Coordinated Control of Second-Order Harmonic Voltage and Current Fluctuations in Cascaded H-Bridge Inverter with Supercapacitor and DC-DC Stage at Variable Output Frequencies

In the cascaded H-bridge inverter (CHBI) with supercapacitor and dc-dc stage, inherent second-order harmonic power flows through each submodule (SM), causing fluctuations in both the dc-link voltage and the dc-dc current. There exist limitations in handling these fluctuations at variable output frequencies when employing proportional-integral (PI) control to the dc-dc stage. This paper aims to coordinately control these second-order harmonic voltage and current fluctuations in the CHBI. The presented method configures a specific second-order harmonic voltage reference, equipped with a maximum voltage fluctuation constraint and a suitable phase, for the dc-dc stage. A PI-resonant controller is used to track the configured reference. This allows for regulating the second-order harmonic fluctuation in the average dc-link voltage among the SMs within a certain value. Importantly, the second-order harmonic fluctuation in the dc-dc current can also be reduced. Simulation and experimental results demonstrate the effectiveness of the presented method.