Grid+Storage Workshop
Increasing feed-in capacity and improving power quality in low-voltage distribution grids
Markus Meyer
Technical University of Munich
Associate Professorship Power Transmission Systems
Munich, 10.03.2016
1. Introduction
2. Objectives and project outline
3. Project partners & respective tasks
4. Concepts for increasing the feed-in capacity of low-voltage grids
a) Innovative inverter concepts
i. Photovoltaic-inverters
ii. Unified Power Flow Controller (UPFC)
iii. Batteries
b) Charging strategy
c) Communication
d) Control strategy
5. Field Test Area
Agenda
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Current Situation
• increasing number of switched-mode power supplies connected to the grid
• high installed capacity of inverter-based power generation in low-voltage
grids
• reverse load flow top-down vs. bottom-up load flow
Emerging Problems
increased node voltages / violation of voltage limits
generation of current and voltage harmonics & neutral wire overloading
voltage unbalance
Introduction
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• Increasing the possible PV-penetration in low-voltage distribution grids
• Maintaining / improving the power Quality according to DIN EN 50160
– voltage quality
– harmonics
– voltage symmetry
Approach
• Development of novel electrical equipment with extended features regarding
voltage control and compensation of harmonics
• Integration of the new electrical equipment into automatic superordinated
control via broadband-powerline (BPL)
Objectives
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• low-voltage UPFC
• new inverters (PV, battery, CHP) contributing to voltage control
• batteries with innovative charging strategies
• broadband-powerline communication between electrical equipment and
superordinated control computer
Project Outline
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Project Partners & Tasks
Manufacturer specialised in voltage control & power quality measurement
equipment
responsible for: development & production of the UPFCs
One of the leading manufacturers of Li-Ion batteries in Germany
responsible for: development of battery-stack & BMS
Company specialised in smart energy solutions
responsible for: development of battery charging strategies
Developer and manufacturer for customised inverters & testing facilities up to
300 kW
responsible for: development & production of the battery- & UPFC-inverters
One of the leading manufacturers of PV-inverters
responsible for: development & production of PV-inverters
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Project Partners & Tasks
Company specialised in instrumentation & control and automation systems
responsible for: geographical information system & grid control centre
German distribution system operator, providing energy for ~70.000 households
responsible for: providing the field test area
Institute for Power Electronic Systems of the TH Nürnberg; research
emphasis lies on power electronics, embedded systems & automation
responsible for: administrative project management & conceptional
studies of inverter topologies
One of the leading providers for BPL-systems
responsible for: broadband-powerline
Associate Professorship Power Transmission Systems; research emphasis
lies on the integration of renewables & their influence on PTS (0,4 – 380 kV)
responsible for: technical project management & development of
superordinated control
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Current technology:
• Q(U); cosφ(P)-droop curves
• voltage control at local grid connection point
Innovative concept:
• voltage control at an external grid node
decreasing reactive power consumption of industrial enterprises
• decreasing settling time (400 ms to 150 ms)
Inverter Concepts – PV-Inverters
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Inverter Concepts – PV-inverter
• reactive power compensation device replaced by reactive power supply ofthe PV inverters
• minimize the reactive power supplied by the external grid
• industry complex with own PV-generation, connected to thelow-voltage grid
• part of active power demandcovered by solar energy
Externes
Netz
Abgesetzer
Messpunkt
PQ
Messwerte
P
Q = f(Qmess)
P
Q = 0
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Current technology:
• coupling / uncoupling of two
transformers with selected transfer ratio
• single-phase stepped voltage regulation
Innovative concept:
• inverter-based concept for single-phase
balancing of phase currents / voltages
• stepless voltage regulation
• reactive power supply
• bypass for short-circuit overload and
service
Line Voltage Regulator
Source: http://www.a-eberle.de/sites/default/files/media/Prospekt_LVRSys_en.pdf
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Inverter Concepts – UPFC
• series connection of the transformersecondary winding
• individual voltage regulation of eachphase (magnitude & phase)
• shunt inverter allows additional reactivepower supply
• balancing of unsymmetrical gridstates
• control of active / reactive power flows through the line
• compensation of harmonics
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Battery & Inverter
Objectives
• increasing self-consumption of solar energy
• reducing strain on power grids via peak shaving, feed-in of reactive power,
active harmonic compensation
• enabling the smart-grid to act as a virtual power plant (VPP)
Use of non-standard battery-inverters
Sophisticated battery-management-system (BMS); charging capacity
dependent on internal battery-parameters to increase battery lifetime
Simulation-based positioning for maximum benefit regarding voltage control
Unusual battery size to achieve aforementioned goals (30 kW, 30 kWheff)
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Battery & Inverter
• Modular design of the battery
• Plug-in modules for a 19-inch rack
(600x1200x2100 mm)
• Module configuration 6s2p
– 260 – 340V
– 38 kWh, 30 kWh nominal
• 600x1200x400 mm for the inverter
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Battery & Inverter
Corepack
• 7s1p Samsung SDI 60 Ah
• 5 temperature sensors inside each
corepack
Module
• 2 serial corepacks
• 45 kg per module
• first prototypes of master & slave boards
built and tested
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Battery Charging Strategy
• Artificial Neural Network (ANN)
• real-time measured input parameters
• historical input parameters
• statistical / numerical forecasts
wind speed temperaturesolar irradiation
prediction
Historical
weather data
Historical
generation data
Battery (SOC)
electrical energy
prices
Artificial
Neural
Network
battery charging
strategiesload forecast
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Communication – Broad Band Powerline
• measurement data, status reports etc. are converted into high-frequencyvoltage signals using the electrical grid as its communication infrastructure
• several repeaters are placed at strategic locations
Challenges: non-linear elements (particularly UPFC), emitted interferencesfrom inverters
Main Control-
Computer
~~=
PV-
Inverter
Battery &
Inverter
~~=
+-
Modulation
BPL-
Modem
BPL-
Modem
Measurement
Data
Modulation
Measurement
Data
Repeater
low voltage grid
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General requirements:
• reliable operation of the controlled grid
• meeting the requirements according to DIN EN 50160
(voltage band, harmonics)
• fully automated mode as well as manual mode possible
processing measurement data from different grid nodes
detecting violations according to DIN EN 50160
Control Strategies for Low-Voltage Grids
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• no detected limit violation according to DIN EN 50160
• active devices (UPFC, PV-inverter) operate according to pre-defined droop-
curves and charging strategies
Autonomous Mode
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limit violation detected
active devices (UPFC, PV-inverter)
operate according to predefined droop-
curves and charging strategies
superordinated control transmits set-
points to the active devices via BPL
Transition Autonomous – Controlled Mode
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Primary control level: UPFCs
Strongest influence on the grid
Secondary control level: PV-inverters
Contribution to the voltage-control by
reactive power supply
Tertiary control level: batteries
Charging strategies to be altered as a
last resort
Controlled Mode – Hierarchic Structure
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Reactive power flow control:
• status feedback of the active devices
• load flow calculation based on measurement
data
result: remaining reactive power reserve
of the low-voltage grid
• Grid operator is able to request delivery of a
certain amount of active/reactive power
Virtual power plant
Controlled Mode with Set-Point
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Field Test Area
Unterfarrnbach (district of Fürth)
• 52 PV-systems at 41 grid nodes
• installed PV-capacity ~ 1 MW
• annual energy consumption ~ 1,5 GWh
(400 loads with electric meters)
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Field Test Area
Equipment to be placed:
• 3 UPFCs
– one at each substation (2 total)
– one at the most critical branch (long line, high PV-feed-in)
• 3 batteries with 30 kW & 30 kWh each
• exchange of 450 kVA inverter power
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Further Steps
• completion of the prototypes
– UPFC
– battery
– PV-inverters
• testing of the devices in the labs of the respective project partner
• testing of the entire system (superordinated control in combination with all
the components) in the lab of the Technical University of Munich
upon successful testing:
transition to field test
Thank you
for your attention!