Modeling and Analysis of Coexisting Slow- and Fast-Scale Instabilities in Current-Mode PI-Controlled H-Bridge Inverter

The characteristic of current-mode H-bridge inverter under PI-control is much more complex than under P-control. When system parameters are not properly designed, the system not only has the potential of slow-scale instability (Hopi), but also has the possibility of fast-scale instability (Period doubling). In previous works on discrete-time modeling and analysis, P-controller is always taken as object of study for simplicity, which is different from practical applications where PI-controller is often adopted. In this paper, a simplified discrete-time model of current-mode H-bridge inverter under PI control is derived. Based on analysis of the proposed model, coexisting slow- and fast-scale instability phenomenon and mechanism have been revealed. Moreover, high accuracy stability boundary has been derived and verified by experiment.