Modelling and control of a series static synchronous compensator using low-frequency, fixed-modulation index techniques

This presentation describes the modelling and control design of a converter used in a static synchronous series compensator (SSSC) application, employing low-frequency, fixed-modulation index strategies. In these, the magnitude of the output waveform is directly related to the DC-bus level by a fixed relation. Consequently, the DC-bus has to be varied to obtain the desired output voltage. A large-signal model for the converter is derived and subsequently linearized to obtain a small-signal model, which was used to propose a control strategy. The theory is then validated experimentally on a novel voltage-source converter (VSC) configuration. A 200=kVA small-scale SSSC test bench, connected to an emulated transmission line was built for this purpose. This configuration has been used for the first time in a 47-MVAR demonstrator built for the Spanish transmission grid.