Power Quality Improvement of Single-Phase Grid-Connected Photovoltaic Inverter

A Dissertation for the Degree of Doctor of Philosophy

Power Quality Improvement of Single-Phase

 Grid-Connected Photovoltaic Inverter

Department of Information and Communications Engineering

Graduate School

Chungnam National University

By

Trung-Kien Vu

Advisor

Se-Jin Seong

February 2011 

 

ABSTRACT*

 

The economical and environmental impacts of fossil fuels have forced society to  investigate sustainable solutions.  The  interest  has

            focused on the renewable energy sources since the green and clean benefits. Consequently, investments in research and development in the field of power electronics have increased proportionally, especially in high voltage and high power grid-connected systems.

 

The distributed power generation (DG) systems are becoming more common as the need  for electric power increases because of taking advantage of using different energy sources such as wind and solar. A few examples are hybrid cars, solar houses or hospitals in remote  areas  where  providing  clean,  efficient  and  reliable  electric power is critical to the loads. In such systems, the power is distributed from the source side to the load side via power electronic converters in the system. At low and medium power applications, the task is often left to single-phase inverters where they are the only interface between sources connected to dc bus and loads connected to an ac bus. This dissertation investigates the power quality improvements to properly regulate  the  power  flow  between renewable  source  and  the  utility network. The control method for single-phase inverters used in low and medium power DG systems is based on (and also takes the advantage of) the well-known d-q transformation (which is mostly employed for three-phase   converters’   analysis   and   control   design).   The transformation requires at least two independent phases for each state variable in the system; thus a second phase must  be created. This virtual-phase can be done by DSP implementation, hence there is no need for additional hardware in the system, making it more attractive and cost effective method. 

 

The Proportional-Resonant (PR) controller based current control scheme,   compared   with   conventional  Proportional-Integral (PI)

            controller, not only provides a superior transient  response but  also provides a zero steady-state error as well as a high disturbance rejection and a low output current THD under grid-tie mode operation. The entire controller can be implemented in a DSP digital control board

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