Modelling of Primary Frequency Control and Effect · PDF fileModelling of Primary Frequency...
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Modelling of Primary Frequency Control and Effect Analyses of Governing System
Parameters on the Grid FrequencyZhixin Sun
Modelling of Primary Frequency Control and Effect Analyses of Governing System
Parameters on the Grid FrequencyZhixin Sun
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Outline Outline
Introduction
Mathematical Model of Primary Frequency Control
Dynamic Test & Parameter Identification
Effects of Parameters of Governing SystemEffect of dead band
Effect of speed droop
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Introduction
FrequencyPrimary frequency control
Secondary frequency control
Frequency is an indicator of overall power imbalance.power increases, frequency risesload increases, frequency falls
Frequency deviation must be controlled within a certain range. (±0.2Hz in China)
Power Plant
Power PlantPower Plant
Power Plant frequency
Power Generation load Demand
Home User
Factory Machine
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Introduction
load increases, frequency falls frequency deviation is greater than the dead band servo-motor increases governing valve opening of steam turbinepower output increases to hold back the decrease of frequency
responses fastutilizes the heat storage of boiler has frequency error in steady state
Primary frequency control (speed droop control)
Rotor-+
load
-+Servo-motor1/Speed droopref
Dead band
Steam turbine
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Introduction
Secondary frequency control
balances the power and load through fuel regulationresponses slowly can eliminate steady state frequency error
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Mathematical Model of Primary Frequency Control
Boiler model
Main steam pressure is the interface between steam turbine and boiler.
Governing valve opening rises Main Steam pressure fallsBoiler responses slowly
Rotor-+
load
-+Servo-motor1/Speed droopref
Dead band
Steam turbine
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Mathematical Model of Boiler
Dg
SpDpsg
Qg wg
1
DsT1
SsT
Dg
Dp
11
s
F
eT s
τ−
+1
1WT s +sg
Qg wgFP
Sp
K
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Mathematical Model of Steam Turbine
Steam Turbine: three cylinders, single reheat
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Power is assumed to be proportional to the pressure before each cylinder
aH+aI+aL=1
Mathematical Model of Steam Turbine
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Power over-regulation of HP cylinder
Mathematical Model of Steam Turbine
Power response of actual unit can reach 60% of regulation targetin the first several seconds
Power response of simulation only reach 38%
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Improved model of Steam Turbine
Mathematical Model of Steam Turbine
1sTCO+1
αH αI αL
++
1sTCH+1
1sTRH+1
++
-+
++
λ
New model
Classic model
Power over-regulation coefficient of HP cylinder: λ=f( pressure ratio, adiabatic index )
pow
er
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Mathematical Model of Steam Turbine
Single Unit
Test of primary frequency control:1.static test of servo-motor for identification of Tact
2.load dump test for identification of Ta
3.dynamic test for identification of the time constants of steam turbine
on line, increases or decreases the reference speed (by 25 rpm)
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Dynamic Test & Parameter Identification
1
2
3
4
PressureValve openingPower
2
3
4 TCO
TRH
TCH
0 10 20 30 40 50
0.0
0.2
0.4
0.6
0.8
1.0
%
t (s)
1
23
4
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Dead band Power percentage1 2 r/min 38.0%2 3 r/min 41.2%3 4 r/min 11.0%4 5 r/min 9.8%
Tab.1 The responses of units under
different load disturbance
Multi-units
Effect of dead band
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Effect of dead band
Dead band =2 rpm Dead band =3 rpm
Dead band =5 rpmDead band =4 rpm
Simulation results
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Effect of dead band
a b c d e f g h
2 r/min capacity 0.25 0.5 0.7 0.9 1 0 0 0
3 r/min capacity 0.25 0.2 0.1 0.1 0 1 0 0
4 r/min capacity 0.25 0.2 0.1 0 0 0 1 0
5 r/min capacity 0.25 0.1 0.1 0 0 0 0 1
Allowed loaddisturbance/%
7.1 7.6 7.9 8.3 8.4 7.6 6.8 5.9
Load disturbance 5% 7.6% 10%
Dead band /r·min-1 2 3 4 5 2 3 4 5 2 3 4 5
Freq variation max /Hz -0.22 -0.21 -0.3 -0.31 -0.31 -0.30 -0.44 -0.45 -0.39 -0.38 -0.56 -0.57
Freq variation Steady state /Hz -0.15 -0.15 -0.15 -0.15 -0.2 -0.2 -0.2 -0.2 -0.25 -0.25 -0.25 -0.25
Steady State Frequency deviations<0.2 Hz
Tab.3 The relationship between different dead band combination and allowed load disturbance
Tab.2 The responses of units under different load disturbance
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Effect of speed droop
speed droop
Freq
uenc
y /H
z
Time /s
unit with speed droop of 4% unit with speed droop of 6%unit with speed droop of 8%unit with speed droop of 10%
Load increases by 10%
%100max ×−
=N
N
nnnδ
Nn—— no-load speed
—— full-load speedmaxn
spee
d
10% capacity with constant speed droop of 4%
10% capacity 90% capacity
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Xi'an Jiaotong University is a top10 university in China,and was founded in 1896. Today, Xi'an Jiaotong University is a comprehensive research university offering programs in nine areas with a major emphasis on science and engineering.
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