Modular multilevel converter composite submodule topology and control

Abstract

The DC-side short-circuit fault suppression of modular multilevel converter (MMC) applied to DC transmission has been a technical problem. According to the different location of cutting off fault current, this study first analyses three possible suppression schemes: AC/DC circuit breaker, bridge arm damper, and MMC submodule (SM) topologies and their respective features. Then, characteristics of SM topologies with DC fault current self-blocking capability are summarised, and an improved composite SM topology is designed based on the full-bridge SM and multilevel capacitor storage structures. The suppression characteristics of the proposed topology under different operation modes, capacitor voltage balancing control during blocking, and self-starting process are also studied. Finally, a simulation model is built in the PSCAD/EMTDC to verify the DC-side short-circuit fault suppression characteristics and control strategies.

Keywords

• HVDC power convertors
• circuit breakers
• capacitors
• network topology
• fault currents
• power convertors
• power transmission faults
• HVDC power transmission
• short-circuit currents
• fault diagnosis
• voltage control
• switching convertors
• improved composite SM topology
• full-bridge SM
• multilevel capacitor storage structures
• different operation modes
• capacitor voltage balancing control
• DC-side short-circuit fault suppression characteristics
• control strategies
• modular multilevel converter composite submodule topology
• DC transmission
• technical problem
• different location
• study first analyses three possible suppression schemes
• AC/DC circuit breaker
• bridge arm damper
• MMC submodule topologies
• SM topologies
• DC fault current
• self-blocking capability