Reliability Evaluation of Weak Transmission Terminal Power Grid with EHV/UHV Direct Current

Nowadays, renewable energy such as wind energy continues developing rapidly. However, renewable energy generation has intermittent and random operating characteristics, and most of China's energy bases are in the northwest, resulting in weak AC networks. At the same time, Extra/ Ultra high voltage direct current transmission will play an important role in multi-area electric power system in China. Therefore, it is urgent to study the reliability of weak transmission terminal power grid with EHV/UHV direct current. Firstly, a generation reliability assessment model for wind farm is built, meanwhile, a simple but effective wake effect model is also proposed. Secondly, the frequency and duration method based on Markov process theory is used for the equivalent to the HVDC transmission system, and its state transition diagram is obtained. Then, the above model is added to the IEEE reliability test system, and the simulation calculation is performed for the system in MATLAB based on the sequential Monte Carlo method. Finally, in view of the results, this paper analyzed the effect of different situations on the system reliability, including different wind speed and wind speed fluctuation, different wind farm site, different wind farm capacity, and different proportion of wind power instead of conventional energy. The reliability of high voltage AC transmission and HVDC transmission is also compared and analyzed.