A Solution for Low Voltage Ride Through of Induction Generators in Wind Farms using Magnetic Energy Recovery Switch

Abstract

Induction generators constitute 30 percent of today’s installed wind power. They are very sensitive to grid voltage disturbances and need retrofitting to enhance their low voltage ride through (LVRT) capability. LVRT of induction generators by shunt-connected FACTS controllers such as STATCOMs have been proposed in earlier studies. However, as this report concludes, in this application their VA-rating requirement is considerably higher than that of series-connected FACTS controllers. One such series FACTS controller is the magnetic energy recovery switch (MERS). It consists of four power electronic switches and a capacitor in a configuration identical to the single-phase full bridge converter. Its arrangement in an electric circuit, however, is different, with only two of the converter’s terminals utilised and connected in series. It has the characteristic of a variable capacitor and is related to FACTS controllers with series capacitors such as the GCSC and the TCSC. Successful operation of MERS for LVRT of induction generators has been demonstrated by simulations and verified by small-scale experiments. Index terms – Low voltage ride through (LVRT), magnetic energy recovery switch (MERS), series-connected FACTS controller, wind power, grid code, induction generator.