IACSIT International Journal of Engineering and Technology Vol. 1, No.3, August, 2009 ISSN: 1793-8236 269 Abstract—Wind power can be used in off-grid systems, also called stand-alone systems, not connected to an electric distribution system or grid. The power conversion unit features a wind-turbine-driven PMSG, a diode rectifier, a buck-boost dc/dc converter, a battery bank, and a dc/ac inverter. In this paper, a distributed generation based on stand alone wind energy conversion system (WECS) using a variable speed permanent magnet synchronous generator (PMSG) is proposed with PWM rectifier and a battery for storing the extra wind energy. The topology for the same condition has been demonstrated using MATLAB Simulink based simulations. Index Terms—Wind energy conversion system, Permanent magnet synchronous generator, Isolated system, battery bank. I. INTRODUCTION Renewable energy sources including wind power offer a feasible solution to distributed power generation for isolated communities where utility grids are not available. In such cases, stand-alone wind energy systems (i.e., systems not connected to the utility grid) can be considered as an effective way to provide continuous power to electrical loads. One of the most promising applications of renewable energy generation lies in the development of power supply systems for remote communities that lack an economically feasible means of connecting to the main electrical grid. For isolated settlements located far from a utility grid, one practical approach to self-sufficient power generation involves using a wind turbine with battery storage to create a stand-alone system. If wind conditions are favorable, these stand-alone wind energy systems usually can provide communities with electricity at the lowest cost. Stand-alone wind energy systems often include batteries, because the available wind does not always produce the required quantities of power. If wind power exceeds the load demand, the surplus can be stored in the batteries [1-2]. The function of an electrical generator is providing a means or energy conversion between the mechanical torque from the wind rotor turbine, as the prime mover, and the Manuscript received June 24, 2009. Rajveer Mittal is with the Department of Electrical and Electronics Engineering, Maharaja Agrasen Institute of Technology, Rohini,Delhi , India K.S Sandhu is with the Department of Electrical Engineering, National Institute of Technology, Kurukshetra, Haryana, India. D. K. Jain is with the Guru Prem Sukh Memorial College of engineering under GGSIP University , Delhi, India local load or the electric grid. Different types of generators are being used with wind turbines. Small wind turbines are equipped with DC generators of up to a few kilowatts in capacity. Modern wind turbine systems use three phase AC generators. The common types of AC generator that are possible candidates in modern wind turbine systems are as follows: • Squirrel-Cage rotor Induction Generator (SCIG), • Wound-Rotor Induction Generator (WRIG), • Doubly-Fed Induction Generator (DFIG), • Synchronous Generator (With external field excitation), • Permanent Magnet Synchronous Generator (PMSG). For assessing the type of generator in WECS, criteria such as operational characteristics, weight of active materials, price, maintenance aspects and the appropriate type of power electronic converter are used. Historically induction generator (IG) has been extensively used in commercial wind turbine units. Asynchronous operation of induction generators is considered an advantage for application in wind turbine systems, because it provides some degree of flexibility when the wind speed is fluctuating. There are two main types of induction machines: squirrel cage and wound rotor. The induction generator based on Squirrel-Cage rotor (SCIG) is a very popular machine because of its low price, mechanical simplicity, robust structure, and resistance against disturbance and vibration. The wound-rotor is suitable for speed control purposes. By changing the rotor resistance, the output of the generator can be controlled and also speed control of the generator is possible. Although wound rotor induction generator has the advantage described above, it is more expensive than a squirrel-cage rotor. The induction generator based on wound rotor is the doubly fed induction generator (DFIG), which is a kind of induction machine in which both the stator windings and the rotor windings are connected to the source. The rotating winding is connected to the stationary supply circuits via power electronic converter. The advantage of connecting the converter to the rotor is that variable-speed operation of the turbine is possible with a much smaller and therefore much cheaper converter. The power rating of the converter is often about 1/3 the generator rating [2-4]. Another type of generator that has been proposed for wind turbines in several research articles is synchronous generator. This type of generator has the capability of direct connection Isolated Operation of Variable Speed Driven PMSG for Wind Energy Conversion System Rajveer Mittal, K.S.Sandu, D.K.Jain