Equivalent electromagnetic model of self-blocking MMC with DC fault isolation capability

Self-blocking MMC (SB MMC) is able to isolate DC fault current and is promising for use in overhead HVDC transmission. Each converter arm of a SB MMC is consisted of half the self-blocking sub-module (SBSM) and half the half bridge (HB) sub-module. This hybrid design achieves the DC fault isolation capability without significantly increase of the cost and power loss. The detailed electro-magnetic simulation of SB MMC with hundreds of voltage levels is time consuming. Since a SBSM can be negatively inserted, the dynamics of SB MMC are different from HB MMC under DC fault condition. The conventional equivalent models of HB MMC are not sufficient for SB MMC. To solve the above challenges, an equivalent electromagnetic model for SB MMC is proposed and verified in this paper.

I. Introduction

Modular multilevel converter (MMC) based on half bridge sub-modules (HB MMC) has the merits of high control flexibility, scalability, modularity, low harmonic distortion and has been well applied to commercialized projects worldwide. HB MMC is vulnerable to DC faults which promotes the intensive research on DC fault tolerant MMC topologies.