Dynamic performance of the modular series connected converter in a 100 kVdc- transformerless offshore wind turbine

The analysis of a series connected modular converter suitable for a light weight transformerless offshore wind turbine is presented in this paper. First, an overview of the research within in the field of transformerless turbines is given. Then, the special generator/converter concept is presented, with a brief introduction to the control system principles. Based on simulations in PSCAD, the impact and benefits of applying a flux weakening scheme in this special application is assessed. Additionally, a possible black-start strategy is demonstrated. Finally, the consequences of an abrupt loss of grid is analysed. The turbine transient response to such a fault is simulated, and the requirements for fault-mitigation are identified.