2014 pv distribution system modeling workshop: pro-active, high penetration pv studies on...

DNV GL © 2013 May 6th 2014 SAFER, SMARTER, GREENER DNV GL © 2013

May 6th 2014

Jonathan Flinn

Pro-Active, High Penetration PV Analysis on Distribution Systems

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PV Distribution System Modeling Workshop

Santa Clara, CA

DNV GL © 2013 May 6th 2014

Contents

Introduction

Objectives of Analyses

Overview of Approach

Technical Criteria

Analysis in SynerGEE

Modeling Advanced Inverter Functions in SynerGEE

Conclusion

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DNV GL © 2013 May 6th 2014

Introduction – DNV GL

Merger of brands, consolidation of experience and expertise

3

DNV GL © 2013 May 6th 2014

An energy technology powerhouse

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Offshore wind Strong expertise in offshore wind, its support vessels and connection to the electricity grid

Innovation Strategic research in energy storage, smart grids and super grids; developments of new standards through joint industry projects

Testing Global leader in testing, inspecting and certifying high-power and renewable energy equipment with world class laboratories

Expert advice In onshore and offshore wind power, solar, smart grids, super grids, infrastructure resilience, energy markets, regulations and use

Power player A strong player across the value chain: renewable and conventional power generation, transmission & distribution and sustainable energy use

DNV GL © 2013 May 6th 2014

Introduction – Jonathan Flinn

MEng Mechanical Engineering with Aeronautics, University of Strathclyde, 2004

MSc Safety, Risk and Reliability Engineering, Heriot-Watt University, 2005

9 years in DNV GL

Worked with pipelines, wind energy, arctic operations, wave and tidal energy

Worked in transmission and distribution since 2011

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DNV GL © 2013 May 6th 2014

Introduction – Pro-Active Approach

Developed in co-operation with HECO

Aim to streamline PV interconnection process

Objectives:

– Improve PV interconnection process

– Identify limits on a circuit-specific basis

– Facilitate efficient network planning

– Identification of limits in advance

– Identify existing risks

– Compare limits with existing PV penetrations

– Identify future limits to PV integration

– Run hypothetical future PV scenarios up to high PV penetrations

– Identify appropriate mitigation measures

– Developed from list of potential mitigation measures

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DNV GL © 2013 May 6th 2014

CA Rule 21

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Complete application received

Screen 1: Connection to distribution system?

Screen 2: Connection to network

Screen 3: Export power causes reverse flow at

voltage regulation devices

Screen 4: Is the aggregate generating facility on

the line section <=15% of line section peak load

Screen 5: Is voltage flicker and/or voltage drop

due to project within IEEE 519 limits

Screen 6: DG <= 10kW

Screen 7: Inverter-based DG <= 250kW meets IEEE 1547 & UL 1741

Screen 8: SCCR within acceptable limits

Screen 9: Interconnection compatible with line

configuration

Perform

Supplemental Review

Does not qualify for

interconnection under Rule

21

Does supplemental

review determine

requirements?

Company provides the

cost estimate and

schedule for IRS to

determine requirements

Generating Facility

qualifies for

interconnection subject

to requirements, if any,

determined by

supplemental review

Generating

Facility qualifies

for Simplified

Interconnection

no

no

no

yes yes

no

no

yes

yes

yes

yes

no

no

no

no

yes

yes

yes

yes no

DNV GL © 2013 May 6th 2014

CA Rule 21

8














configuration

Perform

Supplemental Review



21

Does supplemental

review determine

requirements?


cost estimate and

schedule for IRS to


Generating Facility

qualifies for



determined by

supplemental review

Generating

Facility qualifies

for Simplified

Interconnection

no

no

no

yes yes

no

no

yes

yes

yes

yes

no

no

no

no

yes

yes

yes

yes no

Pro-active approach identifies at which PV penetrations this will occur for each feeder/transformer

DNV GL © 2013 May 6th 2014

CA Rule 21

9














configuration

Perform

Supplemental Review



21

Does supplemental

review determine

requirements?


cost estimate and

schedule for IRS to


Generating Facility

qualifies for



determined by

supplemental review

Generating

Facility qualifies

for Simplified

Interconnection

no

no

no

yes yes

no

no

yes

yes

yes

yes

no

no

no

no

yes

yes

yes

yes no

Pro-active approach identifies specific limitations for each feeder/cluster due to different criteria (thermal loading, voltage violations, etc.),

DNV GL © 2013 May 6th 2014

CA Rule 21

10














configuration

Perform

Supplemental Review



21

Does supplemental

review determine

requirements?


cost estimate and

schedule for IRS to


Generating Facility

qualifies for



determined by

supplemental review

Generating

Facility qualifies

for Simplified

Interconnection

no

no

no

yes yes

no

no

yes

yes

yes

yes

no

no

no

no

yes

yes

yes

yes no

Identification of areas of risk/interest for the feeder, allows focus of analysis on circuit-specific issues

DNV GL © 2013 May 6th 2014

System Boundaries

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Example of system

boundary

One sub-transmission

line, plus all

connected distribution

feeders

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Analysis Approach

Model load independently of solar

– Requires some manipulation of

demand data

Find peak and minimum daytime load

days

Run analyses with varying penetrations

of PV

Use linear interpolation to find

technical limits

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Analysis Approach

Use combinations of load profile and PV penetration

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Load Scenarios

1. Peak Daytime Load

Day

2. Minimum Daytime Load Day

PV Penetration Scenarios

1. No PV 2. Existing PV 3. Existing + Queued PV 4. PV = 15% of Peak Load 5. PV = 30% of Peak Load 6. PV = 50% of Peak Load 7. PV = 75% of Peak Load 8. PV = 100% of Peak Load 9. PV = 135% of Peak Load

DNV GL © 2013 May 6th 2014

Technical Criteria

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Technical Criterion Limit or Trigger

Steady-State Voltage V > 1.05 p.u. or V < 0.95 p.u.

Thermal Loading Loading > 100%

Backfeed Reversal of flow through transformer

Fault Current Available fault current exceeds breaker interrupt rating

Transient Voltage Voltage change > 3% during step change in PV output

Dynamic Voltage Overvoltage / undervoltage due to inverter trips during N-1

Dynamic Frequency Additional load shedding due to inverter trips during N-1

LTC Cycling Increase in LTC operations due to PV operation

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LTC Cycling Studies

An increase in LTC cycling due to PV is not necessarily a significant problem

– If it causes 1 extra operation per week, still very small change

At some point it could become a problem, causing decrease in time between

maintenance, and LTC lifetime

– Number of increased operations per year can be calculated for each PV

penetration, and compared against a limit defined by utility

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Number of Events

Change in Irradiance [W/m2s]

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LTC Cycling Studies

A reverse effect must also be studied:

– PV operation causes reduced current through LTC compared to no-LTC case

– Reduced current may increase LTC contact lifetime

– This effect reverses past point of backfeed, where increased PV causes

increased current

– Chart below comes from Kaukesha UZD LTC Technical Manual

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Analysis in SynerGEE – Model Setup

Load and generation on utilization circuits

aggregated to distribution transformers

PV modeled as generator in SynerGEE (not

negative load)

– Necessary for fault analysis

– Also allows use of irradiance profiles

Existing generators modeled in existing

locations

Hypothetical ‘future’ generators placed by

analyst to allow up to 150% PV Penetration

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DNV GL © 2013 May 6th 2014

Analysis in SynerGEE – Recipe Scripts

SynerGEE allows use of automated

analysis

– Consecutive load flows run using

‘recipe’ commands

– Outputs saved to specified location

– Ideal for use with 24-hour load profiles

Model Cleanup scripts can be used to

make changes between analyses

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Analysis in SynerGEE - Solver

SynerGEE add-on which further increases flexibility

Allows changes to be made to model (more than Recipe or ModClean)

Compiles and post-processes results

Requires some basic programming skills

Flexibility is useful in Advanced Inverter Modeling

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Mitigation of PV Impacts

Mitigant Backfeed Loading Voltage LTC Cycling

Fault Current

Dynamics Transients

Energy Storage X X X X

Curtailment X X X X

Inverter power factor control

X

Inverter disconnection and re-closing control

X X

Equipment upgrades

X X X X

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Energy Storage

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Load > PV:

Load is fed by grid

PV > Load:

Load is fed by PV

PV > Load:

Excess PV charges

battery

Load > PV:

Load is fed

by battery

Mitigates: Backfeed Violations, Voltage Violations

Energy storage systems can be used to prevent backfeed from occurring

Simple model in SynerGEE

is to calculate total reverse

power flow and energy

New battery model in

SynerGEE 5.1 will allow

individual batteries to be

charged and discharged

DNV GL © 2013 May 6th 2014

Curtailments

Curtailment is a smart inverter function

Allows utility to either:

– Reduce output from generator to solve problem

– Disconnect generator completely

Cost to utility is cost of ‘lost’ energy to generator

Simple model in SynerGEE is same as for energy storage:

– Calculate total energy that would be curtailed to prevent backfeed

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Inverter Power Factor Control

Increasing or decreasing VAR output from inverter can regulate local voltage

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Single time-step can easily be

modified in SynerGEE

Automation can run multiple

time-steps consecutively and

identify local voltage problems

using Solver:

Run load flow

Voltage

violation?

Reduce inverter

power factor

Move

to next

time-

step

No

Yes

Complexity of process can be increased

In practice staged reduction in power factor will

be necessary to prevent over-correction

DNV GL © 2013 May 6th 2014

Inverter Disconnection and Re-Closing control

When trips and transient events happen, loss and return of all generators at once

can cause problems due to time delay on LTC

Smart inverters provide options:

– Ramp up of output

– Variable trip settings

– Variable re-closing settings

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DNV GL © 2013 May 6th 2014

Conclusion

Pro-Active Approach can help to streamline PV interconnection process

– Can also help to plan equipment upgrades

Analysis performed in SynerGEE allows flexibility to modify process

– Also allows automation of analysis and post-processing

Flexibility of SynerGEE also allows approximation of advanced and smart inverter

characteristics

– Integration with energy storage

– Curtailment

– Power factor control

– Output ramping

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DNV GL © 2013 May 6th 2014

SAFER, SMARTER, GREENER

www.dnvgl.com

Thank you for your attention

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Jonathan Flinn

[email protected]

(925) 327-3044

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