Performance Improvement in a Renewable Energy Direct Drive Permanent Magnet Machine by means of Soft Magnetic Composite Interpoles

Renewable energy conversion is usually related to a low-speed energy source. Direct drive generation of electricity has some advantages with respect to the use of a gearbox, although it also shows difficulties such as the increased generator cost and weight, which are mainly related to the high torque to be achieved for a given converted power. In addition, the direct drive generator's efficiency tends to be lower, as irreversibility is larger for the same power rating. When using permanent magnet machines, the magnets may have a significant impact on the whole cost of the machine, making designs with a low fraction of the pole covered by the magnet interesting for a better permanent magnetic material use. This provides us to take advantage of a surface-inset magnet machine configuration, in which reluctance torque is used to improve the torque per ampere rating of the machine. The current paper proposes how to change a surface-magnet machine into a surface-inset magnet machine without making the rotor up of laminations, which is expensive especially in very large rotors. Instead of that, the use of soft magnetic composite materials for that purpose is analyzed through finite element calculations and proposed as an optimal choice.