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DNV-BEW T&D Department James MacPherson, Power Systems Engineer
November 8, 2011
Integrating High PV Penetrations Into the U.S. Distribution System,
Experiences with SynerGEE Electric
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Overview Background on High PhotoVoltaic (PV) Penetration Studies
- Hawaiian Electric Company (HECO) - Sacramento Municipal Utility District (SMUD), CPUC CSI RD&D project - Objective: Enable capability to reliably plan and operate with high
penetration of variable renewable resources on the grid - Using SynerGEE to study steady-state limitations of renewable resources
Model Development - Model creation & maintenance - Adding 1000’s of existing & potential PV units to model - PV penetration sweep (load-flow and fault analysis) - Conversion to balanced 3-phase model
Example Results
2
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Distribution Modeling Analytical Tools
• SynerGEE Electric – GL Noble Denton – Steady State Analysis – Voltage Analysis – Balanced and unbalanced load flow – Fault current studies
• Equivalent inverter modeling for steady state and fault analysis
– Harmonics – Time sequential analysis (hourly) – Switching routines – Tap changer impacts – Capacitor control and regulation impacts
• PSS/Sincal – Siemens PTI – Steady State and Dynamic Capability – Same as SynerGEE for steady state
analysis, but also includes – Detailed inverter modeling for fault current
studies – Dynamic/Transient Modeling of
Generators – Sub hourly irradiance data input
3
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
PV Penetration Limits at Different System Levels
4
46kV:12kV
Load Pocket
15 kW Distributed Residential PV
Large Customer PV
NO
3.6 MVAr
W1
W4
W3
W2
46kV:12kV
Area 1
Area 3
Feeder Transformer
Substation
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Model Creation & Maintenance
5
• GIS database continually updated by utility
• Convert GIS database to SynerGEE format
• Run in SynerGEE and identify errors (BEW)
• Identify corrections and where to correct (BEW/utility)
• Propose updates to GIS database
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Model Development: Adding Existing PV to Model
Done in Excel & Access
Input from utility - Address - Rated kW Capacity - Feeder - Phasing at point of interconnection
For each existing PV unit - Convert address to geographical coordinates
(X,Y) - Match to nearest node with same feeder &
phasing
Aggregate existing PV units as necessary
6 Source: HECO 6
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Model Development: Allocating Potential PV
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Model Development: Sweeping Potential PV Capacity with Recipe Objective: Create a Recipe to run multiple analyses, changing PV output, and
saving results to CSV files
• Identify potential PV units • Set Generator Output to “Specify Output %”
• Initialize potential PV % outputs (e.g. 0%)
• Run Analyses (e.g. Load-Flow, Fault, etc.)
• Export Results to Excel (.csv)
• Increment PV % outputs (e.g. +1%, +5%)
Loop Until 100%
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Example Results: Hi Potential PV Sweep
Effect of PV Penetration on - Min/Max Voltage, Max Loading, Tap
Position
9
Backfeeding at - Feeders, Transformers, and Substation - Minimum Daytime Load
0
2
4
6
8
10
12
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
128
180
232
280
337
386
442
491
546
594
643
905
1166
1423
1681
1939
2203
2462
2719
2981
3237
Tap
Posi
tion
Max
Loa
ding
(%),
Volt
age
(120
V b
ase)
Total PV Generation (kW)
"Feeder A" Potential PV Sweep ResultsMinimum Voltage Maximum Voltage Maximum Loading Depot Rd TSF TP
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Feeder 4
Feeder 3
TSF 2
Feeder 2
Feeder 1
TSF 1
Substation
Total kW of PV When Backfeeding Occurs
Total kW of PV When Backfeeding Occurs for Feeders, Transformers, and Substation
≈ Sum of TSF 1 & 2
≈ Sum of Feeders 1 & 2
≈ Sum of Feeders 3 & 4
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Model Development: Fault Analysis with Distributed PV Inverters not yet
modeled in SynerGEE Electric
Need another means of modeling a current source for fault analysis
Current method time-consuming and difficult to automate in PV sweep
PSLF, Sincal - Dynamics &Transient
stability - Inverter dynamic models
from IEEE and WECC guidelines
Equivalent Inverter Model
Low Voltage Network
Representation
Generator
Transformer
3 PH Fault Current on Distribution
Line
Equivalent Fault Contribution from
Inverter
Switch
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Example Results: 3-Phase Fault Current Analysis
0% 1% 2% 3% 4% 5% 6% 7% 8% 9%
10% 11% 12% 13% 14%
0 1000 2000 3000 4000 5000 6000 7000
% C
hang
e in
Fau
lt C
urre
nt fr
om N
o PV
Cas
e
PV Generation on Feeder (kW)
Feeder Max. 3P Fault Current vs. PV Generation
Distributed Potential PV Potential PV at Start of Feeder Potential PV at END of Feeder
5% FC Increase
10% FC Increase
15% PV penetration FC
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Results: Time of Day with PV Irradiance Profiles
Separate solar irradiance profile applied to each feeder
Recipe used to loop through 24 hours
-16
-12
-8
-4
0
4
8
12
16
0
200
400
600
800
1000
1 2 3 4 5 6 7 8 9 101112131415161718192021222324
Tap
Posi
tion
PV G
ener
atio
n (k
W)
Hour
Time of Day PV Generation ProfilesFeeder 1 Feeder 2 TSF Tap Position
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Model Development: Converting SynerGEE Unbalanced 1-P Model to 3-P Balanced Model
Purpose - Need to study dynamic/transient impacts of
distributed PV
Problem - No automatic conversion between SynerGEE and
other load flow software
Solution - Manually convert models into CIM format
Steps for Conversion - Perform single and two phase “roll up” to three
phase in SynerGEE - Export to Excel database - Manual manipulation of SynerGEE data into CIM
format - Import to other load flow software
Investigating the automation of this conversion process
13
Comparison of voltages at specified distances along the feeder
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Summary
Working with SynerGEE to accomplish steady-state load-flow, fault current, harmonics studies
Key needs from SynerGEE: - Inverter PQ model for fault current
analysis - Transient analysis capability - Sub-hourly irradiance inputs
14
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
Contact James MacPherson Engineer, Power Systems BEW Engineering, Inc. 2303 Camino Ramon, Suite 220 San Ramon, CA 94583 Email: James.MacPherson@dnv.com Main: 1-925-867-3330 Phone: 1-925-327-3030
15
© Det Norske Veritas AS. All rights reserved.
Update on High PV Penetration on Transmission and Distribution Grids
16
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