The paper presents a methodology for determining the minimum split DC link capacitance for a family of three-phase, three-level grid-connected bidirectional AC-DC converters operating under arbitrary power factor under restriction of DC-only zero-sequence injection. The approach is based on the recently revealed generalized behavior of split DC link voltages in the above-mentioned converters family while distinguishing between leading and lagging power factors in order to highlight different impacts on split DC link capacitor voltages pulsating components. The minimum capacitance value is derived from the boundary condition, ensuring the mains voltage remains below or equal to the capacitor voltage at all times. It is revealed that operation with the lowest expected leading power factor should be employed as the design operating point. The accuracy of the proposed methodology is validated by simulations and experiments carried out employing a 10 kVA grid-connected T-type converter prototype. The results demonstrate close agreement between theoretical predictions and experiments, confirming the practical applicability of the proposed method.

Active ripple suppression branches (ARSBs) are widely employed in switching power converters interfacing ripple-sensitive devices such as batteries, supercapacitors, hydrogen electrolyzers, fuel cells, and photovoltaic panels. Conventional ARSBs share the main converter DC-link voltage and require inductance comparable to that of the primary power stage, resulting in high semiconductor voltage stress and bulky magnetic components. Recent studies have proposed supplying the ARSB from a lower auxiliary voltage source, significantly reducing both inductance value and semiconductor voltage ratings. This paper shows, however, that lowering the ARSB rating while keeping the series capacitance value unaltered inherently increases residual current ripple, degrading ripple-cancellation performance. It is then demonstrated that this limitation should be overcome by increasing the ARSB capacitance in inverse proportion to the rating reduction, thereby restoring ripple suppression performance. Furthermore, it is revealed that for converters operating at a fixed duty cycle, a unique operating point exists where the ARSB capacitor can be eliminated without sacrificing the ripple attenuation ability of the circuit. The resulting capacitorless implementation reduces component count, size, complexity, and cost while improving ripple suppression. Simulation and experimental results validate the theoretical analysis and confirm the feasibility and effectiveness of the proposed capacitorless open-loop operating ARSB.