Cost effective multi-pulse transformer solutions for harmonic mitigation in AC drives

More and more AC drive installations are requiring manufacturer´s to improve line side harmonics to ultimately meet IEEE Harmonic Std 519-1992 on site. This paper reveals several patented transformer topologies for such an effort. Compared with other harmonic solutions, auto and isolated transformers possess advantages as being simple, reliable, minimal line resonance problems and relatively cost effective. The proposed nine and twelve-phase auto-transformers can be viewed as a polygon winding type, where besides achieving an improved input current harmonics, junction points among various windings along the polygon can be wired out for step-down, unity and step-up voltage transfers. When electrically isolated primary windings are added, unlimited transfer ratio is available for every application. Application of these new industrial transformer devices, along with simple power diode energy conversion methods, result in a robust and reliable system that provides good DC bus regulation for AC drives utilizing a common DC bus configuration. The proposed topologies also provide a high AC input power factor and minimize harmonic currents to the utility interface. The paper provides technical analysis and field site data on the new topologies, as well as per unit metric comparison to other harmonic mitigation techniques versus horsepower size.