A direct coupled 4-quadrant multilevel converter for 16 2/3 Hz traction systems

This paper describes a new direct-coupled 4-quadrant multilevel converter that could be used for traction interface, directly coupled to the MV catenary. Step and PWM-modulation circuits have been realised and allow the low distortion voltage generation, together with load symmetrisation of the steps. The proposed system has been verified on a low power test circuit. Key components for the direct coupling between the MV AC-line and the common DC-link of the application are the reversible DC/DC converters with MF AC-links. The behaviour of the DC/DC converter has been studied with power-flow control and superimposed control of output-voltage. Symmetrical share of the reactive power of the AC link has also been studied. A test-circuit has been realised together with a numerical control implemented on a conventional personal computer.