Network fault tolerant voltage-source-converters for high-voltage applications

This paper presents a new generation of network fault tolerant voltage source converters for use in high-voltage applications. The proposed converter offers a unique feature of dc fault blocking capability (ability to block power exchange between the ac and dc sides during the dc faults, hence no current flows in converter switches). This feature may eliminate the need for a dc-side circuit breaker in applications such as dc power transmission systems. This converter also offers the features available from the modular multilevel converter, such as ac fault ride-through capability, low conversion losses, low harmonic filtering requirement, and extension to a high number of levels without compromising capacitor voltage balancing. In this paper, the ac and dc fault ride-through capabilities of the proposed converter will be demonstrated. Issues such as current and voltage stresses on the converter switches and capacitor voltage balancing are examined.