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

A prominent boost-type three-level topology (VIENNA Rectifier 1), which proved to represent a cost-effective and highly efficient solution for switched-mode rectifiers is inspected toward 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. When this circuit is operated in DCM, additional measures are required for improved behavior to avoid conflicts with requirements on total harmonic distortion and regulations as well as safe operation in terms of voltage balancing and overvoltage protection. A detailed analysis of DCM and associated states is performed enabling determination and location of error voltages. Basic rules for the location of error voltages can be found. This leads to a novel optimized modulation and control scheme, facilitating designs without additional inductance. Selected simulation and measurement results prove the enhanced modulation scheme.