A Modular Series Connected Converter for a 10 MW, 36 kV, Transformer-Less Offshore Wind Power Generator Drive

In the future, large offshore wind turbines are expected to reach a rating of 10 MW. To reduce the corresponding weight increase of the nacelle, research has started to focus on solutions to omit the step-up transformer in each turbine. Therefore this paper investigates a modular converter suitable for a special high power, transformer-less generator drive with 36 kV output DC-voltage. The drive consists of nine converter modules connected in series on the DC-side to obtain a high output voltage. Due to the series connection, extra care has to be taken to achieve equal voltage division between the converter modules. Therefore, a DC-voltage balancing scheme based on a droop control is proposed. The performance of the system will be demonstrated through simulations in EMTDC/PSCAD.