Design and analysis of a gearless, direct grid, permanent magnet induction wind generator

[摘要] ENGLISH ABSTRACT: In this study a new type of gearless, direct-drive wind generator, which can be connected directly to the grid,is proposed. The working characteristics of this generator are based upon the principles of the permanentmagnet induction generator (PMIG). By omitting the need for a gearbox and power electronic converter thisgenerator type has several advantages regarding cost and reliability. Although the PMIG is proposed inprevious studies as favourable for wind power generation, the mechanical complexity and difficultconstruction associated with these types of generators, seems to be the main reason why these generatorsystems are not used.The design methods presented in this study are intended to alleviate these constructional issues by proposingthe split-PMIG (S-PMIG), where the stator winding and the induction cage-rotor windings areelectromagnetically separated. The machine is basically split into two permanent magnet (PM) machines, agrid connected synchronous generator (SG) unit and a turbine connected induction generator (IG) unit. Thesetwo units are mechanically linked by a common PM-rotor. To evaluate this concept a finite element (FE)design analysis is done independently for both machine components. The emphasis of the designoptimisation is the minimisation of the cogging torque, while still having a decent performing, easilyconstructible generator. This generator should also have low load ripple content. Cogging torque can result inthe failure of the turbine to start up, especially at low wind speeds. As this is a directly grid connectedgenerator, torque ripple transferred to the common PM-rotor can destabilise the generator.Based upon the FE designs a preliminary S-PMIG system is constructed and practically evaluated. Due to themodular nature of the design it is possible to implement the synchronous generator part of the S-PMIG inconjunction with a grid-connected solid state converter (SSC). This allows for a useful comparison with theS-PMIG system. Promising results are obtained from initial tests of the S-PMIG directly connected to thegrid. It is shown that the operation of this generator is stable under a wide range of wind load conditions.However, some important machine design issues are identified from these practical results, which couldprove vital in the implementation of future S-PMIG designs.

[发布机构] Stellenbosch University