Phần 19 KHÓA ĐÀO TẠO TÍNH TOÁN ỔN ĐỊNH VÀ ỨNG DỤNG TRÊN PHẦN MỀM PSSE CHO KỸ SƯ HỆ THỐNG ĐIỆN (Mô phỏng đường dây siêu cao áp HDVC trong tính toán ổn định động)

TRANSMISSION &
DISTRIBUTION
A Division of Global Power
POWER SYSTEM STABILITY CALCULATION TRAINING
D8
HVDC Si l ti P t 2
D
ay
8
-
HVDC

Si
mu
l
a
ti
on
P
ar
t

2
November 26, 2013Prepared by: Mohamed El Chehaly
eBook for You
OUTLINE
2
OUTLINE
• General Considerations
•
HVDC Dynamic Models

HVDC

Dynamic

Models
• Com
p
lete HVDC Model in D
y
namic Studies
py
eBook for You
3
GENERAL CONSIDERATIONS
GENERAL

CONSIDERATIONS
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Introduction
4
GENERAL CONSIDERATIONS
Introduction
 DC transmission behavior is dominated by
its controls
 It is not practical to model the detailed
dynamics of the controls because the
bandwidth of these controls is far greater
than that of PSS®E
than

that

of

PSS®E

 Each converter bridge is controlled by a
local feedback loop
local

feedback

loop
 These local loops work independently to
maintain bridge current or voltage at
maintain

bridge

current

or

voltage

at

desired value
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Introduction

5
GENERAL CONSIDERATIONS
Introduction
 The desired values are provided by an
outer control loop that works in a
outer

control

loop

that

works

in

a

supervisory role and coordinates the
action of the several converter bridges
action

of

the

several

converter

bridges

and the AC power system
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Behavior of the Brid
g
es and their Inner
6
GENERAL CONSIDERATIONS
g
Control Loops
 A rectifier bridge may be regarded as an
adjustable voltage source forcing current
through transmission system resistance
di d t i tth t t
an
d

i
n
d
uc
t
ance aga
i
ns
t

th

e cons
t
an
t

voltage source of the inverter
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Behavior of the Brid
g
es and their Inner
7
GENERAL CONSIDERATIONS
g
Control Loops
 A simple current control: open-loop basis
with a gain equal to DC resistance
 A step change in current is applied
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Behavior of the Brid
g
es and their Inner
8
GENERAL CONSIDERATIONS
g
Control Loops
 DC rectifier is a feedback loop controller
that adjusts firing delay to control the DC
current to a setpoint
 A step change in current is applied
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PSS®E Models and Control Loops
9
GENERAL CONSIDERATIONS

Several PSS®E models (CDC4T CDC6T )
PSS®E

Models

and

Control

Loops

Several

PSS®E

models

(CDC4T
,
CDC6T
…
)

treat DC converter pairs as if they move
instantaneousl
y

to their new o
p
eratin
g

y
pg
point when any of their input signals are
changed
 HVDC dynamic models calculate the real
and reactive power loading of the
converters using steady-state converter
relationships
with transformer taps fixed
relationships
with

transformer

taps

fixed

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PSS®E Models and Control Loops
10
GENERAL CONSIDERATIONS

Several models are
not concerned

with the
PSS®E

Models

and

Control

Loops

Several

models

are

not

concerned

with

the

internal dynamic behavior of converters
and DC lines
and

DC

lines


Pseudo steady
-
state
HVDC dynamic

Pseudo

steady
state

HVDC

dynamic

models are not able to directly represent
the mode of operation where the rectifier
firing angle is not at a limit and the
inverter margin angle is also not at a limit
t lli lt (CDC4T CDC6T )
or con
t
ro
lli
ng vo
lt
age

(CDC4T
,
CDC6T
…
)
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PSS®E Models and Control Loops
11
GENERAL CONSIDERATIONS
 HVDC models such as CDCVUP re
p
resent
PSS®E

Models

and

Control

Loops
p
the temporary dynamic condition when
neither converter is at a firing angle or
margin angle limit and both are fighting for
control of current

PSS®E l i l d d l (CASEA1 d

PSS®E

a
l
so
i
nc
l
u
d
e mo
d
e
l
s
(CASEA1
an
d

CDCRL) that represent some high-
frequency controller effects
and
L/R
frequency

controller

effects
and

L/R

dynamics of the DC transmission. These
m
ode
l
s

use

a
n in
te
rn
a
l in
teg
r
at
i
o
n
t
im
e

ode s use a te a teg at o t e
shorter than by other PSS®E models
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Actions by the Controls
12
GENERAL CONSIDERATIONS

 Three distinct t
yp
es of action b
y
the
Actions

by

the

Controls
yp y
controls
 Normal regulation of DC converter operation to
maintain specified constant current or constant
power transfer with coordination of rectifier and
inverter current
setpoints
inverter

current

setpoints
 Temporary overriding of DC converter normal
operating setpoints in response to disturbances of
AC t lt d i f lt
AC
sys
t

em vo
lt
ages
d
ur
i
ng
f
au
lt
s
 Modulation of the DC power setpoint by a
supplementary control device
(assist in the
supplementary

control

device

(assist

in

the

damping of rotor angle swings)
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Actions by the Controls
13

GENERAL CONSIDERATIONS
 Normal re
g
ulation
Actions

by

the

Controls
g
 With sufficient AC voltage for alpha control
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Actions by the Controls
14
GENERAL CONSIDERATIONS
 Normal re
g
ulation
Actions

by

the

Controls
g
 With depressed AC voltage
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Actions by the Controls
15
GENERAL CONSIDERATIONS
 Response following disturbance

When AC or DC voltages reach abnormal levels
Actions

by

the

Controls

When

AC

or

DC

voltages

reach

abnormal

levels

that may cause commutation failures, excessive
currents or unacceptable harmonics
 PSS®E DC models execute these overriding
control actions when positive sequence AC
voltages or DC voltages reach specified levels
voltages

or

DC

voltages

reach

specified

levels
 The modeling of protective action is not possible
 The protection of DC converter is dependent on
individual phase-to-ground and phase-to-phase voltage
wave forms and these are not available in PSS®E
 The protection of each bridge is determined by the
internal details of firing controls with a low-frequency
band
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Protective Actions
16
GENERAL CONSIDERATIONS
 Block


Protective blocking is used to stop the flow of both
Protective

Actions

Protective

blocking

is

used

to

stop

the

flow

of

both

AC and DC current in order to limit the effect of the
fault
 Rectifier usually blocked when an AC fault is
applied on the AC side of the rectifier


Thi i hi d b i l i th fi i

Thi
s
i
s ac
hi
eve
d

b
y s
i
mp
l
y remov
i
ng
th
e
fi
r
i
ng
pulses to all the valves in the converter
 Blockin
g
can be simulated b
y

chan
g
in
g
the
gygg
appropriate ICON or by raising the blocking
voltage threshold to force a block
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Protective Actions
17
GENERAL CONSIDERATIONS
 Bypass

When fault signals of the inverter detect one of the
Protective

Actions

When

fault

signals

of

the

inverter

detect

one

of

the

following
 Commutation failure
 Undervoltage
 Abnormal firing angle or misfire

Provides a DC short
circuit across the converter

Provides

a

DC

short
-
circuit

across

the

converter

bridge
 Blocking four valves in the 6-pulse bridge and
firing the remaining two as a bypass pair
 The DC side is shorted and the AC side is open

Th tifi ill ti t i l t l l l

Th
e rec
tifi
er w
ill
con
ti
nue
t
o c
i
rcu
l
a
t
e a
l
ow
l
eve

l

current
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Protective Actions
18
GENERAL CONSIDERATIONS
 Commutation failure

May occur following an AC system disturbance
Protective

Actions

May

occur

following

an

AC

system

disturbance

close to the inverter station
 Probabilit

y
increased when volta
g
e on the AC side
yg
of the inverter is decreased by 0.1 p.u.
 Repeated commutation failures can lead to
bl ki f th l
bl
oc
ki
ng o
f

th
e va
l
ves
 Happen if the commutation of current from one
valve to another has not been com
p
leted before
p
the commutating voltage reverses across the
ongoing valve

Eti ti l i t ll

E
x

ti
nc
ti
on ang
l
e
i
s
t
oo sma
ll
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Protective Actions
19
GENERAL CONSIDERATIONS
 Commutation failure

Equivalent circuit for three
phase bridge converter
Protective

Actions

Equivalent

circuit

for

three

-
phase

bridge

converter
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Protective Actions
20
GENERAL CONSIDERATIONS
 Commutation failure

Due to voltage magnitude reduction
Protective

Actions

Due

to

voltage

magnitude

reduction
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Protective Actions
21
GENERAL CONSIDERATIONS

 Commutation failure

Due to voltage dip with backward phase
angle
Protective

Actions

Due

to

voltage

dip

with

backward

phase
-
angle

shift
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Protective Actions
22
GENERAL CONSIDERATIONS
 Commutation failure


Due to increased DC current
Protective

Actions

Due

to

increased

DC

current
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Protective Actions
23
GENERAL CONSIDERATIONS
 Commutation failure
Protective

Actions
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24
HVDC DYNAMIC MODELS
HVDC

DYNAMIC

MODELS
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Model CDC4
25
HVDC DYNAMIC MODELS
Model

CDC4
 Ranges of alpha and gamma angles in
power flow and dynamics
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