A phase-shifted multiplexing modulation method for energy balancing in arm-multiplexing modular multilevel converters

• The energy balance in AM-MMCs can be achieved under specific constraints related to the output voltage range, SM capacitance and arm inductance. • The introduction of phase shift angle alters the distribution of modulation voltage, thereby influencing the power transfer among various arms. • The proposed method leverages the topological characteristics of AM-MMCs, enabling equivalent power transmission with a reduced number of SMs. The arm-multiplexing based modular multilevel converter (AM-MMC) has garnered considerable attention due to the minimization of submodules, consequently reducing both footprint and weight of the converter station in HVDC systems. However, the complicated issue of energy balance in AM-MMC, caused by the partial sine waveform generated in the arms, restricts its practical applications. This paper begins by analyzing the operational principles and dynamic models of AM-MMC. It is revealed that the arm energy balance of AM-MMC can be achieved under specific constraints related to the output voltage range, SM capacitance and arm inductance of the converter. Then, to alleviate this constraint and enhance its applicability, a novel modulation method of AM-MMC based on the phase-shift of multiplexing arm voltage is proposed. Furthermore, the relationship between the phase-shifted angle and arm stored energy is derived and the controller of the proposed modulation method is presented. Finally, real-time simulation and experiment test are implemented to validate the effectiveness of the method. In comparison to other energy balancing methods recently introduced for MMCs, this approach does not necessitate the injection of harmonics. Moreover, the proposed modulation method fully leverages the topological characteristics of the AM-MMC, enabling equivalent power transmission with a reduced number of SMs. This advancement facilitates lightweight construction for HVDC applications.