A wind energy conversion system with enhanced power harvesting capability for low cut-in speeds

This paper proposes a new technique for enhancement of energy extraction capabilities in wind energy conversion systems with low cut-in speed. The dc-link voltage is maintained by the grid-side converter in wind energy systems equipped with back-to-back three-phase inverters. This voltage is required to be higher than a certain value to ensure proper operation of the grid-side converter. On the other hand, at low generator voltages, switching times for the generator-side converter cannot be realized due to practical limitations. Accordingly, the system cannot harvest energy at low cut-in speeds. A power electronics system consisting of an isolated SEPIC converter along with an upper-hand control scheme has been introduced and employed to alleviate the aforementioned power extraction issue. The proposed solution, allows for excellent power extraction even at low cut-in speeds by maintaining an appropriate dc-link voltage at various operation conditions. Therefore increasing the overall renewable generation capability in wind-energy systems. The proposed solution can be incorporated in existing wind energy conversion systems with back-to-back three-phase inverters with slight hardware and software modifications. The integrated isolated SEPIC converter handles a fraction of the rated power, therefore leads to reduced cost and size compared to existing systems with integrated full-rated boost converters.