1. WECC Renewable Energy Modeling Workshop Conducted by the WECC Renewable Energy Modeling Task Force (REMTF) and Modeling and Validation Work Group (MVWG) June 17, 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

2. 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, non-proprietary models for planning studies
Alternative to vendor-specific, proprietary, user-written, which are generally not suitable for regional planning

3. WECC REMTF Charter The Renewable Energy Modeling Task Force shall
Develop specifications for generic, non-proprietary, positive-sequence 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)

4. 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,

5. Different Types of Models
Power flow representation
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
REMTF Scope

6. 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

7. WECC-Approved Models
Approved REXX models for PV and Type 3/4 wind power plants
REMTF Module
Usage
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
PV Plants
Type 4 WTG 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

8. Proposed WECC Renewable Energy Model Implementation Plan
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

9. Workshop Agenda Time Topic Speaker 8:30 – 8:45
Introduction and REMTF Overview
Abraham Ellis
8:45 – 9:15
Standards basis
Donald Davies
9:15 – 10:00
Power Flow Representation RE Plants
Dynamic Model Specifications for PV
10:00 – 10:30
BREAK
10:30 – 11:30
Dynamic Model Specifications for Wind
Pouyan Pourbeik
11:30 – 12:00
User Experience with New REXX models
Irina Green
12:00 – 1:00
LUNCH
1:00 – 1:30
PowerWorld Tutorial
Jamie Weber
1:30 – 2:00
PSS/E Tutorial
Jay Senthil
2:00 – 2:30
PSLF Tutorial
Juan Sanchez-Gasca
2:30 – 3:00
Questions for Tutorial
All
3:00 – 3:30
3:30 – 4:30
Experience with Wind and PV Model Validation
Pouyan Pourbeik,
Ryan Elliott
4:30 – 5:00
Open mic: questions, feedback
5:00
ADJOURN

10. Standards Framework for Wind and PV Modeling in WECC D. Davies

11. Power Flow Representation of PV and Wind Power Plants A. Ellis

12. Example of a PV Plant PV Inverters and Pad-mounted transformers
DeSoto PV Plant (2009)
Fort Myers, FL. (courtesy of FPL)
PV Inverters and Pad-mounted transformers
PV Array on fixed of tracking structure
Substation with plant transformers
Substantial MV collector system network, OH or UG radial feeders
Interconnection Line

13. PV Inverter and Transformer
Transformer and AC switchgear
DC switchgear
and inverters
Skid

14. 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 plant-level reactive support, if any (e.g., switched caps, STATCOM)
The goal is to approximate aggregate behavior at the POI

15. Power Flow Equivalencing
Single-machine power flow model
How to obtain equivalent collector system parameters?
Estimate based on typical design parameters
Best way: Calculate from collector system design data (example follows)
Don’t think there are any issues here. The Sandia-led group will put together power flow modeling guidelines that will likely follow the same procedures in the existing wind plant modeling guidelines. But no software developer action should be necessary.

16. Example – 21 MW PV Plant Inverter cluster PV Inverter 1 MW +/-0.95 pf
UG feeders
24 kV
Pad-mounted Transformer
3 MVA
Z=6%, X/R=10 1 4 5 9 8 7 2
SUB 6 3
To utility
Model station transformer and interconnection line explicitly, if they exist.

17. Useful Resource: WECC PV/Wind Power Flow Modeling Guidelines
Example – 21 MW PV System
Collector System Equivalengcing Technique:
Collector System Equivalent on 100 MVA and 24 kV base
From To R X B n
R n^2
X n^2 1 4 3 2 5 9
SUB 12 6 8 7
RESULTS
Partial R sum
9.4788
Partial X sum
6.7666 N 21
Collector System Equivalent
(Same units as R, X & B data)
Req pu
Xeq
Beq
Pad-mounted Transformer Equivalent
pu on 3 MVA base
Useful Resource: WECC PV/Wind Power Flow Modeling Guidelines

18. Useful Resource: WECC PV/Wind Power Flow Modeling Guidelines
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

19. Dynamic Models for PV Power Plants A. Ellis

20. 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

21. Plant-Level Controls

22. PV Inverter Topology and Controls (One Example)
AC Current Controls
Line Current Synch.
Iac, Vac at inverter terminals
DC Dynamics
Not Modeled
Vdc
Process Control (slower)
(MPPT, P/Q control)
Plant Supervisory
Controller

23. Representation of Discrete PV Plants
Two options for dynamic representation
Full-featured PV Plant Model (REXX)
Simplified Model (PVD1)
Both require generator explicitly represented in power flow and equivalent feeder/collector
PVD1 Model
REXX Model

24. REXX PV Plant Model Structure
20 April 2017
REXX PV Plant Model Structure
Requires plant control (REPC_A), inverter control (REEC_B), grid interface (REGC_A), protection

25. 20 April 2017
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)

26. Inverter P/Q Electrical Controls
20 April 2017
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

27. Generator/Converter Model
20 April 2017
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

28. Voltage & Frequency Tolerance
Voltage and frequency tolerance can be roughly represented using standard (V,t) and (f,t) protection models

29. Sample Simulations

30. Simple Dynamic Model (PVD1)
20 April 2017
Simple Dynamic Model (PVD1)
Intended for use with a smaller PV plant or distribution-connected MW-scale plant
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

31. Dynamic Model Specifications for Wind Power Plants P. Pourbeik

32. User Experience With REXX Models I. Green

33. Software Tutorials J. Sanchez-Gasca, J. Senthil, J. Weber

34. Experience with Model Validation P. Pourbeik, R. Elliott

35. Open Discussion

36. Contact A. Ellis, REMTF Chair aellis@sandia.gov