Transcript Impact of DER on Distribution Systems

Impact of DER on Distribution
Systems
Jens Schoene| [email protected]
June 14, 2016
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Who we are
 EnerNex is an engineering consulting company with headquarter in
Knoxville, TN.
 Power System Studies
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Power Quality
Wind and Solar (design, generator modeling,…)
Safety (arc flash, grounding, electromagnetic coupling)
T&D (bulk system analysis, SSR, CSS)
 Smart Grid Engineering Studies
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Advanced Metering Infrastructure (AMI)
Enterprise Architecture
Cyber Security
Microgrid Development
Utility Communication
Grid Modernization Roadmaps
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Jens Schoene
Director of Research Studies - EnerNex
Joined EnerNex in 2007
M.S. & Ph.D., Electrical Engineering,
University of Florida
Dipl.-Ing., Electrical Engineering, University of Paderborn
Areas of expertise are
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transient and harmonic analysis of power systems,
distributed generation interconnection studies,
induction studies,
lightning studies, and
arc flash studies.
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Outline
Impact of DER on Distribution Systems
DER Fundamentals and Recent Developments
DER-Caused Issues and Benefits
Purpose of Simulations
Simulation Tools
Simulation Challenges
Case Study
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DER Fundamentals and
Recent Developments
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Distributed Energy Resources (DER)
DER include Photovoltaics (PV), Storage, Small
Wind, Natural gas fuel cell, Natural gas Co-gen,
Biomass, Biogas, Diesels and Gasoline Engines,
Gas Turbines, Small Hydro Impoundments, Run
of the River Hydro
Can be broadly
classified based on
Energy Source &
Dispatch Capability
Some have inverters
some don’t.
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IEEE 1547
Standard for Interconnecting Distributed Resources
with Electric Power Systems.
Early version hindered leveraging full potential of
DER (no active voltage regulation, trip requirements).
2014 Amendment relaxed requirements.
Full revision of IEEE 1547 in progress.
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Thrusts in Next Revision of 1547
Enhanced voltage regulation and frequency regulation
(governor) characteristics, including mandatory DER
reactive power capability, and control functions (e.g.,
voltage regulation) to utilize this capability.
Mandatory voltage (i.e., fault) and frequency disturbance
ride-through capabilities.
Models and model verification testing.
Expanded testing of short-circuit and overvoltage behavior.
Increased communication and interoperability
requirements.
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California’s Rule 21 Smart Inverter
Requirements
All new inverters required to have “Phase 1”
capabilities:
– Revise the anti-islanding protection to include voltage ride-through
settings
– Default settings for under-/overvoltage ride-through
– Settings for under-/overfrequency ride-through
– Dynamic volt/var operations requirements
– Ramp rate requirements
– Fixed power factor requirements
– Reconnection by soft-start method
Future Phase 2 and Phase 3 focus on
‘Communication’ and ‘Advanced Smart Inverter’
capabilities, respectively.
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DER-Caused Issues &
Benefits
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What are the potential issues?
Category
Issue
Reverse
Overcurrent protection gets “confused” -> false trips, no trips
Power & Fault
Current Flows Line regulators get “confused” -> high/low voltage on DG side
Capacitor switching, Load Tap Changer (LTC) operation, and line
Voltage Regulator (VR) operation caused by cloud shading.
Voltage
Flicker caused by cloud transients.
Fluctuation
Capacitor switching transients (synchronous closing, preinsertion impedance, point-on-wave)
Low/medium PV penetration -> PV offsets load thereby
Feeder
decreasing section loading
Section
High PV penetration -> PV may exceed base load, capacity
Loading
sufficient to distribute surplus power?
Power Losses PV changes loading (see row above). Impact on losses
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… more potential issues.
Category
Issue
Unintentional Utility system reclosing into live island may damage switchgear
Islanding
and loads.
Ground Fault
Single-phase fault -> TOVs on unfaulted phase.
Overvoltage
Harmonics
Harmonics caused by PV inverter
Dynamics
Effect of fast transients caused by cloud shading and system
disturbances. Dynamic interaction of transients with other
conventional and non-conventional control devices.
Unwanted
Control
Interaction
Uncoordinated control actions (e.g., Volt/Var control) between
autonomously acting inverters causing unwanted oscillatory
behavior (hunting).
Feeder
Imbalance
Imbalance caused by uneven distribution of PV causing Neutralto-Earth voltages, Overloaded Neutrals
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DER not just a challenge for
distribution
14 GW Ramp
in ~3 hours
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What are the potential benefits?
Category
Voltage
Control
Benefit
Dynamic control of feeder voltage to
1) keep voltage within acceptable limits and
2) smoothen DER-caused voltage fluctuation.
Ability to create arbitrary load shapes to meet operation needs to
1) shift peak load,
Power Flow 2) prevent steep rises in load demand due to non-coinciding DER
generation peak and load peak (“duck curve”),
3) reduce losses, line loading, etc.
Independent operation of portions of the grid and critical facilities
Reliability
(microgrid) => increasing reliability during disaster.
Economics
Make excess energy generated and/or stored by DER available for
the wholesale market.
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CEATI Gap Analysis: Utility Survey
http://www.ceati.com/projects/publications/publication-details/?pid=50%2F124
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Purpose of Simulations
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Why simulations?
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Purpose
Predict & Mitigate Issues
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Simulation Tools
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Tool Selection:
Lot’s of Tools
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Let’s Categorize…
Operational Tools
Online operation
Facilitate real-time operational
decision.
DMS, Gridiant’s GRIDview,
PowerAnalytic’s Paladin Live, etc.
These are the tools
of our trade.
Planning/Analysis Tools
Offline simulations
Facilitate planning/design decisions
Look at ‘what if’ scenarios
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Planning/Analysis Tools
Steady-State Quasi Steady- Dynamic Analysis
Analysis
State Analysis
Simulation
Time Step
“Snapshot”
Many
“Snapshots”
Generator
Model
Current or
Current or
Voltage Source Voltage Source
Order of
milliseconds
Order of microseconds
Average (RMS)
Model
Transient Model
Typically Positive
Sequence
Full Sequence
Medium
High
Very High
Short Circuit
Time-of-day &
Annual
Simulations
Control system
dynamics
Switching/lightning
surges
Stability
Control interaction
CYME,
OpenDSS
CYME,
OpenDSS
PSLF, PSS/E
EMTP-RV, PSCAD,
DigSILENT
Balanced / Positive or Full Positive or Full
Sequence
Imbalanced Sequence
Complexity
Low
Application Power Flow
Tools
Transient Analysis
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Planning/Analysis Tools
Steady-State
Analysis
Quasi SteadyState Analysis
Dynamic Analysis
Transient Analysis
Increase in Fault Current Contribution due to Addition of PV
vs. Distance from Substation (OpenDSS)
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Increase in fault current, %
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2
1
0
-1
0
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Distance, mi
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Planning/Analysis Tools
Steady-State
Analysis
Quasi Steady- Dynamic Analysis
State Analysis
Transient Analysis
Reverse Power Flow due to Presence of PV and Load Drop (OpenDSS)
Total Power (Case 2)
10
MW (PV)
MW (No PV)
Load
Drop
Power
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Load
Back
0
- 2.8 MW
Reverse Power Flow Region
-5
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Time of Day
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Planning/Analysis Tools
Steady-State
Analysis
Quasi Steady- Dynamic Analysis
State Analysis
Transient Analysis
Fault Response from a PV Plant (PSLF, 2nd Generation PV Model)
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Simulation
Measurement
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Current (pu)
0.35
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0.33
0.32
0.31
0.3
0.29
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Time (s)
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Planning/Analysis Tools
Steady-State
Analysis
Quasi SteadyState Analysis
Dynamic Analysis
Transient Analysis
Short-circuit contribution from PV to a 100 ms 2L-G fault.
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“Right Tool for the Job”
Study
Tool
Power
Flow,
balanced
Power
Flow,
unbalanced
Short
Circuit
Protection
Coordination
Arc
Flash
Harmonic
Analysis
Transient
Analysis
Dynamic
Analysis
Quasi
SteadyState
State
Estimation
Operational
Control
ATP, PSCAD,
EMTP-RV,
Simulink
Aspen, Cape
DesignBase,
Gridiant
NexHarm
PSLF, PSS/E
OpenDSS
GridLAB-D
CYMEDIST
DigSILENT
PSS/SINCAL
Nexant
Grid360
Best choice
Can be done, but not preferred choice
Cannot
bewww.enernex.com
done
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Simulation Challenges
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Simulation Challenges
Modeling PVs
PV generators are complex devices.
Many different types
of inverters out there –
difficult to get information
needed for modeling them
in detail.
Need to fit the complexity
of the model to problem.
Model need to be able to simulate smart inverter controls
– Customizable Volt/Var and Volt/Watt control curves
– Account for over-/undersizing of inverters
– Closed loop control
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Simulation Challenges
Dealing with large systems
Building them requires highly detailed system information
and can be tedious.
System size can cause convergence issues.
Computational intensive
(hours or days for one
simulation run).
Investigated issues often
highly dependent on
system.
Residential Feeder
Where to put future PV?
with Rooftop PV
Model secondary system.
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Simulation Challenges
Variability happens on many time scales
Decades (Small Variation):
- Solar cycle
- Insignificant for PV Studies
Months (Large Variation!):
- Seasons
- Necessitates Annual Simulations
Hours, Minutes, Seconds
(Very Large Variation!!):
- Cloud Transients
- Time of Day
- Necessitates Daily
Simulations with High
Temporal Resolution Data
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Simulation Challenges & Solutions
Lots of Feeders
with Different
Characteristics
Prototypical Feeder Approach
Categorize distribution feeders in categories and model
prototypical feeder for each category.
Large Feeders
Automated Conversion of System Models
Using Matlab to convert feeder with 1000s of buses to
OpenDSS. Each PV system & load explicitly modeled.
PV Causes Issues at
the Customer
Model Secondary System
Explicitly model system from service transformer to PV
location / consumer.
Daily and Seasonal
Variability
Daily & Annual Simulations with Solar Data
Needed to account for varying solar irradiance levels, which
change seasonally and daily.
Variability due to
Clouds
Model Geospatial Diversity
During cloudy conditions, individual PV systems see different
irradiance levels.
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Case Study
Impact of PV on Primary System
http://calsolarresearch.ca.gov/funded-projects/65-improving-economics-of-solarpower-through-resource-analysis-forecasting-and-dynamic-system-modeling
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Distribution Feeder Topology
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Automatic System Conversion
SynerGEE
CYME
EMTP-RV
Centralized Data
Format In MATLAB
Based on OpenDSS
OpenDSS
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OpenDSS
File
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Variability due to clouds
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Simulation Fidelity Matters
Four scenarios that vary
with (1) PV penetration
level and (2) PV location.
Six cases with varying
modeling assumptions
& input data.
Case #4 closest to
reality.
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Summary
Accurate models & methodologies needed for
– Determining DER hosting capacities,
– Evaluating performance of smart inverters (and other
advanced technologies),
– Determining distribution system upgrade requirements.
Main challenges include modeling
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Inverter models (faults, dynamics, controls),
Large systems (primary and secondary),
Solar variability (e.g., geospatial diversity), and
Simulation Tool Selection.
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Discussion
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