Reliability assessment of DC series–parallel offshore wind farms

The remarkable benefits of wind power as an environmentally friendly renewable energy resource have led to an increasing penetration of offshore wind energy in modern power systems. Since the DC series–parallel connection system does not need large capacity DC/DC converters, it can reduce the construction costs of wind farms to some extent. In this study, the models of wind speed, wind direction and the wind turbine output power characteristic are developed. Based on this, the output power of each turbine considering the wake effect can be estimated. Then, the reliability block diagrams are drawn according to component relationships in reliability. Moreover, indexes like the probability of all wind turbine string failure, system unavailability and the average available output power of the power system are proposed to assess the reliability of the DC series–parallel offshore wind farm. A case study is presented to calculate the reliability indexes of different situations, where the amount of wind turbines remains the same while the number of turbine strings varies. It can be concluded that the DC series–parallel offshore wind farm is more reliable when increasing turbine string number, and reference is provided for DC series–parallel wind farm structure optimisation