Design of a combined converter-switch for converting existing AC transmission into HVDC (and back)

Abstract

The paper brief is one out of the first approaches in Turkey to popularize HVDC-light transmissions. It deals with: 1. Lab design and PSCAD modeling of a special bridge controlled AC-DC three load (star-delta) rectifier. It uses 9 group of valves (instead of 6 group valves of common bridge), three lines of former AC transmission, the earth and three DC loads between the lines and earth (or a star-delta inverter). 2. Lab design and PSCAD modeling of a special controlled bridge DC-AC star-delta inverter between three DC source and AC network. It also uses 9 group of valves (instead of common 6 group valves), three input DC lines (and the earth) and three outputs AC transmission lines. 3. Comparison of the bridges construction and modeling results of traditional HVDC-light transmission (6 valves rectifier, traditional DC line and 6 valves inverter) and designed AC-DC-AC transmission (9 valves rectifier, AC line and 9 valves inverter). The proposed star-delta rectifier and inverter can be implemented in common electrical applications such as HVDC transmission, supply of isolated loads, asynchronous grid connection, infeed of small-scale distributed generators (DG), infeed to city centers, for DC grids, converting the AC lines into HVDC light lines, etc.