Characteristics Analysis of Sub-Synchronous Oscillation Caused by DFIG Wind Farm Integrated Into MMC-HVDC System

With the increasing share of renewable energy such as wind energy in power system, flexible DC transmission technology has become an important way to effectively absorb wind energy. But the problem of synchronous sub-synchronous oscillation becomes more and more serious. To reduce the influence of sub-synchronous oscillation on interconnected systems, a Controller for energy conversion system is proposed. It is used to control the synchronous operation of the doubly-fed fan and the rectifier station to connect the doubly-fed wind farm. First, based on the impedance method, a doubly-fed wind farm and multi-module impedance model considering AC/DC dynamic coupling are established. The control energy conversion of wind power generation system, rectifier station and inverter station is designed. Second, according to Nyquist curve and impedance stability criterion, the change of system stability in the process of adjusting controller parameters is observed. Third, the system structure is simulated by MATLAB software. The effectiveness of the controller in the converter station at both ends of MMC is verified. The results show that the new controller can effectively suppress the current offset caused by SSO, and thus improve the power system stability.