Operation and transient performance of a four-terminal MMC based DC grid implementing high power mechanical DC circuit breaker

Abstract

Recently, there has been significant interest in developing the modular multilevel converter (MMC) based DC grids in the power industry. However, the immature DC circuit breaker (DCCB) technology hampers the development of DC grids in overhead lines transmission field. The full controlled power electronic devices based hybrid DCCB has been proposed and researched substantially. But the hybrid type DCCB suffers from the drawback of high cost and low reliability, leading to high capital cost for DC grids that require numerous DCCBs. In this paper, a mechanical type DCCB, consisting of a mechanical switch, a circuit and an oscillation circuit, is proposed. Then, a four-terminal bipolar MMC-HVDC system implementing the mechanical DCCBs is studied. Extensive simulations have been conducted to analyse the transient performance under different fault conditions. The simulation results verify the technical feasibility of this mechanical DCCB in DC grid.

Keywords

• circuit breakers
• hvdc power transmission
• power overhead lines
• power transmission control
• hvdc power convertors
• power electronics
• fault diagnosis
• power grids
• high power mechanical dc circuit breaker
• power industry
• immature dc circuit breaker technology
• controlled power electronic devices
• hybrid dccb
• hybrid type dccb suffers
• high capital cost
• mechanical type dccb
• four-terminal bipolar mmc-hvdc system
• transient performance
• mechanical dccb
• four-terminal mmc based dc grid