Optimum design and technology evaluation of slip permanent magnet generators for wind energy applications

Recently a new type of wind generator concept known as a slip-synchronous permanent magnet generator was proposed. This is a gearless direct-drive generator which also connects directly to the grid, thus omitting the need for a power electronic converter. This generator consists of two machine units, a directly grid connected generator operating at synchronous speed and a directly turbine connected short-circuited generator unit. With the theory of designing the grid-connected permanent magnet generator unit well known, the focus in this study is on the identification and finite element design of the optimum turbine connected generator unit. Several different slip permanent magnet generator technologies are evaluated and a number of interesting novel concepts are introduced. These different generator units are optimised by means of finite element analysis for minimum mass, and very good results are obtained. The finite element results are verified by means of practical measurements.