Distributed Photovoltaic Generation Emulation in Converter Based Power

Grid Emulation System

Anthony Perez,

Mitchell Smith, Wenchao Cao, Dr. Fred WangFinal Presentation

July 17, 2014

Knoxville, Tennessee

Outline

• Objective and Approach

• Emulation Structure of HTB Converters

• Distributed Photovoltaic Model

• Future Work

Objective and Approach

1. Use one converter to emulate one PV unit.

2. Use two converters to emulate two PV units.

3. Use one converter to emulate a radial distribution line with two PV units.

Objective: To emulate a distribution feeder with two PV units

Physical components of two stage PV inverter system

One inverter with PV model

Hardware Test Bed

Two-Area System Topology

Simulations of Two-Area System

Emulation Structure of HTB Converters

Functionality:

1. Current and voltage are measured.

2. Voltage’s value goes to the PV model to generate the current reference.

3. Current’s value goes to a current control loop to generate the signals to the inerter.

Single Inverter System

Single Inverter System Control (Simulink)

Distributed PV model

Current control

Current Control Testing

Different testing have been done to test if the simulation has been well implemented.

The different testing are:

1. Id & Iq current control2. P & Q control

Active Current test

Reactive Current test

A step function was used for this test.

-For Id: a)Step time – 0.2 s b)Range – 0 to 0.5 pu

-For Iq: a)Step time – 0.2s b)Range - 0 to 0.2 pu

P & Q Control

P and Q response when a step change is apply as a reference.

For Q: Step time – 0.2 s Range - 0 to 0.1 pu

For P: Step time – 0.2 s Range – 0 to 1pu

Distributed Photovoltaic Model

Physical components of two stage PV inverter system

One inverter with PV model

Distributed PV model

PV panel model

Distributed Photovoltaic System Model (Simulink)

5-13

Sub part 1:PV panel model

Sub part 2: System control model

Sub part 1: PV Panel Model

5-14

S: solar irradiance (W/m2)T: temperature (deg C)Pmax: Maximum power outputSingle diode model

stcVopstcIsc

VocIscstcPmpP

___max

Simulation model of PV panel

Simulation of PV Panel Model

• Natural conditions variations like temperature and solar irradiance are considered in this work, to see the impacts in the system and to obtain more realistic results.

0 10 20 30 40 500

2

4

6I - V curve with irradiance changes (T = 25 C)

Voltage (V)

Cu

rre

nt (

Am

ps)

S = 600 W/m2

S = 800 W/m2

S = 1000 W/m2

0 10 20 30 40 500

2

4

6

Voltage (V)

Cu

rre

nt (

Am

ps)

I - V curve for temperature variations (S = 1000 W/m2)

T = 25 C

T = 45 C

T = 60 C

0.2 0.4 0.6 0.8 1 1.225

30

35

Time (s)

T (

C)

0.2 0.4 0.6 0.8 1 1.2600

800

1000

Time (s)

S (

W/m

2 )

0.2 0.4 0.6 0.8 1 1.20

0.5

1

Time (s)

Po

we

r (p

u)

Pmax

Q

Sub part 2: DPVS Control Model

Ref. http://www.powerworld.com/files/WECC-Solar-PV-Dynamic-Model-Specification-September-2012.pdf [Western Electricity Coordinating Council]

Q-V droop control

P-f droop control

DPVS Control Model (Simulink)

P-f droop control

Q-V droop control

P & Freq. Droop

-A ramp function was used for this test.

-For freq: slope – 0.5 a)starting time – 0 b)initial output - 60

- Dead-band: 0.05 Hz

Note: The frequency of the constant source is modify to have an step change of 0.3 in 0.5 and 0. 8 s.

0 0.2 0.4 0.6 0.8 1-0.5

00.5

11.5

Time (s)Act

ive

Po

we

r (p

u)

0 0.2 0.4 0.6 0.8 160

60.260.460.660.8

Time (s)

Fre

qu

en

cy (

Hz)

Q & V Droop

-A ramp function was used for this test.

-For freq: slope – 0.2 a)starting time – 0 b)initial output – 0.9

- Dead-band: 0.02 pu

Note: The amplitude of the constant source is modify to change from 1 to 1.1 and 0.9 pu in 0, 0.5 and 0. 8 s respectively.

0 0.2 0.4 0.6 0.8 1-0.3-0.2-0.1

00.10.20.3

Time (s)

Re

act

ive

Po

we

r (p

u)

0 0.2 0.4 0.6 0.8 10.80.9

11.11.2

Time (s)

Vo

ltag

e (

pu

)

System Response with Q & V and P & f Implementation

Reactive Power and terminal voltage waves when the voltage change from 1 to 1.1 pu in 0.5 seconds and to 0.9 pu in 0.8 seconds.

0.1 0.3 0.5 0.7 0.9 1.1 1.2-0.5-0.3-0.10.10.30.5

Time (s)

Q (

pu

)

0.2 0.4 0.6 0.8 1 1.21.20

0.5

1

1.5

Time (s)

Vo

ltag

e (

pu

)

0 0.2 0.4 0.6 0.8 1 1.2

0.2

0.4

0.6

0.8

Time (s)P

(p

u)

0 0.2 0.4 0.6 0.8 1 1.2

60

60.1

60.2

Time (s)

Fre

qu

en

cy (

Hz)

Active power and frequency Waveforms when the frequency it is changed by .3 Hz in .5 and .8 second respectively

Two PV Unit System SimulationA distribution feeder with two PV units

PV 1

PV 2

Two PV Inverter System Simulation

0.2 0.4 0.6 0.8 1 1.20.9

0.95

1

Time (s)

V (

pu

)

0.2 0.4 0.6 0.8 1 1.2

0

1

2

3

x 104

P (

W)

Q(V

ar)

Time (s)0.2 0.4 0.6 0.8 1 1.2

0

1

2

3

x 104

Time (s)

P (

W)

Q(V

ar)

0.2 0.4 0.6 0.8 1 1.2

0.96

0.98

1

1.02

Time (s)

V (

pu

)

To verify the effects of the droop function implementation into the two PV models, it is shown in the graphs below. The reactive power and terminal voltage changes at the terminal of each PV system.

Without Q-V droop With Q-V droop

Q1, Q2

P1, P2

V1

V2

Q1, Q2

V1

V2

P1, P2

Conclusions & Future Work

• A converter based distributed PV emulator with variable irradiance and temperature is designed.

• Different control strategies for the DPVS were implemented in order to maintain the balance in the power grid.

• The implementation of this system into the real HTB configuration is required for future work.

Questions?