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GRID
Carl Barker,
Chief Engineer, HVDC Grids October 2011
IEEE EPEC 2011
HVDC Plenary Session
MaxSine Modular Multi-level Converter : Half link + V
- V
+ V
- V
U
Module Output voltage
• Lowest component count • Only one possibility of output voltage polarity • No capability of suppressing DC-side faults
Main Components in MaxSine ‘Half Bridge’
Half Bridge Power Module Circuit
IGBT (x2)
Capacitor
Bleed Resistor (x2)
Laminated Bus-Bar
Thyristor and Clamp
By-pass Switch
Capacitor +ve Test Connection
Main Terminal 1
Capacitor -ve Test Terminal
FULL-BRIDGE POWER MODULE
Main Terminal 2
Capacitor +ve Test Connection
Main Terminal 1
Capacitor -ve Main Terminal
HALF-BRIDGE POWER MODULE
MaxSine Modular Multi-level Converter : Full link + V
- V
+ V
- V
• Same circuit as ALSTOM STATCOM chain circuit • Output DC voltage can be either polarity • Hence can connect as tap to LCC-HVDC link • Can also suppress DC side faults
U
Module Output voltage
Capacitor +ve Test Connection
Main Terminal 1
Capacitor -ve Test Terminal
FULL-BRIDGE POWER MODULE
Main Terminal 2
Capacitor +ve Test Connection
Main Terminal 1
Capacitor -ve Main Terminal
HALF-BRIDGE POWER MODULE
IGBT (x4)
Capacitor
Bleed Resistor (x2)
Laminated Bus-Bar
By-pass Switch
Main Components in MaxSine ‘Full Bridge’
MaxSine VSC Submodule Constructed
VSC Valve Hall
Complete ±320 kV Converter Station
147m (~482’)
109m (~358’)
The Location
Tres Amigas Is Ideally Situated in Eastern New Mexico Near the Borders of CO, OK and TX Serving as a Three-Way Interconnection of WECC,
Eastern and ERCOT
“Folded Design” VSC
Tres Amigas Conceptual
Two Parallel Half-Bridge Symmetrical Monopoles
4 x Cables: DC Voltage = 1.0p.u. DC Current = 1.0p.u.
Primary Protection
Back-Up Protection
No DC Bias on Windings
Two Parallel Full-Bridge Symmetrical Monopoles
4 x Cables: DC Voltage = 1.0p.u. DC Current = 1.0p.u.
Primary Protection
Back-Up Protection
No DC Bias on Windings
Half-Bridge Bipole
2 x Cables: DC Voltage = 2.0p.u. DC Current = 1.0p.u. 1 x Cable: DC Voltage = 0.1p.u. DC Current = 1.0p.u.
Primary Protection
Back-Up Protection
DC Bias on Windings
NBS
Full-Bridge Bipole
Primary Protection Back-Up Protection
DC Bias on Windings
2 x Cables: DC Voltage = 2.0p.u. DC Current = 1.0p.u. 1 x Cable: DC Voltage = 0.1p.u. DC Current = 1.0p.u.
Hybrid HVDC Interconnections
F F F
F F F
+Q (capacitive)
-Q (inductive)
+P (Inverter)
-P (Rectifier)
Low AC Voltage
High AC Voltage
Constant MVA
Limitation in capacitive
mode
Modular Multi-Level Converter Common PQ Capability Chart Illustration
Half-Bridge Limit
Full-Bridge Limit
Simplified Windfarm VSC HVDC Interconnection
AC
500MW Wind Farm
500MW Wind Farm
1000MWHVDC Link
AC
AC
AC
AC
Isolated Windfarm Receiving End Weak AC System (SCL ~2.1)
Torque and Power Variation at a Windfarm
Exaggerated Wind Power Variation
AC
Rea
l Pow
er
Real Power Imported into an AC System from a HVDC Link with AC Voltage Control
Yy0d11 Yy0d11
1 5 9
7 11 3
12 4 8
6 10 2
R Y B
7 11 3
12 4 8
6 10 2
1 5 9
R Y B
LCC HVDC Modelling
Valve Each Valve could be many series-connected thyristors
A Typical Multi-Level Converter
+ V
- V
+ V
- V
= “Chain-Link” Module
Cur
rent
(kA)
Volta
ge (k
V)
Time (ms)
AC Supply VoltageConverter VoltageAC Phase Current
Cur
rent
(kA)
Volta
ge (k
V)
Time (ms)
AC Supply VoltageConverter VoltageAC Phase Current
DC Grid Configurations: In-shore Point-to-point System
DC Grid Configurations: Offshore Development – Point to Point System
DC Grid Configurations: Offshore Grid System
27
Why do we need DC Grids?
• Interconnection of remote renewable energy sources
• Overcoming “bottlenecks” in the existing AC grids
• Low loss (HVDC) transmission systems
• Controllable power flows over a wide area
• Avoidance of synchronisation over a wide area
• Less environmental impact than AC reinforcement
3000km
132kV
+ V
- V
ONSHORE AC GRID
F
TO ANOTHER DC GRID
Some Applications of DC-to-DC Converters
Multi-terminal VSC Control
• Will a single utility / system owner be prepared to act as the slack bus for all other interconnected systems?
“Slack Bus”
Converter 3 Converter 1
Converter 4
Converter 2
OP2
DC
Voltage
DC Current
OP1 OP3
Converter
2
Converter
3
Converter
4
Converter
1
A three-terminal DC grid
OPB
Vdc
-Idc +Idc
LRSP
OPC OPA
IB IC IA = IB+ IC
IMPORT (A───)
EXPORT (A───)
IMPORT (B─ ─ ─) IMPORT (C— - - —)
EXPORT (B─ ─ ─) EXPORT (C— - - —)
PU Calculated Power
0 100 200 300 400 500 600 700 800 ... ... ...
-0.60
-0.40
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1.20
CALC
ULAT
ED P
OW
ER
P_cal1 P_cal2 P_cal3 P_cal4
DC Grid Control with “PRIORITY”
Example: PRIORITY [0 0 0 0]
Pcal1 = 0.9863 Pcal2 = - 0.3235 Pcal3 = - 0.3235 Pcal4 = - 0.3235
Pcal1 = 0.8728 Pcal2 = - 0.0000 Pcal3 = - 0.4424 Pcal4 = - 0.4152
BEFORE AFTER
PU Calculated Power
0 100 200 300 400 500 600 700 800 ... ... ...
-0.60
-0.40
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1.20
CALC
ULAT
ED P
OW
ER
P_cal1 P_cal2 P_cal3 P_cal4
Example: PRIORITY [0 1 1 1]
Pcal1 = 1.0065 Pcal2 = - 0.3299 Pcal3 = - 0.3299 Pcal4 = - 0.3299
Pcal1 = 0.6691 Pcal2 = - 0.0001
Pcal3 = - 0.3300 Pcal4 = - 0.3300
BEFORE AFTER
Series Hybrid Circuit Wave-shaping on DC side
S 1 S 3 S 5
S 4 S 6 S 2
+ ½ V dc
- ½ V dc
S 4 on S 1
on
+ ½ V dc
- ½ V dc
Hybrid Converter DC Fault response: STATCOM Operation
Conclusion
• Modular Multi-Level Voltage Source Converter (VSC) technology (‘MaxSine’ from ALSTOM Grid) provides a flexible new power transmission tool
• Various topologies can be adopted, each with their own advantages and disadvantages
• Modelling is more complex but through real hardware ALSTOM Grid is able to validate the models developed
• Facilitate the building of future DC grids • Advanced research being undertaken to improve the technology even
further for future schemes
GRID
HVDC