Analysis of a 300 MW variable speed drive for pump-storage plant applications

A 300 MW drive system consisting of a cyclo-converter driven doubly-fed induction machine for pump-storage stations operating in Goldisthal, Germany, is presented. The cyclo-converter supplied by ALSTOM is one of the largest in the world. Major benefits of this innovative concept are the increase of the turbine efficiency by means of speed variation and the high dynamic power control for the stabilisation of the grid. Major benefits compared to classical approaches are identified. Emphasis is placed on the behaviour of the drive at grid failures. A new modified topology is proposed to meet the grid code requirements at various grid failures.