Sistemas CCAT com LCI e VSC
Edson H. Watanabe
Programa de Engenharia Elétrica
Universidade Federal do Rio de Janeiro
COPPE/UFRJ
1
CCAT – Corrente Contínua Alta Tensão
LCI – Line Commutated Inverter
CSI – Current Source Inverter
VSC – Voltage Source Converter
2
DISPOSITIVO SEMICONDUTORES DE POTÊNCIA
DIODOS
TIRISTORES
TRANSISTORES BIPOLARES (fora de uso)
TRANSISTORES MOSFET (fonte de computador)
GTO (Gate Turn-Off Thyristor) (fora de uso)
MCT (Mos Controlled Thyristor) (fora de uso)
IGBT (Insulated Gate Bipolar Transistor
IGCT (Integrated Gate Commutated Thyristor
3
TIRISTOR
Invenção 1957 (GE)
Uso Comercial desde 1962
iA
A
Características: Disparo Controlado
Corte Natural
iG
Fácil Conexão em Série
G
K
Freqüência Baixa (50/60 Hz)
Símbolo
Potência:
SCR (Silicon Controlled Rectifier): 4kV / 3kA
LTT (Light Triggered Thyristor): 8kV / 3.5kA
Uso: Retificadores / Inversores de Alta ou Altíssima
Potência
4
TIRISTOR
Características Básicas
iA
On
Região de
bloqueio
reverso
Reverse
breakdown
Off-to-on if
iG pulse is
applied
vAK
0
Curva
característica i-v
Reverse
breakdown
voltage
Off
Forward
breakdown
voltage
Corte é sempre
natural
Disparo e Corte
R
vS
~
iG
iA vS
iA
vAK
0
T/2
t
vAK
T
5
TRANSISTOR BIPOLAR
Resposta em Freqüência Média
até centenas de kHz,
normal 20 ~ 50 kHz (Centenas de W)
2 ~ 5 kHz (Dezenas de kW)
ton=2s, toff=5s e tstg=5s
Baixa Capacidade de Suportar Surtos de
Tensão ou Corrente
ib
Possibilidade: Segundo Breakdown
iC
C
B
Ganho Baixo de Corrente ( 5 ~10)
E
Símbolo
6
TRANSISTOR MOSFET
Freqüência de Chaveamento
algumas centenas de kHz
ton=100 ns toff=200 ns
Tensão / Corrente
1000 V / 10 A
100 V / 100 A (50 kHz)
D
iG
G
S
Símbolo
Alta Resistência de Condução (Ron)
Alta Perda de Condução
Facilidade de Conexão em Paralelo
Baixíssima Corrente de “Gate”
Exemplo: id=25A, igmáx=1A e igo=0.5A
7
GTO (GATE TURN-OFF THYRISTOR)
Freqüência de Chaveamento
ton= 1 ~ 2 s, toff= 5 ~ 10 s
Corte / Disparo pelo “Gate”
Alta Potência: 6kV / 6kA
iA
A
iG
G
K
Conexão Série:
Difícil, mas possível para poucas unidades
Ganho de Corrente:
Disparo: Igual ao SCR
Corte: Ganho  1/3
Aplicação: Inversores de MW
8
IGBT (INSULATED GATE BIPOLAR
TRANSISTOR)
(Nasce do casamento do transistor bipolar com o MOSFET)
Freqüência de Chaveamento Média:
ton = 0,5 s, toff = 1 s
Ganho de Corrente Muito Alto (Igual MOSFET)
Perda de Condução: menor que no MOSFET
ig
G
Exemplo:
1000 V / 25 A
IgMÁX = 1 A, Igo = 0,5 A
iA
C
Símbolo
E
6,5 kV / 3 kA (maior atual)
9
IGBT (INSULATED GATE BIPOLAR
TRANSISTOR)
Exemplo:
IGBT tipo “press pack” de condução
reversa e 2500 V / 1 k A
10
IGBT (INSULATED GATE BIPOLAR TRANSISTOR)
Chaveamento:
Tensão
Tensão
Corrente
Corrente
(a)
(b)
1,2 kV / 2 kA (200 V/div, 500 A/div, 200 ns/div (a) 25ºC (b) 125º
11
IGCT (GATE COMMUTATED THYRISTOR)
Controllable turn-off current (snubber capacitor)
Características
3kA (0F)
4kA (3F)
Storage time
2,5 s at 3 kA
Turn-on di/dt
1000 A/s
On voltage
Gate trigger current
Thermal Resistence (Junction / sink)
Gate off-current
3,8 V at 3 kA
4 A at 25ºC
0,11ºC/W
= Anode current
Exemplo:
4,5 kV IGCT Com Circuito de Gate
12
POTÊNCIA X FREQÜÊNCIA
(Para um único dispositivo)
SCR
Potência (W)
GTO - IGCT
IGBT
10M
1M
100k
MOSFET
10k
1k
60 100
1k 10k 100 k 1M
Frequência (Hz)
13
ASSOCIAÇÃO SÉRIE / PARALELO
TIRISTORES:
Válvulas de SCR’s: Tecnologia dominada
Exemplo:
Transmissão de Corrente Contínua (Itaipú)
+ de 300 SCR’s em Série
i
Transistores de Alta Corrente:
Conexão em Paralelo:
difícil equalizar a
corrente.
14
CONEXÃO SÉRIE DE GTO / IGCT / IGBT
Problema: Equalização
da Distribuição de
Tensão Durante turn-on
e turn-off
No caso de IGBT existe caso de
dezenas de dispositivos em série
15
APLICAÇÕES
Inversor de Tensão
e
Inversor de Corrente
Id
Chave unidirecional em
tensão e bidirecional
em corrente
Sintetiza
Fonte de
Corrente
Chave unidirecional em
corrente e bidirecional
em tensão
Sintetiza
Fonte de
Tensão
16
HVDC SYSTEMS
Current Source Converter:
(Conventional HVDC System)
• Thyristor-based converter
• Phase angle control
• Current control
Voltage Source Converter*:
• IGBT or IGCT based
converters
• PWM control
• Voltage control
* - ABB: Light HVDC, Siemens: HVDC Plus
17
HVDC SYSTEMS
Advantages:
 Transmission lines are more compact than AC lines
 No need of reactive power compensation in the line
 Highly flexible
 Good for connecting asynchronous systems
(Long distance transmission or back-to-back connection)
 Excellent for long distance transmission
Drawback:
•
High converter cost and few suppliers
18
ITAIPU HVDC SYSTEMS
HVDC Transmission line
765 kV AC Transmission lines
19
Current Source Converter (CSI) or Line
Commutated Conveter (LCI)
Id
L
d
VR
AC
Grid
1
Rectifier
Vd
Inverter
AC
Grid
2
Basic Circuit with 6-Pulse Converter
20
12-Pulse Converter
Y-Y
VR
Y-
Number of pulses are increased to
mitigate problems with low frequency
harmonic generation
21
HVDC Transmission System
Smoothing reactor
DC Line
AC Grid 2
AC Grid 1
Y-Y
Y-
Y-Y
Y-
Y-
AC Filter
Y-Y
DC Filter
DC Line
AC Filter
Y-
DC Filter
Y-Y
22
Converters Characteristics
Id
Rd
AC Grid 1
Vdr
Vdr
Id =
min
1
2
3
Id0
Id
AC Grid 2
Vdi
Vdr-Vdi
Rd
Vdi
min
1
2
3
Id
23
ITAIPU HVDC TRANSMISSION SYSTEM
Total Power = 6.300 MW
2 bipoles of +/- 600 kV / 2625 A
Length  800 km
Total number of thyristors = 18432
(Each valve has 96 thyristors connected in series)
24
Problems with Conventional HVDC Systems
1 – Sensitivity to commutation failure
2 – Consumption of reactive power
Solution:
Capacitor-Commutated Converter - CCC
Id
Rd
AC Grid 1
Vdr
AC Grid 2
Vdi
This system is used in Garabi connection with Argentina
25
CCC X Conventional HVDC
M. Meisingset and A.M. Golé, “A comparison of conventional and capacitor
commutated converters based on steady-state and dynamic considerations,”
AC-DC Power Transmission Conference, IEE, 2001.
26
CCC X Conventional HVDC
M. Meisingset and A.M. Golé, “A comparison of conventional and
capacitor commutated converters based on steady-state and dynamic
considerations,” AC-DC Power Transmission Conference, IEE, 2001.
27
HVDC BASED ON LCI
• The AC system has to have high short circuit ratio
• There are low frequency harmonic generation
• The converters need reactive power for normal
operation
• No black start
28
HVDC BASED ON VSC
Voltage Source Converter:
- IGBT or IGCT based converters
- PWM control
- Voltage control
Advantages:
- Does not need reactive power or even power source
- Can use PWM control and “does not generate
harmonics”
- Black start is possible
29
HVDC BASED ON VSC – Basic Configuration
Vd
CF
AC
Grid 1
• PWM control in both sides “eliminates” harmonic problems
• AC grid can be a weak system and reactive power can be
controlled by the converters
30
AC
Grid 2
HVDC BASED ON VSC – Short Circuit
Vd
CF
AC
Grid 1
AC
Grid 2
• If a short circuit happens in the DC side the diodes
will keep supplying current. An AC circuit breaker has
to protect the converter.
31
HVDC BASED ON VSC – Short Circuit
DC reactor to limit short circuit current
AC
Grid 2
AC
Grid 1
Transmission line
• If a short circuit happens in the DC transmission line
the reactors have to limit the current until the AC side
circuit breaker operates.
32
HVDC BASED ON VSC – Control
Converter 2
Converter 1
P1, Q1
Vd
P2, Q2
CF
AC
Grid 1
AC
Grid 2
• If Converter 1 controls P1, Converter 2 should control
the DC voltage and P1 will be equal to P2.
• (Or vice-versa)
• Q1 and Q2 can be controlled independently both
with capacitive or inductive characteristics.
33
HVDC BASED ON VSC – PWM Control
- Sinus-triangle PWM can be used but it may
produce high losses;
- During transients better to use sinus-triangle method
vcontr
vtri
ol
t
(1/fS)
v
d
t
- A small percentage
of 3rd harmonic can
be added to the
reference voltage to
increase
fundamental
component and use
better the converter.
vo1
34
HVDC BASED ON VSC – PWM Control
- Harmonic elimination method guarantees low losses
(Pulse number varies from 5 to 19)
60
Pulse Width
Notch
Width
1 2 3 4
180º-2
90
º
t
180
º
180º-
180º-4 180º-3
1
Alpha () angles (deg)
0
50
40
200
2
160
120
11th harmonic
30
20
10
3
80
1
40
13th
harmonic
0
0
0
20
40
60
80
100
Fundamental Voltage VS in (%)
35
Application Examples
36
Application Examples: Cross Sound Cable Project
New
Haven
Cable
New York
Shoreharm
330 MW, +/-150 kV, 40 km Cable Transmission
37
Cross Sound Light HVDC – Circuit Diagram
38
Cross Sound Light HVDC - Control
39
Cross Sound Light HVDC - Harmonics
5th
7th
40
Cross Sound Light HVDC - Losses
41
36 MW, 138 kV (DC), 70 km
42
EAGLE PASS – PIEDRAS NEGRAS BtB
43
CONCLUSIONS
 VSC in BtB connection is still a new technology
and may be important for connection of
asynchronous systems, AC weak systems or use
in congested areas;
 The converter controls are independent and does
not need reactive power;
 Harmonic generation is relatively low;
 However, losses are still high (about 2 to 8 times
the losses of a conventional thyristor based
HVDC system).
44