advanced inverter functionality to support grid

Daniel Brooks, Aminul Huque, & Jeff Smith

PC Enhanced Inverters Stakeholder Meeting 2014 April 28

Advanced Inverter Functionality to Support Grid Reliability &

Related Interconnection Requirements Part 2

2© 2014 Electric Power Research Institute, Inc. All rights reserved.

Objectives & Agenda

Agenda: •Bulk System reliability impacts & needed inverter-based generation functionality

•Overview of Distribution System impacts

•Advanced inverter cost considerations

•Key take-aways from Apr 23-24 IEEE 1547 Mtg

•Q&A

Basic Understanding of Need for AdvancedReliability Services from Inverter-Based Generation


PJM Renewable Integration Study Scenario

14% RPS Scenario• Onshore Wind: 28.8 GW

• Offshore Wind: 4.0 GW

• Central Solar: 3.2 GW

• Distributed Solar: 4.1 GW

Recently reported study included scenarios rangingfrom 2% (BAU) to 30% energy from renewables

30% High PV Scenario• Onshore Wind: 47.1 GW

• Offshore Wind: 5.4 GW

• Central Solar: 27.3 GW

• Distributed Solar: 33.8 GW

April 28, 2014

Bulk System Reliability Impacts and Benefits of Inverter Generation Support


General Reliability Concerns

Reliability Functions• Reactive power/voltage control• Active power control

– inertia/primary freq response• Disturbance performance

– voltage & frequency ride through

Other Considerations• Inverter capabilities• Available headroom for wind/PV• Distribute

Inverter-Based Generators must supply Reliability Services as they

Displace Conventional

Sources of thosereliability services!

6 © 2014 Electric Power Research Institute, Inc. All rights reserved.

Wind/PV Reactive Support Range

• Plant requirements can differ – Reduced range at low

wind/PV levels

• Solar PV inverters over-sized for full range at max power output – historically distribution w/unity

PF control

• Dynamic vs. static capability – switched shunts often

included for static range – SVC/STATCOM may be used

for additional dynamic range

Typical Type 3/4 WTG VAR Capability Options

PV Capability (I limits) Vs. Triangle Require.


EPRI PV Voltage Control Project** ResultsImpact of PV Reactive Power Control

Terminal Voltage Control +/-0.95 PF

Terminal Power Factor Control

•Selected Bus Voltage -- July•High solar PV output •PF Control Lower Voltages•Voltage Control More Robust Voltages

**Bulk Electricity System Impacts of Distributed and Transmission System Connected Solar PV, EPRI, Palo Alto, CA: 2012. 1024349.


High Levels of Inverter-Based Generation Can Impact Frequency Stability

Graphics Source: LBNL-4142E Use of Frequency Response Metrics to Assess the Planning and Operating Requirements for Reliable Integration of Variable Renewable Generation, Prepared for Office of Electric Reliability Federal Energy Regulatory Commission, Dec 2010

Sudden Generation

LossNon-synchronous VG may provideinertia & primary

frequency response through power

electronics

VG may displace conventional units &

reduce system inertia & primary

frequency response


59.5

59.6

59.7

59.8

59.9

60

60.1

0 5 10 15 20 25 30 35 40 45

Freq

uenc

y (H

z)

Base(15%)

Base (20%)

Base(30%)

Base(40%)

Nadir

Settled Frequency

UFLS

EPRI Frequency Response Project (WECC)Impact of Wind Without Frequency Response

All Else Constant, as Wind Gen without Freq Control

replaces Thermal Gen, Freq Performance Deteriorates


EPRI Frequency Response Project (WECC)Benefits of Wind With Frequency Response

10

59.5

59.6

59.7

59.8

59.9

60

0 5 10 15 20 25 30 35 40 45

Freq

uenc

y (H

z)

Time (Seconds)

Base (No Wind Inertia and Droop)

With 4% Wind Droop

NadirSettled

Frequency

Frequency Response

135

140

145

150

155

160

0 5 10 15 20 25 30 35 40 45 50

Freq

uenc

y (H

z)

Time (Seconds)

With Wind Inertia (56% CF)Wind Recovery

MW Output of a Unit

Frequency Frequency

135

140

145

150

155

160

Freq

uenc

y (H

z)

59.5

59.6

59.7

59.8

59.9

60

0 5 10 15 20 25 30 35 40 45

Freq

uenc

y (H

z)

Time (Seconds)

Base (No Wind Inertia and Droop)

With Inertia (56% CF)Slow Recovery

Wind Providing Inertial Response

Wind Providing Droop Response

•Wind Inertia & Droop Control Improve Freq Performance•Controls must be tuned to ensure desired performance


ERCOT – Measured Wind Generator’s Response to Low Frequency

SOURCE: Sandip Sharma, ERCOT, “Frequency control requirements and performance in ERCOT ISO,” presented at EPRI/NREL/PJM Inverter Generation Interconnection Workshop, Apr 11-12, 2012.


SOURCE: Sandip Sharma, ERCOT, “Frequency control requirements and performance in ERCOT ISO,” presented at EPRI/NREL/PJM Inverter Generation Interconnection Workshop, Apr 11-12, 2012.

ERCOT – Measured Wind Generator’s Response to High Frequency


Frequency Ride-Through:Risk of Wide-Spread PV Disconnection

50.8

50.6

50.4

50.2

50.0

49.8

49.6

49.4

49.2

Grid

Fre

quen

cy in

Hz

Time in Seconds

0 10 20 30 40 50 60

Source: T. K. Vrana (2011)

Previous Interconnection Rules

German Operating Frequency Limit

Germany

As of 2012 PV Inverters were not required to provide

frequency support and disconnect from the grid if

the frequency reaches 50.2 Hz

This is similar to all current interconnection

requirements in US as per IEEE 1547-2003


Updated Interconnection Rules Reduces Risk of Frequency Instability

Source: T. K. Vrana (2011)

Germany50.8

50.6

50.4

50.2

50.0

49.8

49.6

49.4

49.2

Grid

Fre

quen

cy in

Hz

Time in Seconds

0 10 20 30 40 50 60

Updated Interconnection Rules

Previous Interconnection Rules

German Operating Frequency Limit

German Grid Code Change

Frequency control is required of all generators

Instead of disconnecting @50.2 Hz, gradually reduce active power output (droop curve) in proportion to the

frequency


Distributed PV Low Voltage Ride-Through PJM Example LVRT Impact

Source: Mahendra Patel, PJM.


Five Points Solar Station (inverters not equipped with LVRT)

5 MW PV

10 MW PV

1 M

W e

ach

1 MW each

5 MW PV 10 MW PV Westside Solar Station (inverters equipped with LVRT)

Schindler Sub; 12 kV

Bus

115/12 kV 30 MVA

Phase to Phase fault

Two phases slapped together Fault cleared in 6 cycles (0.1 s) Happened 4 times: 12:52 pm; 12:53 pm; 13:22 pm; 14:21 pm

LVRT – PG&E Experience

March 17, 2012


Voltage Drop to 50% of nominal

for 6 cycles (0.1 s)

Current continues during and after the event

Westside Solar Station with LVRT March 17, 2012 at 12:52pm


Inverters shut down

Voltage Drop to 50% of nominal

for 6 cycles (0.1 s)

Five Points Solar Station w/o LVRT March 17, 2012 at 12:52pm


Loss of 250 MW generation

for a normal 230 kV line fault?

Transmission Line Fault

March 31, 2014

Distribution Feeder Impacts and Inverter Support Benefits


Distribution System Impacts

Voltage• Overvoltage• Voltage variations

Equipment Operation• Feeder regulators• Load tap changers• Switched capacitor banks

Demand• “Masking” peak demand• Reducing power factor

System Protection• Relay desensitization• Unintentional islanding

Power Quality• Harmonics

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

7 8 9 10 11 12 13 14 15 16 17 18 19

Pow

er (p

er-u

nit)

Hour


= Line Regulators= Substation

0.95

0.97

0.99

1.01

1.03

1.05

1.07

1.09

0 60 120 180 240 300 360 420 480 540

Volta

ge (p

u)

Time (sec)

0.95

0.97

0.99

1.01

1.03

1.05

1.07

1.09

0 60 120 180 240 300 360 420 480 540

Volta

ge (p

u)

Time (sec)

Why are Smart Inverters Important?Smart Inverters Mitigating Voltage Issues

22

Voltage at END of feeder

No Control Volt/Var Control

360 420 480 540

*Simulated in OpenDSS


Use of Smart Inverters for Accommodating Large Number of Distributed PV Systems

Solar Rooftop PVSolar Rooftop PV

With volt/var control

Baseline – No PV

20% PV20% PV withvolt/var control

Customer Load Customer PV

VARs

Gen

erat

ed

Capacitive

Inductive

System Voltage

V1 V2 V3 V4

Q1

Q4

Q3 Q2

Volt-Var Control

24 Hour Simulation

Source: J. Smith, T. Key “High-Penetration PV Impact Analysis on Distribution Systems,” Solar Power International, Oct 2011

Initial analysis indicated 25%-100% more PV can be accommodated using

Volt/var control


Smart Inverters for Increasing Hosting Capacity of Distributed PV

PV at Unity Power Factor PV with Volt/var Control

2500 cases shownEach point = highest primary voltage

ANSI voltage limit

ANSI voltage limit

PV with Volt/var Control

ANSI voltage limitANSI voltage limitANSI voltage limit

Increasing penetration (kW)

Max

imum

Fee

der V

olta

ge (p

u)

PV at Unity Power Factor

2500 cases shown2500 cases shown2500 cases shown2500 cases shownEach point = highest primary voltageEach point = highest primary voltageEach point = highest primary voltageEach point = highest primary voltageEach point = highest primary voltageEach point = highest primary voltage

ANSI voltage limit

Max

imum

Fee

der V

olta

ges

(pu)

Increasing penetration (kW)

No observable violations regardless of PV size/location

Possible violations based upon PV size/location

Observable violations occur regardless of size/location

For voltage-constrained feeders, results indicate use of smart inverters can increase feeder hosting capacity for PV

Minimum Hosting CapacityMaximum Hosting Capacity

Minimum Hosting CapacityMax Hosting Capacity

Increasing penetration (kW) Increasing penetration (kW)

March 31, 2014

Cost Considerations for Advanced Inverter Functionality


Inverter Cost and Reliability Impacts PV System Performance

• Inverter cost is a small percentage of the total plant cost/installed cost

• Inverters with grid support functions are not expected cost any higher than current price once the interconnection requirements start incorporating the functional capabilities

• Communication (where needed!) cost will be additional

Average U.S. Utility-Scale PV Price Breakdown (May 2013)

Q1 2013 US PV System Cost Residential - $4.93/W

Commercial-scale - $3.92/W Utility-scale - $2.14/W

National average - $3.37/W

Sources: Sources: GTM Research/SEIA, NREL, Lawrence Berkeley National Lab, BNEF, European Photovoltaic Industry Assn (EPIA), BSW Solar


0

5000

10000

15000

20000

25000

30000

35000

Inst

alle

d PV

Cap

acity

(MW

p) in

Ger

man

y

Year

German Experience of High Penetration of PV

Bright, breezy Sunday between 2pm to 3pm

Grid at that time could take up to 45GW

PV and wind supplied 28.9 GW – more than half the

total!

Solar Wind

Conventional >100MW


0

25

50

75

100

125

150

175

200

225

2005 2010 2015 2020 2025 2030Inst

alle

d PV

Cap

acity

(GW

) in

USA

Years

What if Standards are not Changed?

Source: DOE SunShot Vision Study (Total PV Capacity in U.S. 2008 – 2030)

Retrofitting inverters in a later date could be pretty expensive

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=BoX_X6RFuz7noM&tbnid=gUdhedcs3SzrPM:&ved=0CAUQjRw&url=http://travelbabyonline.blogspot.com/2011/07/worlds-most-expensive-cities.html&ei=2QNfUpuVAsXHrQHjyYHQCw&psig=AFQjCNFydMIHeCzkmI8K6E7aLVE3FlkedQ&ust=1382044755158275

http://www.google.com/url?sa=i&source=images&cd=&cad=rja&docid=3y0j5paH6J6D0M&tbnid=TxDAgo6cXQ5dAM:&ved=0CAgQjRwwAA&url=http://www.techinasia.com/the-worlds-most-expensive-commercials-videos/&ei=jQNfUriNH4-EqQGGtYCABw&psig=AFQjCNEvTBSUfvhS8_5kHZegq99t8PRD5w&ust=1382044941594089

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=nwSL3DR_E5MyNM&tbnid=3aF13yJN68lg-M:&ved=0CAUQjRw&url=http://ashishlive.blogspot.com/2013/02/alarm-clock-myth-how-to-wake-up-early.html&ei=7fheUpXPN8asiQKO24CICQ&psig=AFQjCNHD1xHvn0Xk-X7vQNs9e694QaeoTA&ust=1382042188293736

March 31, 2014

IEEE Standard 1547 Revision Apr 23-24 Meeting Overview


IEEE 1547 Full Revision – 1st WG Meeting Highlights

• Around 90 stakeholders joined the meeting – 50% plus were from utilities including NERC and FERC – 25% were from manufacturers – Remaining were testing labs, national labs, and consultants

• Need for inclusion of abnormal voltage and frequency must ride thru in the standard was clearly expressed by majority – off course there were few exceptions

• Different ride thru requirements for inverter and rotating machines? • Remove or increase the standard’s existing limitation to aggregate capacity of

10 MVA or less? • Need for control, in addition to monitoring provision (for 250MVA and larger),

beyond certain size (yet to be discussed) ? • Revision is considering inclusion to two type tests – Short circuit & loss of

load behavior test • Next meeting (tentative) – June 24-25: 1547.1a & 26-27: Full rev. of 1547 – Most likely again in Las Vegas


Together…Shaping the Future of Electricity

advanced inverter functionality to support grid

Documents