Bipolar Operation Investigation of Current Source Converter Based Wind Energy Conversion Systems

A series-connected current source converter (CSC) based configuration has recently been proposed for offshore wind energy conversion systems. A big challenge exists for such a system that its maximum insulation level is the full transmission voltage due to its monopolar operation. This introduces significant burden to the system in terms of cost, reliability, and flexibility. To solve this issue, a bipolar operation giving a half insulation requirement is proposed and investigated in this paper. However, a unique challenge exists for the CSC-based system when operating under bipolar mode, that is, the dc-link current control. There are two equivalent paths for the dc-link current, which introduces a concern for proper operation of the bipolar system. Accordingly, an optimized dc-link current control is developed in this study. In summary, the bipolar system with the help of the optimized dc-link current control features lower insulation requirement, higher reliability, higher efficiency, and higher flexibility. Finally, both simulation and experimental results are provided.