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Zhixin Workshop on Modelling and Simulation of Coal-fired Power Generation and CCS Process

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Modelling of Primary Frequency Control and Effect Analyses of Governing System Parameters on the Grid Frequency Zhixin Sun
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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

Page 2 Institute of Turbomachinery, Xi’an Jiaotong University

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

Page 3 Institute of Turbomachinery, Xi’an Jiaotong University

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

Page 4 Institute of Turbomachinery, Xi’an Jiaotong University

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

Page 5 Institute of Turbomachinery, Xi’an Jiaotong University

Introduction

Secondary frequency control

balances the power and load through fuel regulationresponses slowly can eliminate steady state frequency error

Page 6 Institute of Turbomachinery, Xi’an Jiaotong University

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

Page 7 Institute of Turbomachinery, Xi’an Jiaotong University

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

Page 8 Institute of Turbomachinery, Xi’an Jiaotong University

Mathematical Model of Steam Turbine

Steam Turbine: three cylinders, single reheat

Page 9 Institute of Turbomachinery, Xi’an Jiaotong University

Power is assumed to be proportional to the pressure before each cylinder

aH+aI+aL=1

Mathematical Model of Steam Turbine

Page 10 Institute of Turbomachinery, Xi’an Jiaotong University

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%

Page 11 Institute of Turbomachinery, Xi’an Jiaotong University

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

Page 12 Institute of Turbomachinery, Xi’an Jiaotong University

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)

Page 13 Institute of Turbomachinery, Xi’an Jiaotong University

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

Page 14 Institute of Turbomachinery, Xi’an Jiaotong University

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

Page 15 Institute of Turbomachinery, Xi’an Jiaotong University

Effect of dead band

Dead band =2 rpm Dead band =3 rpm

Dead band =5 rpmDead band =4 rpm

Simulation results

Page 16 Institute of Turbomachinery, Xi’an Jiaotong University

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

Page 17 Institute of Turbomachinery, Xi’an Jiaotong University

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

Page 18 Institute of Turbomachinery, Xi’an Jiaotong University

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.

Page 19 Institute of Turbomachinery, Xi’an Jiaotong University


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