EES-UETP Microgrid course

DC MICROGRIDS
Prof. Josep M. Guerrero
Microgrid Research Programme – Aalborg University

2Microgrid Research Programme – ET – AAU
 Microgrid Research Programme in AAU
 Microgrid Definition and Operation
 Microgrids Projects
 DC Microgrid Control Architectures

Microgrid Research Programme – ET – AAU 3

 Residential Microgrids - 2013 DK Smart Grid Strategy
(2015 hourly electricity pricing)
 Hydrogen Communities (Vestenkov, Lolland) – IRD
 Small remote/isolated Microgrids
 Large remote Microgrids:
Geographical islands
(70 habited islands in DK)

MicroGrid Research
Programme Areas
AC MicroGrids
DC MicroGrids
 Modeling
 Control & Operation
 Energy Storage
 Protection
 Power Quality
 Standard-based ICT
 Networked Control
 EMS & Optimization
 Multi-Agents
MICROGRID RESEARCH PROGRAMME
6
Figures:
6 Post Docs
12 PhDs
5 Visiting scholars

MICROGRID RESEARCH TEAMMICROGRID RESEARCH TEAM @ AALBORG
Josep M.
Guerrero
Tomislav
Dragicevic
DC MGs
Fabio
Andrade
MGs stability
Qobad
Shafiee
Secondary
Control
Lexuan Meng
Tertiary
Control
Dan Wu
Primary
Control
Chendan Li
MGs
Agents
Yajuan Guan
Ancillary
services for MGs
Nelson Diaz
Energy storage
for MicroGrids
Chi Zhang
LVDC
distribution MGs
Hengwei Lin
Management
and Protection
for Microgrids
Xin Zhao
AC/DC
Hybrid MG
Bo Sun
EV Charging
Stations
Javier
Roldan
LVRT &
PQ
Valerio
Mariani
Nonlinear
Control
Ernane
Coelho
MGs
modelling
Juan C.
Vasquez
Min Chen
Power
Electronics
Yang Han
PQ & MV
MGs
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8
8
Every setup is able to emulate a multi-converter low-
voltage Microgrid, local and energy management control
programmed in real-time control platforms.

9 9
Every setup is able to emulate a multi-converter low-voltage Microgrid, local
and energy management control programmed in real-time control platforms.
MGCC Labview, communication systems, control, 24 DC-AC inverters
Microgrid Research Programme – ET – AAU

Ethernet
Communication
DC Power Line
AC Power Line
10 10Microgrid Research Programme – ET – AAU
The laboratory is
based on 6 workstations
• 4 DC-AC converters,
• LCL-filters,
• ABB Motorized change-over switches
• Kamstrup Smart-meters.

1111 11Microgrid Research Programme – ET – AAU

Bidirectional
powersupply
Electric
Panelboard
Workstation
4
DC power line
AC power line SmartMeters
Cabine
t
Workstation
3
Workstation5
Workstation6
Workstation2
Workstation1
Communication Nodes
12

What is a Microgrid?
Main
Utility Grid
PCC
Household appliances and electronics
DC Coupled Subsystem
Hybrid AC/DC Microgrids
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 Phase I: Design, modelling and control.
 Phase II: Coordination control schemes between microgrid elements, including
communication systems and energy management systems for DC microgrids.
 Phase III: Creation of two Living Labs as a user-centred research concept, to test
innovation systems and elements that can conform a DC microgrid for different
applications.
• Home DC Microgrid Living Lab, at AAU
to research and test DC distribution for
1-2 family houses
• 工业微网设计 Industrial DC Microgrid Living
Lab,
At North China Electrical Power University (China),
for research, demo and test of energy solutions
for commercial buildings.

Danish
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Phase 1.
Phase 2.
Phase 3
380Vdc
Powered Home
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380Vdc
Powered Home
1. Vdc consumer electronics
2. 12/24 Vdc wall sockets
3. 12 Vdc LED lighting
4. 24 Vdc home entertainment system
5. 12 Vdc coffee maker
6. 12 Vdc refrigerator
7. 24 Vdc vacuum cleaner
8. 48 Vdc washing machine
9. 48 Vdc air conditioner
10. 12 Vdc hair dryer
11. 48 Vdc whisper wind turbine
12. PVs connected in 380vdc bus bar
13. 380vdc charger
14. 380vdc busway distribution system

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Functionalities of the EVCS
 P/Q coordination
 Frequency participation
 Voltage support
 Unbalance compensation
 Harmonics sharing

Advantage of DC transmission systems
 no reactive power loading of the transmission line
 complete control of energy flow
 no reactive power loading of the transmission line
 reduced losses
Why Back to Back links?
 Different system frequencies
 No additional short circuit power contribution to connected networks
 Fully controllable power flow

Problems in AC microgrids:
 Synchronization of distributed generators
 Inrush current (transformers, Induction motors, Induction generators)
 Three-Phase Unbalance (single-phase loads, single-phase generators such as
photovoltaic)
Recent Trends
 Introduction of many Inverter loads (AC/DC and DC/AC conversions are included)
 Introduction of distributed generations with DC output (photovoltaic, fuel
cell,variablespeed type wind turbine, microturbine, gas engine)
 Needs for higher quality power
DC-Coupled Microgrids
 DC microgrids/nanogrids
 DC distributed power systems (DPS)
 Applications: VRM, -48 V telecom systems, DC-link for UPS systems
 Isolated systems: avionic, automotive, marine…

300-400V DC Operational and Demo Sites Worldwide (Europe, USA and Japan)
Demonstrations of 300-400V DC MicroGrids in the world

AC Residential system
AC commercial system
DC Microgrid topology

The key application areas for
standardization of dc power use in
buildings include:
✔Interiors and occupied spaces where
lighting and control loads dominate the
need for dc electricity
✔Data centers and telecom central
offices with their dc powered
information and communications
technology (ICT ) equipment
✔Outdoor electrical uses, including
electric vehicle charging and outdoor
light-emitting diode (LED ) lighting
✔Building services, utilities, and HVAC
with variable-speed drive (VSD ) and
electronic dc motorized
equipment.
24 VDC 380 VDC
380 VDC 24 & 380 VDC

EMerge Alliance dc standard as implemented for building interiors
DC 24V- Infrastructure

EA’s dc standards as implemented in a data center

Barriers: The Challenges of Increased DC Use in Buildings
The use of dc power is not without it challenges. These fall into 5 major categories:
1) lack of application and equipment standards for dc power distribution
2) lack of common understanding and basic application knowledge of building
distribution-level dc
3) differences in safety and power protection device application
4) lack of a robust ecosystem to support the use of dc in building-level electrification
5) unclear pathway for moving from ac-centric power distribution to dc-inclusive
distribution schemes.
The first 3 challenges are being addressed with increasing resources by such standards
and trade organizations as:
EA , the European Telecommunications Standards Institute (ETSI ), the International
Electrotechnical Commission (IEC ), IEEE , NE MA, NFPA, the Power Sources
Manufacturers Association (PSMA), the Smart Grid Interoperability Panel (SGI P) of the
National Institute of Standards and Technology (NIST ), UL , and others.

DC Microgrid at Xiamen University, China
 150 kWp PV
 System
 DC Lighting
 Energy Storage
 Air Conditioning
 Electric Vehicle
 Charge Station
 Data Center
 Home
 And Office
 Appliances
Cloud-based energy monitor,
management, and control system
Optimal equipment choice and
operation of direct-current
MicroGrids
Efficiency Comparison:
 DC vs. AC
 Lighting: 92% vs.78%
 AC: 93%vs. 87%
 Data Center: 78% vs.64%
 EV Charger: 94% vs.76%

DC Building (EPARC, Taiwan) DC 380 V
 150 kWp PV
 System
 DC Lighting
 Energy Storage
 Air Conditioning
 Electric Vehicle
 Charge Station
 Data Center
 Home
 And Office
 Appliances
Cloud-based energy monitor,
management, and control system
Optimal equipment choice and
operation of direct-current
microgrids
Efficiency Comparison:
 DC vs. AC
 Lighting: 92% vs.78%
 AC: 93%vs. 87%
 Data Center: 78% vs.64%
 EV Charger: 94% vs.76%

DC Building (EPARC, Taiwan) DC 380 V

Green Home (Korea) DC 380 V
 LVDC 380 V
 MV Distribution level 22.9 kV

Fukuoka Smart House DC 380 V (Japan)
 Home Energy
Management
Systems
 Bidirectional
Meters

Data server
DC microgrids for data centers & servers
Four power conversions can result in a poor efficiency of the
system. Online UPS system is easily available in the market
Supplying digital loads. A classical solution:

PDU -. Power Distribution Unit.
PSU -. Power Supply Unit
DC microgrids for data centers & servers

Example of distributed power architecture
Source: Intechopen
PIBC PBUS PPOL
IBC

Typical AC distribution architecture
(dotted components are optional)
 Commercial UPS system solution
 Two AC buses (AC main & critical AC bus)
 High number of conversions (until 5)
Source: Leonardo Energy

Typical DC distribution architecture
 Front ends are
used
 High voltage DC
bus
 Low number of
conversions

DC distribution architecture with intermediate bus
 Intermediate low
voltage bus

Small scale demonstration comparing conventional a high efficiency AC architecture
(on right) with 380V DC facility-level distribution (on left).
Overhead lights operated on 380Vdc as well.
DC – AC Demonstration Facility

Small scale demonstration setup for AC (top) and DC (bottom)
7% improved efficiency and 6% savings with DC
DC – AC Demonstration Facility

Sendai Microgrid Project

Fukushima

Events timeline for a microgrid in Sendai, Japan, after the March 11, 2011 earthquake.
K. Hirose, “Performance of the Sendai Microgrid During the 2011 Earthquake and Tsunami”

Japan residential DC microgrid

DC Microgrid Ring (Japan)

REbus™ is an open standard for DC electricity distribution.
REbus™ microgrid is a flexible energy network that lets you make and use clean
renewable energy for home, business, school, or neighbourhood. (400V)
Comercial DC Microgrid

Primary Source Units (PSU)
Load Units (LU)
Powerline Communication
• Robust narrowband FSK modulation
• Programmable transmission data rate up to 30kbps
• Programmable communication frequency from
50kHz to 500kHz
• Complete Media Access Control (MAC) logic
• CSMA/CD type collision detection and resolution
• Programmable automatic preamble generation
• Programmable automatic packet-priority
management with four levels
• Error detection (CRC 16) REbus™
Comercial DC microgrid

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f/V Droop Control
Resistive line P-V droop
Resistive virtual impedance
Virtual inertia f-P
Virtual synchronous gen
DC droop
P-V droop
I-V virtual resistance
DC inertia V-P
Virtual dynamo
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COORDINATED CONTROL FOR
ISLANDED MICROGRIDS
DC Low voltage MicroGrid coordinated
control:
DC Microgrids: Bus voltage signaling
www.microgrids.et.aau.dk

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PRIMARY CONTROL OF A DC

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SECONDARY CONTROL OF A DC

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TERTIARY CONTROL AND EMS IN

 DC System Optimization ---- Local Generation Control
Typical Efficiency Curve
Constraints
• Capacity
• DC Bus Voltage
• System Dynamics
Objective
• System Overall Efficiency
Output Current (A)

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Adaptive VR
System Damping
System efficiency

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 The research is based on droop controlled paralleled dc-dc converters.
 In primary control level, adaptive virtual resistance method is proposed and
implemented for changing the load sharing ratio among converters.
 Secondary control for system damping is proposed to achieve desirable system
damping level when tertiary control shifts virtual resistance.
 Tertiary control for system efficiency optimization is proposed and
demonstrated to be capable of improving system level efficiency.

 Centralized Optimization Method
Primary
Primary
Secondary
Tertiary
Communication Links
Central Controller
Adv.:
1. Reliable solution
2. Strong supervision
3. Easy implementation.
Dis-Adv.:
1. Failure on comm. and central controller
may cause the failure of the whole system
2. Low flexibility and expandability
3. Not suitable for sighly distributed system.
Obstacle of Distributed Optimization:
Optimization requires reliable global information
Solution: Consensus Algorithm

 Tertiary Agent based Distributed Hierarchical Control

 DC System Optimization ---- Local Generation Control
Study Case

 Multi-agent Based Distributed Optimization
#1
#2
#3
#4

 Complete control architecture

 Conclusion
 Consensus algorithm is used for distributed information sharing
 Genetic Algorithm is implemented in tertiary level for obtaining optimal
output current of each converter considering the operation sequence of
each converter
 Virtual resistance is adjusted so as to follow the optimal current reference
given by tertiary control
 Simulation results demonstrate the effectiveness of the method, however,
the system stability considering the impact of communication and
consensus algorithm need to be further analyzed

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Dragicevic, Tomislav; Pandžić, Hrvoje; Škrlec, Davor; Kuzle, Igor; Guerrero, Josep M.; Kirschen, Daniel ” Capacity
Optimization of Renewable Energy Sources and Battery Storage in an Autonomous Telecommunication Facility.
I E E E Transactions on Sustainable Energy, 2014.
Dragicevic, Tomislav; Shafiee, Qobad; Wu, Dan; Meng, Lexuan; Vasquez, Juan Carlos; Guerrero, Josep M. / Modeling
and Control of Flexible HEV Charging Station upgraded with Flywheel Energy Storage.
Proceedings of the 11th International Multi-Conference on Systems, Signals and Devices, SSD 2014. IEEE Press, 2014.
El Fadil, Hassan; Giri, Fouad; Guerrero, Josep M. / Modeling and Nonlinear Control of Fuel Cell / Supercapacitor
Hybrid Energy Storage System for Electric Vehicles.
In: I E E E Transactions on Vehicular Technology, 2014.
Dragicevic, Tomislav; Vasquez, Juan Carlos; Guerrero, Josep M.; Skrlec, Davor / Advanced LVDC Electrical Power
Architectures and Microgrids : A Step towards a New Generation of Power Distribution Networks.
In: I E E E Electrification Magazine, Vol. 2, No. 1, 03.2014, p. 54-65 .
Dragicevic, Tomislav; Guerrero, Josep M.; Sucic, Stepjan / Flywheel-Based Distributed Bus Signalling Strategy for the
Public Fast Charging Station. In: I E E E Transactions on Smart Grid, 2014.
Gouveia, C.; Moreira, C.L.; Lopes, J.A.P., "Microgrids emergency management exploiting EV, demand response and
energy storage units," PowerTech (POWERTECH), 2013 IEEE Grenoble , vol., no., pp.1,6, 16-20 June 2013
J.A. Peças Lopes, Silvan A. Polenz, C.L. Moreira, Rachid Cherkaoui, Identification of control and management
strategies for LV unbalanced microgrids with plugged-in electric vehicles, Electric Power Systems Research, Volume
80, Issue 8, August 2010, Pages 898-906.

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Oct. 14 – Oct. 15
2013
Nov. 26 – Nov. 27
2013
Oct. 16 – Oct. 17
2013
Oct. 28 – Oct. 30
2013
Industrial/PhD course on
EMS and Optimization in
Microgrids - In Theory
and Practice

Microgrid
research and
activities
77

78 78
Juan C. Vasquez juq@et.aau.dk
Josep M. Guerrero joz@et.aau.dk
www.microgrids.aau.dk

EES-UETP Microgrid course

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