Inverter Voltage Regulation Settings
that Always Work
PES General Meeting, Boston, MA
July 20, 2016
Thomas E. McDermott, tem42@pitt.edu
2
A test circuit for PV inverter control includes both grid
voltage and solar output variability.
0.0134W
240 V
Vindex=3.7838
j0.0088W
~~
220 kVA
200 kW
1289.7 kWh
3
Changes in DER output will produce changes in DER
terminal voltage.
Estimated % Voltage Change:
V/√3
R1
X1
Vdrop
Vdrop 
Pn+jQn
Un/√3
100
( R1  jX 1 )( Pn  jQn )
2
Un
dV
 (100  Re Vdrop ) 2  (Im Vdrop ) 2  100
Un
(R, X in ohms, Sn in MVA, Un in kV)
4
The Intelligent Volt-VAR function attempts to hold a
constant voltage using percent available VARs.
Source: “Common Functions for Smart Inverters, v3”, EPRI 3002002233, February 2014
5
Volt-VAR can mitigate fluctuation, but constrains operation
(e.g. voltage reduction requires communication).
Aggressive setting
Vindex=1.905
1073.1 kVArh
Proposed as a no-harm default
Vindex=3.6864
113.1 kVArh
6
vars (p.u. available)
vars (p.u. available)
Major burden of choosing settings - detailed studies
needed and the wrong choice makes things worse.
Voltvar Response
1
0.5
0
-0.5
-1
0.94
0.96
0.98
1
1.02
1.04
1.06
1.08
1.1
1.06
1.08
1.1
Voltage (p.u.)
Voltvar Response
1
0.5
0
-0.5
-1
0.94
0.96
0.98
1
1.02
1.04
Voltage (p.u.)
Source: Abate, McDermott, Rylander and Smith, “Smart Inverter Settings for Improving
Distribution Feeder Performance”, IEEE PES General Meeting, Denver, CO, July 2015.
7
“Percent available” output means the physical slope
[VARs/volt] varies.
+
-
S
Plant G(s)
Control K
Would you choose to make this gain block
non-linear or time-varying?
What was the intent? “’Available VARs’” implies whatever the
DER is capable of providing at the moment, without
compromising Watt output. In other words, Watt output takes
precedence over VARs in the context of this function”.
Source: “Common Functions for Smart Inverters, v3”, EPRI 3002002233, February 2014, p. 9-3.
8
Dynamic Reactive Current function uses a moving
average to define the voltage set-point.
Vindex=0.8896
Source: “Common Functions for Smart Inverters, v3”,
EPRI 3002002233, February 2014
538.8 kVArh
9
Adaptive Voltage Regulation provides the best of both
intelligent volt-VAR and dynamic reactive current.
Qbias (for IVVC)
Vreg
+
V
sys
S
DV
K
DQ +
+
S
2
2
Srated
- Pout
Qnew
2
2
 S rated
- Pout
Dt 


Vreg   DV 1  e
1
Qout
Grid
Vsys
10
Adaptive Voltage Regulation mitigates fast voltage
fluctuation while tracking slower grid voltage trends.
Vindex=0.8860
Vindex=0.8725
Longer time constant’s effect
464.6 kVArh
712.4 kVArh
11
Voltage regulation set-point and reactive power can be
limited, if desired.
Vindex=0.9395
Vindex=2.0127
814.1 kVArh
318.9 kVArh
12
Instead of attempting to regulate the grid voltage,
dispatch reactive power (i.e. the bias point is not zero).
Vindex=0.9638
Vindex=0.9132
658.7 kVArh
763.8 kVArh
13
Results from an actual feeder with 1.7 MW of PV show
that Adaptive Voltage Regulation performs well.
Vindex=1.2242
3560.7 kWh
Vindex=0.1825
473.1 kVArh
14
Conclusion – Adaptive Voltage Regulation should be the
default behavior of PV inverters.
• These default settings work well (so far…):
– Slope = 100
– Tau = 300 s
– 0.95 ≤ Vreg ≤ 1.05 [pu]
• Without smart-grid communications
– No need for detailed coordination studies
– No wake-up time for inverter’s voltage response
• With smart-grid communications
– Fail-safe behavior
– Dispatch reactive power, just like shunt capacitors
• Use a default high-frequency roll-off as well
15
The Volt-Watt function can limit steady-state voltage
rise, especially with low X/R ratios (Hawaii uses this).
Source: “Common Functions for Smart Inverters, v3”, EPRI 3002002233, February 2014
Simplified Formula:
DV  RDP  X DQ
But do we really want to control DV this way, even if DP has more leverage
than DQ?
1
Case Studies of Advanced Inverters
in the Grids
Soonwook Hong, Ph.D.
Engineering Fellow, Grid Integration
soonwook.hong@solectria.com
2
What is an "advanced (PV) Inverter"?
Conventional PV inverter
- Generates real power and provides fundamental protective functions
Advanced Inverters (Grid Support Utility Interactive Inverter: UL1741SA Def)
In addition to the conventional PV inverter capabilities,
- Generates reactive power for voltage regulation purpose
- Provides ride through operation with grid events
- Provides communication capability
- Provide other functions to increase distribution power quality, reliability and
stability
3
30MW Concentrated PV Plant in Alamosa, Colorado
504EA x Yaskawa-Solectria Solar 82kW PVI82 PV Inverters (2011)
Power Curtailment, PFC, Reactive Power Control, Voltage Regulation
4
1MW PV Plant in Massachusetts
2EA x Yaskawa-Solectria Solar SGI500 500kW PV Inverters
Figure courtesy of NGRID, EPRI
5
Volt-var function
Reactive power capability: 600kW (reactive power spans from -150kvar to -500kvar)
Figure courtesy of EPRI
• PV Plant voltage increases high with the volt-var function disabled
• Feeder voltage is regulated best at the PV plant
6
Volt-var function
Reactive power capability: 600kW (reactive power spans from -150kvar to -500kvar)
Assiged Curve
Inverter Interpretation
Measured Samples
Voltage Offset = 0.3%
Figure courtesy of EPRI
77
Power Factor Control Case
1.7 MW site in Cedarville NJ
4.7 miles from substation 12kV feeder, 6MW mid-day load
Concerns of local overvoltage
Utility has closed circuit for more PV
0.5 MW
1.7 MW
Picture courtesy of Pepco Holdings
8
Power Factor Control Case
PF = 1.0
3.0% of points
exceed +5% limit
PF = 0.97 (inductive)
< 0.1% of points
exceed 5% limit
Figure courtesy of Pepco Holdings
Voltage Regulation is achieved with power factor control
All PV plants in Hawaii are required to use 0.95 PF (inductive) according to Rule 14H
9
Other Popular Grid Support Functions
•
•
•
•
•
•
Remote Shutdown
Power Curtailment
Voltage/Frequency Ride Through
Volt-watt, Frequency-watt
Ramp Rate Control
Communication Interface
10
Thank you
1
Advanced Islanding Detection
Michael Ropp, PhD, PE
Northern Plains Power Technologies
Brookings, SD 57006 USA
2
The islanding issue
When a recloser or other breaker opens to form an island with a close
match between real and reactive sources and loads, the breaker
interrupted no current and the island can be hard to detect.
3
High-pen challenges
• Mixtures of different distributed energy resources
(DERs) using different islanding detection
methods
• Mixtures of inverters and rotating machines
• Conflicts between the need for grid support/ride
throughs, and effective islanding detection
• Incompatibility with low-inertia systems
• The usual protection tradeoff: cost vs. speed vs.
sensitivity vs. selectivity.
4
Islanding detection options
5
Power line carrier permissive
(PLCP)
Signal generator sends guard tone; if receiver sees it, that’s permission
to run. Pros include effectiveness for all DER combinations and a good
“value-add” proposition; cons include cost and propagation issues.
6
Synchrophasors
Reference synchrophasor broadcast to all DERs; DERs process locally.
Pros include effectiveness, a high “value added” proposition, and
pathways to low cost; cons include a less favorable sensitivity-selectivityspeed tradeoff than PLCP.
7
Don’t count out advanced passives
• Harmonic signature recognition
• Cross-correlation and other statistical
techniques
• The historical challenge with passives is
getting both selectivity and sensitivity—who’s
up to the challenge?
8
Thank you!
Michael Ropp
Northern Plains Power Technologies
michael.ropp@northernplainspower.com
1
Residential Smart Inverter Pilots:
Lessons Learned (So Far)
Ben York, Ph.D.
Senior Engineer, EPRI
IEEE PES GM – July, 20th 2016
Developing the Integrated Grid
Phase I
Phase 2
Integrated Grid
(IG) Concept
Benefit/Cost
Assessment
Feb 2014
Feb 2015
Phase 3
IG Pilots
Now
http://integratedgrid.epri.com/
Pilot Projects Underway
SRP Residential Advanced Inverter
AEP I&M Clean Energy Solar
 For planned or existing
technology deployments
Alliant Energy Star Power
APS Utility Owned Residential PV
WeEnergies Grid-Interactive Microgrid
• Understand capability of DER
Entergy PV + Energy Storage
• Power system analysis to
understand integration
Hoosier Utility Scale PV
HydroOne Impact &Value of ES
SCE DES Valuation
NYPA/CenHud PV + ES New Paltz
• Implement approach
• Collect and analyze data to
assess field performance
• Assess costs and benefits of
integrating DER
NYPA/ConEd PV + ES CUNY SHINES
KCPL EV Infrastructure
TVA Integrated Value of DER
LGE Energy Storage
Exelon/Peco Microgrid Study
Xcel Energy ES Grid Modernization
NCEMC Microgrid
ConEd ES Valuation
4
What’s Unique About a Residential Smart
Inverter Pilot?
•
•
•
•
•
Safety Listing Required
Local Optimization Opportunity
Limited Configuration Options
Strength in Numbers
Lengthy Communication Chain
5
APS Solar Partner Program
• APS owned, operated, and
maintained residential rooftop PV
systems with advanced inverters
SPP Use Cases
• APS customers receive bill credit of
$30/month for 20 years lease
EQUIPMENT DEFFERAL
• Total 10MW (≈1500 PV systems)
with 4 MW energy storage
• External advisory council
comprising of utility, academia,
regulators, and researchers
COMMUNICATIONS
INVERTER CONTROL & FUNCTIONALITY
STRESS & VOLTAGE MANAGEMENT
ENERGY STORAGE
6
SRP Advanced Inverter Project
• Deploy ~1,000 advanced inverters
• Goals:
– Test functionality and grid benefits
– Define future interconnection requirements
and determine communication needs
– Prepare for higher penetrations of solar
– Enable customer choice while maintaining
reliability
• Systems in 3 components
– #1: “Set it and forget it”
– #2: Seasonal Settings
– #3: DMS-level Control
7
Challenging Road to Safety Listing
SIWG Recommendations
on UL1741
Solution?
SpecialPurpose Utility
Interactive
Inverter
Source: “Recommendations for Updating the Technical Requirements for Inverters in
Distributed Energy Resources” SIWG. Jan. 2014
8
Maturing Communication
Medium
Cellular
AMI
Internet
Modbus
Standard Protocol
DNP3
SEP2.0
(IEEE 2030.5)
Others?
SunSpec
Modbus
OpenADR
DER Effectiveness Depends on Technology
Readiness
Inverter follows assigned volt-var curve
√
Inverter doesn’t follow volt-var curve
X
10
Results Are Possible!
Volt-VAR Control
Results Are Possible!
Active Power Limit
11
12
Thanks!
Visit us at:
integratedgrid.epri.com