AC-AC Type Isolated Modular Multilevel Cascaded Converter (I-M2C2) based on Common DC Bus

This paper introduces a new type of direct AC-AC single-stage isolated modular multilevel cascaded converter(I-M
²
C
²
). The characteristic of this I-M
²
C
²
is that it can directly carry out constant frequency or variable frequency AC / AC conversion from three-phase to single-phase to realize power transmission of low-frequency or equal frequency. The converter topology uses high-frequency magnets to achieve the required isolation, and it does not need intermediate DC link, which reduces the intermediate conversion. Therefore, the topology has the potential of higher overall efficiency. The converter has three basic voltage ports: three-phase medium voltage AC (MVAC (T-P)), single-phase medium voltage AC (MVAC (S-P)) and low-voltage direct current (LVDC). It is suitable for interconnection of offshore and onshore wind farms with power grid, electric traction of urban rail or new energy grid. This paper introduces the topology, sub-module (SM) modulation and average equivalent model of I-M
²
C
²
. The effectiveness and superiority of the proposed topology are verified by simulation results.