© 2015 Electric Power Research Institute, Inc. All rights reserved.

Aminul Huque, PhD Technical Leader

Inverter Reliability Workshop 2015 NREL Photovoltaic Reliability Workshop – Golden, CO

February 25, 2015

Smart Inverter Grid Support Functions

and Potential Impact on Reliability

2 © 2015 Electric Power Research Institute, Inc. All rights reserved.

Smart Inverters

“There is an immediate need for new solar to be fitted with “smart inverters” to provide necessary voltage support to integrate effectively and prevent costly renovations and reliability impacts” – Western Electric Industry Leaders, Aug 2013

WEIL Western Electric Industry Leaders

3 © 2015 Electric Power Research Institute, Inc. All rights reserved.

DER Interconnection Standards and Guidelines IEEE 1547 and others are recognizing the importance of DER providing grid support …

2005

2011

FERC SGIP (Small Generator Interconnection Procedure)

IEEE 1547-2003 2003

2000 California Rule 21

Updated California Rule 21 (consistent with IEEE 1547-2003)

IEEE 1547a-2014 2014

2015 Updated California Rule 21

(goes far beyond IEEE 1547a-2014)

2018 IEEE 1547rev-201x

DER must disconnect in response to abnormal voltage/frequency condition

Must not actively regulate voltage

Expected to require minimum V/F ride through and voltage and frequency support capability for Bulk and Distribution system reliability

May actively participate in voltage regulation by changing real/reactive power

May modulate active power in response to frequency

DER may also provide ancillary grid services Future standards/interconnection

guidelines

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Smart Inverter Grid Support functions Remote ON/OFF Power Factor Control Volt / var Volt / Watt Frequency /Watt Reactive Power Control Low/ High Voltage and Frequency Ride Through Power Curtailment

Go to www.epri.com and search 3002002233

IEC 61850-90-7 IEC 61850 Object Models for Photovoltaic, Storage, and Other DER inverters Draft Version 10a

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Voltage Regulation by Reactive Power Support

Power factor mode Volt-var mode Active power-power factor mode (Volt/Watt) Reactive power mode

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Volt-Var Function Max Var (vars before watts) Mode; Inverter was operating at rated power

0

10

20

30

40

50

60

70

80

90

100

-80

-60

-40

-20

0

20

40

60

8093

%

94%

95%

96%

97%

98%

99%

100%

101%

102%

103%

104%

105%

106%

107%

kW

kVAR

Voltage (% of Nominal)

kVar (max) Nebland Inverter Settings kW

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Reactive Power Support – Impact on Efficiency

93.0%

93.5%

94.0%

94.5%

95.0%

95.5%

96.0%

-40% -30% -20% -10% 0% 10% 20% 30% 40% 50%

Effic

ienc

y

Reactive Power Output (% of Nominal Power)

75kW Power Level

41kW Power Level

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270

275

280

285

290

295

300

0

20

40

60

80

100

120

0 20 40 60 80 100 120

Aver

age

of 3

Phas

e L-

N V

olta

ges

(V)

Activ

e Po

wer

(kW

)

Time (s)

kW VLN

Volt-Watt Function

0%

20%

40%

60%

80%

100%

120%

0.00

20.00

40.00

60.00

80.00

100.00

120.00

99% 100% 101% 102% 103% 104% 105% 106% 107% 108% 109% 110%M

ax W

att O

utpu

t ( %

of M

ax)

Activ

e Po

wer

(kW

)

Average of 3Phase L-N Voltages as % of VN

kW kVar EUT curve

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Frequency-Watt Function Voltage Step: VN to Target Voltage (up to 108.6% of VN)

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Low Voltage Ride Through

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Active Power Limiting/ Curtailment

100% 75%25% In 4 secondsIn 6 seconds

Demand Response

Generation Curtailment

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Potential Impact on Inverter Reliability

Reactive power support for voltage regulation – increased loss/ increased operating temperature

Active participation in voltage regulation through volt-var mode may increase period of inverter operation at higher current magnitude – potential impact on device life span

Providing reactive power support during night time will significantly increase the operating hours

Industry practice of higher PV array DC to inverter AC ratio will also require the inverter to operate at higher current level for longer duration

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13

Questions

Contact: Aminul Huque, PhD Technical Leader, EPRI 865-218-8051 mhuque@epri.com