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

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)

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

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

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 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

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

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

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 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

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

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.

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.

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 0.03682 0.00701 0.000000691 3 0.33136 0.06307 2 0.02455 0.00467 0.000001036 0.22091 0.04205 5 9 1.98816 0.37843 0.02557 0.02116 0.000000235 0.23016 0.19042 SUB 12 3.68251 3.04673 6 8 0.03747 0.00868 0.000000561 0.33726 0.07809 7 0.02109 0.02501 0.000000199 0.75925 0.90025 1.70831 2.02555 RESULTS   Partial R sum 9.4788 Partial X sum 6.7666 N 21 Collector System Equivalent (Same units as R, X & B data) Req 0.021494 pu Xeq 0.015344 Beq 0.000005 Pad-mounted Transformer Equivalent pu on 3 MVA base Useful Resource: WECC PV/Wind Power Flow Modeling Guidelines

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

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

Plant-Level Controls

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

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

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

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)

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

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

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

Sample Simulations

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

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