Three phase AC-DC power converters are vastly applied in industrial applications including adjustable speed drives, uninterruptible power supplies, battery energy storage systems, electroplating welding units and inverters.AC-DC rectification is usually performed using diode or thyristor bridge rectifier with a large output capacitor. This type of rectifier operates at low power factor and injects significant amount of harmonics into the power system. Harmonics in the input current have many adverse effects such as: distortion of input voltage, increased conduction losses, increased volt-ampere rating of the power system equipment’s, error in metering and malfunctioning of utility relays and many other problems. Six switch three phase rectifiers are one of the preferred topologies for implementation of active input current shaping in three phase AC-DC converters. This circuit suffers from high switching losses and severe problems due to reverse recovery of switches anti-parallel diodes. Several examples of soft switching auxiliary circuits for six switch boost converter are reviewed in this thesis. In a method, current harmonics are generated on the DC side of the diode bridge rectifier by a modulation circuit and then injected into the main using an injection circuit. Modulation and injection circuits can be either passive or active which are fully reviewed. Modular approach and three or four switch converters are other reviewed solutions to improve the power factor. For fewer component count and simplified control and drive, three phase PFC rectifier can be implemented using a converter with just one switch. Single switch three phase PFC converters are divided into two categories of discontinuous voltage mode and discontinuous current mode converters that both are investigated. In this thesis, a solution is proposed to avoid discontinuous current at the input of the diode bridge rectifier. Three switches and three high frequency transformers are applied to shape the input AC current especially at the zero voltage crossings. Proposed rectifier operates at high switching frequencies and therefore, the auxiliary circuit volume is low. Also, a new three phase power factor correction circuit base on DVM Cuk converter is introduced. DVM Cuk converter has excellent power factor with very low harmonic content. This is due to the fact that in this converter discharging mode of capacitor does not affect the input current. Also, a new single stage, single switch, soft switching three phase power factor correction converter is introduced. The proposed discontinuous current mode Cuk and SEPIC converters have the capability to step up or step down the voltage and only employ a single switch. Also, the efficiency is improved due to the achieved zero current and zero voltage switching at turn on and turn off instants without any extra switch. Keywords: Three phase AC –DC converter, Three phase rectifier, Power factor correction.
