Module2-Automatic-Generation-control.ppt
- 1. Automatic Generation Control (AGC) by Dr. Deependra Kumar Jha ME (Power Systems), PhD (Electric Power System Engineering) Professor, Department of Electrical Engineering School of Engineering & Technology, Galgotias University 1
- 2. Outline Purpose and Overview of AGC Automatic Generation Control (AGC) System modeling: control block diagram AGC for single generator AGC for 2 generators AGC for multi generators Area Control Error (ACE) 2
- 3. Purpose of AGC To maintain power balance in the system. Make sure that operating limits are not exceeded:- ◦ Generators limit ◦ Tie-lines limit Make sure that system frequency is constant (not change by load). 3
- 4. Overview of AGC Load is always changing. To maintain power balance, generators need to produce more or less to keep up with the load. When Gen < Load (Gen > Load), generator speed and frequency will drop (rise). => We use this generator speed and frequency as control signals! 4
- 5. 3 Components of AGC Primary control ◦ Immediate (automatic) action to sudden change of load. ◦ For example, reaction to frequency change. Secondary control ◦ To bring tie-line flows to scheduled. ◦ Corrective actions are done by operators. Economic dispatch ◦ Make sure that the units are scheduled in the most economical way. This presentation covers only primary and secondary control of AGC. 5
- 6. AGC for Single Area • System Modeling • Single Generator • Multi Generators, special case: two generators 6
- 7. System Modeling: Turbine-Governor Model Small signal analysis model, relating mechanical power to the control power and the generator speed. Where = Small change in control setting power = Small change in governor synchronous speed = Small change in mechanical output power = Regulation constant = Transfer function relating mechanical power to control signals 7 C P M P T G sT sT 1 1 1 s GM R 1 + - C P M P s GM R
- 8. Speed-Power Relationship R P s G P C M M 1 8 From synchronous turbine-governor: small signal analysis model, At steady state (s → 0, → 1), we have R P P C M 1 s GM
- 9. Static Speed-Power Curve From, Primary control: Immediate change corresponding to sudden change of load (frequency) Secondary control: Change in setting control power to maintain operating frequency. The higher R (regulation), the better. 9 R P P C M 1 Slope = -R 1 M P 2 M P 1 C P 2 C P M P = = 1 2 0
- 10. Turbine and Generator Load Model Turbine Model Generator load model 10 1 Kp STp ( ) F s ( ) D P s ( ) g P s - + 1 Kt STt ( ) g P s ( ) E Y s
- 11. AGC for Single Generator closed loop power control system as below. 11 C P 1 1 g T Kg Kt sT sT R 1 + - 1 Kp STp ( ) F s ( ) D P s ( ) g P s - +
- 12. AGC for Multi Generators Consider effect of ◦ power flows in transmission lines, and ◦ loads at each bus to mechanical power of each generator. This analysis assumes that every bus is a generator bus. 12
- 13. Power Balance Equation at Each Bus At each bus, Where = Generator i power = Load power at bus I = Power flow from bus i Consider small changes, i Di Gi P P P 13 2 G P 1 G P Gi P Di P i P i Di Gi P P P G1 G2 3 D P 1 D P 2 V 1 V 3 V G3 2 D P 3 G P 2 P 1 P
- 14. Load Power Equation ( ) Assume that Where = Small change of load input = Small change of load power = Small change of voltage angle Substitute in power balance equation, We have 14 Li i Li Li i Li Di P D P D P Di P i Li P Di P i Li i Li Gi P P D P i Di Gi P P P
- 15. Mechanical Power of Each Generator ( ) Linearized equation relating mechanical power to generator power and generator speed. Where = Small change in mechanical power of generator i = Small change in electric power of generator i = small change in internal voltage angle of generator i From, We have 15 Gi i i i i Mi P D M P Mi P Gi P i Gi P i Li i Li Gi P P D P i Li i Li i i i i Mi P P D D M P
- 16. Generator Block Diagram From, We can write where 16 i Li Mi i i i P P P D s M ~ 1 i Li i Li i i i i Mi P P D D M P Li i i D D D ~ i i D s M 1 s 1 + - - Mi P Li P i i i P
- 17. AGC for Multi Generators: Block Diagram 17 s GMi i R 1 + - s GPi i Mi P Li P Ci P i P + - - i i Pi D s M s G ~ 1 Ti Gi Mi sT sT s G 1 1 1 Change in tie-line power flow
- 18. Tie-line Model ( ) From power flow equation, Approximate at normal operating condition, we have Then, for small change, Where is called stiffness or synchronizing power coefficient 18 i P n k k i ik k i i B V V P 1 sin n k k i ik i B P 1 n k k i ik n k k i ik i T B P 1 1 ik T
- 19. Tie-Line Block Diagram From and We have, 19 n k k i ik i T P 1 s 1 n k k i ik i s T P 1 s 1 + + + ik T i P i i + - + - + - k
- 20. AGC for 2-Generator: Block Diagram 20 s GM 2 2 1 R + - s GP2 2 2 M P 2 L P 2 C P 21 2 P P + - - 2 s - s GM1 1 1 R + - s GP1 1 1 M P 1 L P 1 C P 12 1 P P + - - 1 s + -1 12 T
- 21. AGC for 2-Generator: Static Speed-Power Curve Load increases. Frequency drops. Steady state is reached when frequency of both generators is the same. 21 1 M P 2 M P M P 1 2 0 + = Change in total load 1 M P 2 M P
- 22. Steady State Frequency Calculation: 2 generators From Consider the frequency at steady state, 22 i Li i i i Li i i i i Mi P P D P P D M P ~ ~ line tie L M P P D P 1 1 1 1 ~ line tie L M P P D P 2 2 2 2 ~ 2 1 1 1 1 R PM 2 2 1 R PM 2 1 2 1 2 1 1 1 ~ ~ R R D D P P L L
- 23. AGC for Multi Areas Simplified Control Model Area Control Error (ACE) 23
- 24. Simplified Control Model Generators are grouped into control areas. Consider An area as one generator in single area, and, Tie-lines between areas as transmission lines connecting buses in single area. We can apply the same analysis to multi- area!! However, we have to come up with frequency-power characteristics of each area. Actual application of this model is for power pool operation. 24
- 25. Power Pool Operation Power pool is an interconnection of the power systems of individual utilities. Each company operates independently, BUT, They have to maintain ◦ contractual agreement about power exchange of different utilities, and, ◦ same system frequency. Basic rules ◦ Maintain scheduled tie-line capacities. ◦ Each area absorbs its own load changes. 25
- 26. AGC for Multi Areas During transient period, sudden change of load causes each area generation to react according to its frequency-power characteristics. This is “called primary control”. This change also effects steady state frequency and tie-line flows between areas. We need to Restore system frequency, Restore tie-line capacities to the scheduled value, and, Make the areas absorb their own load. This is called “secondary control”. 26
- 27. Area Control Error (ACE) Control setting power of each area needs to be adjusted corresponding to the change of scheduled tie-line capacity and change of system frequency. ACE measures this balance, and is given by, for two area case. Where = Frequency bias setting of area i (>0) and 27 1 12 1 B P ACE 2 21 2 B P ACE i B i Li i R D B 1
- 28. ACE: Tie-Line Bias Control Use ACE to adjust setting control power, , of each area. Goal: ◦ To drive ACE in all area to zero. ◦ To send appropriate signal to setting control power, Use integrator controller so that ACE goes to zero at steady state. 28 Ci P Ci P
- 29. AGC for 2-Area with Tie-line Bias Control: Block Diagram 29 s GM 2 2 1 R + - s GP2 2 2 M P 2 L P 2 C P 21 2 P P + - - 2 s - s GM1 1 1 R + - s GP1 1 1 M P 1 L P 1 C P 12 1 P P + - - 1 s + -1 12 T -1 + + + + s K2 s K1 1 2 12 P 21 P 1 B 2 B 1 ACE 2 ACE