Soft-switching single-phase-three-phase converters with near unity power factor

A power converter system is proposed which incorporates soft switching both on the output stage and on the single-phase input stage and which is capable of operating in four quadrants and with near unity power factor. The circuit discussed as an example is based on the resonant DC link inverter topology and consequently employs discrete pulse modulation. This has far-reaching consequences for the modulation strategy. Despite this, it is shown that control over individual harmonics is possible, allowing the designer to determine the characteristics of the input stage. The power converter topology is compared with conventional diode-bridge input types and found to have improved figures for total harmonic distortion, peak input current and psophometric current, which is an important indicator in the rail traction field. It is also seen that the weight and size of the power converter can be reduced owing to the lower filtering and heat-sinking requirements. The results obtained by simulation are compared with practical results derived from a low-power test-rig