Purpose of Advanced Inverters Mitigation and Grid support

PV Distribution System Modeling Workshop

Presenter: Richard Bravo, SCE

Solar PV Inverters Advanced Features

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SCE started assessing solar PV inverters in 2009

• Tested multiple U.S. standard inverters (res. and comm.)

• Tested several “Smart Inverters”

• Provide feedback to national and state standards

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Ramp Rate

• Potential benefits – Prevent unintended over-voltages on distribution circuits

– Provide time for utility voltage support devices to adjust states properly

– LOCAL VOLTAGE SUPPORT

Voltage Ride Through • Potential benefits

– Prevent unnecessary disconnection

– Prevent longer voltage recoveries

– Provides limited short circuit

– Prevent/contain voltage events (FIDVR, etc)

– SUPPORT GRID STABILITY

3

Dynamic Watts/Hz • Potential benefits

– Prevent unnecessary disconnection

– Prevent unintended over-voltages during surplus generation

– SUPPORT GRID STABILITY

4

Autonomous Volt/VAR Support • Potential benefits

– Prevent unintended under/over-voltages

– Support motor VAR demand

– Allow CVR when needed

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– Support voltage imbalance when VARs are independent in each phase

– SUPPORT LOCAL VOLTAGE

Auxiliary Power Supply • Potential benefits

– Power to loads during emergency events

– Powers outlet isolated (does not back-feed in to the grid)

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– CUSTOMER SUPPORT LOCAL VOLTAGE

Distribution

BUS

SUBSTATION FIELD

Th

even

in

Eq

uiv

alen

t

Isc=17KA

Feeder “A” CB1

ISC= 17.5kA

Feeder “B”

L1a

L2a

CB2

ISC= 17.5kA

L1b

L2b

Feeder “C” CB3

ISC= 17.5kA

Feeder “D”

L3a

L4a

CB4

ISC= 17.5kA

L3b

L4b

Feeder “E” CB5

ISC= 17.5kA

Feeder “F”

L5a

L6a

CB6

ISC= 17.5kA

L5b

L6b

Circuit Breakers Impacts

7

P_1a=7MW G1a

Isc=430A

17.0kA 17.43kA

P_1a=7MW G1a

Isc=430A

17.86kA

• Distribution circuits were designed for one way power flow

• DG will alter this power flow and provide additional fault current

• DG could provoke CB to go above their ratings

Solar PV

Generation3

Rural Circuits Impacts

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Distribution

BUS

Distribution feeder

Cap1

SW4

Load4

M

CB1

Cap2

Cap3 Cap4

DISTRIBUTION

SUBSTATION

Cap5

FIELD

P

Q

Infi

nit

e B

us

SW3

SW1 SW2

Load5

M

Load2

M

Load1

M

Load6

M

Load3

M

Solar PV

Generation1

Solar PV

Generation2

SWY

SWX

• Utilities are facing challenges during DG interconnections specially at rural areas

• DG can provoke OV due to cable limitations

VR

FIDVR Impacts

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• Present inverter standards will trip inverters during low voltage ( FIDVR) events

• Events will worsen with higher DG penetration with current standards

• A good VRT settings can support the grid during these type of events

Solar PV Inverters Advanced Features

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ADVANCED FEATURE

PRESENTLY

AVAILABLE?

BENEFITS

RAMP RATES Prevent local overvoltages during low-load/high-gen

VRT Support transmission system

FRT Support transmission system

WATTS-HZ DYNAMIC SUPPORT Supports grid during over generation conditions

VOLTAGE (VAR) SUPPORT

(PHASE INDEPENDENT)

Supports local voltage

Support voltage imbalance due to 1Φ load/generation

VOLTAGE SUPPORT AT NIGHT TIME Supports grid specially during high load conditions

10% ABOVE RATING FOR GRID Owner not lose revenue during grid support

STANDARD COMMUNICATIONS Owners/utility

AUXILIARY POWER SUPPLY Provide owners emergency power

Some day solar PV inverter may help:

– Damping voltage oscillations

– Reduce/eliminate Flickering

– Voltage support during emergencies

– Reduce/eliminate harmonics

– Support some micro-grids

Conclusions

• Advanced features may need to be modified based on needs – Residential inverter features infrastructure needed to communicate

– Commercial grid-tied inverter features may be practical for utilities to adjust

• Develop testing standards – To comply with UL certification

• Utilities will face additional work when advanced features are adopted: – Develop and validate advanced inverter models

– Study the effects on present voltage support devices

– Pilot advanced inverters

– Design and build communications infrastructure

– Revise interconnection standards/procedures

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Richard Bravo

Southern California Edison

richard.bravo@sce.com

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