Comparison of Active and Passive 9-Phase Wind Turbine Conversion System for an all DC Grid

This paper presents a comparison of a wind turbine generator (WTG) system when connected to voltage source converter (VSC) providing active control in an existing wind generation scheme with a WTG system connected to a passive uncontrolled rectifier in an all-DC wind generation scheme. The all-DC system utilizes a medium voltage DC (MVDC) for the collector grid and a high voltage DC (HVDC) for transmission grid. It also replaces the WTG low voltage generator with a high voltage hybrid generator (HG) eliminating two back-to-back VSCs in existing systems, hence simplifying the WTG power conversion. Walney wind farm in the UK is selected as a benchmark system, its characteristic are studies and the all-DC system is laid out in the same structure as the Walney wind farm. The steady state analyses of the all-DC and Walney wind farm are evaluated and compared in terms of power, efficiency, and mass. The paper shows benefits and drawbacks of a HG connected to an active VSC compared to a HG connected to a passive rectifier, and makes a case for the application of HG in all-DC grids. Simulation results and measurements from a scaled down laboratory prototype HG system are compared, which show a good agreement, hence confidence in the models and approach.