Configuration of power conversion systems for flow battery

Customised Technology for Customer Success

THE ENERGY STORAGE COMPANY

Configuration of power conversion systemsfor flow battery applications

E. A. Lewis 16th June 2010

This document contains confidential and proprietary information of Converteam and must not be used forany purpose other than that for which it is supplied by Converteam. Its contents must not be disclosed to

any other person nor copied in whole or in part without the prior written consent of Converteam

FOR CUSTOMER SUCCESS Slide 2

CUSTOMISED TECHNOLOGY FOR CUSTOMER SUCCESS E Lewis Flow Cell Issue A Slide 2 © 2010 Converteam UK Ltd. All rights reservedCOMMERCIAL IN CONFIDENCE

Introduction

Converteam and Prudent Energy are collaborating on the design of a range ofVanadium Redox flow cell energy storage systems.

This presentation describes the evolution of the initial flow cell energy storagesystem rated at 200 kWatts.

The initial design is complete and four systems are under manufacture.

The four systems will be installed on an AC grid in China during 2010.



Converteam

Converteam is a company with more than 100 years experiencein power conversion, with the knowledge of GEC, AEG, CGEAlsthom and Westinghouse. Converteam is now owned byBarclays bank 1/3 rd, LBO bank 1/3 rd and managers 1/3 rd.

Converteam is an engineering companyproviding customised designs, solutionsand systems for converting electricalenergy into productive performance.

Powergeneration

Power transmission& distribution

Converteammotors andconverters

M



Converteam Energy Storage Technology

Converteam can supply the optimum energy storage solution for any project :

Lithium ion energy storage.

Super-capacitor energy storage.

Rotary energy storage in flywheels.

Flow cell energy storage.



Prudent Energy

One of few companies in the world having capabilities of deliveringcommercial MW-class energy storage solutions.

Provides proprietary VRB energy storagesolutions for grid and renewable energystorage applications.

Founded in 2006 with headquarters in Beijing.

Branches in Vancouver, Canada.

Employees are 19 in R&D, 8 in sales, 27 inmanufacturing and 26 in engineering.

Manufacturing Facilities in China with presentcapacity of 3MW per shift.

Expansion to 10MW in 2010 and 25MW in 2011.

Controls all substantial patents including 24issued patents and 38 pending patentapplications in 34 countries

Recognized as the only commercialized VRBsolution provider by China State Grid.

Company Overview Low Cost Manufacturing

Global Footprint



The Vanadium Flow Cell Energy Storage Technology

AC gridElectrochemical energy storagesystem at ambient temperature.Same unique element Vanadiumused in both reaction half cells, sono cross contamination problems.The electrolyte never wears out, sovery low maintenance.Unlimited deep cycles for 10 yearswith very fast charge and discharge.Most unique features are :

MW rating setsreaction cell size.MWh rating setstank size.Vanadium is easilyavailable.Works by proton &electron transfer.DC volts low at 150to 250 volts DC.



Flow Cell Module

Modules are now on test



The Diode Bridge Converter For Flow Cells

AC grid

Diode bridgeDC bus

Flow cell DC output voltage

“ VDC “

AC supply voltage“ VAC “

Diode

AC volts100 5000 150 200 250

00 50

100

150

250

200

300350

DC volts

With a diode bridge the DC output voltage isdirectly set by the AC supply voltage.VDC = Peak of the VAC.So VDC = √ 2 x VAC, see the red line.The flow cells requires a voltage of 150 to 250volts DC depending on current flow and charge.For VDC = 150 volts, then VAC = 106 volts AC.No output voltage control is possible.This circuit can not be used with flow cells.

Transformer



The Thyristor Bridge Converter For Flow Cells

AC grid

Thyristor bridgeDC bus


“ VDC “


Thyristor

AC volts100 5000 150 200 250

00 50

100

150

250

200

300350

DC volts

Transformer

With thyristors the DC output voltage can bereduced down to zero by the control signalsent to the thyristors.With thyristors VDC maximum = √ 2 x VAC.For an AC supply voltage = 180 volts outputvoltage control is possible within the blue area.This circuit is ideal for flow cells.Unfortunately the thyristor circuit can not meetthe AC grid code requirements.



The IGBT Bridge Converter For Flow Cells

AC grid

IGBT bridgeDC bus


“ VDC “


IGBTDC volts

AC volts100 5000 150 200 250

00 50

100

150

250

200

300350

Transformer

With insulated gate bipolar transistors IGBTs “the diodes are essential as the AC current isconstantly switching between an IGBT and theadjacent diode.Due to the diodes VDC minimum = √ 2 x VAC.For an AC supply voltage = 106 volts outputvoltage control is possible within the blue area.This circuit can be used for flow cells but the ACsupply voltage has to be very low.The circuits meets the AC grid code requirements.For optimal cost a more complex circuit is needed.

DiodeHarmonicfilter



The Origin Of The Power Converter Technology

The most common power system for high power wind turbines uses two fully ratedPWM inverters to change variable frequency generated AC power, to DC power at aconstant DC voltage and then in to fixed frequency AC Grid power.This is the heart of the flow cell converter system.

690 V

PWM Filter

PWM voltage

AC supply inverter

Clean current PWM current

ACGrid

Generator inverter

Direct coupledAC generator



The Available Inverter Modules

A complete range available to over 30 MW .

2 & 3 level inverters.Flat pack IGBTs.Glycol watercooling system.

3 level inverters.Ceramic IGBTs.Deionised watercooling system.

MW

Volts

51 30

6600

0

2 level inverters.Flat pack IGBTs.Air cooled.

3300

440

15

690

900

0

3 Level

2 Level

For a typical 200 kW flow cell design the optimum Converteam inverter is theDelta module rated at up to 690 volts and 1000 amps AC. The Delta invertermodule is very cost effective as it produced in high volumes for wind turbines.



The Inverter Module Used

Converteam Delta module ratings :

MVDL643 = 643 amps AC at 690 volts AC.MVDL800 = 800 amps AC at 690 volts AC.MVDL1000 = 1000 amps AC and 690 volts AC.

Two overload ratings110 % overload at rated output.150 % overload at reduced rated output.

Coolant is water with added ethylene glycol.

More than 10 per day produced.

More than 4 GW supplied.



Circuit For The Prudent Flow Cell Order

Harmonicfilter DC bus

ACgrid

DC to DCIGBT inverter

Flow cell

AC to DCIGBT inverter

If a single stage input inverter was used for a typical 200 kW design :For an AC voltage tolerance of +/- 20% the AC supply = 106 x 0.8 = 85 volts AC.This would need an AC current of ( 2 x 105 ) / (√ 3 x 85 ) = 1360 amps AC.This would use two Delta inverter modules in parallel and would have high losses.

The selected design uses two Delta inverter modules in series :The AC to DC input inverter operates at 440 volts AC with an 800 volt DC bus.This needs an AC current of ( 2 x 105 ) / (√ 3 x 440 ) = 260 amps AC.The DC to DC output inverter can control the flow cell voltage from 0 to 250 volts DC.This is ideal as it also provides the initial charging action of the flow cell.This dual combination uses the same number of delta modules as the single stagedesign and the lower currents give lower losses than the single stage design.



Power flow Power flowPower flow Power flowPower flow Power flowPower flow Power flow

Operating Mode 1 Storing And Delivering Power


ACgrid


Flow cell


The system is either importing, exporting or storing AC power.The AC power is controlled by an external control signal.Can change from importing to exporting power in one AC mains cycle.No limit on the number or depth of the charge and discharge cycles.Can also supply AC reactive power at the same rating as the power rating.The AC reactive power is controlled by a separate external control signal.The system is thus able to operate with an AC power factor of +/- 0.7per unit.Meets all grid code performance specifications.Can also complete the initial flow cell charging from zero volts DC.



Operating Mode 2 For Grid Fault Conditions

The system operates to deliver the MVArs specified by the relevant Grid code.For a partial grid loss can deliver MWatts and MVArs.For a complete grid loss can only deliver MVArs.A Grid loss either recovers within a few seconds or is a longer time Grid loss.For the initial grid loss a small UPS keeps the micro processors operational but theauxiliary systems can shutdown for a few seconds.If the Grid loss persists will go to either the Self Sufficient Waiting Mode 3 or the IslandMode 4.


ACgrid


Flow cell


Power flow Power flow



Operating Mode 3 In Self Sufficient Waiting Mode

ACgrid




Flow cell

If the AC grid power is lost for more than a few seconds it is necessary to restartthe flow cell controls and pumps, to bring the flow cell system to the optimumconditions for long term energy storage.The way that this is achieved is not shown as it is Converteam IPR and subject to apatent application.

Power flow toauxiliary systems

AC contactor



Operating Mode 4 In Island Generating Mode


If required the system can act as an island generator.The AC to DC inverter then generates the required AC voltage and frequency for theAC grid.This can continue as long as the flow cell has sufficient energy.


ACgrid


Flow cell

Power flow Power flow



The Standard Power Converter System

PWM filter cubiclePWM filter cubicle PWM inverter cubiclePWM inverter cubicle



Energy Storage Fills The Gap

Grid powerReserve Grid power stations

123

Operating Grid power stations

123

Renewable Grid generation

12345

Grid frequency

Dynamic energy store12345

An integrated energy storage policy can meet all the requirement of Grid Coderegulations and enable wind power to be fully integrated.Can increase the revenue of wind farms and supply synthetic inertia power to the grid.

Reduced gridinertiaenergyStore



One Reason Why National Grids Need Energy StorageG

rid fr

eque

ncy

in H

z

Time in hours & minutes11.30 11.35 11.40 11.45 11.50 11.55

Total generation loss = 1.993 GW

48.8

48.6

49.2

49.4

49.0

12.00

4

1 = Loss of 345 MW main generation.2 = Loss of 1237 MW main generation.3 = Loss of 132 MW other generation.4 = Loss of 279 MW other generation.5 = Disconnections started

Data supplied courtesy of William Hung of National Grid

5

50.4

50.2

50.0

49.8

49.6

1

3

2

This happened in the UK during 2008 and the grid was shutting downand needed forced disconnections to survive.



Medium Voltage Flow Cell Design

Shows a typical 10 MW medium voltage inverter system.

3 level inverter

ACgrid

NP

LV DC toMV DC

DC link

Isolated reversingLV DC to MV DC converter

FlowcellOnly needs 3 modules

To many extraisolated flow cells



ProEVAr Is The Integrated Solution

This is a cost effective way to implement.Power converter already needed for grid code to supply MVArs.Power converter can also be used to also supply dynamic grid power by adding flow cells.

Flowcell

Flowcell

Flowcell

Flowcell

Onshore to offshorecable

OffshorePFC Offshore generators

AC supplycable

ACsupply

DCDC

DCDC

DCDC

DCDC

Flow cell array



Conclusions

The Converteam’s energy storage system’s abilities include :Absorbing and delivering energy.

Fast response times below 0.1 seconds.

Has same grid code performance as wind turbines.

Can supply MWs and MVArs.

Can operate in an island mode

Can supply synthetic inertia to simplify turbine designs.

Can smooth power flow.

Can store energy to permit confident pool price bidding based on forecast wind .

Can store energy to sell latter at a high pool price.

Can provide the 20 % df/dt margin required by National grid.

Can maximize energy delivered to maximize revenue.

Can enable simpler wind turbines to be produced with smaller inverters.

Available with different storage methods to be optimal for any given application.

Useable in any application both on land and at sea.

Customised Technology for Customer Success

THE ENERGY STORAGE COMPANY

Thank you

This document contains confidential and proprietary information of Converteam and must not be used forany purpose other than that for which it is supplied by Converteam. Its contents must not be disclosed to

any other person nor copied in whole or in part without the prior written consent of Converteam

Configuration of power conversion systems for flow battery

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