Design and Implementation of a High Power Density Bipolar Multi-Level Active Power Pulsation Buffer for Single-Phase Converters

Active power decoupling methods in single-phase systems aim to reduce the required capacitance for twice-line frequency power ripple buffering, with added power conversion (i.e., active techniques) to improve the energy utilization ratio of the capacitors. While many active buffer solutions can improve the energy utilization ratio of the capacitor to a certain extent and reduce the required capacitance, they require the use of high energy density ceramic capacitors to achieve comparable power density to the passive electrolytic capacitor bank solution. The ceramic capacitors have to be carefully assembled and packaged, and they are also costly and heavy in weight. In this work, a bipolar ripple port converter, which allows the use of the minimum buffering capacitance in single-phase conversion with 100% energy utilization ratio, is implemented with metal film capacitors, and two flying capacitor multilevel (FCML) legs operated as a full-bridge to shrink the filter inductor size and improve efficiency. A compact hardware prototype with a new digital control scheme is implemented. Experimental results demonstrating the active power ripple decoupling at 2 kW, 400 V dc bus are provided and discussed.