Distributed Energy ResourcesOperational Impacts

Jenny Riesz

Principal, Operational Analysis & Engineering

About AEMOWe operate Australia's National Electricity Market and power grid in Australia’s eastern and south-eastern seaboard, and the Wholesale Electricity Market and power grid in south-west WA.

Both markets supply more than 220 terawatt hours of electricity each year.

We also operate retail and wholesale gas markets across south-eastern Australia and Victoria’s gas pipeline grid.

Collectively NEM & WEM traded over A$20 billion in the last financial year.

Ownership

Marketparticipants

40%Governments of Australia

60%

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Growth in DER

Rooftop PV

Storage

AEMO’s forecast for the NEM:

• Distributed Energy

Resources (DER) are

growing rapidly

• The transition to

decentralised resources

could represent the

most significant power

system transformation

since it was established

3

Context

Rooftop PV

Minimum demand in South Australia:

4

DER generation will soon match

entire demand in some NEM

regions.

• What will this mean for the

power system?

• How do we affordably

maintain security and

reliability for customers

throughout this transition?

• What actions do we need to

take?

Technical challenges

Voltage management

• Emerging challenges

managing

transmission &

distribution voltages at

times of low

operational demand

Visibility

• Need for collection of

standing data on DER

installed for

forecasting, system

planning, and stability

studies

VPP management

• Unmanaged rapid

movement of large

virtual power plants

could cause increased

need for frequency

control, and system

security challenges

Orchestration

• Need for coordination

between AEMO and

distribution networks

in DER dispatch

Emergency Frequency

Control Schemes

• Emergency Frequency

Control Schemes and

special protection

schemes may no

longer operate

successfully under

high rooftop PV

conditions

System restoration

• Unmanaged DER

operation may

interfere with

progressive restoration

of load during a

system restart process

System Strength

• Potential for system

strength challenges to

emerge at the

distribution level,

affecting DER

operation, protection,

etc.

PV feed in management

• Need for mechanisms

to actively manage

and optimise DER

generation to maintain

dispatch flexibility

A suite of technical

challenges identified,

requiring action to

maintain system security

for customers.

Performance standards

• Need for review of

performance

standards for DER to

ensure they

adequately support

system security needs

Dynamic models

• Dynamic models do

not generally capture

the behavior of DER

during disturbances

with sufficient

accuracy.

Focus on these two in

this presentation

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Disturbance ride-through • Disturbance ride-through essential for maintaining power

system security

• Problematic DER behaviour identified for:

• Voltage disturbances

• Frequency disturbances

• Voltage phase angle jump (instantaneous phase shift in sinusoidal voltage waveforms)

• Widespread disconnection of DER during disturbances could lead to system black

• Must be addressed prior to installation via appropriate performance standards

• Following slides present case studies and issues identified

• This is work in progress! Preliminary results only.

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Voltage disturbances

3rd March 2017Demand in South Australia:

• Series of faults resulted in the loss of

~610 MW of generation in SA

• Flows on Heywood interconnector

increased to ~918 MW.

• Estimated that demand reduced

~400 MW

• Estimated that distributed PV

reduced by ~150 MW (40%)

• Loss of more PV would have

increased flows on Heywood

interconnector further.

Analysis by Naomi Stringer, UNSW Sydney

Data from Solar Analytics

Generation by distributed PV:

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Data from Solar Analytics

(~200 distributed PV

systems) confirms

disconnection of some

inverters:

18th January 2018

• Fault on 500 kV network in

Victoria

• ~160 distributed PV sites

monitored by Solar Analytics

• Aggregate distributed PV

generation observed to reduce by

28% (~180 MW loss estimated

across VIC).

Analysis by Naomi Stringer, UNSW Sydney

Data from Solar Analytics

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Bench testing of PV inverters

• Bench testing program• Collaboration with UNSW Sydney, funded by ARENA

• Laboratory conditions

• Tested 5 inverters so far (preliminary findings)

• Voltage testing results:• Two inverters observed to trip during a short duration voltage sag. Need to clarify

in standard.

• Only 1 inverter performed Volt-Watt response correctly. The other 4 inverters were either too slow, or result in a disconnection. Need to clarify in standard.

10Bench testing by UNSW Sydney as part of an ARENA-funded collaboration with AEMO, TasNetworks & ElectraNet

Frequency disturbances

Frequency disturbances

Analysis by Shabir Ahmadyar, UNSW Sydney

Data from TasNetworks

25 Aug 2018, 1:11pm

Estimated PV capacity factor: 44%

Possible reduction in PV generation: 18%

13 Aug 2018, 8:43am

Estimated PV capacity factor: 21%

Possible reduction in PV generation: 48%

• Frequency disturbances recorded at a

primarily residential feeder in

Tasmania

• Frequency falls to below 49Hz over

~5s

• Active power supplied to the feeder

increases suddenly

• Further investigation underway to

determine whether this is due to DER

disconnection, and whether this

feeder is representative of all

Tasmanian PV

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Bench testing of PV inverters• Laboratory conditions

• Preliminary frequency testing results:

• Two inverters observed to trip too quickly on under-

frequency.

• Appears to be a serious non-compliance with AS4777.2-

2015.

Under frequency ride-through

• One inverter tripped on RoCoF levels above 0.4Hz/s.

• RoCoF ride-through not addressed in standard at present

RoCoF

• One inverter responds slowly to an over-frequency (~30s)

• Strictly compliant with the standard, but not useful for

assisting with frequency management

Over-frequency droop

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Inverter trips in t < 50 ms

Grid frequency step 50 → 45Hz (Inv #2)

Bench testing by UNSW Sydney as part of an ARENA-funded

collaboration with AEMO, TasNetworks & ElectraNet

Emergency frequency control

• DER over-frequency droop response could become essential for system security

• Few centralised units operating at times of high DER generation – inadequate capacity to trip to

correct an emergency over-frequency

• Needs to be adequately fast

• Required in emergency situations where contingency size exceeds frequency reserves, typically

large disturbances, high RoCoF

• But slow enough to avoid mal-operation (need adequate time to measure a stable grid frequency)

• Could rapid ramp down of bulk rooftop PV cause distribution voltage issues?

• And could this lead to widespread PV tripping on under-voltage?

• Enable mandatory Volt-Var responses to allow DER to assist with local voltage management while

responding to frequency?

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Phase angle jump

Phase angle jump

Voltage phase

jump magnitudeInverter 1 Inverter 2 Inverter 3 Inverter 4 Inverter 5

15° ✓ ✓ ✓ ✓ ✓

30° Disconnection

Temporary

reduction of power

injected to grid✓

Temporary

reduction of power

injected to grid✓

45° - - ✓ - ✓

90° - - ✓ - ✓

• Observed challenge in California for

utility-scale PV

• Inverter mis-calculates frequency and

activates protection

• Addressed in IEEE 1547-2018 (requires

ride-through for up to 60° jump)

• Bench testing indicates this applies

for distributed PV inverters in the

NEM for voltage phase angle jumps

• Unclear the degree to which phase

angle jump may be visible in the

distribution network

• Examining high speed data

Bench testing of

distributed PV

inverters: (preliminary

findings)

16Bench testing by UNSW Sydney as part of an ARENA-funded collaboration with AEMO, TasNetworks & ElectraNet

High speed data

• High speed data recorded at a local

distribution feeder in QLD, primarily

residential, high levels of distributed

PV

• Several events recorded with high

levels of distributed PV operating,

and see increase in load post

disturbance

• Further investigation to determine

whether this is due to DER

disconnection

• The voltage dip is very shallow.

Could be due to phase angle jump.

Further investigation underway.

15th Feb 2017, 10:34am

12th March 2017, 1:27pm

Analysis by Shabir Ahmadyar, UNSW Sydney

Data from Energy Queensland 17

Adaptation of DER standards

Possible changes to DER performance standards

• Extend as much as possible

Voltage ride-through

• Ride-through requirements for multiple

voltage disturbances

Multiple voltage disturbances

• Default enablement

• Determine relative priorities of control

schemes

• Consider smaller deadbands and settings

aligned with international standards

Volt-Var and Volt-Watt

• Determine appropriate requirements,

considering periods with most generation

from DER

Momentary cessation

• Extend as much as possible

Frequency ride-through

• Ride-through requirements for RoCoF

RoCoF ride-through

• Specify required response times

Over-frequency response

• Require response from already

curtailed inverters

• Specify response times

• Storage systems move to

discharging?

• Other loads (eg. electric vehicles)

Under-frequency response

• Specify ride-through requirements

Phase angle jump

• Emergency feed-in management,

remote querying of device settings,

remote changes to settings

Interoperability

• Review appropriate coverage, including

sizes & types of DER, and consumer

loads

Coverage

• Review compliance mechanisms

Compliance

• Device & architecture properties

Cyber security

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Voltage Disturbances: Frequency Disturbances: Other:

For consultation, implementation to be determined

DERWorkstream

Networkincentives

Datavisibility

System & Marketframework

Technical standards& connections

Operationalprocess

Industry-widecollaboration

Workstreamobjectives

Networkregulation &pricing facilitate DER andbetter customer serviceofferings.

Visibility of DER foroperational, forecasting,planning, and market(incl settlement) functions.

A consistent access regime for all market participants within the confines of customer consent and privacy.

Integrate DER into energy,ancillary and reserve markets.

Market arrangements recognise non-retailer models, including third-party/aggregator concepts.

Evolve market arrangement to a distributed market model.

Where appropriate,a nationally consistentapproach to DERconnections anddevelop DERtechnical standards.

To better understandoperational challenges and DER capabilities to inform operationalprocesses and tools.

Enablers Pilot programs

Cyber security

Digital & Technology Strategies

Integrating DER to maximise consumer value

Industry working together to deliver outcomes for consumers

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•DER represents a significant transition for the electricity

industry

• The impact of DER on power system security must be

considered as a priority

•By identifying challenges early, we can implement the

measures required to affordably maintain security and

reliability for customers throughout this transition

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