HVDC Technology

Voltage Source Converters

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Neil Kirby – Alstom Grid – IEEE PES T&D Expo, Chicago, April 2014

Voltage Source Converters • Introduction

• Circuit Configurations

• Converter Operation

• Real / Reactive Power

• Converter Arrangements

• Main Circuit Equipment

• Station Layouts

• Multi-Terminal HVDC

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Introduction • Voltage Source

Converter HVDC – ABB HVDC Light™

– Siemens HVDC Plus™

– Alstom HVDC MaxSine™

• Based on Transistor rather than Thyristor – IGBT or similar

• Simpler Transformers – No DC Stress

– Reduced Harmonics

• Simple Buildings

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VSC Circuit Configurations

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= ~

= ~

= ~

= ~

= ~

= ~

= ~

= ~

= ~

= ~

Symmetrical Monopole

Asymmetrical Monopole

Asymmetrical Monopole

Ground Return

Bipole

VSC-HVDC 2 Basic Approaches •Series-Connected IGBTs

Conceptually simple circuit

Requires PWM

High switching losses

Harmonic problems from PWM

•Multi-level circuit

Low switching losses

Easily “scaleable”

Virtually no harmonics

More complex controls

U

+½Udc

-½Udc

+ V

- V

+ V

- V

= chain link module - V

+V +V

-V -V

U

+½Udc

-½Udc

VSC Converter Operation

• Modular Multilevel Converter (MMC)

• Individually switched modules

• Synthesized/Generated AC Waveform

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V

I

0

Current reverses polarity for 120°. This is ESSENTIAL for capacitor charge balancing!

IGBT1 or D2

IGBT1 or D2

IGBT2 or D1

-Idc/3

+Idc

V

I

0

Current reverses polarity for 120°. This is ESSENTIAL for capacitor charge balancing!

IGBT1 or D2

IGBT2 or D1

IGBT2 or D1

-Idc

+Idc/3

Rectifier Operation Inverter Operation

V

I

0

Current reverses polarity for 120°. This is ESSENTIAL for capacitor charge balancing!

IGBT1 or D2

IGBT1 or D2

IGBT2 or D1

-Idc/3

+Idc

V

I

0

Current reverses polarity for 120°. This is ESSENTIAL for capacitor charge balancing!

IGBT1 or D2

IGBT2 or D1

IGBT2 or D1

-Idc

+Idc/3

Rectifier Operation Inverter Operation

LCC

Valve

Winding

Voltage

VSC Converter Operation

7

)t(sin2

acI

3

IdcIvalve

Real Power

Only

{ {

Real + Reactive

Power

1 / 3 I DC 1 / 3 I DC

1 / 3 I DC

1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) 1

/ 2 I AC ( pk )

1 / 2 I AC ( pk ) 1 / 2 I AC ( pk ) 1 / 2 I AC ( pk )

DC Current

AC Current

Real / Reactive Power

8

XT

XLIMB

2

VAC VVSC

ICONV

ΔV

I

Vvsc

Vac

V Re

Im

d

Phasor Diagram Equivalent Circuit

Real / Reactive Power

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DC

Voltage

Line-to-Ground

Valve Voltage

Line-to-Ground

Transformer

Secondary Voltage

Line-to-Ground

AC System Voltage

V1 V2 V3

IAC

XTX XLIMB

V1

V2

V3

IAC XTX. IAC.XLIMB

IAC

V2

V3

Reactive Generation Mode Reactive Absorption Mode

..

V1

IAC XTXIAC XLIMB

IAC

Real / Reactive Power

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+Q

(capacitive)

-Q

(inductive)

+P (Inverter)

-P (Rectifier)

Low AC Voltage

High AC Voltage

Constant MVA

Main Circuit Equipment

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• IGBT Converter

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

Converter Arrangements

• Modular Flexibility

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Main Circuit Equipment • Transformer

– Galvanic isolation between the AC and DC systems

– Provides voltage at a suitable level for the converter

– Provide circuit impedance to facilitate load flow

– Fault current limiting impedance

– Limits effects of AC voltage variation on converter operation (tapchanger)

– Extends range of var output at selected DC voltage and power electronic module current rating (tapchanger)

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Main Circuit Equipment

• Limb / Arm Reactor – Minimize bridge switching circulating current

– Provide circuit impedance to facilitate load flow

– Limit fault current

– Air Core

– Normally Outdoors

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Main Circuit Equipment

• Soft-Start Circuit

– Energization Inrush Current Limit

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Station Layouts

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Station Layouts

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Caprivi HVDC Converter Station – ABB

South-West HVDC Converter Station – Alstom

TransBay Cable HVDC Converter Station – Siemens

Multi-terminal HVDC • South-West Link

(Sweden)

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Phase 1: South West Link

• 4 x VSC Converter Stations

• 2 x 720MV links, +/- 300kV DC,

Line+Cable

Phase 2:

• 2 x VSC Converter Station in north

• Connection of Barkeryd Converters

to North

2 Converters

2 Converters

(Sweden)

2 Converters

(Sweden)

Multi-Terminal • Creating a Future DC Grid

– DC Breakers

– Alternative Converters

• Full Bridge, etc

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Questions?

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