Asymmetric Duty Control of a Dual-Half-Bridge DC/DC Converter for Single-Phase Distributed Generators

A dual-half-bridge (DHB) converter is integrated with a half-bridge 60-Hz inverter as a converter/inverter system for a small distributed generator. This topology provides an isolation between the power source and the load with a 100-kHz transformer, and therefore, the system volume is small. On the other hand, it reduces the number of switching devices greatly. However, the half-bridge inverter causes severe capacitor-voltage fluctuations. The unbalanced voltage problem can be solved by controlling the converter switching: In addition to the conventional phase-shift control method, an asymmetric charging method is used that charges the upper and lower secondary capacitors differently. This means that the voltage imbalance is corrected by adjusting the switching time of the secondary switches. Furthermore, a decoupling control algorithm can be derived from this approach. The usefulness of this method is then validated by simulation and experimental results.