The rapid evolution of voltage Source Converters as ... · PDF fileThe rapid evolution of voltage Source Converters as applied to High Voltage ... Basic HVDC Transmission DC link Transformer

Tuesday 30 June 2015

The rapid evolution of voltage Source Converters as applied to High Voltage

DC power transmission

Carl Barker

Chief Engineer HVDC Applications

© ALSTOM 2013. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it is complete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Presentation title - 06/07/2015 – P 2

HVDC Today Finding an increasing market demand

• Firewall – Protects one AC

system from the other

• Controllable

• Lower transmission cost

• Lower transmission losses

Installed DC Power (GW)



Basic HVDC Transmission

DC link

Transformer

Receiving

End

Sending

End

Idc

RT

t

Idc

t

Iac

t

Inverter Rectifier

V1 V2

TR

VVIdc

21

Iac



HVDC Today Point-to-Point Links are dominant

Brazil Gulf States

Rio Madeira – Bipole 2

3150 MW 2375 km Transmission

GCCIA

1800 MW 50 Hz / 60 Hz Back-to-Back



Why the predominance of

Line Commutated Converter HVDC?



LCC not VSC

Ld

3

6 4

iA

1

2

V’d

5

~

~

~

iB

iC

LS

LS

LS E1

Vd

Id

A

B

C

B

A

1

C

6

3

2

5

In thyristor based converters the

topology that provides economic

AC-DC-AC conversion also suffers

the risk of “Commutation Failures”



LCC not VSC

Typical Rating

(125mm, 8.5kV thyristor)

~35kA peak

Typical Conditions at

first positive peak

of recovery voltage:

V ~ 5kV peak

Tj ~ 140°C

Time (° elec)

1080°720°360°0

Va

lve

Cu

rre

nt

Va

lve

Vo

lta

ge

Ju

nc

tio

n T

em

pe

ratu

re

Typical

Conduction

angle = 330°

Breaker

opens

here

Maximum

Stress



LCC not VSC

Voltage

Withstand

Junction Temperature

Normal

Operation Commutation

Failure

Thyristor

Capability



LCC not VSC

Voltage source conversion

not ideal considering

thyristor technology

Cd

3

6 4

iA

1

2

5

~

~

~

iB

iC

LS

LS

LS E1

Id

A

B

C

Ifault

Ld

3

6 4

iA

1

2

5

~

~

~

iB

iC

LS

LS

LS E1

Id

A

B

C

Ifault

Current source conversion

universally adopted for

HVDC transmission



Evolution of HVDC Transmission Voltage

1970 1980 1990 2000 2010

200kV

400kV

600kV

800kV

1000kV

1200kV

1960 1950 2020

500kV becomes de facto standard for single 12-pulse bridge per pole

Multiple 12-pulse bridges per pole

Single 12-pulse bridge per pole

Rio-Madeira

Itaipu 600kV

Cahora-Bassa 533kV

Xiangshaba-Shanghai; Yunnan-Guangdong

Ningdong-Shandong

First 1100kV project planned in 2014



Early HVDC Transmission

Mercury Arc Valves

Italy-Sardinia HVDC

1967

200 MW, 200 kV



Thyristor Development

H100 H200 H300 H400

Oil-insulated,

oil-cooled.

4kV, 37mm

thyristors,

3 in parallel.

Air-insulated,

air-cooled.

4.0kV 56mm

thyristors,

2 in parallel.

Air-insulated,

water-cooled.

5.2kV, 100mm

thyristors.

Air-insulated,

water-cooled.

8.5kV or 7.2kV

100mm, 125mm

or 150mm

thyristors

~ 1970 ~ 1980 ~ 1988 ~ 2004

Air-insulated,

water-cooled.

8.5kV or 7.2kV

100mm, 125mm

or 150mm

thyristors.

~ 2015

Series….



HVDC Today Two product types in todays market



Early VSC for HVDC Transmission



VSC for HVDC

Five-Level Floating Capacitor Converter



2 level converter (SPWM)

Up to 60 MW (1997…1999)

3 level converter (3PWM and SPWM)

260 MW to 350 MW (2000…2002)

2 level converter (OPMW)

350 MW and above (2004 ….)

All IGBT valves

1st generation

2nd generation

3rd generation

Early VSC and its development



Basic Structure of VSC

±Udc

Uac

Uout

t

Uout

Uac

SPWM, 3PWM and OPWM – what’s it mean?

Pulse Width Modulation (PWM):



Noting that:

v= 𝐿 ∙𝑑

𝑑𝑡𝑖

It can readily be seen that the inter-turn voltage stress on the phase reactor

will be very high.

This has necessitated the need for a special reactor design with a high-degree

of shielding/inter-winding insulation.

±Udc

Uac

Uout

Early VSC Stations



Early attempts at multi-level converters



Early attempts at multi-level convertion


dcV

2dcV

2dcV

dcV

Note: For the output voltage waveform

shown: Vdc1=Vdc/2, Vdc2=Vdc,

Vdc3=3Vdc/2

2/12 VdcVVVe dcdcdcout

2/1 VdcVVe dcdcout

2/23 VdcVVVe dcdcdcout

2/3 VdcVVe dcdcout

1dcV3dcV

eout

2dcV

dcV

dcV



The development of power rated semi-

conductors with turn-off capability



Two-Level

The History of MMC

https://canalrivertrust.org.uk/anderton-boat-lift

The Anderton Boat Lift

Built by Emmerson Murgatroy &

Co. Ltd in 1875 to lift boats

50 feet from the River weaver to

the Trent & Mersey Canal https://www.flickr.com/photos/tahitipix/1464242128/

Built by Thomas Telford in

1822 to lift boats 64 feet

between two levels of the

Caledonian Canal.

Neptune's Staircase







https://www.flickr.com/photos/tahitipix/1464242128/

https://www.flickr.com/photos/tahitipix/1464242128/



Early MMC Converters



Early MMC Converters



Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

Volts

Time

Volts

What is a Modular Multi-Level Converter?



T2962.2

3V

2V

V

0

-V

-2V

-3V

Output Voltage

A “Chain” with three “Links”

V V V

STATCOM Principles



Power system applications of multi-level converters

The first practical device for power applications with

turn-off capability was the:

Gate Turn Off (GTO) Thyristors



T2840.2

Power system applications of multi-level converters

VS

XL ~ 0.2pu

STATCOM TCR - TSC SVC

XL=1.0pu

VS

STATCOM TSC TCR

VS

I Leading I Lagging 1.0pu 1.0pu

Xc=1.0pu



T6732

One STATCOM Link

GTO Gate Drive Units

GTO

Anti-parallel Diode

di/dt reactor

Auxiliary Inverter

Overvoltage limiting “dump” capacitors



Today’s Modular Multi-Level Converter



AC current path in a VSC converter

Viewed from the AC

side the + and – DC

busbars are star points

for two parallel 3-phase

circuits 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 )

+ ve DC

- ve DC



AC and DC current paths in a VSC converter

I DC

I DC

1 / 3 I DC 1 / 3 I DC

1 / 3 I DC





The MMC for HVDC Transmission Applications



Modular Multi-level Converter – Half Bridge

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

T1

C

T2

+

Vm

T1

C

T2

+

T1

C

T2

+ T2 conducting

Vcapacitor

Vm

T1 conducting

SM = Sub-Module



Comparison of IGBT Technologies

IGBT Module

Advantage −Available from many suppliers −Many sizes and ratings available −Relatively low cost

Disadvantage −Open-circuit failure mode −Maximum rating available: 4.95MW (3.3kV, 1500A) −Poor transient current rating of diode

The device operation was

proposed in the late 60’s but

further work in the 70’s led to

the first commercial product in

1983. Further developments

led to an improved device

(avoiding DC lock-up) in 1984

with a voltage rating of 1200V



The need for fast controls


In todays high voltage multi-level converters we are effectively

controlling many controllers in parallel, both their interactions

with the AC and DC system and with each other.

It’s a bit like flying in formation!



The need for better communications

Illumination and image transfer

Communications

Sensors

Fibre Optics Applications

1960 2013

Early fibre was used in bundles for illumination and image transfer (cool-light, endoscopes, image-intensifiers).

Fibre communication has been the major application for many years. Data rates and distances have increased following huge advances in the technology.

But fibre sensors are set to dominate in the future.



Fibres for data communication

Step index fibre: Light is guided by total internal reflection. Different rays travel at different angles – arrive different times. Suits low data rates and short distance with LED sources.

Graded index fibre: Higher angle rays travel faster to arrive together. Higher data rates and longer distance, works with LED sources.

Single mode fibre. Single wave front is guided by the core, not contained by it. Ideally matched to Surface Mount laser sources for long haul and high data rates.



The first multi-level converter for HVDC transmission




+ + + + + + + +

V

0 8

4

VSC Generation 1: Modular Multi-Level Converter (MMC)



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

The ALSTOM Modular Multi-Level Converter



VSC: Sweden - South West – Phase 1

• Power: 2 x 720MW • monopole scheme • Voltage DC: +/-300kVdc • Voltage AC: 420kVac • Client: Svenska Kraftnät • Technology: VSC • Distance Point to Point: 200km • Ground Cable

Phase 1: South West Link

-4 x VSC Converter Stations

-2 x 720MW links, +/- 300kV DC, OHL & Cables (by others)

Award in December 2011 to Alstom Grid 3m



-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200 250 300 350

Electrical Degrees (°)

Vo

ltag

e (

pu

)

Modular Multi-Level Converter

operation has many discrete steps

Modelling and Testing

“Development of a Modular Multi-

Level Electro-Magnetic Transient

Model of the Alstom Grid VSC

(MaxSine)”, C D Barker, N M Kirby, W

Liang, R S Whitehouse, Dr A Gole, U

Gnanarathna, CIGRE Canada 2011,

Halifax, Paper 124

But then how do we test the

controllers?



New testing Requirements



Progress of HVDC VSC schemes



Where are we going?



Modular Multi-level Converter Half Bridge - DC Fault

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

T1

C

T2

+

DC Pole to Pole Fault:-

• T2 Diode Conducts

• Fault current uncontrolled

• Fault current can only be

stopped by

• a) AC breaker

• b) DC breaker



LCC HVDC Recovery from a line-to-ground fault

Fault recovery to pre-fault DC

voltage

Failed recovery to pre-fault voltage

followed by recovery to 0.8pu DC

voltage

Overhead

Transmission

Line FaultFault

recovery

Time

Fault

Clearing

Time

Fault

ReignitionRecovery to

0.8pu Voltage



Modular Multi-level Converter – Full Bridge

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

SM

T1

C

T2

+

Vm

T3

T4

+Vc

Vm

-Vc

T1

C

T2

+ T3

T4

T2 + T3

conducting

T1

C

T2

+ T3

T4

T1 + T3

OR

T2 + T4

conducting

T3

T4

T1

C

T2

+

T1 + T4

conducting



Modular Multi-level Converter

T1

C

T2

+



HVDC: The Alternate Arm Converter Full-Bridge

Series Valve



VSC AC

System

3rd harmonic voltages balance

across delta windings.

Hence, no voltage differential

so no 3rd harmonic current flow.

We don’t just have to use sinewaves!



←Valve voltage

←Line-to-line voltage

We don’t just have to use sinewaves!



Series Bridge Converter

Red, H-Bridge converts 80% of

power

Switching losses are minimised

by, Yellow, half-bridge chainlinks

providing zero voltage soft-

switching

6th harmonic voltage cleaned by

a few full-bridge, blue, chainlinks

on H-bridge output

Low footprint (over HB-MMC) as

only one HB Chainlink valve

across the DC rail

Cost savings over HB-MMC

Half-Bridge

Full-Bridge

Series Valve



Controlled Transition Bridge

Parallel converter style

approach

Allows switching losses to be

managed by Chainlinks

Reduces filtering requirements

over LCC

Maintains high current

capability

Chainlink capacitor small

Complex control requirements

Half-Bridge

Full-Bridge

Series Valve

www.alstom.com

Documents

The rapid evolution of voltage Source Converters as ... · PDF fileThe rapid evolution of voltage Source Converters as applied to High Voltage ... Basic HVDC Transmission DC link Transformer