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University of Illinois Urbana-Champaign
Integration and Interconnection of
Distributed Energy Resources
Geza Joos, Professor
Electric Energy Systems Laboratory
Department of Electrical and
Computer Engineering
McGill University
4 November 2013
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Overview and issues addressed
 Background
 Distributed generation and resources – definition and classification
 Benefits and constraints
 Grid integration issues
 Grid interconnection and relevant standards
 Distribution systems standards
 Steady state and transient operating requirements
 Protection requirements
 General requirements – types of protection
 Islanding detection
 Concluding comments
 Distributed energy resources – microgrids and isolated systems
 Future scenarios
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Electrical power system – renewable generation
Generation
Transmission
HVDC
Conventional
Storage
Custom Power
Distribution
FACTS
Renewables
Industry
Transportation
Commercial
Residential
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Future electric distribution systems – a scenario
(Microgrid)
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Distributed generation – definition – classification
 A subset of Distributed Energy Resources (DER), comprising
electrical generators and electricity storage systems
 Size – from the kW (1) to the MW (10-20) range
 Energy resource
 Renewables – biomass, solar (concentrating and photovoltaic), wind,
small hydro
 Fossil fuels – microturbines, engine-generator sets
 Electrical storage – batteries (Lead-Acid, Li-Ion)
 Other – fuel cells (hydrogen source required)
 Connection
 Grid connected – distribution grid, dispersed or embedded generation,
may be connected close to the load center, voltage and frequency st by
the electric power system
 Isolated systems – voltage and frequency set by a reference generator
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Distributed generation – definition – features
 Not centrally planned (CIGRE) – is often installed, owned and
operated by an independent power producer (IPP)
 Not centrally dispatched (CIGRE) – IPP paid for the energy
produced and may be required to provide ancillary services
(reactive power, voltage support, frequency support and regulation)
 Connection – at any point in the electric power system (IEEE)
 Interconnection studies required to determine impact on the grid
 May modify operation of the distribution grid
 Types of distributed generation
 Dispatchable (if desired) – engine-generator systems (natural gas,
biogas, small hydro)
 Non dispatchable (unless associated with electricity storage) – wind,
solar
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Distributed generation – installations
 Typical installations, from large to small
 Industrial – Generating plants on industrial sites, high efficiency, in
combined heat and power (CHP) configurations
 Commercial
 Residential installations, typically solar panels (PV)
 Features of smaller power dispersed generation
 Can typically be deployed in a large number of units
 Not necessarily integrated in the generation dispatch, not under the
control of the power system operator (location, sizing, etc)
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Distributed generation – drivers
 Promoting the use of local energy sources –
wind, solar, hydro, biomass, biogas, others
 Creating local revenue streams (electricity
sales)
 Creating employment opportunities
(manufacturing, erection, maintenance,
operation)
 Responding to public interest and concerns
about the environment – public acceptance can
be secured
 Green power – Greenhouse Gas (GHG)
reduction
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Distributed generation – technical benefits
 Enhanced reliability – generation close to the load
 Peak load shaving – reduction of peak demand
 Infrastructure expansion deferral – local generation
 Distribution (and transmission) system loss
reduction – generation close to load centers
 Lower grid integration costs – local generation
reduces size of connection to the main grid
 Distribution voltage connection (rather than
transmission) – ease of installation and lower cost
 Voltage support of weak distribution grids
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Distributed generation – typical installations
 Typical power plant types
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Hydraulic, 5-10 MW
Biomass, 5-10 MW
Biogas, 5-10 MW
Wind, 10-25 MW
 Total installed power (2011): 61
plants, 350 MW
 Connection: MV grid (25 kV,
nominal 10 MW feeders typical
for Canadian utilities)
Ref: Presentation Hydro-Quebec Distribution, 2011
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Hydro-Quebec – on-going projects 2011-2015
 Biomass
 4 plants
 25 MW on MV grid
 Commissioning 2012-2013
 Small hydro
 8 plants
 54 MW on MV grid
 Commissioning 2010-2013
 Wind power plants
 5 plants
 125 MW on MV grid
 Commissioning 2014-2015
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DG connection to the grid – options
 Connection options
 Distribution network – low (LV), typically 600 V, and up to 500 kW
 Distribution network - medium voltage (MV), up to 69 kV, typically 25
kV, up to 10-20 MW
 Transmission network – aggregated units, typically 100 MW or more
 Power system impacts
 Distribution – local, typically radial systems
 Transmission – system wide, typically meshed systems
 Differing responsibilities and concerns
 Distribution – power quality (voltage), short circuit levels
 Transmission – stability, voltage support, generation dispatch
 Integration constraints – in relation to the electric power grid
 Power quality – should not be deteriorated
 Power supply reliability and security – should not be compromised
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Integration and interconnection issues
 Integration of the generation into existing grids – constraints
 Operating constraints – maximum power (IPP paid for kWh produced),
desired operation at minimum reactive power (unity power factor)
 Dealing with variability and balancing requirements (if integrated into
generation dispatch) – characteristic of wind and solar installations
 Integration into the generation dispatch – requires monitoring, energy
production forecasting
 Interconnection into the existing grid – constraints
 Connection to legacy systems – protection coordination, transformer
and line loading, impact on system losses
 Reverse power flow – from end-user/producer to substation
 Increased short circuit current – DG contribution
 Operational issues – grid support requirements and contribution
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Specific DG interconnection issues
 Generation power output variability
 Short term fluctuations – flicker (wind, solar)
 Long term fluctuations – voltage regulation, voltage rise at connection
 Reactive power / Voltage regulation – coordination
 Reactive compensation – interaction with switched capacitor (pf)
 Voltage regulation – impact on tap-changing transformer operation
 Impact on Volt/Var compensation – interference
 Harmonics and static power converter filter interaction
 Voltage distortion produced by power converter current harmonics
 Resonances with system compensating capacitors
 Islanding and microgrid operation
 Operation in grid connected and islanded modes – transfer
 Microgrids – possibility of islanded operation – aid to system restoration
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DG interconnection and control requirements
 Reactive power and power factor control – required
 Voltage regulation – may be required (using reactive power)
 Synchronization – to the electric power system
 Response to voltage disturbances – steady state and transient
 Response to frequency disturbances – steady state and transient
 Anti-islanding – usually required (to avoid safety hazards)
 Fault, internal and external – overcurrent protection
 Power quality – harmonics, voltage distortion (flicker)
 Grounding, isolation
 Operation and fault monitoring
 Grid support – larger units
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General DG standards
 Distributed resources (DR) standards
 IEEE 1547, Standard for Interconnecting Distributed Resources with
Electric Power Systems and applies to DR less than 10 MW
 Generally applicable standards for the connection of electric
equipment to the electric grid.
 IEEE in North America and IEC in Europe, cover harmonic interference
and electrical impacts on the grid.
 Most commonly used are the IEEE 519 and the IEC 61000 series.
 Utility interconnection grid codes and regulations – issued by
regional grid operators as conditions for connecting DGs to the
electric grid
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Operational requirements – larger installations
 Based in part on conventional generation (synchronous) – may
apply to DGs connected to the distribution grid
 Voltage regulation – may be enabled
 Frequency regulation – may be required
 Low voltage ride through (LVRT) – may be required
 Power curtailment and external tripping control – may be required
 Control of rate of change of active power – ramp rates
 Other features – typically required for large wind farms (> 100 MW,
transmission connected), may be required for farms > 5-25 MW
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control of active power on demand
reactive power on demand
inertial response for short term frequency support
Power System Stabilization functions (PSS) – special function
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DG protection issues – general considerations
 Operational requirements
 Distribution system – must be protected from influences caused by DG
during faults and abnormal operating conditions
 DG – must be protected from faults within DG and from faults and
abnormal operating conditions caused by distribution circuits
 Specific considerations
 Impact of different DG technologies on short circuit contribution and
voltage support under faults – induction generators, synchronous
generators, static power converters (inverters)
 Impact of power flow directionality (reversal) on existing distribution
system protection
 Instantaneous reclosing following temporary faults
 Utility breaker reclosing before DG has disconnected – may lead to outof-phase switching – avoided by disconnecting the DG during the autoreclosing dead time (as low as 0.2 s)
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Protection system – role and requirements
 Role – to detect and isolate only the faulty section of a system so
that to maintain the security and the stability of the system
 Abnormal conditions – include effect of short circuits, overfrequency, overvoltages, unbalanced currents, over/under
frequency, etc.
 Protection system requirements
 rated adequately
 selective – will respond only to adverse events within their zones of
protection
 dependable – will operate when required
 secure – will not operate when not required
 Faults seen by the DG
 Short circuits on the feeder
 Loss of mains – feeder opening and islanding
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Protection functions of a DG interconnection
PCC -HV
bus
T1
PCC -LV
bus
cb1
Line2
Line1
~
Line3
cb4
S
cb7
cb2
T2
R7
cb
T3
R7
L3
cb5
TL
cb8
L1
DG1
-
PCC - HV side
L2
L4
PCC - LV side
DG2
DG - LV side
Distance
Automatic recloser
Frequency (over and under frequency)
Pilot differential
Fuses
Voltage (over and under voltage)
Phase directional overcurrent
Voltage (over and under voltage)
Overcurrent (instantaneous and delayed)
Ground directional overcurrent Overcurrent (instantaneous)
Loss of mains (islanding)
Automatic recloser
Underfrequency
Synchronization
Undervoltage
Phase directional overcurrent
Loss of earth (grounding)
Overvoltage
Ground directional overcurrent
Neutral overcurrent
Transformer differential
Negative sequence (voltage, current)
Directional overcurrent
Reverse power flow
Zero sequence
Generator (loss of excitation, differential)
Distance relay
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DG islanding detection – requirements
 Unintentional islanding defined as DG continuing to energize part of
distribution system when connection(s) with area-EPS are severed
(also referred to as “loss of mains”)
 IEEE 1547 - the DG shall cease to energize the Area EPS circuit to
which it is connected prior to reclosure by the Area EPS
 Repercussions of an island remaining energized include:
 Personnel safety at risk
 Poor power quality within the energized island
 Possibility of damage to connected equipment within the island,
including DG (due to voltage and frequency variations)
 Utility grid codes may allow islanded operation during major
outages – may help restore service in distribution system
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Islanding detection techniques – passive
 Passive approaches
 Frequency relays (Under/Over-frequency) - use of the active power
mismatch between island load and DG production levels
 Voltage relays (Under/Over Voltage) - based on voltage variations
occurring during islanding, resulting from reactive power mismatch
 ROCOF relays (Rate Of Change Of Frequency – resulting from real
power mismatch in the case an island is created
 Reactive power rate of change – resulting from reactive power
mismatch in the case an island is created
 Other approaches
 Active protection – based on difference in area-EPS response at DG
site when islanded; injection of signature signals at specific intervals
 Communication-based protection – using a communication link
between DG and area EPS (usually at the substation level) to convey
info on loss of mains (and possibly activate a transfer-trip)
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Alternative approach – intelligent relays
 Alternative (intelligent) proposed approach – passive, using only
measured signals (current, voltage and derived signals)
 Use of a multivariate approach to develop a data base of islanding
patterns
 Use of data mining to extract features from the running of a large
number of operating conditions (normal) and contingencies (faults)
 Use of extracted features to develop decision trees that define relay
settings
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DG variables monitored – multivariable approach
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Feature extraction – methodology
 Data Mining – a hierarchical procedure that has the ability to
identify the most critical DG variables for islanding pattern
detection, or protection handles
 Decision Trees – define decision nodes; every decision node uses
different DG variables to proceed with decision making on
identifying the islanding events
 Training data set – islanding (contingencies) and non-islanding
events
 Time dependent decision trees generated – extracted at different
time steps up to the maximum time considered/allowable
 Choice of decision tree for relay setting (best) – based on
Dependability (ability to detect an islanding event as such) and
Security (ability to identify a non-islanding event as such) indices
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Performance requirements – islanding detection
 Requirements - defining maximum permissible islanding detection
time (typically 0.5 to 2 s)
 Performance indices
 Dependability and Security indices
 Speed of response, or detection time
 Existence of non detection zones
 Constraints
 accounting for Interconnection Protection response times (reclosers)
 detection of islanding and tripping before utility attempts reclosing (out
of phase reclosing may be damageable)
 Nature of relay and impact on performance requirements – short
circuit detection needs to be faster that islanding detection – allows
additional to refine the decision tree
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Real Time Simulator set up – basic relay testing
Slave subsystem #1
Distribution
system
Part 1
Utility
B-1
B-2
T1
CB-1
SC level:
1000MVA
X/R: 10
Slave subsystem #2
B-8
B-18
Distribution
system
CB-2
15 MVA
120k- 25kV
B-9
L-1
L-10
CB-4
Part 2
L-11
B-10
15 MVA
2.4kV- 25kV
T2
B-11
DG
10MVA
Master subsystem
Islanding
relay
Feature
Extractor
Decision
Tree
Voltage and
Current at
DG end
Tripping
Signal
Islanding protection relay
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Decision trees – typical results
Δf ≥ 0.16
YES
NO
Islanding
Δf ≥ -0.1
NO
YES
Islanding
Q ≥ 0.1
NO
YES
Non-Islanding
Δf < 0
NO
Islanding
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YES
Non-Islanding
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Comparative performance – relay settings
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Protective Device
Setting
Time delay
Intelligent
Decision Tree
100 ms
Under Frequency
59.7 Hz
100 ms
Over Frequency
60.5 Hz
100 ms
ROCOF
0.1,0.25,0.5 Hz/s
0ms, 50ms
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Dependability indices – comparative evaluation
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Security indices – comparative evaluation
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Non detection zones – comparative evaluation
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Feasibility and performance of intelligent relays
 The proposed data mining approach is capable of
 Identifying the DG variables that capture the signature of islanding
events, in any given time interval
 Recommending variables and thresholds for protection relay setting
 The islanding intelligent relay
 Operates within prescribed time requirements (or faster)
 Can be configured for delayed operation possible
 Dependability and security indices typical better than existing passive
techniques
 Offers improved performance, including smaller non detection zones
 Can be configured for different types of DG (rotating and power
converters based), multiple DG systems and mixed DG type systems
 Can also be used for short circuit detection (including high impedance
faults) and other types of faults
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Impact of DG technology on protection design
 DG operation dependent upon the type of generator used
 Rotating converters: synchronous and induction generators
 Static power converter interfaces (inverter based): wind turbine (Type
4), solar power converters
 Mixed: doubly-fed induction generators (wind turbine, Type 3)
 Impact of the type of generator connected to the grid on protection
design
 Short circuit level – typically lower in inverter based systems (1-2 pu)
 Transients – fully controlled in inverter based systems, dependent on
controller settings
 Speed of response of real and reactive power injection – typically much
faster in inverter based systems
 Real and reactive power capability and control – independent control in
inverter based systems
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DER integration – opportunities in microgrids
 DER integration into distribution systems
 As individual systems, either generation or storage, connected to a
feeder or in a substation
 Integrated into a self managed system, or microgrid
 Aggregated to form a Virtual Power Plant
 Microgrid definition – a distribution system featuring
 Sufficient local generation to allow operation in islanded mode
 A number of distributed generators and storage systems, including
generation based on renewable energy resources
 A local energy management system
 A single connection to the electric power system, with possibility of
islanded operation
 The controllers required to allow connection and disconnection and
interaction with the main
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Microgrid – types and uses
 Microgrid deployment drivers – general and current
 Increasing the resiliency and reliability of critical infrastructure and
specific entities, in the context of exceptional events (storms) –
reducing dependence on central generation and the transmission grid
 Facilitating the integrating renewable energy resources – managing
variability locally
 Taking advantage of available local energy resources – renewables
and fossil fuels (shale gas)
 Reducing greenhouse gases and reliance on fossil fuels – costs
 Types, applications and loads
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Military bases – embedded or remote
Large self managed entities – university campuses, prisons
Industrial and commercial installations
Communities – managing storage and generation locally
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Isolated/autonomous grids – applying DER
Solar
Wind
Battery
storage
Distributed
Energy
Resources
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Photovoltaics
Isolated
Microgrid
PCS
Wind
generator(s)
ESS
Diesel
plant
Grid
Interface
Community
loads
Synchronous
generator
Conventional
Generation
Dump
load
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Benefits of storage and demand response
 In conjunction with renewable DG
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Reducing power variations in variable and intermittent generation
Ability to provide voltage support and voltage regulation
Enabling operation of DG at peak power and efficiency
Power quality – voltage sag and flicker mitigation
Possibility of islanded operation – microgrid operation
 Distribution system benefits
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Ability to dispatch/store energy and manage peak demand
Reduced line loading – managing line congestion
Frequency regulation, black start, reactive power
Ability to provide other ancillary services
Ability to perform arbitrage on electricity prices – market context
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Electrical storage technologies
Discharge
Period (h)
10.000
1.0000
CAES
Redox
Flow
0.1000
Lead
Acid
Battery
Flywheel
0.0100
Double
Layer
Capacitor
0.0010
0.0001
0.001
NaS
0.01
0.1
Pumped
Hydro
SMES
1
10
100
1000 10000
Power Rating (MW)
Source: Fraunhofer UMSIGHT
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Demand response – characteristics
 Available loads
 Electric hot water heaters – thermal storage
 Other curtailable loads – on critical
 Electric vehicle battery storage systems
 Features of loads
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Dispersed – low power, large numbers are required
Availability – short duty cycles
Controllability – usually only in curtailment, possibly as additional laod
Duration of service – limited curtailment
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Storage vs demand response – interchangeable?
 Demand response
 Benefits: instantaneous response
 Drawbacks: unavailability, discrete control, requires a large number of
loads (stochastic behavior)
 Others: no power quality issues, but discrete steps
 Operational: energy restoration time management
 Implementation, hardware: minimal
 Electrical storage
 Benefits: fully controllable, can inject energy into the system
 Drawbacks, implementation: complex, requires power electronic
converters, life expectancy, maintenance
 Other: losses (standby), energy efficiency
 Operational: recharging management
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Distributed energy reources – scenarios 2020
 Scenario 1 – Low DG penetration (<10 %), connection mostly to the
MV grid – business as usual
 Reduction of impact on existing grid – power quality (flicker, voltage
variation)
 Source of power (MW) – limited contribution to voltage and frequency
regulation
 Islanding required in case of loss of mains
 Scenario 2 – Increase in DER penetration (> 20 %?), connection
mostly to the MV grid – individual or in microgrids
 Integration into the generation dispatch – need for monitoring and
forecasting production (wind and solar)
 Participation in ancillary services – voltage and frequency regulation
 Requirements to remain connected for temporary loss of mains – low
voltage ride through
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Distributed energy resources – scenarios 2020
 Scenario 3 – Increase in the penetration of DER, with connection to
the MV grid and the low voltage grid – PV panels, smaller units,
controllable loads, including electric vehicles
 For MV connections, same considerations as for Scenario 2
 For low voltage connections (residential, commercial), with a large
number of units, a number of outstanding questions
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Integration in generation dispatch – included?
Participation in ancillary services – frequency/voltage regulation?
Role of smart grids in managing a large penetration
Financial consideration – generation (feed-in tariffs), ancillary services
impacts on the grid – power quality (voltage rise), distribution system
loading
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