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WECC Renewable Energy Modeling Workshop: Developing Non-proprietary Models for Solar and Wind Generation

The WECC Renewable Energy Modeling Task Force (REMTF) conducted a workshop to develop generic, non-proprietary models for solar and wind generation. This workshop aimed to improve accessibility and reliability of the bulk power system. Approved models for PV and wind plants were discussed, along with the implementation plan for the WECC Renewable Energy Model.

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WECC Renewable Energy Modeling Workshop: Developing Non-proprietary Models for Solar and Wind Generation

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  1. WECC Renewable Energy Modeling WorkshopConducted by the WECC Renewable Energy Modeling Task Force (REMTF) and Modeling and Validation Work Group (MVWG)June 17, 2012 - Salt Lake City, UTAbraham Ellis, Ryan Elliott, Ben Karlson – Sandia National LaboratoriesDonald Davies, Kent Bolton – WECCPouyan Pourbeik – EPRIJuan Sanchez-Gasca – General ElectricJay Senthil – SiemensJamie Weber – PowerWorldIrina 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, http://www.nerc.com/files/IVGTF_Report_041609.pdf

  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 PV Plants Type 4 WTG Plants Type 3 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

  9. Workshop Agenda

  10. Standards Framework for Wind and PV Modeling in WECCD. Davies

  11. Power Flow Representation of PV and Wind Power PlantsA. Ellis

  12. Example of a PV Plant 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)

  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 4 5 1 9 7 8 2 SUB 6 3 To utility Model station transformer and interconnection line explicitly, if they exist.

  17. Example – 21 MW PV System Collector System Equivalengcing Technique: Collector System Equivalent on 100 MVA and 24 kV base Pad-mounted Transformer Equivalent pu on 3 MVA base Useful Resource: WECC PV/Wind Power Flow Modeling Guidelines

  18. 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 PlantsA. 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 • Requires plant control (REPC_A), inverter control (REEC_B), grid interface (REGC_A), protection

  25. 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 • 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 • 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) • 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 Intended for use with a smaller PV plant or distribution-connected MW-scale plant

  31. Dynamic Model Specifications for Wind Power PlantsP. Pourbeik

  32. User Experience With REXX ModelsI. Green

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

  34. Experience with Model ValidationP. Pourbeik, R. Elliott

  35. Open Discussion

  36. ContactA. Ellis, REMTF Chairaellis@sandia.gov

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