2014 PV Distribution System Modeling Workshop: Capabilities of Advanced Inverter: John Berdner, Enphase

1. Capabilities of
Advanced
Inverters
John Berdner
Director of Worldwide Standards

2. Overview of Presentation
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Nomenclature for Advanced Inverters and Functions
Ride through Functions
Voltage Ride Through, Frequency Ride Through
Real Power Control Functions
Frequency/Watt, Volt/Watt
Reactive Power Control Functions
Volt/VAr
Communications
Commanded Operation, Autonomous Profiles
Communication issues

3. Nomenclature
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Need to be careful about
using anthropomorphic
terms…
- What comes after
“advanced” inverters?
- What comes after “smart”
Inverters ?
Suggestion:
Inverters with real and
reactive power control
functions
EPRI “Common Functions for Smart Inverters, Version 3”
An excellent overview of functions / capabilities / issues

4. Ride Through Functions
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Historically inverters were programmed to get offline
quickly in response to grid voltage or frequency
excursions
- Existing regulatory structures in the US did not
adequately address ride through requirements.
- Requirements were written as “must disconnect” not
as “must remain connected”
- As levels of Distributed Energy Resources (DER)
increase this strategy becomes problematic.
- Loss of large amounts of DER in advance of load
shedding can lead to cascade failure.

5. L/H Voltage Ride Through
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EPRI Common Functions For Smart Inverters V3, page 14-2

6. Voltage Ride Through Issues
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Inverters can provide controlled full current down to
near zero voltage for extended periods of time but…
there are some issues.
- Very low voltages are normally seen in response to
feeder faults and additional fault current may be
undesirable.
- At very low voltages, frequency measurement signal
to noise ratio deteriorates
- Very low voltage operation of inverters may increase
power supply costs and complexity
Focus of requirements to date has been on what
happens at beginning of event. Of equal import is what
happens when / how the DER returns to service.

7. L/H Voltage Ride Through
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0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.20
1.30
0.01 0.1 1 10 100 1000
Voltage(perUnit)
time (seconds)
Operating Regions - Must Remain Connected
OV_MSC UV_MSC
Normal Operation Region High (NORH)
Undervoltage Region 2MSC - UV2MSC
Undervoltage Region 1 - UV1MSC
Overvoltage Region 1 - (OV1MSC)

8. Frequency Ride Through
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EPRI Common Functions For Smart Inverters V3, page 15-2

9. Frequency Ride Through Issues
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Inverters can provide controlled full current down to
very low frequencies for extended periods.
- Frequency excursion is normally in response to
system level events.
- Low frequency behavior needs to be coordinated
with local load shedding schemes.
- Inverters are less sensitive to damage from low
frequency operation than rotating machines.
During high frequency excursions ride through and
Frequency / Watt functions are normally used together.
- Real power may be programmed to be at zero before
reaching the ride through limits.

10. Real Power Control Functions
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Real power control functions modulate real power
output in response to changes in Voltage or frequency
Typical Real Power Control functions include:
- Volt / Watt
- Reduces real power output with rising voltage
- May be possible to increase power with lower voltages
if storage is present in the system
- Can be used with ramp rate control on initial startup.
- Frequency / Watt
- Reduces real power output with rising frequency
- May be possible to increase power with lower voltages
if storage is present in the system
- Can be used with HF ride through for more stability

11. Example: Real Power Control Function
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Example Volt Watt Diagram Parameters
- Dead band (Vnom – V2) = no power reduction
- Response Gradient %P/Volt = (P3-P2)/(V3/V2)
- Other considerations – Response time, averaging
intervals, intentional delay

12. Reactive Power Control Functions
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Reactive power control functions modulate reactive
power output in response to changes in Voltage, or real
power output.
Typical Reactive Power Control functions include:
- Volt / VAr with Watt priority (available VAr or VV11).
- Provides VAr support with no reduction in real power
- VAr capacity varies inversely with solar resource
- Volt / VAr with Var priority (available VAr or VV12).
- Provides VAr support and may reduce real power
- VAr capacity is independent of solar resource
- May require specific Tarriffs or Rates
- Watt /Var (not common in the North America)

13. Example: Reactive Power Control Function
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Example Volt VAr Diagram Parameters
- Dead band (V3 – V2) = no power reduction
- Response Gradient %Qa/Volt = (Q4-Q3)/(V4/V4)
- Other considerations – Response time, averaging
intervals, intentional delay

14. Communication – Commanded Operation
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Inverters respond in “near real time” to commands from
the utility.
Example commanded modes:
On/Off (P&Q = 0)
Fixed Real Power (may require storage)
Maximum Real Power
Fixed Power Factor
Mode Change – Profile A or Profile B

15. Communication – Autonomous Profiles
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High speed SCADA communications is not cost
effective for high numbers of smaller systems.
Inverters can be pre-programmed with one or more
autonomous operating profiles.
- Inverters would then continue to operate according
to this profile until commanded to do otherwise.
- Provides high speed response without need for
high speed communications
Updates to profiles or changes in operating modes can
occur over public IP networks
- Customer Network or Cellular Modem (M2M)
Mode changes might also be possible over AMI system.

16. Communication – Issues 1
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Cyber Security of communication to DER systems
No global standard communication protocols
- DNP 3 is one common protocol used by utilities.
- Not well suited to control of large numbers of inverters
- Not used by all utilities
- IEC 61850 Data model may be a common language
- Sunspec Mapping to IEC 61850 for inverters
- DNP 3 to IEC 61850 for Utilities
Response time will be dependent on communication
system used
Not all systems will receive / respond to commands
(Stochastic planning needed)

17. Communication – Issues 2
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Undefined demarcation points for communication
protocols
- Where are various protocols used ?
- Who is responsible for protocol translations ?
- DNP 3 to IEC 61850 based protocol
- IEC 61850 protocol to inverter specific protocol
Undefined commercial issues
- Who is responsible for processing commands ?
- Inverter manufacturers, system aggregators,
system owners
- How are ongoing “back end” costs covered ?

18. Questions
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Thank you for your attention
John Berdner
jberdner@enphaseenergy.com