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Impact of Large Scale PV Generation Vijay Vittal – Arizona State University Sara Eftekharnejad – TEPCO Gerald Heydt – Arizona State University Brian Keel – SRP Jeffrey Loehr - SRP 1

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Impact of Large Scale PV Generation

Vijay Vittal – Arizona State UniversitySara Eftekharnejad – TEPCO

Gerald Heydt – Arizona State UniversityBrian Keel – SRP

Jeffrey Loehr - SRP

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Reference Source

• This presentation is based on the following transactions paper

Eftekharnejad, S., V. Vittal, G.T. Heydt, B. Keel, J. Loehr, “ Impact of Increased Penetration of Photovoltaic Generation on Power Systems,” IEEE Transactions on Power Systems, Vol. 28, No. 2, pp. 893-901, May 2013.

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Characteristics of System Studies

• Entire WECC represented for high PV penetration studies

• Photovoltaic systems are added to the zones within the Arizona area

• Light loading conditions of the month of April

• Peak PV outputs

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Base Case Modifications

Utility-Scale

• 200 MW cumulative for SRP and 400 MW for APS by 2015

Commercial and Residential Rooftop

• Spread across the valley at local 69 KV buses

South East valley (near Abel)

South West valley (near Palo Verde)

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Representation of Commercial and Residential Rooftop PVs• Power flow studies:

Rooftop PVs are represented as PQ buses:– Constant loads with

zero reactive power capability

– Constant impedances corresponding to the negative power injections

PV

LoadUnit Station Transformer

Transmission

System

• Dynamic studies: Same model used for steady state and dynamic studies

• Rooftop PVs are added to the 69kV level buses across the valley to the SRP and APS zones

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Arizona Solar MapAn Arizona solar map is utilized to locate the existing PV installations based on the zip codes of the SRP substations

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Utility Scale PVs• Power flow studies: Modeled as PV buses• Conventional generators with reactive power

capability represent the utility scale PVs in power flow studies

PVPad-mounted Transformer

Collector System

Station Transformer Transm

ission System

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Utility Scale PVs• Use existing WECC

generic convertermodel– General Electric

type 4 wind turbine generator

• DC side dynamics such as MPPT are neglected

• Both DSATools and PSLF have the equivalent model available in the model library

Source: K. Clark, N. Miller, R. Walling, “Modeling of GE Solar Photovoltaic Plants for Grid Studies”, April 2010.

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Utility Scale PVs

•Converter Model

•Protective Relay settings

•Electrical Control Models

PV Array Model

Inverter Model

Connection to Network

d-q voltage

d-q current

DC voltage

Reactive power Control

Desired q-axis current

DC current

AC voltage

Power Factor

Network Model in PSLF

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Steady State Analysis

Impact of increased penetration of PV solar on static voltage stability and control at low loads

• Various PV penetration levels were studied (up to 50 %)• Roof top PVs modeled as PQ buses and utility scale PVs modeled as PV buses

• High voltages were observed at 20-30% PV generation levels• At higher PV generation levels steady state voltages will decrease

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Steady State Analysis

• Steady state analyses are carried out in presence of high PV penetration levels

• Various PV generation levels are studied for power flow studies.

(MW) generation Total(MW) generationPV Total

(%) n PenetratioPV =

PV Gen. (MW)

Level %

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SRP Voltages

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 0.1 0.2 0.3 0.4 0.5 0.6

VPV-Vbase(p.u.)

PV Penetration %

PINKERTO

RIOVERDE

PAPAGOBT

BRANDOW

34E17N

GLENBR02

GLENBROO

WHEELER

FOUNTAIN

MCMULLIN

GILA 2

295E8.4N

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Dynamic Analysis

Impact of increased penetration of PV solar on transient stability at low loads•Frequency•Relative rotor angle•Voltage

•20% PV generation is used for system studies

•PSLF GE type 4 wind turbine models for full converter dynamic modeling

•DC side dynamics are neglected

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Case Studies14

Case Study 1Detrimental Impact on the transmission system:– Three phase fault on

15021 PALOVRDE 500 kV

– Cleared after 4 cycles– Double line outage of

15061 RUDD-15089 JOJOBA while the fault is cleared

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Case Study 1

4.5 5 5.5 6 6.5 7 7.5 80

20

40

60

80

100

Time (sec)

Rela

tive r

oto

r an

gle

(d

eg

ree)

Gen 888 20% PVGen 888 no PVGen 1567 20% PVGen 1567 no PV

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Case Study 2Beneficial Impact on the transmission system:– Three phase fault on

15089 JOJOBA 500 kV – Cleared after 4 cycles– Double line outage of

15089 JOJOBA-14007 GILARIVR while the fault is cleared

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Case Study 2

4.5 5 5.5 6 6.5 7 7.5 8 8.5 90102030405060708090

100

Time (sec)

Rel

ativ

e ro

tor a

ngle

(deg

)

Gen 1567 20% PVGen 1567 no PVGen 888 20% PVGen 888 no PV

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Effect of Cloud Cover

• Residential roof top PVs are dropped due to the cloud cover

• Output of the PVs are reduced to 50% of the nominal values

• A case with 20% PV generation is simulated in DSATools

• The effect of cloud cover is simulated in TSAT

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Effect of Cloud Cover

0 10 20 30 40 50 60 70 801.03

1.035

1.04

1.045

1.05

1.055

1.06

1.065

1.07

Time (sec)

Volta

ge (p

.u.)

21.E1.0S 69.0ANDERSON 69.0ARCADIA1 69.0BRANDOW 69.0BROADWA2 69.0DOBSON 1 69.0FLUME 69.0INDIANB1 69.0KNOX 69.0KYRENEST 69.0OWENS 2 69.0RIVERSI2 69.0SANTAN 69.0SOUTHERN 69.0

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Conclusions• High penetration of PV resources results in:

– Increase in steady state voltages– High voltages on 69 kV buses with 20% penetration level

(over voltages up to 10%)– Increased voltage dips during contingencies (e.g. 0.12 p.u.

more voltage dip)– Increased oscillations in relative rotor angles

• With motor loads the large voltage dips could lead to further worsening of voltage recovery

• Cloud cover affects the bus voltages and may cause a significant voltage drop depending on the cloud characteristics

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