Low voltage DC distribution - SGEM Resultssgemfinalreport.fi/files/S1-1 LVDC 2011-Eng.pdf · Low...

31.3.2011 Tero Kaipia 1

Low voltage DC distribution

Concept and technology overview Tero Kaipia

Pasi NuutinenPasi SalonenPasi PeltoniemiAndrey LanaAntti Pinomaa

31.3.2011Tero Kaipia 2

Development of LVDC distribution system

Concept and technology overview

Tero KaipiaPasi NuutinenPasi SalonenPasi PeltoniemiAndrey LanaAntti Pinomaa

r

= =

=

r

rectifier

MainsProtection

+750 VDC

-750 VDC

N20 kV

r

DSOTSOAggregatorMarkets

m m

Load

Load

Load

Load

Load

Load

= =

==

=

Pow

er lin

e si

gna

l20

kV

==

r

= =

=

r

rectifier

MainsProtection

+750 VDC

-750 VDC

N20 kV

r

DSOTSOAggregatorMarkets

m m

LoadLoad

LoadLoad

LoadLoad

LoadLoad

LoadLoad

LoadLoad

== ==

===

=

==

Pow

er lin

e si

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l20

kV

==

==

Lappeenranta University of Technology 31.3.2011Tero Kaipia 3

Development drivers

EnvironmentClimate changeLandscape issuesLand-use issuesImpregnantsElectric and magnetic fields

Energy policiesLegislationEnergy efficiency objectivesReduction of emissions and oil dependency

Renewables, DG and EVsDemand response

Society and socio-economicsSafe use of electricityReasonable pricingSupply securityEnergy efficiency actionsFunctional markets

Regulation of network businessAllowed profit regulationQuality of supplyCost efficiencyEnergy efficiency

Utility stake holdersProfit expectationsPredictable rulesCompany imageConsolidation

CustomersCustomer expectations on

Quality of supplyPricingFunctional markets

Changes in energy usage patternsEnergy efficiency actionsDynamic loadsEVs and DG

Equalitypricingservice quality

Technical developmentAutomation and communication techniquesDG and energy storagesBuilding automationUnderground cablingPower electronicsDistributed intelligencePreventive maintenance techniquesSoftware development

Power QualitySecurity of supplyEMI and EMC, distortionSensitivity of system and load appliances

Recourses and competencesHuman resourcesOutsourcingTools and methods to aid decision making

Smart Grid visionsSelf healing and proactive power systemMarket and grid oriented system controlNo market limitations

Role of power electronics in future

electricity distribution infrastructure

Products of mechanical

engineering and metals industry

Products of electronics and

electrotechnics industry

Products of mechanical

engineering and metals industry

Products of electronics and

electrotechnics industry

Network infrastructure and assetsAging infrastructureAllowed profit regulationRevenue expectations of ownersSupply quality expectationsMajor disturbance vulnerabilityIncreasing prices of conventional network componentsDecreasing prices of emerging technologies


Price index of industrial products

Product prices of electronics industry have decreased in average 5 %-units annually. The decrease have slowed down during past three years to the level of 1 %-unit/a.

Product prices of conventional metals and mechanical industry have increased in average2 %-units annually. The increase was rapid between years 2003 and 2009, achieving value of4 %-units/a.

Source: Finnish technology industries association, 2011


Roadmap to LVDC in Finland

LVDC technique1 kV AC techniqueTraditional AC


Overall research objectives

1. Facilitate improvement of supply qualityOptimising voltage quality for each customer, filtering voltage fluctuations and provide possibility for reducing short interruptions, increasing amount of protection areas in the network

2. Decrease the life cycle costs of electricity distributionDecreasing investment costs, optimising maintenance needs, increasing the level of network control and surveillance, supporting conversion towards underground cabled distribution networks

3. Support increase of small scale generation in distribution networksProvide simple generation management and standardised connection interface, ease network protection, enable active power flow control, decrease outage times due to network faults

4. Create opportunities for new business in distribution networks for service providers

VPP-management, network monitoring and local management, data transfer5. Support improvement of energy efficiency of the electric energy chain

Decreasing transmission losses, providing possibilities for reducing losses in final use, load control and load peak levelling

6. Develop and verify technical solutions to achieve profitable system configurations


Concept of LVDC electricity distribution

LVDC system providesSafe and reliable electric energy transmission from the MV network to the LV customersConstantly good-quality voltage supply for customersAn easy-to-control connection point for small-scale generation units and storagesA ready-to-use platform for smart metering, demand management and network controlLow costs of constructing and operating the distribution network

According to the EU low voltage directive LVD 2006/95/EC rated voltage of a low voltage DC system is between 75 and 1500 VDCAn LVDC distribution system comprises power electronic converters and DC connection between the converters

The entire low-voltage network is converted to DCEach customer is connected through a DC/AC inverterLateral medium-voltage AC lines are replaced with an LVDC grid

110/20 kV Substation

Unipolar customer connection

AC/DCDC/AC

DC/AC DC/AC

DC/AC

AC/DCBipolar LVDC system


AC/DCDC/AC

DC/AC DC/AC

DC/AC

AC/DC


AC/DCDC/AC

DC/AC DC/AC

DC/AC

AC/DCBipolar LVDC system

20 kV main line

NOP


Concept of rural LVDC distribution


Concept of urban LVDC distribution

LVDC20/PJ

DC/AC

AC

LVDC20/1/0.4 kV

DC/AC

0.4 kV 0.4 kV

20/0.4 kV 20/0.4 kV20 kV

0.4 kV 0.4 kV

L

DC

AC

AC

AC

AC

AC

DCDCDC DC

AC

ACAC

AC

P

Backup connection

Suburban district

Indoor DC

AC 20 kV

Urban district

Public lighting

LVDC20/PJ

DC/AC

AC

LVDC20/1/0.4 kV

DC/AC

0.4 kV 0.4 kV

20/0.4 kV 20/0.4 kV20 kV

0.4 kV 0.4 kV

L

DC

AC

AC

AC

AC

AC

DCDCDC DC

AC

ACAC

AC

P

Backup connection

Suburban district

Indoor DC

AC 20 kV

Urban district

Public lighting


General properties of LVDC system

Technical propertiesRated DC voltage: 1500 VDC or ±750 VDC (±700 VDC in galvanic continuous system)Max. DC voltage pulsation 10 %Max. DC voltage fluctuation in normal operation -25 % - +10 %Customer AC voltage in normal operation 230 VAC ±0% 50 Hz ±0.1 Hz, THD < 5 % (inside measurement accuracy)Transmission of power <500 kW up to 10 km (case-specific techno-economic solutions)Communication between all converters

Basic functionalitiesMinimisation of reactive power transmissionConstant control of customers’ supply voltageFiltration of voltage distortionsSelf diagnostics of convertersIntelligent network protection and fault locating

Interactive functionalitiesContinuous system supervisionPower quality supervision and statistics compilationGrid side power demand controlControl of EV chargingMarket information exchange

Optional featuresUn-interruptible power supply during outagesPower flow control in MV network interfaceIntentional islandingPFC in MV network interface

0.00.5

1.01.5

2.02.53.03.5

4.04.5

0 1 000 2 000 3 000 4 000 5 000

Length of line [m]

Pow

er [p

u]

10 % max. voltage drop400 VAC

±750 VDC

1500 VDC (unipolar)

Cable: AXMK 4 x 35 mm2

25 % max. voltage drop1000 VAC

Zero

Zero

Parallel connection

Parallel connection

Parallel connection

Zero

Zero

Parallel connection

Zero

Zero

Parallel connection

Parallel connection

Parallel connection

Parallel connection

Parallel connection

Transmission capacity comparison


LVDC system layout


Intelligent customer interface in LVDC system

TSO/DSO/Market players

TSO/DSO/Market players

Information systems

CommunicationCommunication

Interactive Customer GatewayInterface architecture

Home automationHome automation

GridGrid

StorageStorage GenerationGeneration

Data storage

Data storage

Control systemControl systemcontrol, measurements

measurements (control)

measurements, control


LoadsLoads

Internal controlInternal control

=

kWh

CustomersCustomers


LVDC and network management

TSO/DSO/Market playersTSO/DSO/

Market players

Information systems



GridGrid


Data storage

Data storage





LoadsLoads


=

kWh

Power technolog

y

Power technology


Market players

Information systems

CommunicationCommunicationCommunicationCommunication


GridGrid


Data storage

Data storage





LoadsLoads


=

kWh

Power technolog

y

Power technology

==

kWhkWh

Power technolog

y

Power technology


Market players

Informat ion systems



GridGrid

StorageStorage

GenerationGenerat ion

Data storage

Data storage

Control systemControl system

control, measurements




LoadsLoads


=

kWh

Power technology

Power technology


Market players




GridGrid

StorageStorage


Data storage

Data storage






LoadsLoads


=

kWh

Power technology

Power technology

==

kWhkWh

Power technology

Power technology


Market players




GridGrid

StorageStorage


Data storage

Data storage






LoadsLoads


=

kWh

Power technology

Power technology


Market players




GridGrid

StorageStorage


Data storage

Data storage






LoadsLoads


=

kWh

Power technology

Power technology

==

kWhkWh

Power technology

Power technology


Market players




GridGrid

StorageStorage


Data storage

Data storage






LoadsLoads


=

kWh

Power technology

Power technology


Market players




GridGrid

StorageStorage


Data storage

Data storage






LoadsLoads


=

kWh

Power technology

Power technology

==

kWhkWh

Power technology

Power technology

Control systemControl system measurements, controlCommunicationCommunication

measurements,LoM

INCA

INCA

INCA

INCA

DSODSOInformation systems measurements

supervision and management

supervision and management

network protectionnetwork

protection

protection,supervisionprotection,supervision




DC


Key research topics

System engineeringConceptual development and functionalitiesDistribution business impactsConfiguration and constructionElectric safety and protectionEnergy efficiency

ComponentsConvertersFiltersMechanical structuresMeasurement technologyReliabilityEnergy efficiencyProtection systemCables

ImplementationLaboratory research platformRural environment pilot system

Network analysesEconomyEnergy efficiencySupply securityPower qualityVoltage levelTopologyProtection

Tools and methodsSystem modellingSimulation environmentsControl engineeringLoad flowFault analysisPlanning, management

ICTSystem supervision and controlCommunication techniquesData security


Safety and protectionSafety issues are important when implementing new solutions

Contact voltages and currents remain on safe level when the DC network is operated isolated from ground (IT)Grounding scheme of public DC and customer’s AC networks have to equal if galvanic isolation is not provided in their connection pointCustomer equipotential bonding and grounding impedances are important in all grounding schemes

Safety, protection and possible grid events have to be considered in converter design and control

The most simple converter structures provide inexpensive, reliable and energy efficient voltage conversion but are challenging from safety perspective due to galvanic connection between DC and AC networksGalvanic isolation provides “easy” way from safety viewpoint but is challenging from economy, energy efficiency and converter topology viewpointsCommon mode disturbances due to inverter modulation cause excess voltage stress for the components in customer AC networks

ICT solutions in the LVDC provide possibility of intelligent protection systemIntegration of protection functions into converter control algorithms give freedoms for power switch current capacity dimensioningRemote tripping and interlocking can be used to ensure selectivityTeleprotection algorithms such as differential protection provide interesting alternative for solving the protection challenges of microgrids and island operation


Basic protection system layouts

Fuse

FilterDC

AC

Insulationmonitor

Surgearresters

Residualcurrentdevice

300 mA

Circuit breakersResidual current devices 30 mA

Load

Moulded casecircuit breaker

Moulded casecircuit breaker

ACDC

ACDC

Change ofcable cross-section

Fuse

Insulationmonitor

Fuse

FilterDC

AC

Surgearresters

Circuit breakersResidual current devices

Load

ACDC

HF inverter(galvanic isolation)

DCAC

Inverter includes:• Switch fault indication including

start-up prevention• Circuit breaker shunt trip for breakers

both sides of inverter (DC/AC), breakers are opened in case of inverter fault

B6

DCAC

Insulation monitor and mains circuit breaker B/C 16 - 63

Insulationmonitoring

relay

PE

Over voltage protectors Up 500 V

Residual current devices

30 mA, B-type, 40 A

MMJ / ML2.5 mm2

Tube inst.

B10

B16

Circuit breakersMMJ / ML1.5 mm2

Tube inst.

N

L

Voltage source inverter

MMJ / ML1.5 mm2

Tube inst.


30 mA, B-type, 40 A

Irsd>

Irsd>

Irsd>

Controlled circuit breaker

Main earth coupling

I >

2 I >2 I >>U >

I >

I >I >>

from

pub

lic n

etw

ork

Inverter includes:• Switch fault indication including

start-up prevention• Circuit breaker shunt trip for breakers

both sides of inverter (DC/AC), breakers are opened in case of inverter fault

B6

DCAC

Insulation monitor and mains circuit breaker B/C 16 - 63

Insulationmonitoring

relay

PE

Over voltage protectors Up 500 V


30 mA, B-type, 40 A

MMJ / ML2.5 mm2

Tube inst.

B10

B16

Circuit breakersMMJ / ML1.5 mm2

Tube inst.

N

L

Voltage source inverter

MMJ / ML1.5 mm2

Tube inst.


30 mA, B-type, 40 A

Irsd>

Irsd>

Irsd>

Controlled circuit breaker

Main earth coupling

I >

2 I >2 I >>U >

I >

I >I >>

from

pub

lic n

etw

ork

Detailed protection scheme for galvanic continuous LVDC system (IT)

PE

DCAC

DC breakerscircuit breakers

PE

Insulationmonitor

Couplingdevice

ACDC

ACDC Customer main

earth coupling

Substation earth coupling

+750

N

-75020 k

V M

V-s

ide

DC

AC

I >

2 I>2 I>>

3 I>

3 I>>

2 I>2 I>>

to c

usto

mer

pre

mise

s

to customer premises

Distribution transformer

PE

DCAC

DC breakerscircuit breakers

PE

Insulationmonitor

Couplingdevice

ACDC

ACDC Customer main

earth coupling

Substation earth coupling

+750

N

-75020 k

V M

V-s

ide

DC

AC

I >

2 I>2 I>>

3 I>

3 I>>

2 I>2 I>>

to c

usto

mer

pre

mise

s

to customer premisesto customer premises

Distribution transformer

DC network Customer’s AC network


Converter technology

Converters with (HFL, High-frequency-link converter) and without galvanic isolationTwo and three level solutionsFilter topologies and core materialsLosses reductionSize and mass reductionLifetime extensionReliability improvementDesign guidelines and methods

Two-level full-bridge

HFL-IHC

Loads230 VACLoads230 VAC

Resonance HFL-ZVSC

Three-level full-bridge

750 VDC

230 VAC

1 kVA Resonance HFL-ZVSC

Sources: Peltoniemi, P., Dissertation, LUT 2010Kampe, M., Takala, J., Juntunen, R., Karttunen, J., B.Sc. thesis, LUT 2009


Low voltage DC cables

Conventional low voltage AC power cables suitable for LVDC distribution!Insulation material should be non-polar dielectric, because of high frequency signal of PLC -> XLPE insulationXLPE insulation withstand DC voltage stress in all circumstances better than than PVC insulationConcentric neutral conductor with groundings provides shield against high frequency interferences

0

20

40

60

80

100

120

AXMK 25 AXMK 35 AXCMK AMCMK MCMK AMKA MMJ

Kaapelityyppi

Tasa

jänn

ite (k

V)

DC

Moi

stur

e &

100

°C h

eat&

DC

DC

-vol

tage

Cable typeDC voltage withstand capacity of conventional low voltage cables

Source: Suntila, T., M.sc. thesis, TUT 2009


Energy Efficiency

Total energy losses can be reduced 30–40 % by increasing efficiency of customer-end converters

LV system losses [kWh] 400 VAC LVDC Difference Transformers 2917 3157 8 % Lines 4577 1061 -77 % Rectifiers - 1903 100 % Inverters - 7092 100 % Total 7494 13214 76 %

1. asiakas

3. asiakas

4. asiakas

2. asiakas

5. asiakas

6. asiakas

7. asiakas

Uh [%] = 9,5 %

Uh [%] = 10,3 %

Uh [%] = 5,2 %

Uh [%] = 3,1 %

174 mAMKA 35

94 mAMKA 35

579 mAMKA 35

374 mAMKA 25

223 mAMKA 70

372 mAMKA 70

199 mAMKA 35

370 mAMKA 70

75 mAMKA 16

144 mAMKA 25

40 mAMKA 16

33 mAMKA 70

1. asiakas

3. asiakas

4. asiakas

2. asiakas

5. asiakas

6. asiakas

7. asiakas

Uh [%] = 9,5 %

Uh [%] = 10,3 %

Uh [%] = 5,2 %

Uh [%] = 3,1 %

174 mAMKA 35

94 mAMKA 35

579 mAMKA 35

374 mAMKA 25

223 mAMKA 70

372 mAMKA 70

199 mAMKA 35

370 mAMKA 70

75 mAMKA 16

144 mAMKA 25

40 mAMKA 16

33 mAMKA 70

Asiakas Energia Ryhmä Huipputeho[kWh] kW kVAr

1. 17720 1 5,2 1,52. 10580 1 3,1 0,93. 19830 2 14,7 4,2 4. 19815 8 5,3 1,65. 17680 6 7,2 2,06. 1290 6 0,5 0,17. 35700 6 13,8 3,8

Cust. Energy/a curve Peak power

Customer

Customer

Customer

Customer

Customer

Customer

3. Customer

0 %

10 %

20 %

30 %

40 %

50 %

60 %

70 %

80 %

90 %

100 %

0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %S/Sn [%]

Hyö

tysu

hde

[%]

. Converter efficiency


Energy Efficiency

Annual energy efficiency overcomes rated power efficiency as main indicator of total energy efficiency performance of convertersMain source of converter losses are produced in filters and power switches

Filter structures and modulation control need to be optimised with respect to the life cycle total costs of a converter

Customer inverter structures have high impact onEnergy efficiency of DC/AC and AC/DC conversionsreliability and maintainability of the systemSafety and security of systemPrice of inverter

Modular parallel converter structures have impact on energy efficiency and costs but also to reliability and total costs

DC distribution in customer premises and dispersion of inverters?

750 V DC

750 V/440 V 750 V/230 V

Public LVDC network

Distribution board

750 V/220 V

750 V DC

750 V/440 V 750 V/230 V

Public LVDC network

Distribution board

750 V/220 V


Network planning

Strategic planningHow to evaluate the strategic role and application potential of LVDC distribution?What is the impact of the LVDC on other network structures?

Long term detailed planningWhere the LVDC system can be used, how to pinpoint the suitable application targets?How the application of the LVDC system affect on MV network nearby the application target

Detailed target planningWhat are the optimal LVDC network constructions in particular application target?

LVDC system planning is a part of dynamic planning process of MV networksWhere is the line between network planning and component design?

i.e. DC capacitor or reactor dimensioning can be included in both


Strategic planning– Application potential analysis

-10 %

0 %

10 %

20 %

30 %

40 %

50 %

0 0,5 1 1,5 2 2,5 3

Keskijännitehaarajohdon pituus [km]

Kust

annu

sero

[€/k

m]

0 %

2 %

4 %

6 %

8 %

10 %

12 %

Joh

toha

aroj

en o

suus

tark

aste

ltavi

sta

jo

hto

haa

rois

ta [%

]20 kV AVO

20 kV PAS

20 kV KAAP

20 kV haarajohdot

Kust

annu

sero

[%]

10 % KJ-haarajohdoista kustannussäästö on

rakenteesta riippuen 3-15 %

DC ei kannata

4 % haaroista, säästetään5 -18 %

3,2 % haaroista, säästetään8 -20 %


jne.

yhteensä n. 39,5 % haaroista, DC:llä

säästetäänkeskimäärin 20 -30 %

DC kannattava

-10 %

0 %

10 %

20 %

30 %

40 %

50 %

0 0,5 1 1,5 2 2,5 3

Keskijännitehaarajohdon pituus [km]

Kust

annu

sero

[€/k

m]

0 %

2 %

4 %

6 %

8 %

10 %

12 %

Joh

toha

aroj

en o

suus

tark

aste

ltavi

sta

jo

hto

haa

rois

ta [%

]20 kV AVO

20 kV PAS

20 kV KAAP

20 kV haarajohdot

Kust

annu

sero

[%]

10 % KJ-haarajohdoista kustannussäästö on

rakenteesta riippuen 3-15 %

DC ei kannata

4 % haaroista, säästetään5 -18 %



jne.

yhteensä n. 39,5 % haaroista, DC:llä

säästetäänkeskimäärin 20 -30 %

DC kannattava

10 % branches, 3-15 % savings 4 % branches, 5-18 % savings

3 % branches, 8-20 % savings

2 % branches, 10-25 % savings

Total: 40 % branches,20-30 % savings

Application targets and cost effects

LVDC profitable

LVDC not profitable


Detailed planning– Supply area optimisation

LVDC level

20/0.56/0.56 kV +rectf.

Customers = loads

20 kV level

L(x)

L(x)20/0.56/0.56 kV +rectf.

LVDC level

20/0.56/0.56 kV +rectf.

Customers = loads

20 kV level

L(x)

L(x)20/0.56/0.56 kV +rectf.

esdisturbancmajor of Costs

DjLV_md

AMV_md

costs outage lStatistica

Custrep4

mINV

D ncrep3

ncPF

Bj TDrep2RectMVT

A

feeder

DRncDR

feeder

HSRncHSR

feeder

nc

RZ

R

ZPF

losses of Costs

8760

0

NLCust

,NL_NINV_NLB

,NL_NRect_NL,NL_NMVT_NL

LL

Custm,,INV_LL

D

2posMV

2ngMV

LV_LL

B,,Rect_LLN_LL

2

N

MVTMVT_LL

A

2MV

MV_LL

L

costsInvestment

CustNINV_in

2,LV_inNRect_inNMVT_in1,MV_in

...

...8760

...

...8760

,8760

...

...

87608760

876087608760...

...

,...

,,,,,

,,THD,,

,,

...

...,,,,

nci

ncnc

mjj

m

jvj,

,

,,

i

j

xm

wjvji

jii

i

mmmm

k TDkncnck

ncjkincnc

ncjj

iii

nc

nc

nc

nc

ncrcncnc

nc

mcncZ

nc

repncZi

mxm

jjwjvj

jN

xmxmk

kkk,n2kk

kk

jjkiwjwj

jv

iii,n1

iii

mm

Dkkknkkk

Bjjkijj

Aiinii

LVDC

CC

tbaW

tbaW

tbaW

laWaW

tbaWtbWtbW

dt

PCPCPtUtUC

tSCplcstUtS

tUtS

lC

tSCPS

tSC

cstUtSlC

h

SC

plcslCSCSCcslCC

A

C

B

P1

MV/LV +rectification.

LVDC grid - N +?

Which pole should I connect to?

- N +?

Which pole should I connect to?

Bipolar or unipolarconnection line?

- N +

Bipolar or unipolarconnection line?

- N + ?


Detailed planning– Harmonics and power losses

100

80

60

40

20

5

0,00

5,00

10,00

15,00

20,00

25,00

30,00

35,00

40,00

3 11 13 23 25 35 37

Network load, %

IndividualCurrent

HarmonicDistortion (RMS)

%

Harmonic order

No load loss

Extra loss

Resisitive loss

Conventional load loss excl harmonics

Extra loss due to harmonics

Unloaded Rated load Actual load Actual load ( excl harmonics ) ( incl harmonics )

Load loss ~10%

Source: Hulshorst, W.T.J., et Al., Kema 2009

100

80

60

4020

5

0,00

10,00

20,00

30,00

40,00

50,00

60,00

70,00

80,00

90,00

100,00

3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 Network load;%

IndividualCurrent

HarmonicDistortion (RMS)

% Harmonic order

2 4 6 8 10 120

2

4

6

8

10

Harmonic order, n

Har

mon

ic c

urre

nt, A

Crec

=1000µF and Cinv

=250µF.

Meas.Sim.

Supply transformer primary

Supply transformer secondary

DC network

Supply transformer losses

Source: IEC 61378-1

nh

SECE

nh

WEL

LLtotLL hIIPPh

IIP

IIPP

1

8,02

111

1

22

11

2

11_

Conventionalload loss

Eddy current lossin windings

Stray lossesConventionalload loss

Eddy current lossin windings

Stray losses

IL = RMS value of the sinusoidal current including all harmonicsI1 = RMS value of the fundamental current, at rated loadIh = RMS value of the harmonic current of order hPLL1 = copper losses of the fundamental freqency at rated loadPWE1 = winding eddy loss at rated frequency and loadPCE1 = connectors eddy loss at rated frequency and loadPSE1 = stary loss in structures at rated frequency and load

n

hL II1

2

hh

II Lh 5

2,11


Detailed planning– Harmonics and power losses

Distortion losses in DC network form ~20-30 % of the total line losses when capacitors are dimensioned only on technical basis (voltage ripple + stability)Economical dimensioning can lead to larger capacitor sizes

Name CASE 1 CASE 2 CASE 3 CASE 4 Capacitors Rated Oversized Undersized Undersized

1.2mF 2.4mF 600µF 1.2mF

720µF 1.4mF 720µF 360µF Power losses in kW

0.485 0.11 1.51 0.54

0.074 0.072 0.067 0.081

1.31 1.31 1.36 1.31

0.31 0.325 0.37 0.355 Total 2.179 1.81 3.3 2.28

capacitorlossesh

rtransformeh

networkdc CostpricePP


Planning of operation and start-up

+

-

R L

CVf vc

700800900

100011001200130014001500

0 200 400 600 800 1000 1200

vc [V]

s [m]

Y

D

DC-

volta

ge [%

]

Time [ms]

100 %

110 %

90 %

75 %

20010020

Shed load(voltage control and direct load group control)

Start-up immediately

Odo

ta

Shut down60 %

0

120 %Shut down

1000

Odo

ta

Start-up after random delay

Nor

mal

op

erat

ion

300-500 ms

DC-

volta

ge [%

]

Time [ms]

100 %

110 %

90 %

75 %

20010020

Shed load(voltage control and direct load group control)

Start-up immediately

Odo

ta

Shut down60 %

0

120 %Shut down

1000

Odo

ta

Start-up after random delay

Nor

mal

op

erat

ion

300-500 ms

Capacitor voltage after start-up as a function of cable length with star and delta-connected secondary

Example of converter operation based on DC voltage


LVDC in residential buildings

Majority of low-voltage electronic devices use internally DC voltages

Internal SMPS convertersResistive heating and lights work both with DC and AC, and some even better with DC

DC voltage level can be higher than the level used in LV AC circuits at present

Higher transmission capacityInternal voltages of electronic devices are not suitable for distribution

Case 1 has only one voltage level, 230 VAC produced with a centralised inverterCase 2 has 750 VDC for heating and 230 VAC for other devicesCase 3 has multiple voltage levelsCase 4 is similar to Case 3, but there is 750 VDC instead of 440 VDCCase 5 provides two voltage levels, 750 VDC and 220 VDC

Public ±750 V LVDC

Customer network LAPPEENRANTAUNIVERSITY OF TECHNOLOGYFINLAN D

LAPPEENRANTAUNIVERSITY OF TECHNOLOGYFINLAN D

Source: Paajanen, P., M.Sc. thesis, LUT 2009


LVDC in residential buildings

0

200

400

600

800

1000

1200

1400

1 2 3 4 5

Case

Ann

ual l

oss e

nerg

y [k

Wh]

Appliance lossesCable lossesDC converter lossesInverter losses

Single converter

Multiple converters

0

500

1000

1500

2000

2500

3000

3500

1 2 3 4 5

Case

Tota

l cos

ts [e

ur]

DC converter investmentinverter investmentinverter lossesDC converter lossesAppliance lossesCable lossesCable investment

Internal DC networks reduce the total costs of distribution and improve energy efficiencyCost optimum leads also to energy efficiency optimum

Losses and investments of the power electronic devices are in a decisive role when comparing different distribution systems

Source: Paajanen, P., M.Sc. thesis, LUT 2009

Public ±750 V LVDC

Customer network LAPPEENRANTAUNIVERSITY OF TECHNOLOGYFINLAN D

LAPPEENRANTAUNIVERSITY OF TECHNOLOGYFINLAN D


Simulation models

EMTDC/PSCAD


Simulation modelsValidation against measurements crucial

Source: Vornanen, T., TUT, Nordac 2010


Objectives for research platform development

Provide test environment for technical solutions, functionalities, analysis methodology and design methods of LVDC technologyStudy implementation of research results in practical environment

Provide feedback for component development and for practical product development

Operation in variable surrounding conditions and equipment reliabilitySuitability of mechanical structures from installation and maintenance perspectiveProtection against electromagnetic interferences and fieldsCo-operation with interconnected systems

Integration with existing network supervision and management systemsCommission inspections and authorised approvals of structures

Verification of electrical safety-practical environment hazard voltages and currentsInstallation documentation, electric work safety and warning signs

Feedback for standardisation development Customer feedback

Laboratory environm

entR

eal network environm

ent


Laboratory research platform

Entire system isolated from earth (IT)SMA Hydro Boy 1 kVA converterSerial bus controlled DC power supplySerial bus controlled relay boardSeven contactors for resistive load controlArtila Matrix 512 embedded PC for higher level control and data communicationsRequired protection devices and contactors for fault testing

50 kVA 400/565/565 V supply transformer6-pulse diode bridge and 6-pulse half-controlled thyristor bridge rectifiers200 m DC cable, AXMK 4x16Two single-phase inverters without galvanic isolation transformers

160 A (inv. 1) and 75 A (inv. 2) IGBT modulesTwo TI DSP control boards and dSPACE control environment

r

= =

=

r

rectifier

+750 VDC

-750 VDC

N

r

ProcessPC

==

400/565/565 V50 kVA e

Controllable DC power supply

Inverter

Relay card

I1U1

I2

U2

DSPACE

P1, P2

Batteries

External control signals

market information– prices– bids– forecasts

system information– capacity limits– power balancing


820 m

Inv. #1

400 m

Inv. #2AC/DC

Inv. #3

320 m

200 m

Practical environment research platform

Co-effort of Suur-Savon Sähkö Ltd. and LUT, started in 1/2010Installation environment

Developing recreational dwelling and detached house areaapproximately 2 km of underground cabled networkin first phase 4 customers, fed by 3 inverters

Research platform for testing and developing both DC technology and interactive distribution network functionalities

Real-environment practical component and functionalities testingDevelopment needs of components and feed back of system operationDevelopment needs of installation techniques and inspection methods


Practical environment research platformSystem layout – Rectifier substation


Practical environment research platformSystem layout – Rectifying substation

Process PC, system control board and communication

Main circuit breakers

Thyristor controllers

Insulation monitoring

Measurement board

Thyristors

DC-output

DC capacitors (not yet installed)


Practical environment research platformSystem layout – Inverter substations

Cabinet

to customer

to customer

to customer

Uv IvUDCIDC

UDC

UDC

IDC

IDC

Uv

Uv

Iv

Iv

I

I

I

Cabinet

Cabinet

Optical fibre to rectifier substation



PEProcess

PC

ProcessPC

ProcessPC

D Yn

Inverter Filter

Transformer

DC-network

Customers

Control board


Further researchLaboratory research platforms for LVDC technology

Testing and prototyping new technical solutionsVerification of active functionalitiesBenchmarking of converter solutions

Practical environment research platform – rural LVDC networksTesting of the LVDC technology in actual installation surroundingsGuidelines for system installation and inspectionsPublic opinions and feed back from electricity end-users, DSOs and other related industry

Analysis and development of LVDC technologyDevelopment of technical solutions and algorithms for different applications of the LVDC distribution

Optimal system constructions for versatile applicationsOptimal control strategies for converter and system control in different operational conditions

Improvement of the technical and economical performance of the LVDC system by the means of converter technology and network configurations

Development and analysis of converter topologies with and without galvanic isolationDetermination of measures for improving energy efficiencySolutions for ensuring electric safety during operation, maintenance and installation

Development of calculation algorithms for network management, system analysis and for different planning tasks

System modelling and development of analysis methodologyDevelopment of methods and guidelines for optimisation of the LVDC system structures and componentsDevelopment of methods and tools for the LVDC system supervision

Connection of DG and energy storages into LVDC networkSystem control needs and algorithmsConnection interface development

Intelligent protection and active management of LVDC systemProtection function developmentIntegration of protection system in converters and efficient application of ICT


LVDC - Pros and Cons

1. Full control of customer’s supply voltage

2. Improved LV transmission capacity

3. Less distribution transformers and MV lines

4. Improved supply security

5. Reduced risk of storm caused blackouts (in OHL networks)

6. Reduced total costs of distribution networks

7. Decreasing cost development of power electronic components

8. Flexible connection point for DG and storages

9. Natural basis for island operable microgrids

Backbone of smart distribution

1. Complicated system construction

2. Additional losses due to converters

3. Increased need of maintenance

4. Shorter life-time of components

5. Lack of standardisation

6. New technology without decades long experiences

+ -

31.3.2011 Tero Kaipia 39

Low voltage DC distribution - SGEM Resultssgemfinalreport.fi/files/S1-1 LVDC 2011-Eng.pdf · Low...

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