pv inverter island detection evaluation using power hardware-in-the-loop (PHIL) techniques

1. NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
PV Inverter Island Detection Evaluation Using
Power Hardware-in-the-Loop (PHIL) Techniques
Barry Mather, Ph.D.
Senior Electrical Engineer
Power Sys. Engineering Center
barry.mather@nrel.gov
PV System Symposium
PV Grid Integration Workshop
San Jose, CA, May 10th, 2016

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Outline
2
• Goal and motivation
• Overview of the PHIL setup
• Presentation of results
• PHIL vs. RLC tank (IEEE 1547/UL 1741
tests)
• A look at the strength of implemented
island detection algorithms
• Island detection with induction motors on
circuit
• Conclusions

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PV Inverter Islanding – Still a major concern
3
Motivation:
• The risk of a high-pen PV circuit forming an
island has yet to be inexpensively mitigated:
• Some utilities require DTT
• Some PV inverter manufactures have
“beefed-up” detection algorithms
• IEEE 1547.1 is under revision – what should
be tested?
Goal:
• Develop methods for evaluating PV inverter
island detection performance under more
realistic conditions to better quantify risk

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PV Inverter Island Detection Evaluation
What is present in the next slides
was developed through a
collaboration between NREL and
FSU CAPS.
Collaborators: K., Schoder, J.
Langston, M. Steurer ,J. Hauer
and F. Bogdan
IEEE 1547 – 2003 requires a
DER to cease to energize within 2
seconds of a electrical island
forming.
4
PV
Inverter
-
+ A
B
C
N
resonant
at 60 Hz
DC
Source
Va
Vb
Vc
R, L, C
Load
Bank
Islanding
Switch
Simulated
GridDUT
IEEE 1547 / UL 1741 Anti-islanding test
See: K. Schoder, et al. Power Hardware-in-the-Loop-Based Anti-Islanding Evaluation and
Demonstration, NREL Tech. Report TP-5D00-64241, Oct., 2015.

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Amplifier
AC
Voltage
References
Voltage
Reference
RTS
Load bank and
Feeder Emulation
PV Emulation
Protection
Monitoring,
Trend Data Logging,
Data capture
Simulation of
PHIL-Setup
Amplifier
DC
Voltage and current
Measurements
VDC
ref
IDCVDC Ia,b,c Va,b,c
PV Inverter
3-phase
DC
String
-
+
L1
L2
L3
N
PE
References
Current measurement(s)
Voltage measurement(s)
Rs
VA,B
ref
Transformer
4.16kVV/480V(DY)
O2(1)
Switch
Load Bank
R-L-C
wye
Ia,b,c Iga,b,c
SW
Vsw,cVa,b,c
PHIL Power
Interface
RT Model
Va
Vb
Vc
Rp
Rg
I1(10)
1:100
PHIL-Based Island Detection Evaluation
From: M. Steurer et al. Advanced Anti-Islanding Testing with Power Hardware-in-the-Loop,
3rd Annual International Workshop in Grid Simulator Testing, Nov., 2015.

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RLC vs. PHIL Island Detection Results
6
RLC type testing , 20 kW inverter operating at 8 kW with a QF = 1
Va, Vb, Vc Ia, Ib, Ic

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RLC vs. PHIL Island Detection Results
7
PHIL type testing , 20 kW inverter operating at 8 kW with a QF = 1
Va, Vb, Vc Ia, Ib, Ic

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RLC vs. PHIL Island Detection Results
8
Island detection
time comparison
for RLC and PHIL-
based evaluation:
RLC – Red
PHIL - Blue

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Determining the Strength of AI Detection
9
A 60 kW PV
inverter is operation
at 54 kW but other
perfect PQ sources
are modelled at 1,
2, 3, and 4 times
the inverters
operating power to
test the strength of
island detection
algorithms
Non-Islanding Inverter-
based Generation

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Investigating the Impact of Nearby Loads
10
A 60 kW PV Inverter
is operating at 54
kW and a 60 kVA
induction motor is
operating nearby
(modelled in RTS).
Result – half of the
experiments
resulted in detection
times over 2 sec. –
Please note that QF
= 2 in this case. Island Detection Times with
a 60 kVA Induction Motor
Nearby

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Investigating the Impact of Nearby Loads
11
A 60 kW PV Inverter
is operating at 54
kW and a 221 kVA
induction motor is
operating nearby
(modelled in RTS).
Result – no island is
ever detected.
Vline-line
Freq.

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Conclusions
12
• PHIL methods were developed to evaluate PV inverter
islanding scenarios – experimental results show
reasonable agreement between island detection times.
• Island algorithms seem quite robust to non-islanding
generators on the same circuit.
• Experimental results indicate that concern over induction
motors/generators proves to be warranted
Moving forward: what level of island detection
performance should we require of distributed PV
and how should it be evaluated via certification
tests?

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Thank you for your attention
Contact:
Barry Mather Ph.D.
National Renewable Energy Laboratory
barry.mather@nrel.gov
(303)-275-4378