power control agc1

7/27/2019 Power Control AGC1

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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC)

1

Power System Control and Operation:

Automatic Generation Control (AGC)


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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 2

Outline

Read chapter 11: 11.0-11.6.

Homework: 11.2, 11.6

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)


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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).


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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), generatorspeed and frequency will drop (rise).

=> We use this generator speed and frequency

as control signals!


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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.


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AGC for Single Area

System Modeling

Single Generator

Multi Generators, special case: two

generators


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System Modeling: Turbine-Governor Model

Small signal analysis model, relating mechanical powerto 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

CP MP

TG

sTsT 11

1

sGM

R

1

+

-

C

P

MP

sGM

R


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Speed-Power Relationship

From synchronous turbine-governor: small

signal analysis model,

At steady state (s 0, 1), we have

RPsGPCMM

1

R

PPCM

1

sGM


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Static Speed-Power Curve

From,

Primary control: Immediate

change corresponding tosudden change of load

(frequency)

Secondary control: Change in

setting control power to

maintain operating frequency. The higher R (regulation), the

better.

R

PPCM

1

Slope = -R

1MP 2MP1CP 2CP

MP

= =

1

2

0


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System Modeling: Generator Model

This model relates mechanical power to power

angle, ignore change of voltage.

Note that power angle is not voltage angle ( )

TDsMs 21

MP

G iiV +

-ii

E

sjX iiV

ii


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AGC for Single Generator

Since , we can draw

closed loop power control system as below. 0

CP

TG sTsT 11

1

R

1

+

-

TDsMs 2

1MP

s


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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.


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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,

iDiGi PPP

GiP

DiP

iP

iDiGi PPP

2GP

G1 G2

1GP

3DP

1DP

2V

1V

3V

G3

2DP

3GP

2P1P


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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

LiiLiLiiLiDi PDPDP

DiP

i

LiP

DiP

iLiiLiGi PPDP

iDiGi PPP


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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

GiiiiiMi PDMP

MiP

GiP

i

GiP

iLiiLiGi PPDP

iLiiLiiiiiMi PPDDMP


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Generator Block Diagram

From,

We can write

where

iLiMi

ii

i PPP

DsM

~

1

iLiiLiiiiiMi PPDDMP

Liii DDD

~

ii DsM

1

s

1+-

-

MiP

LiP

i

i

iP


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AGC for Multi Generators: Block Diagram

sGMi

iR

1

+

-

sGPi

iMiP

LiP

CiP

iP

+

-

-

ii

Pi

DsMsG ~

1

TiGi

Mi

sTsTsG

11

1

Change in tie-line

power flow


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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

iP

n

k

kiikkii BVVP

1

sin

n

k

kiiki BP

1

n

k

kiik

n

k

kiiki TBP

11

ikT


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Tie-Line Block Diagram

From and

We have,

n

k

kiiki TP

1

s

1

n

k

ki

ik

i

s

TP

1

s1

++

+

ikT

iP

ii

+

- +

- +

-

k


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AGC for 2-Generator: Block Diagram

sGM2

2

1

R

+-

sGP222MP

2LP

2CP212 PP

+

-

-2

s

-

sGM1

1

1

R

+

-

sGP1

1

1MP1LP

1CP

121 PP

+

-

-

1

s

+

-1

12T

Load

Frequency 2

Different phase angle Transfer power 12

Frequency 1

Governor 2 sense

speed , try to

mechanical power

Governor 1 sensespeed , try to

mechanical power

Steady state: New

(lower) system

Frequency


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AGC for 2-Generator:


Load increases.

Frequency drops.

Steady state is reached

when frequency of bothgenerators is the same.

1MP 2MP

MP

1

2

0

+ = Change in

total load

1MP 2MP


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Steady State Frequency Calculation:

2 generators

From

Consider the frequency at steady state,

But, , ,and

Then,

iLiiiiLiiiiiMi PPDPPDMP ~~

linetieLM PPDP 1111

~

linetieLM PPDP 2222 ~

21 1

1

1

RPM

2

2

1

RPM

21

21

21

11~~

RRDD

PP LL


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Note that

In single area- multi generators case, we have

not discuss how to systematically bring back the

new steady state frequency by adjusting control

power. We will discuss this in the following section.


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AGC for Multi Areas

Simplified Control Model

Area Control Error (ACE) Example 11.5


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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 linesconnecting 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.


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Power Pool Operation

Power pool is an interconnection of the powersystems 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.


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ELEN 460:Power System Control and Operation:

Automatic Generation Control (AGC) 27

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.


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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

1121 BPACE

2212 BPACE

iB

i

Lii

RDB

1


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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.

CiP

CiP


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AGC for 2-Area with Tie-line Bias Control:

Block Diagram

sGM2

2

1

R

+ -

sGP2

22MP

2LP

2CP212 PP

+

-

- 2s

-

sGM1

1

1

R

+-

sGP1

1

1MP1LP

1CP

121 PP

+

-

-

1

s

+

-112T

-1

+

+

+

+

s

K2

s

K1

1

2

12P

21P

1B

2B

1ACE

2ACE

Load 2

Frequency 2

Different phase angle Transfer power 12

Frequency 1

Governor 2 sense

speed , try to

mechanical power

Governor 1 sense

speed , try to

mechanical power

ACE 2 < 0

ACE 1 = 0

Setting control power 2

Frequency 2

Different phase angle

Governor 2 sense

speed , try to

mechanical power

Transfer power 12

Governor 1 sense

speed , try to

mechanical powerFrequency 1

Steady state:

Maintain Frequency

Set control power 2 > 0


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AGC for 2-Area with Tie-line Bias Control :


Load in area 2 increases.

Frequency of both area

drops.

ACE makes Control

power of area 2

increases.

Steady state is reached

when frequency is back

at the operating point andgenerator in area 2 take

its own load.

1MP 2MP

MP

1

2

0

+ = Change in load 2

1MP 2MP

2

1MP

2MP


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Example 11.5

Two-area system,

Find change in frequency, ACE, and appropriatecontrol action.

A B

MW100000 A

L

A

G PP MW000,1000

B

L

B

G PP

sec/MWperrad015.0A

R sec/MWperrad0015.0B

R0 BL

A

L DD

MW10 ALP


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Example 11.5: Frequency Calculation

From,

And,

And,

We have,

21

AB

A

LAB

A

LA

A

L

A

M PPPPDP

BABA

B

LB

B

L

B

M PPPDP

A

A

MR

P1

B

B

MR

P1

secperrad0136.0

0015.0

1

015.0

1

10

11

BA

AL

RR

P


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Example 11.5: ACE Calculation

First, find from

Then,

MW9091.00136.0015.0

11

A

A

M

RP

MW091.9 A

L

A

MABAB

A

L

A

M PPPPPP

MW091.9 ABBA PP

ABP

MW100136.0015.01091.91

A

ABA

RPACE

MW00136.00015.0

1091.9

1

B

BAB

RPACE


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Example 11.5: Control Action

ACE indicates each area action to the change of

load.

ACE of area B is zero, this means that nothing

should be done in area B. ACE of area A < 0, this means that area A

should increase the setting control power by

(-10) = 10 MW to cover its own load.

power control agc1

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