Enhanced control scheme for three-phase/three-level rectifiers at partial load

A prominent boost-type three-level topology, which proved to represent a cost effective and highly efficient solution for switched mode rectifiers is inspected towards its operation at discontinuous conduction mode (DCM). This mode of operation occurs not only at high input voltage in conjunction with low load currents but even at medium loading in the vicinity of mains voltage zero crossings. And since the requirements on THD conflict with the actual behavior of the circuit when operated at DCM measures are needed for optimization. A detailed analysis of DCM and associated states is performed. Basic rules for the location of error voltages can be found. This leads to a novel measure to optimize the modulation and control scheme respectively, facilitating designs without additional inductance. Selected simulation and measurement results prove the enhanced modulation scheme.