Large-scale renewable energy transmission via the voltage source converter (VSC) based high-voltage direct current (HVDC) is a crucial development direction for constructing a new-typed power system in China. However

renewable energy is characterized by volatility

intermittency

and randomness. When the sending-end modular multilevel converter (MMC) cannot adapt to the rapid fluctuations in renewable energy output

its energy balance will be disrupted by the active power difference between the AC and DC sides

causing issues such as wideband oscillations and exacerbated circulating currents. To solve the problem mentioned above

a novel energy balance-based control method for MMCs connected to wind farms is proposed in this paper

enabling the MM C to effectively adapt to fluctuations in renewable energy output and naturally maintain circulating current at a relatively low level. Firstly

the evolution principle illustrating topology decomposition and reconfiguration of the MMC is revealed. Secondly

the control method for AC internal voltage is proposed

which combines the energy balance between the half MMCs and voltage amplitude support. Thirdly

the DC internal voltage is defined

and its control method is proposed based on the MMC's overall energy balance. Then

independent control of each bridge arm is achieved by integrating the energy balance of the bridge arms with both the AC and DC internal voltages. Finally

an electromagnetic transient simulation model is built with PSCADIEMTDC

and the efficacy and practicality of the proposed method are demonstrated through extensive simulation experiments.