A Hybrid modular multilevel converter (HMC) has the advantages of a smaller number of sub-modules

smaller converter size

and DC fault ride-through capability compared with the traditional modular multilevel converter

which is more advantageous in applications with space requirements. This paper proposes a hybrid modular multilevel converter submodule pre-charge control strategy for HMC under different operating conditions of active and passive power supply. Based on an in-depth analysis of the HMC working mechanism

six charging states of HMC under two working conditions are given

and an equivalent mathematical model of the charging circuit is established. Considering the inter-phase and intra-phase capacitor voltage balance and switching frequency limitation

a pre-charging method for switching combinations of different states of HMC is put forward

and a method for calculating the current-limiting resistor is also provided. Finally

the HMC-HVDC simulation model is constructed to validate the proposed pre-charging control strategy under the two operating conditions

proving that the proposed method can smoothly increase the capacitor voltage to the rated value under low switching frequency.