SiC MOSFET Active Harmonic Filter for THDi Correction A 1,000 kVA transformer feeding six-pulse VFDs, spot welders and single-phase loads is a textbook harmonic source. Field measurements on such busbars typically show current THD of 25–40 % at the PCC, with the 5th and 7th orders dominant. Third-order currents add up in the neutral conductor and overheat it. Fixed capacitor banks rar...