Period-bubbling and mode-locking instabilities in a full-bridge DC-AC buck inverter

In this study, the non-linear dynamics of a full bridge DC-AC inverter controlled by fixed frequency pulse-width modulation which is widely used in solar energy systems is investigated. The main results are illustrated with the aid of time domain simulations obtained from an accurate non-linear time varying model of the system derived without making any quasi-static approximation. Results reveal that for high filter time-constants, the system loses stability via Hopf bifurcation and exhibits mode-locked periodic motion and for low filter time-constants, via period-doubling bifurcation resulting in period-bubbling structures and intermittent chaos. The mode-locked instability is also theoretically verified using Jacobian matrix derived from an averaged model and that of period-bubbling instability is verified using monodromy matrix based on Filippov´s method of differential inclusions. Furthermore, extensive analyses are performed to study the mechanism of the emergence of intermittency and remerging chaotic band attractors (or Feigenbaum sequences) for variation in filter parameters and to demarcate the bifurcation boundaries. Phase portraits and Poincaré sections before and after the bifurcations are shown. Experimental results are also provided to confirm the observed bifurcation scenario.