Oscillation Mechanism and Mitigation of MMC-HVDC Based on Bifurcation Theory for Wind Farm Integration

Modular multilevel converter based highvoltage DC transmission (MMC-HVDC) technology has become a feasible approach from grid integration of large wind farms. As oscillations has been reported on certain number of MMC-HVDC projects with wind power, the mechanism and analytical methods are urgent issues for studying. The current commonly used modeling methods cannot meet the characteristics of MMC topology due to the complex pulse mode shown in a switching period. Therefore, a new method is proposed to effectively solve the stroboscopic mapping modeling problem of multilevel converters. On the basis of traditional proportional resonant (PR) control, a time-delay feedback control (TDFC) loop is added to effectively suppress the current oscillation. Taking the 21 level MMC topology as an example, the discrete model is obtained by the method of switch state traversal, and the correctness of the theoretical analysis and the proposed strategy of oscillation current suppression is verified by simulation.