An algorithm for the start-up control of modular multilevel voltage source converter based high voltage direct current (VSC-HVDC) for wind farm integration is proposed. Charging the submodule capacitor is the core of start-up control

which can be divided into two stages. For the first uncontrollable diode-rectified stage

the equivalent mathematical model of modular multilevel converter (MMC) is developed to provide theoretical basis for the selection of the value of current-limiting resistor. For the second high-frequency rectified stage

a selection range for the slope parameter of DC voltage control loop is proposed to suppress the over currents of grid side MMC. The simulation results have verified the effectiveness of the proposed start-up control strategies. This work is supported by National Natural Science Foundation of China (No. 51261130471).