A simple structure passive MPPT stand-alone wind turbine generator system

Variable-speed wind turbines are commonly used in stand-alone wind turbine generator systems (SWTGS). Therefore, achieving maximum power point tracking (MPPT) at different wind speeds for variable-speed wind turbines is the key to increase the annual energy yield of SWTGS. Many MPPT methods have been proposed. Such methods can be classified into two types: the power signal feedback (PSF) method and the hill-climbing searching (HCS) method. Although these methods differ, they have a common property: all rely on a DC/DC converter or some other electrical control device. Given that SWTGS are typically used outdoors, high reliability is necessary. However, the electronic components contained in the electrical control device are highly likely to break down when exposed to extreme weathers, thereby resulting in the low reliability of SWTGS for outdoor use. Conventional MPPT methods fail to overcome this drawback. Thus, a change in perspective is necessary to find a highly optimal MPPT solution. This study proposes a simple structure passive MPPT SWTGS. A natural characteristic of the system input power versus rotor speed curve is that it approaches the maximum power point (MPP) curve of the matching wind turbine. This feature enables the proposed system to track the MPP automatically without relying on any electrical control device. Therefore, the proposed system eliminates hundreds of electronic components found in these control devices, thereby resulting in high reliability. Another significant advantage of this new system is that the new permanent magnet generator contained in the proposed system has a highly simple structure, similar to that of conventional generators. Therefore, the proposed system is easy to manufacture and thus presents a practical solution.