Power Electronics and Controls in Solar Photovoltaic Systems

Introduction

This chapter will discuss current developments in the controls and power electronics that enable the PV systems to become a real power source for the grid system. In the last decade, the PV power supplied to the utility grid has been gaining more and more visibility due to several reasons. First, there have been considerable incentives for developers, second, there have been technology advances, and finally, both fuel prices and environmental concerns have pushed the interest forward. Power electronics and control technologies will play a key role in changing the characteristics of a renewable energy system to an active power source in the near future. The expected trends in power electronics and control technologies for solar energy systems are also discussed in this chapter.

Renewable energy systems are presently undergoing a rapid change in technology and use. This rapidly growing interest in various aspects of clean energy is a reaction to the major energy-related challenges of the humanity. These efforts involve renewable energy sources, distributed generation systems, and conservation of energy in a variety of the electromechanical energy systems such as industrial drivers, electric and hybrid cars, etc. The renewable energy systems (RES) are now a major contributor to the grid power. In classical power systems large power generation plants located at adequate geographical places produce most of the power, which, is then transferred to the large consumption centers over long distance transmission lines. The system control centers monitor and regulate the power system continuously to ensure the quality of the power, namely frequency and voltage. However, now the overall power system is changing and a large number of dispersed generation (DG) units, including both renewable and non-renewable sources such as wind turbines, PV generators, fuel cells, etc. are being developed and installed. Solar energy alone has an almost exponential growth in installed capacity and applications in the last three decades. A widespread use of the renewable energy sources in distribution networks and a high penetration level will be seen in the near future in many places. To interface a renewable energy source efficiently to a load or grid the power electronic converters are performing power conditioning, voltage boosting, power flow control and power quality improvements.

Power electronics has changed rapidly during the last decades and the number of applications has been increasing mainly due to the development of semiconductor devices and microprocessor technology. For both, higher performance has been steadily increasing for the same area of silicon, while at the same time, price has been continuously reducing. Power electronics, being the technology of efficiently converting electric power, plays an important role in the field of modern electrical engineering. It is an essential for the integration of the DG units in order to achieving high efficiency and performance. A power converter is the interface between a generator and the load or the grid. For most of the power converters, the power may flow in both directions, though this is dependent upon topology and applications. Three important issues are of concern using such systems, the reliability, the efficiency and the cost. In the last decades, the trends are that power electronic conversion is shrinking in volume, size and weight. It has also been shown that more integration and functions that are more available are the keys to being competitive. The key driver of this development is the advances in the device technology.