Performance Enhancement of ICN-Based Single-Stage AC-DC Converters Using Reconfigurable Inverters

This article presents a reconfigurable inverter design for the recently proposed impedance control network (ICN) based single-stage ac-dc converters, targeting improvement in their efficiency and power density. This reconfigurable-inverter design effectively compresses the range of input voltages to the ICN converter by operating its two inverters in parallel at low line and in a stacked fashion at high line input. In addition to retaining the wide range zero voltage switching and near zero current switching operation characteristic of the ICN converter, the proposed reconfigurable inverter design benefits all the converter's transistors and magnetic components as it simultaneously reduces the peak voltage stress on its inverter transistors, rms currents through its rectifier transistors, the resonant inductance requirement, and the step-down burden on its transformer, thus improving the overall performance. A novel active voltage balancing scheme for the stacked mode of operation of the two inverters is also proposed. An enhanced version of this active voltage balancing strategy is also discussed, which ensures soft-switching of the inverter transistors by deliberately introducing slight inverter voltage imbalances of appropriate magnitude. A universal-input (90-265 V-rms), 20-V output, 330-W, 300-kHz reconfigurable-inverter-based ICN ac-dc converter prototype is built and tested. This prototype achieves a power density of 44.5 W/in(3), and peak efficiencies of 94% at low line (120 V-rms) and 93.8% at high line (230 V-rms). Compared to the basic ICN converter prototype, this prototype achieves 17% higher power density and has 23% and 9% less loss at low and high line input, respectively.