Principle, Design and Application of the DC Chopper for VSC-HVDC Based Offshore Wind Farm Integration

DC choppers (DCCs) are typically used in VSC-HVDC connected large offshore wind farm integration systems, where their role is to prevent system over-voltage in the event of an AC grid fault by absorbing the surplus power fed from the wind farm. The existing DDC solutions can be classified into three categories based on the arrangement pattern of their braking resistors, namely, centralized, distributed and hybrid solutions. This paper summarizes the state of the art of DCCs in large offshore wind farm integration applications and discusses the features of different solutions. Focusing on the hybrid DCC solution, which is applied for the first time in the BorWin6 offshore wind integration project, its operating principle, control strategies, design and testing are presented. The simulation and experimental results show that the hybrid DCC has a good low fault ride-through (FRT) performance and offers a flexibility to trade off the pros and cons of centralized and distributed solutions.