Reactive power control of a direct grid connected slip synchronous permanent magnet wind generator

In this paper a possible reactive power control method is developed for the direct-drive direct-grid connected slip permanent magnet wind generator. By using a solid-state-assisted on-load tap changer transformer, the terminal voltage of the generator can be varied. In this way the generator can be operated in over- or under-excited mode, allowing for discreet control over the reactive power output of the generator. Solid-state switches are used in the transformer switchgear to increase the lifetime of the diverter circuit. Along with the transformer, two small capacitor banks are also used to deliver additional reactive power when needed. The performance of the system is simulated and the results are evaluated against the grid code specifications of the National Energy Regulator of South Africa.