Composition and Control of a New Type of Hybrid Voltage-Source Converter Based on DRUs and FB-MMC for Large-Scale Offshore Wind Power Integration and Transmission
Chengdong Wang, Asif Ali, Frede Blaabjerg
Abstract
The composition and control of a new type of hybrid voltage-source converters are proposed based on diode rectifier units (DRUs) and full-bridge modular multilevel converter (FBMMC) to reduce the topside volume and weight of offshore wind farm (OWF) converter stations. The relationship between FBMMC DC voltage ratio and its modulation index is presented to obtain the FB-MMC active power capacity. The equilibrium point is analyzed using numerical calculations. Then, a controller derived from proportional-integral controller is adopted to control FB-MMC DC voltage and a reactive power controller is added to balance the reactive power of OWF, FB-MMC and DRU, by which the PCC voltage is established for wind turbine converters (WTCs) grid access. In addition, the DC short circuit fault and offshore short circuit fault recovery strategy is also presented. Finally, two specific case parameters are calculated and a simulation model in RSCAD is developed to validate the effectiveness and feasibility of the topology as well as the proposed control strategy of the hybrid voltage-source converter.