Introduction to Hvdc Vsc Alstom
Transcript of Introduction to Hvdc Vsc Alstom
GRID
August 2010
Dr Radnya A Mukhedkar
Group Leader, Senior Principal Engineer
System Design
Introduction to HVDC
VSC HVDC
P 2
The Voltage Sourced ConverterSingle Phase
VSCSteady DC
Voltage Input
+
Alternating Voltage Output
P 3
The Voltage Sourced ConverterThree Phase
Steady DC Voltage
Input
+
Alternating Voltage Output
VSC
P 4
AC/DC System Schematic – Ideal Load Flow
DC Voltage
Line-to- Ground
Valve Voltage
Line-to- GroundTransformer
Secondary Voltage
Line-to- GroundAC System Voltage
V1 V2 V3
IAC
XTX XLIMB /2
I
V 3
V1
VRe
Im1
3V
X
)sin(VP
VX
V)cos(VQ
VX
)sin(P
113V
X
V)cos(VQ
P 5
Voltage Waveforms
T 0557.3c
Acceptable Approximation ifSufficient Steps are Used
VSC Synthesis of a Sine Wave
Ideal Waveform
Simplest Possible Waveform
P 6
The Voltage Sourced ConverterSingle Phase, 2-level
Steady DC Voltage
Input
+
Alternating Voltage Output
Neutral
VSC
P 7
VSC: Three Main Classes
Complex Transformer
+
Simple Converters
Simple Transformer
+
Complex,
“Multi-level” Converters
Reduction in Harmonic Distortion
+
Increased Rating
Simple Transformer
+
Simple Converters
with PWM
P 8T 0811.1
Complex Transformer + simple converters
SimpleVSC
SimpleVSC
SimpleVSC
SimpleVSC
Output Voltage
Output Voltage
Output Voltage
Output Voltage
Resultant Output Voltage
P 9
Simple Transformer, Simple Converter + PWM
Output Voltage
Simple VSC
, filteredOutput Voltage
P 10
Multi-Level Converter
Output Voltage
Multi-level VSC
P 11
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What is a multi-level converter?
Total Flexibility
P 12
VSC Converter: phase arm
½Udc
½Udc
DC Transmission
SystemAC
Terminal
VSC Phase Unit
U
+½Udc
-½Udc
Line-Neutral voltage (ideal)
P 13
Semiconductors for VSC
Voltage-Sourced Converters require semiconductors which can carry current in both directions and withstand voltage in the positivedirection
The following types of device have the appropriate properties:
Thyristor derivatives:
− GTO: Gate Turn-Off thyristor− GCT: Gate Commutated Thyristor (= a GTO with a better gate
drive)− IGCT: Integrated Gate Commutated Thyristor (=a GCT with the
gate drive “integrated” into the semiconductor package)
Transistor derivatives:
− BJT: Bipolar Junction Transistor (only for low power and low frequency)
− MOSFET: Metal-Oxide Semiconductor Field Effect Transistor (only for low power)
− IGBT: Insulated Gate Bipolar Transistor− IEGT: Injection Enhanced Gate Transistor – similar to an IGBT
Do not confuse IGBT and IGCT!!
P 14
Basic 2-level inverterOne phase arm
U
+½Udc
-½Udc
Line-Neutral voltage
½Udc
½Udc
DC Transmission
System
=VSC Valve
VSC Valve
V1
VSC Valve
V2
AC
P 15
VSC Valves of the ‘Controllable Voltage Source’ type
½Udc
½Udc
DC Transmission
System U
+Udc
Valve Voltage
VSC Valve
V1
VSC Valve
V2
AC
0
U(V1) U(V2)
GRID
Circuit Types
P 17
Neutral-point clamped inverterOne phase arm (3 level)
½Udc
½Udc
DC Transmission
System
=VSC Valve=Diode Valve
U
+½Udc
-½Udc
Line-Neutral voltageV1
V2
V3
V4
AC
P 18
Neutral-point clamped inverterThree-phase circuit (3 level)
½Udc
½Udc
DC Transmission
System
V1
V2
V3
V4
AC
V1
V2
V3
V4
AC
V1
V2
V3
V4
AC
P 19
Neutral-point clamped inverterOne phase arm (5 level)
¼Udc
¼Udc
DC Transmission
System
U
Line-Neutral voltage
¼Udc
¼Udc
=VSC Valve
=Diode Valve
+¼Udc
-¼Udc
+½Udc
-½Udc
V1
V2
V3
V4
V5
V6
V7
V8
AC
P 20
Flying Capacitor inverterOne phase arm (3 level)
½Udc
½Udc
DC Transmission
System U
+½Udc
-½Udc
Line-Neutral voltageV1
V2
V3
V4
½Udc
AC
P 21
VSC with series-connected chain link modulesa.k.a. Modular MultiLevel Converter
“Half-Link” “Full-Link”
Output Voltage Output Voltage
P 22
VSC-HVDC2 Basic Approaches
Series-Connected IGBTs
� Conceptually simple circuit� Requires PWM� High switching losses� Harmonic and EMC problems
from PWM
Multi-level circuit
� Low switching losses� Easily “scaleable”� Virtually no harmonics� More complex controls
+ V
- V
+ V
- V
+ V
- V
+ V
- V
= “Chain-Link” Module
U
+½Udc
-½Udc
U
+½Udc
-½Udc
GRID
Valve Design
P 24
VSC with series-connected half-chain links
+
IGBT2D2
IGBT1D1
A
N
P
N
Valve Output VoltageEquivalent to:
Cannot electronically suppress faults on the DC side. Need to open the AC circuit breaker instead.
P 25
VSC with series-connected full-chain links
+
IGBT1
IGBT2
IGBT3
IGBT4
D1 D3
D2 D4N
P
A BVdc
Valve Output VoltageEquivalent to:
Can suppress faults on the DC side by blocking the chain links (or putting them “in reverse”)
Or
P 26
Circuit Topology
Line reactance (L) split
Becomes a means of protection
� The number of modules = the number of devices in a conventional circuit
� Requires twice the number of devices
Capacitor
Module
Stepped WaveformOverall Topology
Power Module
M2
M3
M4
M5
M6
Timeπ/2α
1 π−α1
α2
α3
π−α2
π−α3
π
2ν
3ν
−2ν
−3ν
ν
−ν2π
module high
module high
module high
module high
module high
module high
P 27
VSC Valves - Sub-module Components
VSC Sub-Module
Inter Sub-module Connector
IGBTIGBT1
IGBT2
R1
C1
D1
D2
T1
SW1
Bypass Switch
P 28
Main Components in ‘Half Bridge’
Half Bridge Power Module Circuit
IGBT (x2)
Capacitor
Bleed Resistor (x2)
Laminated Bus-Bar
Thyristor and Clamp
By-pass Switch
P 29
IGBT (x4)
Capacitor
Bleed Resistor (x2)
Laminated Bus-Bar
By-pass Switch
Main Components in ‘Full Bridge’
GRID
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