Design Optimization of Directly Grid-Connected PM Machines for Wind Energy Applications

The focus of the study in this paper is on the design of unconventional directly grid-connected PM wind generators without power electronic converters. As a case study, this analysis is based on a novel direct-drive wind generator system known as a slip-synchronous permanent-magnet (PM) wind generator. Attention is given to the definition of the design requirements of the directly grid-connected synchronous-generator unit from the relevant grid code specifications and to find the optimum design subject to these requirements. Due to the direct-grid connection, there are clear differences in the design requirements of this machine and those of conventional PM wind generators connected to the grid via a converter. Four different generator topologies are evaluated with regard to the ease of manufacturing, active mass, PM content, and suitability for direct-grid connection. Both simulated and measured results are given for an experimental direct-grid slip-synchronous PM generator.