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A three-phase, multilevel rectifier using active voltage injection with one MOSFET device is presented. The injector consists of a bidirectional switch that modifies the behavior of a 12-pulse rectifier resulting in either 24-pulse or multilevel pulsewidth-modulated (PWM) operation. The resultant input currents are almost sinusoidal, the line current THD being 2.36% for 24-pulse operation and 1.06% for PWM operation. The MOSFET current is 2.9% of the load current. The circuit operation, idealized waveforms and modulation strategy are explained and experimental results are presented. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A new converter topology for a three-phase multi- pulse rectifier circuit is described. This converter draws almost sinusoidal currents from the ac system with very low harmonic content and typically less than 3% total harmonic distortion. The topology uses only passive components and has a lower component count than other rectifier circuits with similar performance. Two six-pulse rectifier bridges are connected in series, fed by a series connection of transformers, to form a 12-pulse system. An additional low power harmonic injection circuit enhances the performance of the circuit to obtain low harmonic current pollution levels that are comparable with those achieved from a 24-pulse rectifier. The circuit operation is explained and experimental results are presented. [ABSTRACT FROM AUTHOR]