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This paper presents a three-phase voltage-source 36-pulse converter that draws almost sinusoidal currents. The converter results from the combination of a series-connected 12-pulse voltage-source rectifier with a passive voltage-injection circuit and a bidirectional switch, referred to as hybrid injection. The voltage-injection circuit uses a single-phase rectifier bridge and a single-phase transformer. Both the voltage-injection circuit and the bidirectional switch operate at six times the supply frequency and have a low rating. In this paper, the converter operation is explained and analyzed. Subsequently, the converter is evaluated experimentally using a 4-kW 400-Hz prototype, where the [THD.sub.I] of the line currents was measured to be below 1.2%. Index Terms--AC-DC power conversion, aircraft power systems, power quality, rectifiers.

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. Index Terms--High-power factor rectification, three-phase multipulse rectifier.

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. Index Terms--Autotransformers, rectifier bridges, sinusoidal currents, three-phase multipulse rectifier circuit.