WECC Renewable Energy WECC Renewable Energy Modeling WorkshopModeling 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 LaboratoriesDonald Davies, Kent Bolton – WECC

Pouyan Pourbeik – EPRIJuan Sanchez-Gasca – General Electric

Jay Senthil – SiemensJamie 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 planning2

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

4

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

5

RE

MT

F S

cope

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

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 W

TG P

lant

s

PV P

lant

s

Type

4 W

TG P

lant

s

• 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

• Approved REXX models for PV and Type 3/4 wind power 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 AgendaTime Topic Speaker

8:30 – 8:45 Introduction and REMTF Overview Abraham Ellis8:45 – 9:15 Standards basis Donald Davies

9:15 – 10:00 Power Flow Representation RE PlantsDynamic Model Specifications for PV Abraham Ellis

10:00 – 10:30 BREAK 10:30 – 11:30 Dynamic Model Specifications for Wind Pouyan Pourbeik11:30 – 12:00 User Experience with New REXX models Irina Green12:00 – 1:00 LUNCH 1:00 – 1:30 PowerWorld Tutorial Jamie Weber1:30 – 2:00 PSS/E Tutorial Jay Senthil2:00 – 2:30 PSLF Tutorial Juan Sanchez-Gasca2:30 – 3:00 Questions for Tutorial All3:00 – 3:30 BREAK

3:30 – 4:30 Experience with Wind and PV Model Validation

Pouyan Pourbeik,Ryan Elliott

4:30 – 5:00 Open mic: questions, feedback All5:00 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

DeSoto PV Plant (2009) DeSoto PV Plant (2009) Fort Myers, FL. (courtesy of FPL)Fort Myers, FL. (courtesy of FPL)

Substation with Substation with plant transformersplant transformers

PV Array on fixed of PV Array on fixed of tracking structure tracking structure

PV Inverters and Pad-PV Inverters and Pad-mounted transformersmounted transformers

Substantial MV collector system Substantial MV collector system network, OH or UG radial feedersnetwork, OH or UG radial feeders

Interconnection Interconnection LineLine

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

14

Power Flow Equivalencing

15

How to obtain equivalent collector system parameters?

1.Estimate based on typical design parameters2.Best way: Calculate from collector system design data (example follows)

Single-machine power flow model

1 4

2

3

59

7

6

SUB

8

PV Inverter1 MW+/-0.95 pf

Pad-mounted Transformer3 MVAZ=6%, X/R=10

UG feeders24 kV

Inverter cluster

To utility

Model station transformer and interconnection line explicitly, if they exist.

Example – 21 MW PV Plant

16

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 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 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 pu Beq 0.000005 pu

j0.008530.000857

j0.05970 0.00597

M

ZZ TTeq

Pad-mounted Transformer Equivalent

Collector System Equivalent on 100 MVA and 24 kV base

pu on 3 MVA base

21

2

N

nZjXRZ

I

iii

eqeqeq

I

iieq BB

1

Collector System Equivalengcing Technique:

Example – 21 MW PV System

17Useful 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

18Useful 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

20

Plant-Level Controls

PV Inverter Topology and Controls (One Example)

GATE DRIVE

CIRCUITRY

PV Array Voltage Source Converter Grid

Iac, Vac at inverter terminals

Vdc

AC Current ControlsLine Current Synch.AC Current ControlsLine Current Synch.

Plant SupervisoryController

Plant SupervisoryController

Process Control (slower)(MPPT, P/Q control)

Process Control (slower)(MPPT, P/Q control)DC D

ynam

ics

DC Dyn

amics

Not M

odel

ed

Not M

odele

d

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

23

÷

Vt

N

D×

Q Priority (Pqflag =0)Iqmax = ImaxTDIqmin = -IqmaxIpmax = (ImaxTD2-Iqcmd2)1/2

P Priority (Pqflag =1)Ipmax = ImaxTDIqmax = (ImaxTD2-Ipcmd2)1/2

Iqmin = -Iqmax

÷

0

Ipmax

Iqmin

Iqmax

0.01

N

D

×

Vt0 Vt1 Vt2 Vt3

1

0

V0 V1

DqdvQmx

QmnQref

Vrflag

Freq

Ft0 Ft1 Ft2 Ft3

1

0

Frflag

Ip

Iq

It = Ip +j Iq

-11 + sTg

11 + sTg

Ipcmd

Iqcmd

PVD1

XcIt

Qref

-Freq_ref Ddn

fdbdPdrp

Pref

Pext

Pdrp

Fvl

Ffh

Ffl

MINIMUM

Fvh

FvlFfhFfl Fvh

Q Control

P Control

Current Limit Logic

IqcmdIqcmd’

IpcmdIpcmd’

Generator Model

Network Solution

Plant Level V/Q Control

Plant Level P Control

VrefVreg

QrefQbranch

PrefPbranchFreq_ref

Freg

Qext

Pref

REPC_A

Pqflag

REEC_B REGC_AVt Vt

Iq

Ip

REXX Model

PVD1 Model

REXX PV Plant Model Structure• Requires plant control (REPC_A), inverter control

(REEC_B), grid interface (REGC_A), protection

24

Q Control

P Control

Current Limit Logic

IqcmdIqcmd’

IpcmdIpcmd’

Generator Model

Network Solution

Plant Level V/Q Control

Plant Level P Control

VrefVreg

QrefQbranch

PrefPbranchFreq_ref

Freg

Qext

Pref

REPC_A

Pqflag

REEC_B REGC_AVt Vt

Iq

Ip

PV Plant Controller

25

• 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

26

• 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

• 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)

30

÷

Vt

N

D×

Q Priority (Pqflag =0)Iqmax = ImaxIqmin = -IqmaxIpmax = (Imax2-Iqcmd2)1/2

P Priority (Pqflag =1)Ipmax = ImaxIqmax = (Imax2-Ipcmd2)1/2

Iqmin = -Iqmax

÷

0

Ipmax

Iqmin

Iqmax

0.01

N

D

×

Vt0 Vt1 Vt2 Vt3

1

0

V0 V1

DqdvQmx

QmnQref

vrrecov

Freq

Ft0 Ft1 Ft2 Ft3

1

0

frrecov

Ip

Iq

It = Ip +j Iq

-11 + sTg

11 + sTg

Ipcmd

Iqcmd

PVD1

XcIt

Qref

-Freq_ref Ddn

fdbdPdrp

Pref

Pext

Pdrp

Fvl

Ffh

Ffl

Fvh

Fvl

Ffh

Ffl

Fvh

×

• 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

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 Chairaellis@sandia.gov