**1. Introduction**

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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

© 2012 Abarzadeh et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Abarzadeh et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

small-scale wind turbines enabling them to operate with optimum speed to extract maxi‐ mum power from wind [1,2,4].

For rural and remote areas, the small-scale stand-alone wind power system with a battery bank as the energy storage component is common and essential for providing stable and re‐ liable electricity [2,7-10]. For the stand-alone wind power system, the load is a battery that can be considered as an energy sink with almost constant voltage. The battery can absorb any level of power as long as the charging current does not exceed its limitation. Since the voltage remains almost constant, but the current flows through it can be varied, the battery can be also considered as a load with a various resistance [2,11,12].

There is increasing market for a grid connected small wind generating system (without bat‐ tery storage) for home owners and small businesses in rural areas. In this case the excess en‐ ergy form the wind generator is fed to the utility grid. The AC grid can also be a diesel grid or a battery/diesel mini hybrid grid. A grid connected inverter structure which extracts ener‐ gy even at low wind speeds will assist in reducing capital cost and offer opportunities for interfacing small-scale wind generators with the AC grid. Conventional grid connected wind turbines use a charge controller to charge the batteries and a grid connected inverter to process power from the battery to the utility grid [4].

This chapter presents a power electronic energy conversion system for small-scale standalone wind power system with a battery bank as the energy storage component and grid connected power electronic interface for interfacing variable speed small-scale wind genera‐ tors to a grid. Small-scale wind turbine consist of permanent magnet synchronous generator (PMSG), AC/DC converter, DC/DC converter as the maximum power point tracking control‐ ler, inverter and load.
