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