The invention discloses a Modular Multilevel Converter (MMC) direct circular current inhibition method suitable for an asymmetric
AC power grid. The circular current inhibition method derives a
capacitance voltage fluctuation expression of an asymmetric
system, and analyzes components of an imbalance
voltage reference value for the circular current inhibition. A control strategy is suitable for two different negative
sequence control objects. A result shows that the
active component of the reference value is a second
harmonic component no matter what kind of condition the AC
system is operated in. The imbalance
voltage reference value for circular current inhibition is obtained by direct calculation without a Proportional Integral (PI) controller or a
resonance controller. The positive sequence, the negative sequence and the zero sequence circular current components in an operation state of the asymmetric
power grid are simultaneously inhibited. At the same time each phase has an independent structure. The MMC direct circulation inhibition method is suitable for the symmetric or asymmetric AC
system. A double end MMC-HVDC (High-
Voltage Direct Current) model is constructed on a
Power Systems Computer Aided Design / Electromagnetic Transients including DC (PSCAD / EMTDC) time-domain
simulation platform. The validity of the MMC direct circular current inhibition method under the conditions of the symmetric and asymmetric power grids provided by the invention is verified.