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!