3-Phase AC-DC Converter Topologies with Higher Frequency Transformer Isolation for Utility Grid Interface

Two AC-DC converter topologies for 3-phase utility grid interface using high frequency (HF) or medium frequency (MF) transformers have been proposed in this paper. The transformer primary side converter structure is similar in both the topologies (say T-I and T-II), but the secondary side converter structures as well as the modulation schemes are different. The line-frequency AC voltage from the utility is first converted to HF or MF AC using three 1-phase AC-AC converters. The AC-AC converters can be unidirectional if power flow is desired in only one direction. The transformer core can be of silicon steel, amorphous or nano-crystalline material. The secondary side of topology T-I consists of a 3-phase PWM rectifier, while topology T-II consists of three 1-phase boost power factor correction (PFC) stages with a common output DC-bus. Both topologies avoid DC-link capacitors on the primary side and allow for high density power conversion. Potential applications include electric vehicle battery charging, telecom power supply, adjustable speed drives, server power supplies, etc. Simulation results and experimental waveforms from laboratory prototype evince the operation of the topologies.