Minimum DC Link Capacitance for a Family of Three-Phase Three-Level Grid-Connected Converters Operating with Unity Power Factor

The paper presents a method for derivation of the minimum split DC link capacitance in three-phase three-level DC-AC converters operating with unity power factor with neither active balancing circuits nor AC zero sequence injection. It is shown that due to the fact that partial DC link voltages and AC-side phase voltages obtain extremum values at different instants, it is possible to reduce the minimum value of the former below maximum value of the latter while still ensuring correct operation of the power stage. Minimum attainable split DC link capacitance values are therefore obtained according to boundary case of tangency between the above-mentioned voltages. Analytical derivations are accurately verified by simulations and experiments, demonstrating close agreement.