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The increasing rating and improved performance of self-commutated semiconductor devices have made DC power transmission based on voltage-source power convertors (VSCs) possible. This technology is called VSC transmission. The main components in a DC scheme are depicted and their functions explained. The features of three main categories of convertor topology suitable for DC transmission are described. Three specific convertors viz. two-level, three-level diode-clamped and four-level floating-capacitor convertors for a 300 MW scheme are compared in terms of costs, DC capacitor volume, commutation inductance and footprint. The floating capacitor convertor is shown to yield the lowest system cost.