Abstract
The modular multilevel converter (MMC) has been used in the field of HVDC transmission due to its many advantages, but its voltage imbalance problem of sub-module capacitors affects the stable operation of the system. There are two kinds of methods for solving the capacitor voltage imbalance of the MMC sub-module. The one is voltage balancing algorithm and the other one is improved topology. However, the complexity of the voltage balancing algorithm increases sharply when the number of voltage levels is high, which is not suitable for the MMC system with a high number of voltage levels. In this paper, a new topology with bidirectional voltage self-balancing capability is proposed. This topology adds the voltage balancing circuit between sub-modules on the conventional MMC topology, realizing voltage self-balancing without voltage balancing algorithm, and having a better effect of inhibition phase-to-phase circulation. The bidirectional voltage balancing capability, the voltage balancing effect and the circulation inhibition effect of the bidirectional voltage self-balancing topology are verified by MATLAB/Simulink simulation and experiment.
Highlights
With the booming world economy, global electricity consumption continues to grow
Traditional thermal power generation has been unable to meet the demand for electricity growth brought about by economic development, and thermal power generation is widely considered to be the main cause of global warming
The topology is connected in parallel with a diode on the basic of the conventional modular multilevel converter (MMC) structure, and each phase circuit includes four bridge arms, which can realize voltage self-balancing of the sub-module capacitor
Summary
With the booming world economy, global electricity consumption continues to grow. Traditional thermal power generation has been unable to meet the demand for electricity growth brought about by economic development, and thermal power generation is widely considered to be the main cause of global warming. The topology is connected in parallel with a diode on the basic of the conventional MMC structure, and each phase circuit includes four bridge arms, which can realize voltage self-balancing of the sub-module capacitor. It would increase the volume of MMC. 2) VOLTAGE SELF-BALANCING FUNCTION VERIFICATION It can be seen from the comparison between Fig. and Fig. that the sub-module capacitor voltage of the open-loop carrier phase shifting is diverging, and the quality of the output AC voltage waveform is poor.
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