Abstract
Mechanical gearboxes are typically employed with doubly-fed induction generator based wind turbines to convert the turbine's low speed mechanical power into high-speed mechanical power to drive the electrical generator. The main drawback of this solution is the gearbox's reliability and maintenance. Direct-drive wind turbines, on the other hand, employ a large volume and weight permanent magnet generator. An emerging alternative being promoted by the research community is one where a magnetic gearbox is used in conjunction with a doubly-fed induction generator. This alternative maintains the reduced size doubly-fed machine, and aims to overcome the mechanical gearbox problems. This paper introduces a new wind turbine architecture based on a novel three port magnetic gearbox (3PMGB). The proposed magnetic gearbox provides additional power harvesting and system control benefits through its electrical output port. The proposed 3PMGB configuration is derived from the conventional planetary magnetic gearbox where N-phase coils forming a modular winding are fixed around the ferromagnetic pole-pieces of the planetary magnetic. The turbine mechanical power is thus divided into mechanical power to drive the electrical generator, and electrical power that can be used to feed the power required by the rotor circuit. This configuration offers complete isolation between the rotor circuit and the grid. The transformer used to feed the rotor circuit can be then dispensed with. Moreover, this proposed system can be used to improve the ancillary service of the electrical power generated by wind through employing a storage system to the DC-link of the back-to-back converter for power leveling purposes.