comparison of full and reduced scale solar pv plant · pdf filepv plant models in...

Comparison of Full and Reduced Scale Solar PV Plant Models in Multi-Machine Power

Systems

Sachin Soni, George Karady, Mahesh Morjaria, and Vladimir Chadliev

1

IEEE Transmission and Distribution Conference 2014

Chicago, Illinois

2

Presentation Outline

1. Grid Connected Solar PV Plants

2. Centralized PV plant model for load flow representation

3. PV Plant model components / subsystems

4. Modified IEEE 39 bus test system

5. Model Simulation results

6. Conclusions

Grid Connected PV Plant Topology

3

WECC Guide for Representation of Photovoltaic Systems in Large-Scale Load Flow Simulations, August 2010

4

WECC Renewable Energy Modeling Task Force (REMTF) PV Plant Power Flow Model

• Equivalent generator represents the total generating capacity of all inverters

• Equivalent pad-mounted transformer represents aggregate effect of all step-up transformers

• Equivalent collector system branch represents the aggregate effect of the PV plant collector system

Load Flow Representation

Model approximate PV plant load flow characteristics at the interconnection point

WECC Guide for Representation of Photovoltaic Systems in Large-Scale Load Flow Simulations, August 2010

5

Collection System Equivalent

𝑍𝑒𝑞 = 𝑅𝑒𝑞 + 𝑗𝑋𝑒𝑞 = 𝑍𝑖𝑛𝑖

2𝐼𝑖=1

𝑁2

𝐵𝑒𝑞 = 𝐵𝑖

𝐼

𝑖=1

𝐵𝑒𝑞 𝑅𝑒𝑞 𝑋𝑒𝑞

E. Muljadi, C. P. Butterfield, A. Ellis, J. Mechenbier, J. Hochheimer, R. Young, N. Miller, R. Delmerico, R. Zavadil, and J. C. Smith, "Equivalencing the Collector System of a Large Wind Power Plant," in IEEE PES General Meeting, June 2006.

6

Overall Model Structure for Central Station PV system Overall model structure consists of the following -

• Generator model (REGC_A) to provide current injections into the network solution

• Electrical control model (REEC_B) for local active and reactive power control

• Optional plant controller model (REPC_A) to allow for plant-level active and reactive power control

WECC Generic Solar Photovoltaic System Dynamic Simulation Model Specification – September 2012

7

Generator /Converter Model Functional Block Diagram


Current regulator to inject inverter current into external network in response to real and reactive current commands. • User settable reactive current

management during high voltage events at the generator (inverter) terminal

• Active current management during

low voltage events to approximate the response of the inverter PLL controls during voltage dips

• Power logic during low voltage

events to allow for a controlled response of active current during and immediately following voltage dips

8

Local Reactive Power Control

• Constant power factor, based on the inverter power factor

• Constant reactive power, based either on the inverter absolute reactive power or, plant controller model

Local Active Power Control

• Reference active power from solved power flow case or from power plant controller model.

• Current Commands subject to Converter thermal ratings


Electrical Controller Model

Multi-Machine Plant Model

9

R = 0.15100 Ohms/mile

X = 0.78052 Ohms/mile

Xc = 0.1819 Ohms/mile

1.4 mile

230 kV Line A



Xc = 0.1817 Mohms/mile

Length = 2.1 Mile

230 kV Line B




Length = 2.3 Mile

230 kV Bus A 230 kV Bus B

230 kV Gen-Tie

Bus

Utility Grid

230 kV Gen-Tie




Length = 1.0 Mile

Y

Y Y

Y

SUT-A

Size 54 MVA

Primary230 kV Wye Grounded

Sec 34.5 kV Wye Grounded

%Z = 9.000%

X/R = 43.7

SUT-B

Size 54 MVA

Primary 230 kV Wye Grounded

Sec 34.5 kV Wye Grounded

%Z = 9.000%

X/R = 43.7

SW-SWGR #A SW-SWGR #B

Feeder 1 Feeder 2 Feeder 3 Feeder 4 Feeder 5

34.5 kV

01-PVCS

25.20 MW

34.5 kV

02-PVCS

36.54 MW

34.5 kV

03-PVCS

30.24 MW

34.5 kV

04-PVCS

28.98 MW

34.5 kV

05-PVCS

26.46 MW




2.1 mile




2.1 mile




1.8 mile




2.2 mile

34.5 kV Bus 34.5 kV Bus

Possible Representations • Single Machine model -

Equivalenced at POI

POI

34.5 kV PVS Bus

• Two Machine Model – Equivalenced at 34.5 kV PVS buses

34.5 kV PVCS Bus

• Five Machine Model – Equivalenced at 34.5 kV medium voltage PVCS collector system bus

10

IEEE 39 Bus Test System

T. Athay, R. Podmore, and S. Virmani, "A Practical Method for the Direct Analysis of Transient Stability," in IEEE Transactions on Power Apparatus and Systems, vol. PAS-98, pp. 573-584, 1979

Modifications to IEEE 39 Bus System

• Power output of generator 9 connected at Bus 38 is reduced to 100 MW.

• In order to maintain same power injection at Bus 29 as in actual system the load at Bus 29 is disconnected.

• Voltage regulator and power system stabilizer of generator 9 were disconnected to expose PV plant to more severe conditions.

PV Plant Model

• Full scale model comprises of 117 inverters

• Each inverter rated at 1350 kVA with power factor operating range from 0.93 lead to 0.93 lag

• 9-cycles LLLG fault is applied at Bus 26

11

Feeder Impedance For Each Scenario

• System equivalent impedance calculated using WECC power flow modeling guide

• Collection system impedance for each scenario on 34.5 kV and 100 MVA base

Test Scenarios Section R (p.u.) X (p.u.) B (p.u.) Full Scale Model All Sections 0.00504 0.00201 0.00022

Single-Machine model Full feeder 0.00493 0.02681 0.03261

Two-Machines model Section-I 0.01226 0.06558 0.01432

Section-II 0.00812 0.04488 0.01829

Five-Machines model

Section-I 0.02189 0.09342 0.00534

Section-II 0.02382 0.13667 0.00898

Section-III 0.02314 0.13641 0.00692

Section-IV 0.00327 0.12009 0.00602

Section-V 0.02841 0.14302 0.00565

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Response for One Machine and Full Scale Models

0

0.2

0.4

0.6

0.8

1

1.2

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Vo

ltag

e (

p.u

.) BUS 40

0

20

40

60

80

100

120

140

160

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Act

ive

Po

we

r (M

W)

Time (Sec.)

-15

15

45

75

105

135

165

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Re

acti

ve P

ow

er

(MV

AR

)

0

0.2

0.4

0.6

0.8

1

1.2

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Vo

ltag

e (

p.u

.) BUS 101

BUS 125

BUS 155

BUS 190

BUS 217

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Re

acti

ve P

ow

er

(MV

AR

)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Act

ive

Po

we

r (M

W)

Time (Sec.)

One Machine Equivalent

Single Equivalent Inverter rated 157.95 MVA, p.f. operating range of +/- 0.93

Full Scale Model

117 Inverters each rated 1.35 MVA

All capable of +/- 0.93 p.f.

13

0

0.2

0.4

0.6

0.8

1

1.2

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Vo

lta

ge

(p.u

.)

BUS 40

BUS 45

0

30

60

90

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Acti

ve P

ow

er

(MW

)

Time (Sec.)

-10

10

30

50

70

90

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Rea

cti

ve P

ow

er

(MV

Ar)

0

0.2

0.4

0.6

0.8

1

1.2

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Vo

lta

ge

(p

.u.)

BUS 50

BUS 52

BUS 54

BUS 56

BUS 58

-5

5

15

25

35

45

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Rea

cti

ve P

ow

er (

MV

Ar)

0

10

20

30

40

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Acti

ve P

ow

er

(M

W)

Time (Sec.)

Two Machine Equivalent

Equivalent Inverter 1 rated 66.15 MVA


p.f. operating range of +/- 0.93

Five Machine Equivalent






p.f. operating range of +/- 0.93

Response for Two Machine and Five Machine Models

14

Steady State and Dynamic Simulation Results at POI

Simulated Cases

Measured Parameters at POI

Active Power (MW)

Reactive Power (MVAr)

Voltage (p.u.)

Single Machine Equivalent 144.8 -23.5 1.062

Two Machine Equivalent 144.8 -23.7 1.061

Five Machine Equivalent 144.9 -23.7 1.061

Full Scale Model 144.9 -23.7 1.061

0

0.2

0.4

0.6

0.8

1

1.2

0.00 1.15 2.33 3.53 4.73 5.93 7.13 8.33 9.53

Vo

ltag

e a

t P

OI (

p.u

.)

Time (Sec.)

ONE MACHINE MODEL

TWO MACHINE MODEL

FIVE MACHINE MODEL

FULL SCALE MODEL

• No significant change observed in measured

Active power, Reactive power and Voltage at

POI during steady-state analysis.

• Ensures computational efficiency without loss

of any information about system behavior.

• Root mean square (RMS) error for voltage

measured at POI for one-machine, two-

machine and five-machine reduced scale

model are 0.06%, 0.28% and 0.357%

respectively.

• Reduced order models are suitable for both

online (operation) and offline (stability)

studies

15

Conclusions

• RMS error calculated for measured voltage response is less than even 1%.

• Ensures computational efficiency without loss of any information about system

behavior.

• Reduced order model can represent the complete PV plant in similar manner as a

full scale model.

• Reduced order models are suitable for both online (operation) and offline

(stability) studies

16

Questions?

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