Power Electronics in Small Scale Wind Turbine Systems

Although fossil fuel is the main energy supplier of the worldwide economy, due to its ad‐ verse effects on environment, the scientists look for alternative resources in power genera‐ tion. Electricity generation using renewable energy has been well recognized as environmentally friendly, socially beneficial, and economically competitive for many appli‐ cations. Wind turbines, photovoltaic systems, full cells and PATs are main resources for dis‐ tributed generation systems [1]. Compared with other renewable energy, wind power is more suitable for some applications with relatively low cost [2,3]. Wind turbine system (WTS) technology is still the most suitable renewable energy technology. While most large companies are focusing on large wind turbines of the utility scale, small wind turbines as distributed power generators have attracted a growing interest from the general public, small farms and remote communities [4]. In recent years, the level of interest in small-scale wind turbine generators has been increasing due to growing concerns over the impact of fossil-fuel based electricity generation [5]. According to the American Wind Energy Associa‐ tion (AWEA) annual wind industry report, the U.S. market for small wind turbines (<100kW) grew 78% in 2008 adding 17.3 MW of installed capacity. Over 10,000 small wind turbines were sold in the U.S. in 2008 [6]. UK based consultants Gerrad Hassan also predicts that small wind turbine sales have the potential to increase to well over US$750 million by 2005 [4]. Small-scale wind turbines are particularly advantageous for power generation at a household level [5]. A small-scale wind turbine consists of a generator, a power electronic converter, and a control system. Among different types of small-size wind turbine, perma‐ nent magnet (PM) generator is widely used because of its high reliability and simple struc‐ ture [1,2]. The power electronic converter topology used depends on the required output power and cost of the system. Control systems are used to control the rotational speed of