1. Mitchell Smith, Wenchao Cao, Dr. Fred Wang
Distributed Photovoltaic Generation Emulation in Converter Based Power Grid Emulation System
Anthony Perez,
Mitchell Smith, Wenchao Cao, Dr. Fred Wang
Final Presentation
July 17, 2014
Knoxville, Tennessee

2. Outline
Objective and Approach
Emulation Structure of HTB Converters
Distributed Photovoltaic Model
Future Work

3. Objective and Approach
Objective: To emulate a distribution feeder with two PV units
Physical components of two stage PV inverter system
One inverter with PV model
Distributed generation have been increasing in the last years. We see everyday more solar systems installed in the roof of houses. As consequence we need more research in this area to see how this systems affect the power grid. The objective of this project is to emulate a distribution feeder with two PV units. Inside of each PV units there are PV panels, a DC/DC boost converter and an inverter. For this emulation we are not considering the DC/DC converter. The graph in the bottom shows the representation of the PV units used in this work. The approach of this research is to: use one converter to emulate one PV unit, use two converter to emulate two PV units and finally, use one converter to emulate two PV units.
Use one converter to emulate one PV unit.
Use two converters to emulate two PV units.
Use one converter to emulate a radial distribution line with two PV units.

4. Hardware Test Bed
HTB is transmission network emulator. It is designed to emulate a large scale power system using interconnected converters. This figure shows the physical implementation of HTB. In this system it is possible to emulate: generators, loads and transmission lines. This system can be controlled in the visualization room.

5. Two-Area System Topology
This is the circuit implementation of HTB. It consist of two clusters connected by a transmission line emulator.

6. Simulations of Two-Area System
This is the two area system simulation implemented at Simulink. This system is compose of four generators, three loads. As you can see in the picture everything looks the same and the reason for that is because it is an emulation and the only thing that makes them behave differently from each other is the control function commands. The control function command are located in each box at the right side of the figure. Each box correspond to one emulation.

7. Emulation Structure of HTB Converters
Functionality:
Current and voltage are measured.
Voltage’s value goes to the PV model to generate the current reference.
Current’s value goes to a current control loop to generate the signals to the inerter.
This is how an emulation works in HTB. First the current and voltage are measured. The measured voltage goes to the system model to generate the current reference and send it to the current control in combination with the measured current. Finally the current control will send the gate signals to the inverter.

8. Single Inverter System
The first approach was to use one converter to emulate one PV unit. This is a single inverter system and it is the first system that I worked on. You can see in the figure what the PV unit represent in the Simulink simulation. What is inside of the control box?

9. Single Inverter System Control (Simulink)
Distributed PV model
Current control
This figure represent the what is inside of the single inverter system’s control box. As you can see it consists of two parts. The first one is the PV model control and the other one is the current control.

10. Current Control Testing
Different testing have been done to test if the simulation has been well implemented.
The different testing are:
Id & Iq current control
P & Q control
Active 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
The first testing was done to the current control. This was made to verify the effectiveness of the current control before implanting the other parts. As you can see in the picture, the current control is able to track the reactive and active current when a step function is added.
Reactive Current test

11. P & Q Control
With this test we verify the active and reactive power control by adding a step function in .2 seconds the values goes to the corresponding values.
P and Q response when a step change is apply as a reference.
For P: Step time – 0.2 s
Range – 0 to 1pu
For Q: Step time – 0.2 s
Range - 0 to 0.1 pu

12. Distributed Photovoltaic Model
Physical components of two stage PV inverter system
One inverter with PV model
Distributed PV model
As I said before, the distributed PV model is divided in two parts: PV panel model and the system control model.
PV panel model

13. Distributed Photovoltaic System Model (Simulink)
This is inside the PV model control box. It is divided in two parts: maximum power implementation control and the other is the distributed PV control model.
Sub part 1:PV panel model
Sub part 2: System control model

14. Sub part 1: PV Panel Model
S: solar irradiance (W/m2)
T: temperature (deg C)
Pmax: Maximum power output
Single diode model
Simulation model of PV panel
The dynamic model of the PV panel was designed using the single diode model. Also it is considered the solar irradiance and temperature. The graph in the bottom present the actual implementation of the PV panels. To output the maximum power…

15. 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.
Pmax Q

16. Sub part 2: DPVS Control Model
Q-V droop control
P-f droop control
Ref. [Western Electricity Coordinating Council]

17. DPVS Control Model (Simulink)
P-f droop control
Q-V droop control

18. 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.

19. 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.

20. 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.
Active power and frequency
Waveforms when the frequency it is
changed by .3 Hz in .5 and .8
second respectively

21. Two PV Unit System Simulation
A distribution feeder with two PV units
PV 1
Now that all the modules are implemented and tested for the single PV unit system I proceed to work with the two PV unit system simulation.
PV 2

22. Two PV Inverter System Simulation
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
P1, P2
P1, P2
Q1, Q2
Q1, Q2 V1 V1 V2 V2

23. 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.

24. Questions?