1. Advanced Mechanical Design December 2008
Discrete Time Modeling And Control Of DC/DC Switching Converter For Solar Energy Systems
Shaghayegh Kazemlou
Advisor: Dr. Shahab Mehraeen
Louisiana State University
Advanced Mechanical Design
December 2008

2. Outline Part I: Grid-connected Renewable System
Part II: Converter Discrete-Time Model
Part III: Converter Discrete-time Control Design
Part IV: Simulation Results
Part V: Summary and Future Works

3. Grid-connected Renewable System
Part I
Grid-connected Renewable System
Advanced Mechanical Design
December 2008

4. Solar power generation system
Solar System Model
Solar panels
DC-DC buck converter
Grid-tie inverter (GTI)
Solar power generation system
stabilizing the inverter DC-link capacitor
Omitting solar power oscillations
Objective

5. Grid-Tie Inverter Synchronous Generator (SG) controller dynamics
Solar power generation system
controller
dynamics
Synchronous Generator (SG)

6. Grid-Tie Inverter Model/Observer
SG dynamical equations
Inverter dynamical equations
( )
Inverter gain ( ) and ac voltage angle ( ) are the control inputs

7. Converter Discrete-Time Model
Part II
Converter Discrete-Time Model
Advanced Mechanical Design
December 2008

8. dc-dc buck converter control system
Objective: Maintaining the solar power constant by adjusting duty cycle d

9. Converter Discrete-Time Model
Converter discrete-time equations
Photovoltaic array output current is a nonlinear function of

10. Converter Discrete-time Control Design
Part III
Converter Discrete-time Control Design
Advanced Mechanical Design
December 2008

11. State Feedback Controller
Input:
Tracking error :
stable

12. Neural Network function approximation
: activation function
Weight estimation error :
NN weight update law :
: positive design constant

13. Advanced Mechanical Design December 2008
Part IV
Simulation Results
Advanced Mechanical Design
December 2008

14. Simulation Results System parameters AVR+PSS mechanism for inverter
operational frequency of the converter : 10 kHz
three-phase resistive load with on each phase
Disturbance : load change from to at
solar module maximum power :
solar module maximum power point voltage :

15. Converter input voltage
Simulation Results
Solar Voltage Less than MPP Voltage:
Converter input power
Converter input voltage
Disturbance between t=1.4s to t=1.6s

16. Simulation Results Solar Voltage Less than MPP Voltage:
Converter output voltage
Converter inductance current
Converter input current

17. Simulation Results Solar Voltage higher than MPP Voltage:
Converter input power
Converter input voltage
Converter output voltage

18. Simulation Results Input Voltage Adjustment to Load Change:
Converter input power
Converter input voltage
Converter output voltage

19. Summary
The inverter is controlled by a novel stabilizer similar to power system stabilizer (PSS).
The interaction of the solar array dc-dc converter with the GTI is addressed.
A nonlinear discrete-time model of a photovoltaic-connected buck converter was presented.
Adaptive neural network (NN) controller is employed to enhance stability of dc-dc converter connected to grid-tie inverter (GTI) in the presence of power system disturbances.
Simulation results of the controller imply that the converter input voltage and power as well as the inductor current are stabilized which verifies the accuracy of the converter discrete-time model and the effectiveness of the proposed discrete-time controller.

20. Recommendations for Future Works
Improve the efficiency and effectiveness of discrete-time adaptive neural network in the power system stability and control
The system model can be developed to a more general distributed generation system where other renewable generators or synchronous generators all are interconnected. In this case each system is influenced by other subsystem’s states and a more general control method is necessary.
The solar system connected dc-dc converter can be modeled in a dc distribution system with interconnected subsystems working in high penetration of renewable generation.

21. Thank You for Your Attention