Evaluation of AC Current Ripple in case of Split-Capacitor Three-Phase Four Wires Inverters

This paper deals with a split capacitor three-phase four-wire inverter, able to deal with unbalanced ac currents and/or voltages. The considered topology can be used in many applications such as photovoltaic systems, chargers for electrical vehicles, active filters, and in general all the grid-connected applications. One parameter that must be considered in the converter design is the ac (output) current ripple, which should be determined and minimized in order to improve the system efficiency. In this paper, the evaluation of the ac current ripple for the three-phase split-capacitor inverter is developed with reference to both balanced and unbalanced output conditions. In particular, the peak-to-peak and the rms current ripple are analytically determined as a function of the modulation index, for each phase. Initially, reference is made to single-carrier sinusoidal PWM, being, in general, a simple and effective solution. The interleaved multiple-carrier PWM strategy is then considered in order to mitigate the current ripple in the neutral wire, while not affecting its phase counterpart. Numerical simulations have been carried out in order to verify the analytical developments.