A Second-Harmonic Suppression Method Based on Differentiated-Capacitance Design for Input-Parallel Output-Series DAB Fed Single-Phase VSI

In the single-phase voltage source inverter (VSI), the instantaneous output power pulsates at twice the line frequency, generating second-harmonic voltage in dc bus. Bulky electrolytic capacitors or additional auxiliary circuits are used in traditional methods, which inevitably limit the system lifetime, efficiency, and power density. In this article, the input-parallel output-series (IPOS) dual active bridge (DAB) with differentiated-capacitance design is adopted as the front-end dc–dc stage. The pulsating power is compensated by the energy gap that the differentiated output capacitors release. The small-signal model of the IPOS DAB fed VSI is built, and based on which, the voltage-complementary algorithm is proposed. Then, the preferred zone and optimization scheme of the main circuit parameters are designed according to the quantitative analysis of the suppressing effect. Furthermore, a 625-W IPOS DAB fed VSI design example is presented and tested. The experimental result shows that at least seven times the capacitance requirements can be reduced without any additional components, and the power quality of both the input current and the output voltage is well guaranteed.