WECC Renewable Energy
Modeling Workshop
Conducted by the WECC Renewable Energy Modeling
Task Force (REMTF) and Modeling and Validation
Work Group (MVWG)
June 17, 2012 - Salt Lake City, UT
Abraham Ellis, Ryan Elliott, Ben Karlson – Sandia National Laboratories
Donald Davies, Kent Bolton – WECC
Pouyan Pourbeik – EPRI
Juan Sanchez-Gasca – General Electric
Jay Senthil – Siemens
Jamie Weber – PowerWorld
Irina Green – CAISO
PV and Wind Plants
• Wind, and increasingly PV, represent a significant
amount of generating capacity in WECC
– 2015HS case: 16GW wind, 4GW of PV (~15% of min load)
– Additional >1GW of distribution-connected PV
– PV and wind capacity projected to increase rapidly
• Adequate models are required for compliance with
reliability standards and generator interconn. studies
• WECC REMTF is leading effort to develop generic, nonproprietary models for planning studies
– Alternative to vendor-specific, proprietary, user-written,
which are generally not suitable for regional planning
2
WECC REMTF Charter
• The Renewable Energy Modeling Task Force shall
– Develop specifications for generic, non-proprietary, positivesequence power flow and dynamic simulation models for
solar and wind generation for use in bulk system studies
– Coordinate implementation of models in commercial
simulation software
– Develop model application and validation guidelines
– Coordinate with stakeholders
• REMTF reports to the WECC Modeling & Validation
Work Group (MVWG), which in turns reports to WECC
Technical Studies Subcommittee (TSS)
Modeling Needs and Standards
• Improving accessibility to PV and wind power plant
models is indispensable to properly assess the
reliability of the bulk power system
• NERC’s point of view:
“Validated, generic, non-confidential, and public standard power flow and
stability (positive-sequence) models for variable generation technologies are
needed. Such models should be readily validated and publicly available to
power utilities and all other industry stakeholders. Model parameters
should be provided by variable generation manufacturers and a common
model validation standard across all technologies should be adopted...”
Reference: NERC IVGTF Special Report, Accommodating High Levels of Variable Generation,
http://www.nerc.com/files/IVGTF_Report_041609.pdf
4
Different Types of Models
• Power flow representation
REMTF Scope
– Facility loading, voltage stability & control
• Positive-sequence dynamic models
– Large-signal stability, rotor angle stability
• Short circuit models
– Breaker duty, protection design/coordination
• Detailed, full-order models
– Electromagnetic phenomena
– Control interaction
5
REMTF Efforts Over Time
• Wind Generation Modeling Group (WGMG)
established in 2005
– Produced 1st generation of generic wind models
• Transitioned into Renewable Energy Task Force
(REMTF) in 2011
– Worked on 2nd generation of generic wind models
and generic PV models
• Recent scope expansion (work in progress)
– Short circuit guides, plant controller, energy storage
WECC-Approved Models
REPC_A
Wind/PV plant controller
REE_A, REE_B
Wind /PV electrical controls
REGC_A
Generator/Converter model
WTGT_A
Drive Train
WTGAR_A
Aerodynamic model
WTGPT_A
Pitch control
WTGTQ_A
Torque control
Type 3 WTG Plants
Usage
Type 4 WTG Plants
REMTF Module
PV Plants
• Approved REXX models for PV and Type 3/4 wind power plants
• Approved models for distributed PV and Type 1/2 wind plants
– PVD1 for small and distributed PV (simplified model)
– WT1G + WT1T + WT1P/A for Type 1 wind plants
– WT2G + WT2T + WT2P/A + WT2E for Type 2 wind plants
Proposed WECC Renewable
Energy Model Implementation Plan
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Key stakeholder input (REMTF, IEEE, IEC)
Model specifications approved by MVWG and TSS
Prototype model implementation tested
Model validation against plant-level field data (difficult and ongoing)
Models implemented in release version of commercial software programs
Model user guidelines
Webinar on WECC/REMTF model development, deployment process
Update Approved Dynamic Models List
WECC workshop on RE modeling
Model validation guidelines and tools (in process)
WECC request for data submittal using new models, with grace period
Workshop Agenda
Time
8:30 – 8:45
8:45 – 9:15
9:15 – 10:00
10:00 – 10:30
10:30 – 11:30
11:30 – 12:00
12:00 – 1:00
1:00 – 1:30
1:30 – 2:00
2:00 – 2:30
2:30 – 3:00
3:00 – 3:30
3:30 – 4:30
4:30 – 5:00
5:00
Topic
Introduction and REMTF Overview
Standards basis
Power Flow Representation RE Plants
Dynamic Model Specifications for PV
BREAK
Dynamic Model Specifications for Wind
User Experience with New REXX models
LUNCH
PowerWorld Tutorial
PSS/E Tutorial
PSLF Tutorial
Questions for Tutorial
BREAK
Experience with Wind and PV Model
Validation
Open mic: questions, feedback
ADJOURN
Speaker
Abraham Ellis
Donald Davies
Abraham Ellis
Pouyan Pourbeik
Irina Green
Jamie Weber
Jay Senthil
Juan Sanchez-Gasca
All
Pouyan Pourbeik,
Ryan Elliott
All
Standards Framework for Wind and
PV Modeling in WECC
D. Davies
Power Flow Representation
of PV and Wind Power Plants
A. Ellis
Example of a PV Plant
DeSoto PV Plant (2009)
Fort Myers, FL. (courtesy of FPL)
PV Inverters and Padmounted transformers
PV Array on fixed of
tracking structure
Substation with
plant transformers
Substantial MV collector system
network, OH or UG radial feeders
Interconnection
Line
PV Inverter and Transformer
Transformer and AC
switchgear
DC switchgear
and inverters
Skid
PV/Wind Plant Power Flow Model
• Single machine model is suitable for bulk studies
– Equivalent representation of inverters, pad-mounted
transformers, and MV/LV collector system
– Explicit representation of substation transformer and plantlevel reactive support, if any (e.g., switched caps, STATCOM)
– The goal is to approximate aggregate behavior at the POI
14
Power Flow Equivalencing
How to obtain equivalent
collector system parameters?
Single-machine power flow model
1. Estimate based on typical
design parameters
2. Best way: Calculate from
collector system design data
(example follows)
15
Example – 21 MW PV Plant
Inverter cluster
PV Inverter
1 MW
+/-0.95 pf
UG
feeders
24 kV
1
4
Pad-mounted Transformer
3 MVA
Z=6%, X/R=10
5
9
8
7
2
SUB
6
3
To utility
Model station transformer and
interconnection line explicitly, if they exist.
16
Example – 21 MW PV System
I
Collector System Equivalengcing Technique:
Z eq  Req  jX eq 
Z n
i 1
2
i i
N2
I
Beq   Bi
i 1
Collector System Equivalent on 100 MVA and 24 kV base
From
To
1
4
2
R
X
B
n
R n^2
X n^2
0.03682 0.00701
0.000000691
3
0.33136
0.06307
4
0.02455 0.00467
0.000001036
3
0.22091
0.04205
4
5
0.02455 0.00467
0.000001036
9
1.98816
0.37843
3
5
0.02557
0.02116
0.000000235
3
0.23016
0.19042
5
SUB
0.02557
0.02116
0.000000235
12
3.68251
3.04673
6
8
0.03747 0.00868
0.000000561
3
0.33726
0.07809
7
8
0.02455 0.00467
0.000001036
3
0.22091
0.04205
8
9
0.02109 0.02501
0.000000199
6
0.75925
0.90025
9
SUB
0.02109 0.02501
0.000000199
9
1.70831
2.02555
RESULTS
Partial R sum
Partial X sum
N
9.4788
6.7666
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Collector System Equivalent
(Same units as R, X & B data)
Req
0.021494 pu
Xeq
0.015344 pu
Beq
0.000005 pu
Pad-mounted Transformer Equivalent
Z Teq 
ZT
0.00597  j0.05970

 0.00085  j0.00853 pu on 3 MVA base
M
7
Useful Resource: WECC PV/Wind Power Flow Modeling Guidelines
17
Reactive Capability
• Equivalent generator reactive capability
– Varies with output level, voltage level, type of generator
• Inverter/WTG and plant-level reactive control
– PF or Q control, V/Q droop, or closed-loop V-control
• May need to adjust according study scenario
Useful Resource: WECC PV/Wind Power Flow Modeling Guidelines
18
Dynamic Models for PV Power Plants
A. Ellis
REMTF Dynamic Model Specs.
• Consistent with established modeling approach at the
transmission (bulk system) level
– Positive-sequence, for large-scale bulk-level simulations
– Suitable for use with equivalent (single-generator) power
flow plant representation
– Reproduce fundamental dynamic characteristics following
electrical disturbances (as opposed to wind/solar events)
– Bandwidth: Steady-state to 5 Hz; faster dynamics expressed
algebraically or ignored
– Generic: parametrically adjustable so that equipment of the
same type (e.g., Type 3 WTG plants, PV plants, etc.)
– Available as standard library models in commercial software
20
Plant-Level Controls
PV Inverter Topology
and Controls (One Example)
PV Array
Voltage Source Converter
Grid
GATE
DRIVE
CIRCUITRY
AC Current Controls
Line Current Synch.
Vdc
Process Control (slower)
(MPPT, P/Q control)
Iac, Vac at
inverter terminals
Plant Supervisory
Controller
Representation of Discrete PV Plants
• Two options for dynamic representation
– Full-featured PV Plant Model (REXX)
– Simplified Model (PVD1)
PVD1 Model
Vrf lag
PVD1
Ff l FfhFvh Fvl
Fvl
1
Vreg
Vref
Qref
Qbranch
Pref
Pbranch
Freq_ref
Freg
Pext
Vt
REPC_A
0
Vt REGC_A
REEC_B
Fvh
Vt 0 Vt 1 Vt 2 Vt 3
N
Pref
Plant Level
P Cont rol
Qext
Pref
Q Cont rol
P Cont rol
Iqcmd’
Ipcmd’
Iqcmd
Current
Limit
Logic
Ipcmd
Iq
Generat or
Model
Ip
0
It
Qmx
Qref
Qmn
Xc
D
Dqdv
N
V0 V1
Iqmax
÷
×
Iqmin
f dbd
Freq_ref
Ddn
-
Freq
Ff l
1
0
Ft 0 Ft 1 Ft 2 Ft 3
REXX Model
Frf lag
Ip
1
1 + sTg
It = Ip +j Iq
0.01
Qref
Pqf lag
Ipcmd
×
D
Vt
Net work
Solut ion
Ipmax
÷
Pdrp
Plant Level
V/ Q Cont rol
MINIMUM
Ffh
Pdrp
Iqcmd
Iq
-1
1 + sTg
Q Priorit y (Pqf lag =0)
Iqmax = ImaxTD
Iqmin = - Iqmax
Ipmax = (ImaxTD2- Iqcmd2)1/ 2
P Priorit y (Pqf lag =1)
Ipmax = ImaxTD
Iqmax = (ImaxTD2- Ipcmd2)1/ 2
Iqmin = - Iqmax
• Both require generator explicitly represented
in power flow and equivalent feeder/collector
23
REXX PV Plant Model Structure
• Requires plant control (REPC_A), inverter control
(REEC_B), grid interface (REGC_A), protection
Vt
REPC_A
Vreg
Vref
Qref
Qbranch
Pref
Pbranch
Freq_ref
Freg
Plant Level
V/ Q Cont rol
Qext
Plant Level
P Cont rol
Pref
Q Cont rol
P Cont rol
Vt REGC_A
REEC_B
Iqcmd’
Ipcmd’
Iqcmd
Current
Limit
Logic
Ipcmd
Iq
Generat or
Model
Ip
Net work
Solut ion
Pqf lag
24
PV Plant Controller
• Reactive control options: V control, Q control, V/Q droop control
• Active power control options: P control, P/freq droop control (governor
response)
25
Inverter P/Q Electrical Controls
• Local PF or Q control with overriding voltage dip response
• Active power limits and rate-of-change limit
• Current limiter with P or Q priority
26
Generator/Converter Model
• High voltage Iq logic: (software-specific, integration with network solution)
• Low voltage Ip control: (approximate PLL response during voltage dips)
• Low voltage Ip control: allow for controlled active current response during
and following voltage dips
27
Voltage & Frequency Tolerance
Voltage and frequency tolerance can be roughly represented
using standard (V,t) and (f,t) protection models
28
Sample Simulations
29
Simple Dynamic Model (PVD1)
vrrecov
PVD1
Ffh
Fvl
1
0
Pext
Ff l
Fvh
Vt 0 Vt 1 Vt 2 Vt 3
N
Pref
0
Qmx
Qref
Qmn
Xc
D
Dqdv
N
V0 V1
Iqmax
÷
Qref
×
Iqmin
f dbd
Freq_ref
Ddn
-
Freq
Ff l
1
0
Ft 0 Ft 1 Ft 2 Ft 3
f rrecov
1
1 + sTg
Ip
Intended for use with
a smaller PV plant or
distribution-connected
MW-scale plant
It = Ip +j Iq
0.01
It
•
•
•
•
Ipcmd
×
D
Vt
Fvl
×
Ipmax
÷
Pdrp
Fvh
Ffh
Pdrp
Iqcmd
-1
1 + sTg
Iq
Q Priorit y (Pqf lag =0)
Iqmax = Imax
Iqmin = - Iqmax
Ipmax = (Imax2- Iqcmd2)1/ 2
P Priorit y (Pqf lag =1)
Ipmax = Imax
Iqmax = (Imax2- Ipcmd2)1/ 2
Iqmin = - Iqmax
Reactive power control with Q-V droop and line drop compensation
Active power (high) frequency droop
Voltage-frequency protection with dead band and recovery logic
Dynamic inverter current limit logic with P or Q priority
30
Dynamic Model Specifications for
Wind Power Plants
P. Pourbeik
User Experience With REXX Models
I. Green
Software Tutorials
J. Sanchez-Gasca, J. Senthil, J. Weber
Experience with Model Validation
P. Pourbeik, R. Elliott
Open Discussion
Contact
A. Ellis, REMTF Chair
aellis@sandia.gov