DC fault ride-through control strategy of wind power integrated DC transmission system based on modified MMC

Abstract

MMC-HVDC(Modular Multilevel Converter based High Voltage Direct Current) technology adopted bipolar overhead lines is an effective method for large-scale long-distance wind farm sending system. Aiming at the problems of DC fault blocking and surplus power in wind power integrated through DC transmission system, an M-CT-MMC(Modified Current-Transferring MMC) with the functions of DC fault blocking and energy dissipation to fully exploit the function of dissipative resistors while achieving DC fault ride-through. In terms of DC fault blocking, the cost increase caused by the arm switch being additionally subjected to DC voltage bias is avoided by interconnecting the lead wires of the M-CT-MMC bridge arm absorption branch to construct a three-phase neutral point, and DC fault current can be effectively blocked through the coordination of auxiliary branches. In terms of the dissipation of surplus power, a control mode switching strategy of bipolar M-CT-MMC is designed for self-absorption and non-self-absorption conditions, which can actively absorb power dissipation while improving the power transfer capability of non-fault pole. Based on the power dissipation requirements, a group switching control strategy of dissipative resistors is designed to avoid overloading of non-fault pole M-CT-MMC, so as to realize the DC fault ride-through under different operating conditions. Finally, the effectiveness and feasibility of the proposed DC fault blocking and power dissipation coordinated control strategy are verified based on MATLAB/Simulink simulation platform.