Flexible DC Power Grids
Power Electronics as Key Enabler
Prof. Dr. ir. Dr. h.c. Rik W. De Doncker
Dipl. Ing. Marco Stieneker
10.06.2016
E.ON Energy Research Center: Overview
•
•
•
2
June 2006: the largest research co-operation in Europe between a private
company and a university was signed
Five new professorships in the field of energy technology were defined across
four faculties, i.e. I3 “avant la lettre”
Research areas: energy savings, efficiency and sustainable power sources
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Research Fields at
E.ON Energy Research Center
3
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Structure of the Institutes ISEA and PGS
Chair for Power
Electronics and
Electrical Drives
– LEA
Power electronics and
drives systems with a
voltage < 1000 V
Power electronics and
drives systems with a
voltage > 1000 V
Mobile energy storage
systems
Stationary energy storage
systems
Prof. De Doncker
Chair for
Electrochemical Energy
Conversion and
Storage Systems
– ESS
Prof. Sauer
4
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Locations of ISEA and PGS
• Jägerstraße
− LEA: low-power power electronics and drive
systems
− ESS: modelling, diagnostics and cell
characterisation, post mortem laboratory
• Mathieustraße, E.ON ERC
− LEA: high-power power electronics and drive
systems
− ESS: MW grid-connected energy storage
− Other institutes of E.ON Energy Research
Center: ACS, EBC, FCN, GGE
• Hüttenstraße
− ESS: vehicle integration, grid integration, pack
design, pack and cell characterisation
− IFHT, P3 E&S, Streetscooter, GSE
5
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
In the beginnings there was Direct Current (DC) Distribution
• Edison’s Pearl Street installation (1882)
− Local dc supply for incandescent lighting
in lower Manhattan, New York
− 6 constant current dynamos (invented by
Werner Siemens) with 100 kW each
− Two-wire 110 V distribution, soon replaced
by three-wire 200 V system
• Disadvantages of early dc
− Low voltage, high currents
 High cost due to large amount
of copper
 Only limited distance between
generation and load possible
− No “dc transformer” available
Source: IEEE Power & Energy Magazine
6
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
In the beginnings there was Direct Current (DC) Distribution
• Edison’s Pearl Street installation (1882)
− Local dc supply for incandescent lighting
in lower Manhattan, New York
− 6 constant current dynamos (invented by
Werner Siemens) with 100 kW each
− Two-wire 110 V distribution, soon replaced
by three-wire 200 V system
• Disadvantages of early dc
− Low voltage, high currents
 High cost due to large amount
of copper
 Only limited distance between
generation and load possible
− No “dc transformer” available
Source: IEEE Power & Energy Magazine
7
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
The Rise of Alternating Current (AC)
• Development of ac systems starting in the 1880s
− Voltage transformation using “secondary generators”
(Gaulard and Gibbs)
− Development of polyphase ac motors and other ac equipment (Tesla,
Westinghouse)
• The final breakthrough of ac
− Illumination of the 1893 Chicago World’s Fair
− Accelerating decline of dc distribution
• Long-distance ac transmission in the 1890s
(Niagara project)
Source: IEEE Power & Energy Magazine
8
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
The Rise of Alternating Current (AC)
• AC was a compromise: more difficult to control voltage at user end
• Power quality standards require precise control of voltage and frequency
− VAR compensation
− active power control
− FACTS
VGen = jωLN∙I + RN∙I + VLoad
consumer
9
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
+ producer = prosumer
Why DC?
Energy Consumption Worldwide
Million tons Oil-Equivalent
Coal
Renewables
Hydro
Nuclear
Gas
Oil
Year
10
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Source: BP Statistical Review of World Energy, June 2015
Why DC?
Gross Energy Consumption in Europe
11
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Energiewende – Scientific Facts
•
Considering the German Federal Government CO2 targets and nuclear
fission policies, several studies come to the conclusion that the only
viable options for 2030 and 2050 are:
− 2030  100% of all electrical energy should come from renewables
− 2050  90% of all primary energy should come from renewables
•
This implies increased use of electrical energy (as already suggested in
earlier EU-DGTREN studies, to reduce CO2) to minimize fossil fuel
consumption by increased efficiency and increased automation (smarts)
12
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Energiewende – Challenges
•
•
All scientists and engineers agree: aside from fusion, there is no “silver
bullet” solution. Hence, many local solutions will co-exist that are
adopted to local geographical, meteorological and economical
conditions, policies and regulations  flexibility at all levels is needed
Challenges of large scale use of renewables for electrical grids:
− On the one hand many small decentralized units connected to distribution
and low voltage grid (micro- and mini-CHP, Wind, PV, solar, “prosumers”)
− On the other hand many large-scale wind farms, PV farms and solar power
stations, that have to transmit the energy over long distances
− Power generation of wind and solar (PV) is volatile, which requires medium
and long-term energy storage
13
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
2000 – Before Market Liberalization (EU29)
Large centralized power plants, little coupling between grids
14
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
2010 – Ten Years after Market Liberalization
Fast growing market of decentralized generation
15
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Concept for a CO2 Neutral Electrical Energy Supply System
Technically Possible - Scenario for EU-27 + 2 (linear extrapolation)
16
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Concept for a CO2 Neutral Electrical Energy Supply System
About 1/3 in HV
Interesting
observation:
transmission
system may
need minimal
upgrade to
DC. ETG Task
Force claims
that DC can
be integrated
at lower cost
in existing
infrastructure.
17
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Concept for a CO2 Neutral Electrical Energy Supply System
About 1/3 in HV, 1/3 in MV
Interesting
observation:
medium
voltage
distribution
grid will need
upgrades as it
becomes an
exchange
platform
between local
producers
and
prosumers.
18
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Concept for a CO2 Neutral Electrical Energy Supply System
About 1/3 in HV, 1/3 in MV, 1/3 in LV
Interesting
observation:
Low-voltage
distribution in
factories,
buildings and
homes needs
to exchange
energy
flexibly to MV
grids to
provide D2SM
and storage
functionality
19
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Flexibility technologies and storages are needed for areal and time
shifting of energy – 1st Transition to interconnected smart grids
20
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Demand Side Management
(private households)
21
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
© Andrei Merkulov / Fotolia
© exclusive design / Fotolia
Flexibility technologies and storages are needed for areal and time
shifting of energy – 2nd Implement demand side management
Demand Side
Management (industry)
Demand Side Management
(private households)
22
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
© Andrei Merkulov / Fotolia
Demand Side
Management (industry)
© Petair / Fotolia
© exclusive design / Fotolia
Power-toHeat
© coppiright / Fotolia
Flexibility technologies and storages are needed for areal and time
shifting of energy – 3rd Develop dual use storage systems
Double use storage
system
Hanno Böck / https://hboeck.de/
Flexibility technologies and storages are needed for areal and time
shifting of energy – 4th Develop fast and large storage systems
Demand Side Management
(private households)
23
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
© Andrei Merkulov / Fotolia
Demand Side
Management (industry)
© Petair / Fotolia
© exclusive design / Fotolia
Power-toHeat
© coppiright / Fotolia
© Vladislav Kochelaevs / Fotolia
Energy storage
systems
Power-to-Gas (Chemicals)
Double use storage
system
Flexible DC Power Grids
Outline
• Flexibility of DC Grids
• General Advantages of DC Technology
• DC-DC Converter
• Material Demand
• DC in Power Collection, Power Distribution and Power Consumption
24
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Flexible DC Power Grids
Outline
• Flexibility of DC Grids
• General Advantages of DC Technology
• DC-DC Converter
• Material Demand
• DC in Power Collection, Power Distribution and Power Consumption
25
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Main Technical Problems of Classical AC Grids
Transmission is interconnected, but MV and LV AC grids are radial
Classical Substation
26
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Main Technical Problems of Classical AC Grids
Radial AC grids offer simple coordination
Classical Substation
27
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Main Technical Problems of Classical AC Grids
Radial AC grids offer high reliability but are grossly underutilized
Classical Substation
28
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Main Technical Problems of Classical AC Grids
Prosumers must exchange energy via transmission grid
Classical Substation
29
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Future Flexible MV grids should be interconnected
Exchange between prosumers possible
Intelligent Electronic Substation
30
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Future Flexible MV grids should be interconnected
Higher redundancy with high utilization of distribution grid possible
Intelligent Electronic Substation
31
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Flexible DC Power Grids
Outline
• Flexibility of DC Grids
• General Advantages of DC Technology
• DC-DC Converter
• Material Demand
• DC in Power Collection, Power Distribution and Power Consumption
32
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Increasing the transmission capacity Fundamentals of AC and DC
•
AC – Alternating Current
•
•
•
•
33
Voltage and current are sinusoidal
quantities
Frequency 50 or 60 Hz
Power p(t) = v(t) ∙ i(t)
Reactive power must be
considered
• DC – Direct Current
− Voltage and current constant
• Higher utilization of materials and
components
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
AC versus DC grids
…Beer versus wine? That is the question in Germany!
•
AC Grid
conventional
34
•
AC Grid
reactive power
compensation (FACTS)
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
•
DC Grid
Increasing the transmission capacity Using AC Cables for DC
• Voltage ratings of ac wires
• Phase – Ground:
• Phase – Phase:
300 V
500 V
• Power rating of wire
•  Three-phase wire:
• VN,ac = 230 V, IN = 16 A, λ = 0.95
PN = 3 ∙ VN,ac ∙ IN ∙ λ = 10,48 kW
• Using DC
•  monopolar:
PN
•  bipolar: Vdc
PN
35
Vdc
= Vdc ∙ 2 ∙ IN
= 2 ∙ 2 ∙ VN,ac
= Vdc ∙ 2 ∙ IN
= 2 ∙ VN,ac = 325 V
= 10,4 kW
= 650 V
= 20,8 kW
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Increasing the transmission capacity Capacity of Overhead lines
• Same mast and safe operating area
• Transmission capacity could be increased using
DC
− With redesigning the mast:
− Without redesign:
36
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
times 3,5
times 2
Motivation for DC in an AC World
Why DC in an AC world?
P
37
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
P
Motivation for DC in an AC World
~1.5..2 % less losses
Active Power Flow Control
P
38
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
P
Motivation for DC in an AC World
Reactive Power Flow Control
Q
39
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Q
Motivation for DC in an AC World
DC – DC Conversion is more efficient than AC – DC Conversion
40
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Motivation for DC in an AC World
Why DC in an AC world?
41
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Flexible DC Power Grids
Outline
• Flexibility of DC Grids
• General Advantages of DC Technology
• DC-DC Converter
• Material Demand
• DC in Power Collection, Power Distribution and Power Consumption
42
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Operating Principles of the Dual-Active Bridge Converter (DAB)
• Single phase DAB
Three phase DAB
• Alternative modulation methods wide
soft-switched operating range
• Reduced current ripple
• High power density
■𝑃=
43
′
𝑉in 𝑉out
𝜑
𝑋ser
1−
𝜑
𝜋
• 𝑃=
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
′
𝑉in 𝑉out
2𝜑
𝑋ser
3
𝜑2
− 2𝜋
Medium-Voltage DC-DC Converter
Electronic Transformer – “Edison’s missing Link”
• Power of 5 – 20 MW per unit, scalable to a power of several GW
• Highly efficient (up to 99,2 %)
• Medium-frequency transformer (500-2000 Hz)
− Reduction of weight
− Via SiC devices > 10 kHz
UDC2
UDC1
44
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Medium-Frequency High-Power Transformer
• Close cooperation with a manufacturer for custom-built transformers
• Silicon steel transformer is designed according to requirements of a dual-active
bridge
− S = 2.2 MVA (single phase), f = 1000 Hz
• Dimension for single-phase transformer 2.2 MVA
− 700 x 700 x 475 mm - Mass of 400 kg
− Increased power density by a factor of 10 compared to 50 Hz transformer
45
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Switching Loss Reduction Through Snubbers
• Snubber capacitors parallel to the switches
do not require current limiting resistors due
to soft-switching nature of the converter
• Benefits of lossless snubber
− Considerable loss reduction
− Easy series connection enabling high-voltage
applications
− Reduced stress on insulation materials
− Improved reliability
Soltau, N.; Lange, J.; Stieneker, M.; Stagge, H.; De Doncker, R.W., "Ensuring soft-switching operation of a three-phase dual-active bridge
DC-DC converter applying an auxiliary resonant-commutated pole," 16th European Conference on Power Electronics and Applications (EPE'14), 2014
46
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Future Trends of High-Power Semiconductors
• Application in High-Power DC-DC Converters
47
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
HV to MV Substation based on Dual-Active Bridge Converters
• Limited power of single converter
• Parallel / series connection
− Reduced size of capacitor with proper control
• Similar modules could be manufactured for
various applications
• Combination of storage systems with
existing HVDC concepts is possible
48
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Flexible DC Power Grids
Outline
• Flexibility of DC Grids
• General Advantages of DC Technology
• DC-DC Converter
• Material Demand
• DC in Power Collection, Power Distribution and Power Consumption
49
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Material Price Development
Passives more expensive, silicon cost downfall
• Tendencies
€/MVA
− LMEx prices of metals continue increasing (Copper, Al, Si-Steel)
− Prices of silicon keeps going down (Inverters from 500 €/kVA down to 25
€/kVA over past 25 years, down to 5 €/kVA by 2020) due to increase of
production volumes, new generations of power semiconductors, new
materials and higher switching frequencies and voltage levels
50
Price inverter
Price transformer
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Milestone: in 2013
breakeven was
reached between
inverter and 50 Hz
transformer cost
approx. 20 €/kVA
Material Usage in Power Transformers
Frequency matters!
• Weight distribution of copper and Sisteel in machines and transformers:
• Copper: 25 – 30 %
• Iron lamination: 70 – 75 %
• Specific weight Fe: 8 g/cm³
• Specific weight Cu: 9 g/cm³
• Standard 50 Hz Transformer: 2.5
kg/kVA
• DC-DC converter @ 1 kHz, 5 kV
• 1,000 Hz Transformer: 0.25 kg/kVA
51
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Standard AC Grid Configuration for Transmission and Distribution
•
AC grids are based on transformer technology
− Designed for top down energy transmission
− Constant voltage and constant frequency
− Flexible AC grids (FACTS) will require major investments in infrastructure
and power electronic energy conversion and storage systems
− In 2000, EU29 had 685GW installed capacity, i.e. 13,7 Mton on Cu and SiSteel in generators and transformers, i.e. 109,6 B€ (at price of 8 €/kg)
20,000 ton/GW
52
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Multi-Terminal HVDC (Overlay Grid) with Standard AC Collector Fields
and AC Grid – High Cost
Renewables will require 17,8 Mton Cu & Fe at
cost of 142 B€
53
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Multi-Terminal HVDC (Overlay Grid) with Standard AC Collector Fields
and AC Grid – High Cost
Renewables will require 17,8 Mton Cu & Fe at
cost of 142 B€
54
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Urban grid
Multi-Terminal HVDC with Medium-Voltage DC Collector Field and DC
Grids – Lower Cost
Renewables will require 9,1 Mton Cu & Fe at
cost of 73 B€, but is a DC urban grid less expensive?
55
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Urban grid
Flexible DC Power Grids
Outline
• Flexibility of DC Grids
• General Advantages of DC Technology
• DC-DC Converter
• Material Demand
• DC in Power Collection, Power Distribution and Power Consumption
56
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Offshore DC Collector Grids for Wind Parks
Motivation
•
•
•
•
•
Status: AC Collector Grids
• Electrical drive trains, e.g.
690 V
• Internal dc-link voltage of
~1.2 kV
Wind turbine step-up transformer 33 kV
Cluster transformer
150 kV
HVDC transmission
± 320 kV
Conversion steps: AC – DC – AC – DC
690 V
33 kV
Source: Siemens
150 kV / ± 320 kV (dc)
33 kV / 150 kV
Source: Siemens
Source: Siemens
57
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Offshore DC Collector Grids for Wind Parks
Motivation
•
Advantages for WT
• Reduction of weight
• No grid-side converter, filter
• No step-up transformer
• Less control demand
• No grid synchronization
• No active/reactive power-flow control
• Less demand for maintenance and repair
• Less investment and installation costs
• Higher Efficiency (1.5 .. 2 % less losses)
Source: Siemens
58
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Offshore DC Collector Grids for Wind Parks
Centralized Power-Electronics Components
59
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Exemplary Projects
MVDC Collector Grid for Offshore Wind Farms
•
Increased efficiency
• 2% higher compared
to AC systems
• Simple more reliable
wind turbines
•
•
•
•
New technology challenges
• Protective devices
• Electronic transformer (DC-DC converter)
Offers development platform for
future DC distribution systems
Smaller and lighter transformers
• Weight reduced to 30 %
Reduced costs
• Smaller off-shore
platforms
• Reduced LCC
• Reduced installation,
transportation and
investment cost
• Improved reliability
60
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
LV Prosumers Connected to AC Grid
Electric Vehicles and “Smart Homes” – AC In-House
61
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
LV Prosumers Connected to AC Grid
Electric Vehicles and “Smart Homes” – DC In-House
62
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
LV Prosumers Connected to MVDC Grid
Electric Vehicles and “Smart Homes” – DC In-House
63
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
All-electric Home (eHome)

Unidirectional
Low power

AC conversion
(for old machines)
Low power
 Unidirectional
Medium power


64
Bidirectional
High power
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Bidirectional
Medium power
Distribution Grid
Classical 4-wire 400 V AC Grid
• 30 kW (peak) connection power of each house hold
• 4-wire cables
• Reduced current densities to limit line voltage drop to 5 %
− J = 1.1 … 5.8 A/mm2
−
 A = 19..120 mm2 (Cu)
−
 A = 29..180 mm2 (Al)
• Increased voltage drop may occur in case of asymmetrical loads
− Neutral wire carries current
• High installed peak apparent power (30 kVA each customer) is required for fuse
coordination with loads that draw high in-rush currents, such as line start motors,
capacitors, etc.
65
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Distribution Grid
MVDC grid based on ± 5 kV DC
• 5 kW (peak) power connection to each home
−
−
−
−
All loads are converter fed with current limiting capability
Inverter-fed drives avoid high peak in-rush currents
Storages reduce peak power; peak power prices can be avoided
Appliances and loads are coordinated in smart homes and buildings
• Current densities given by thermal cable limits, not by line voltage drop
− J = 5 A/mm2 (Cu)
− J = 4 A/mm2 (Al)
 A = 2..3 mm2
 A = 2..4 mm2
• Higher line voltage drop can be allowed than in equivalent ac grids
− Voltage drop can be compensated by dc-dc converter installed at each customer to step
down the voltage to ± 380 V
• Lower installation power required
• Assumed dc-dc converter cost of 45 €/kW in 2015, down to 25 €/kW in 2020
66
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Distribution Grid
Typical Urban Grid Structure
• Branch A
− 21 households
− Max. total power: 98 kW
− Length: 461 m
• Branch B
− 34 households
− Max. power: 129 kW
− Length: 715 m
• Branch C
− 10 households
− Max. power: 68 kW
− Length: 185 m
• Connection to transmission line
− Max. power: 250 kVA
67
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Comparison
AC vs. DC
AC
DC
DC
Households (á 4 persons)
65
1,300
Connection to upstream grid in kW
250
5,000
Installed DAB in kW
Cost dc-dc converters 2015 (€)
Cost dc-dc converters 2020 (€)
575
12,500
25,875
8,625
517,500
172,500
Cost AC Transformer (€)
5,000
Cable cost (Cu) (€)
23,000
580
460,000
11,612
Cable cost (Al) (€)
3,100
62
62,000
1,240
Total costs (Cu) (€)
28,000
9,205
560,000
184,112
Total costs (Al) (€)
8,100
8,687
162,000
173,740
Assumptions:
Only differences in investment costs considered here!
68
AC
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
100,000
Comparison
Economic Evaluation
AC
Households
DC
AC
65
DC
1300
Investment in EUR
8,100
8,687
162,000
173,740
Operation in EUR
8,610
823
172,000
16,450
Total in EUR
16,710
9,510
334,200
190,190
•
•
Lower energy loss of dc grid compensates higher investment costs
DC distribution grids allow easy integration of
•
•
•
•
renewable energies (PV)
Storage systems (batteries)
charging stations for e-mobility
In-house dc grids lead to further cost savings and higher reliability, less
maintenance
Assumptions:
25 years, standard load-profile,
energy costs for consumer 0,25 EUR/kWh, energy costs for DSO 0,11 EUR/kWh
69
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Electrical Grid
AC vs. DC – Grid : Basic structures
pdc
 Discontinous power absorption
AC- Grid
 Intermediate storage of energy
Udc
0
FIlter
Rectifier
AC / DC
Conversion
π
ωt
2π
PFC
=
0
=
•> 5%
• Less component
=
~
=
~
≈ 1,00 % Losses
≈ 5..11 % Losses
≈ 0,37 % Losses
=
Identical conditions.
Efficiencies are typical values;
Better or worse efficiencies are possible.
70
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
=
380 Vdc
count
• Lower conversion
losses
DC - Grid
=
•
η ≈ 89 % .. 95 %
≈ 2..3 % Losses
≈ 3..8 % Losses
230 Vac
 Application of electrolytic capacitors for storage
 Limitation of product lifetime, additional costs
=
•
≈ 2..3 % Losses
η ≈ 97 % .. 98 %
Electrical Grid
AC vs. DC – Grid : Comparison
AC- Grid
~
230 Vac
~
η ≈ 97 % .. 98 %
=
~
η ~ 79.6 .. 90 %
=
~
=
η ≈ 92 % .. 97 %
η ~ 65 % .. 83,3%
=
230 Vac
η ≈ 92 % .. 97 %
=
•
count
=
PV
• Lower
=
η ~ 82 .. 92 %
transmission
losses
Battery
DC - Grid
η ~ 88,5 % .. 92,2 %
=
=
~
380 Vdc
~
230 Vac
=
•
• ≈ +10 %
• Less component
=
η ~ 94 .. 96 %
=
=
η ~ 94 .. 96 %
71
=
PV
Battery
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Identical conditions.
Efficiencies are typical values;
Better or worse efficiencies are possible.
Automotive Charging
• Charging e-cars in city centers
Contactless charging
•
•
•
•
72
Conducted charging
Contactless charging provides high flexibility and high user comfort
Efficiencies during charging around 90% are achievable
Conducted charging imply a negative impact on the townscape
Conducted charging station is subjected to burglary and vandalism
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Summary and Conclusions
• The “Energiewende” will move us towards
− More electrical systems
− More decentralized energy production
− Greater diversity in energy sources
• Design of distribution systems will determine success of “Energiewende”
• Power electronics will remain the most important key enabling technology
− High flexibility
− High efficiency
− Good controllability
• Possible integration into existing ac infrastructure
73
Flexible DC Power Grids | Prof. Rik W. De Doncker, Dipl. Ing. Marco Stieneker |
PGS | ESAS Summer School, Bologna | 10.06.2016
Flexible Electrical Networks
FEN-Consortium
One of Europe´s biggest research landscapes is being built on
Campus Melaten and Campus West
RWTH Aachen Campus:

19 research clusters

More than
− 100 unique testing facilities
− 120 companies participating
already

Area: 800,000 m²

Investment volume 2 billion € for
buildings and infra-structure

Approximately 10,000 new direct and
indirect jobs
Campus
West
Campus
Melaten
Source: StädteRegion Aachen/RKW/ rha/Machleidt +
Partner
Cluster area
Central infrastructure
Campus
Mitte
The RWTH Aachen Campus – an integrated and interdisciplinary campus which combines
research, development, education and life.
Flexible Elektrische Netze FEN-Consortium |
Page 75
Three research areas and three activity fields of FEN
RWTH Competence Network
Flexible Elektrische Netze FEN-Consortium |
Page 76
Industry
BMBF-funded projects: four interconnected research projects
Administration
Project 1: Modeling, Planning, Conceptual Design and Assessment
of Future Grids
Leader: Prof. Moser, IAEW
Project 4:
Design, Construction and
Testing Campus FEN
Research Grid
Leader: Prof. De Doncker, PGS
Project 2:
Electrical Equipment
and Grid Technologies
Leader: Prof. De Doncker, PGS
Project 3:
Control,
Operation Systems,
Automation
Leader: Prof. Monti, ACS
BMBF Research Campus
Kooperation
Flexible Elektrische Netze FEN-Consortium |
Page 77
Lighthouse Project
Research Grid on University Campus
4 MW CWD
Test bench for
wind energy
converters
0,1 MW EHome
Research project smart
home, connection to
medium-voltage
1 MW IME
Heavy Drive
Train Center
5 MW PGS
Test bench for
power
electronics and
electrical drives
Flexible Elektrische Netze FEN-Consortium |
Page 78
Increasing the transmission capacity 11 kV superconductor demonstrated cheaper than 110 kV GIL
79
Flexible Electric Networks of the Future | Prof. Rik W. De Doncker |
PGS | PED | 13.04.2016