Intelligent Approach to MPPT Control Strategy for Variable-SpeedWind Turbine Generation System

Recently, wind generation systems are attracting great attentions as clean and safe renewable power sources. Wind generation can be operated by constant speed and variable speed operations using power electronic converters. Variable speed generation is attractive because of its characteristic to achieve maximum efficiency at all wind velocities (Pena et al. 2000; Senjyu et al. 2006; Sakamoto et al. 2006; Ramtharan et al. 2007; Fernandez et al. 2008), the improvement in energy production, and the reduction of the flicker problem. In the variable-speed generation system, the wind turbine can be operated at the maximum power operating point for various wind speeds by adjusting the shaft speed. These characteristics are advantages of variable-speed wind energy conversion systems (WECS). In order to achieve the maximum power control, some control schemes have been studied. A variable speed wind power generation system (WPGS) needs a power electronic converter and inverter, to convert variable-frequency, variable-voltage power into constant-frequency constant-voltage, to regulate the output power of the WPGS. Traditionally a gearbox is used to couple a low speed wind turbine rotor with a high speed generator in a WPGS. Great efforts have been placed on the use of a low speed direct-drive generator to eliminate the gearbox. Many of the generators of research interest and for practical use in wind generation are induction machines with wound-rotor or cage-type rotor (Simoes et al. 1997; Li et al. 2005; Karrari et al. 2005; Wang & Chang 2004). Recently, the interest in PM synchronous generators is increasing. High-performance variable-speed generation including high efficiency and high controllability is expected by using a permanent magnet synchronous (PMSG) for a wind generation system. Previous research has focused on three types of maximum wind power extraction methods, namely tip speed ratio (TSR) control, power signal feedback (PSF) control and hill-climb searching (HCS) control. TSR control regulates the wind turbine rotor speed to maintain an optimal TSR. PSF control requires the knowledge of the wind turbine’s maximum power curve, and tracks this curve through its control mechanisms. Among previously developed wind turbine maximum power point tracking (MPPT) strategies, the TSR direction control method is limited by the difficulty in wind speed and turbine speed measurements