power Pant Project Based on uzzy Anaytic Hierarchy Process in the Eary Operation" Second Internationa Workshop on Computer Science and Engineering,China, Vo 1, pp Yinsong Wang., Xinghuo Yu., (Nov. 2010), New Coordinated Contro Design for Therma-Power-Generation Units IEEE Transactions on Industria Eectronics, Vo 57, Issue11, pp Qingi Wang Yuanwei Jing Lifu Wang Zhi Kong, (07 Aug 2009) The appication research of compound contro based on the fuzzy neura network inverse method Contro and Decision Conference, China, pp Lee, K.Y., Van Sicke, J.H., Hoffman, J.A., Won-Hee Jung, Sung-Ho Kim, (Dec. 2010), Controer Design for a Large-Scae Utrasupercritica Once-Through Boier Power Pant IEEE Transactions on Energy Conversion, Vo 25, Issue 4, pp