A Passive 36-Pulse AC–DC Converter With Inherent Load Balancing Using Combined Harmonic Voltage And Current Injection

A combination of two, simple, passive injection circuits is used to eliminate virtually all the low-order harmonics from the line currents of a standard 12-pulse rectifier, transforming its performance into that of a 36-pulse system. A line current total harmonic distortion of 1.51% is achieved in a 15-kW, 400-Hz prototype. The basic 12-pulse rectifier comprises two 6-pulse bridges that are series connected on both the ac and dc sides along with a 50%-rated, delta-star, phase-shifting transformer, while each injection circuit principally consists of a small transformer that operates at six times the supply frequency and carries around 1% of the total power throughput. The injection techniques are also valid for a fully isolated transformer arrangement. Full details of the circuit operation and design are reported