2014 PV Distribution System Modeling Workshop: Purpose of Advanced Inverters- mitigation and grid support: Richard Bravo, SCE

1. Purpose of Advanced Inverters
Mitigation and Grid support
PV Distribution System Modeling Workshop
Presenter: Richard Bravo, SCE

2. 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

3. 2
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

4. 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
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5. Dynamic Watts/Hz
• Potential benefits
– Prevent unnecessary disconnection
– Prevent unintended over-voltages during
surplus generation
– SUPPORT GRID STABILITY
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6. 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

7. 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

8. Distribution
BUS
SUBSTATION FIELD
Thevenin
Equivalent
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
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P_1a=7MWG1a
Isc=430A
17.0kA 17.43kA
P_1a=7MWG1a
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

9. Solar PV
Generation3
Rural Circuits Impacts
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Distribution
BUS
Distribution feeder
Cap1
SW4
Load4
M
CB1
Cap2
Cap3Cap4
DISTRIBUTION
SUBSTATION
Cap5
FIELD
P
Q
InfiniteBus
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

10. 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

11. 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

12. 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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13. Richard Bravo
Southern California Edison
richard.bravo@sce.com
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