Slow-Scale and Fast-Scale Instabilities in Voltage-Mode Controlled Full-Bridge Inverter

This paper discusses the slow-scale and fast-scale instabilities of a voltage-mode controlled full-bridge inverter which is widely used in AC power supply applications. The main results are illustrated by exact cycle-by-cycle simulations. It is shown that the slow-scale instability is a type of low-frequency instability which manifests itself as a Hopf-type low-frequency oscillation in the whole line cycle, whereas the fast-scale instability is a type of local instability which manifests itself as a period-doubling bifurcation in some intervals of a line cycle. An averaged model and an improved discrete-time model are used to theoretically analyze the slow-scale and fast-scale instabilities, respectively. Finally, experimental results are presented to verify the results from simulations and analysis. Our work has revealed more instabilities which are likely to occur in the inverter, and has provided a convenient means of predicting stability boundaries to facilitate the design of the inverter.