A novel doubly fed wind energy power split system with par-tialscale converter and control strategy

normally, renewable energy resource is clean, inexhaustible, low maintenance and running costs. Wind energy is considered as an option to solve the environmental issues, due to it is widespread throughout the world. Until now, single rotor wind power generator is widely used in practice. The DFIG system and direct-drive synchronous generator (DDSG) system are currently the mainstream machine for wind turbine [1]. The main merit of the DFIG system is in no need of PM material and only need about 30% converter capacity, hence the whole system is lower cost. However, the additional gearbox, the slip ring and brushes inevitably lead to maintenance problems and low reliability. To the opposite, the DDSG system is famous for high efficiency, low mechanical loss and low maintenance cost. The gearbox can be canceled in high number of poles of PMSG. But, the DDSG system has to be equipped with correspondingly full-scale converter [2]. The existing low speed high torque direct-drive machine is bulky size and large material consumption. To overcome above problems, magnetic gear is introduced into the wind generator as the power split [3]. In [3], the wind turbine system was based on planetary gearbox, which power split to a synchronous generator and a servo PMSM. The system structure and control strategy are complex compared to traditional system. In addition, planetary gearbox is a mechanical device which has inevitable mechanical problems such as frictional loss, high maintenance and audible noise. A novel brushless doubly fed power split system is proposed to substitute for the planetary gearbox in this paper. The extracted wind energy is divided into two parts by the magnetic-field-modulated blushless double rotors machine (MFM-BDRM). The major part of the power directly flows to the power grid through the generator. A small proportion power of the rest is delivered to the backback converter. For a given wind speed, a MPPT (maximum power point tracking) control strategy is designed to extract the maximum wind energy by controlling the converter. This system has high torque density, high-reliability and low-cost characteristic.