A comparative investigation of three PM-less MW power range wind generator topologies

As the wind energy penetration range increases steadily and the high energy PM costs are rising dramatically, PM-less large power wind generators with high performance are needed. Apart from extending the range of cage rotor induction generators, doubly-fed induction generators and dc excited heteropolar-rotor (standard) synchronous generators, especially for direct drives (very low speed) and multibrid (with single stage transmission (5/1-8/1 ratio)), new topologies have to be investigated to reduce initial costs and weights for high enough efficiency and energy annual yield. The present paper investigates by quasi 2D-FEM two dc stator polarized (to increase machine side PWM converter voltage utilization, that is to reduce peak kVA ratings and costs of the machine side PWM converter) directly-driven switched reluctance generators (one with circumferential field and one with transverse flux (with circular coils)) for 6MW and 12 rpm design, to show that for about same active material weight only the latter provides good enough efficiency (above 93% for 89 tons of copper and laminated stator and rotor cores). Additionally, the paper investigates, by a detailed nonlinear analytical design methodology, with sensitivity design inquires, the claw pole synchronous generator topology for a multibrid wind generator of 3 MW, 75 rpm generator for a 15 rpm wind turbine with above 94 % efficiency for unity power factor (diode rectified output) for around 10 tons of copper and iron core materials. Though the case studies refer to large wind generators the same topologies are believed worth considering for powers less than 1 MW and even less than 100 kW. Similar topologies may be applied to micro-hydro generators. The results are promising but further in depth modeling, design and control studies of such novel PM-less topology are required before declaring them fit for industrial wind generators.