Low Voltage DC Grids
Prof. Eberhard Waffenschmidt,
Cologne University of Applied Science,
Ulrich Böke,
Philips Research Eindhoven
13. Mar. 2013
Content
� Application: Commercial Buildings
� AC conversion effort
� Efficiency
� Cable losses
� Experimental setup
Prof. Eberhard Waffenschmidt 2
DC Grids in Buildings
3Prof. Eberhard Waffenschmidt
Large lighting installations:
Office space
Supermarket
Photographs by
E. Waffenschmidt
Effort for AC to DC conversion
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Philips Xitanium 35 W LED driver
Lampentreiber mit AC-Teil
Typically, more than 50% of space can be saved
Input FilterBridge rectifier
Power factor
correction
Storage
electrolytic
capacitor
AC part =
Photograph by
U. Boeke
LED-driver comparison
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Yes, this is the same scale as on the left side.
Photographs by
L. Yseboodt
Lamp driver input stage
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Component AC supply DC wide
voltage range and
reverse polarity
protection
DC narrow
voltage range,
mechanical rev.
polarity protection
Filter Required
because of PFC
Required
because of DC-DC
Can be omitted
with linear driver
Rectifier Required Required for reverse
polarity
Omitted
Power factor
correction (PFC) /
DC-DC converter
Required
for P > 25W
Required to match
wide voltage range
Not necessary
Elcap storage Required
to avoid flickering
Required
because of dips
Can be omitted, if
dips are accepted
Linear LED driver
� High efficiency
possible
� If voltage range
is narrow
Prof. Eberhard Waffenschmidt 7
LED Output Power and Losses
0
0.2
0.4
0.6
0.8
1
1.2
0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2
Supply voltage Us / Umin
Po
we
r P
/ P
led
0%
20%
40%
60%
80%
100%
120%
Effic
ien
y
LED Power
Power Loss
Efficiency
η = 90%
∆U = ± 5%
Efficiency gain with DC
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Typical AC lamp driver:
~5 % losses
Filter Rectifier PFCElcap
storageLamp
driver
Efficiency gain with DC
9Prof. Eberhard Waffenschmidt
AC grid:
~5 %
rectifier
losses
DC grid:
~2 %
rectifier
losses
Eff. Gain: ~5 %
Simple supply from AC grid:
~3 %
cable
losses
~1 %
cable
losses
Photovoltaic
generator
DC micro grid in a Building
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With solar generator and battery storage
Lamps and air conditionAC mains connection
Photographs by
E. Waffenschmidt
Battery storage
Efficiency gain with DC
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AC grid:
~4%
losses
Gain:
~10..13% losses
Micro-grid with solar and storage:
DC grid:
~2..3%
losses
~2..3%
losses
~2..3%
losses
Operation voltage: Cable losses
12Prof. Eberhard Waffenschmidt
Same copper cable:
Relative cable losses
(equivalent to copper effort)
Remark:
380 Vdc requires
similar insulation as
230 Vac
Standardization on 380 V DC
� International Electrotechnical Commission (IEC)
� Many standards covering low voltage DC grid systems already
� SMB SG4 working group “LVDC distribution systems up to 1500V DC”
− Managing new standardization projects at IEC technical committees (TC)
� National standardization working groups
− Germany: TBINK-LVDC working group at DKE/VDE
� European Telecommunication Standardisation Institute (ETSI)
� European Standard: EN 300 132-3-1 V2.1.1 (2012-02)
− Value: Definition of DC appliance inrush current limits and measurement setup
� EMerge Alliance
� Standardization working group on 380 V DC power grids for datacenters
� Standardization working group on 380 V DC for campus and microgrids
13
DCC+G - Direct Current Components & Grid
� Aims
� Demonstrate higher efficiency:
− 5 % of DC power grids
− 7 % of solar power systems
� Development of new power semiconductors
14
European co-funded R&D Project
www.dcc-g.eu
Demo DC-Grid with Solar Support
� Grid Voltage
380 V DC
� Solar Modules
2 kWp
� 56 LED Lamps
37 W, adapted LED
drivers
� Reference system
with 230 V AC
� Operation since
2012
Prof. Eberhard Waffenschmidt 15
DC Micro grid
MPPConverter
SolarModules2 kWpk
54 LEDDC-Drivers + Lamps
37 Wdc
Rectifier
380V=
AC Reference
MainsGrid230V~
SolarModules12 kWpk
MPPConverter
and PV inverter
230V~
18 LEDDrivers+ Lamps 39 Wac
Demo DC-Grid with Solar Support
� Grid Voltage
380 V DC
� Solar Modules
2 kWp
� 56 LED Lamps
37 W, adapted LED
drivers
� Reference system
with 230 V AC
� Operation since
2012
Prof. Eberhard Waffenschmidt 16
Photographs by
E. Waffenschmidt
Conclusion
DC grids offers
� Miniaturisation of power electronic modules
� Lamp drivers with less components
� Less power losses in the system
…only with suitable specifications
� Narrow voltage tolerance
� Reasonable operating voltage like 380 V DC
Prof. Eberhard Waffenschmidt 17
Contact
18Prof. Eberhard Waffenschmidt
Corresponding author:
Prof. Dr. Eberhard Waffenschmidt
Electrical Grids,
Institute of Electrical Power Engineering,
Faculty of Information, Media and Electrical Egineering (F07)
Betzdorferstraße 2, Raum ZO 9-19
50679 Cologne, Germany
Tel. +49 221 8275 2020
http://www.f07.fh-koeln.de/fakultaet/personen/professoren/
eberhard.waffenschmidt/index.html
Co-author:
Ulrich Böke, Philips Research Eindhoven, The Netherlands
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