Narrow Results

This paper investigates the interaction of fast-scale and slow-scale bifurcations in the boost converter under current-mode control operating in continuous conduction mode. Effects of varying some chosen parameters on the qualitative behaviors of the system are studied in detail. Analysis is performed to identify the different types of bifurcation. Boundaries of stable region, slow-scale bifurcation region, fast-scale bifurcation region, interacting fast and slow-scale bifurcation regions are identified.

The complex dynamics and coexisting fast-slow scale instability in current-mode controlled buck converter with constant current load (CCL), operating in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM), are investigated in this paper. Via cycle-by-cycle computer simulation and experimental measurement of current-mode controlled buck converter with CCL, it is found that a unique fast-slow scale instability exists in the second-order switching converter. It is also found that a unique period-doubling accompanied by Neimark–Sacker bifurcation exists in this simple second-order converter, which is different from period-doubling or Neimark–Sacker bifurcations reported previously. Based on a nonlinear discrete-time model and the corresponding Jacobian, the effects of CCL and input voltage on the dynamics of current-mode controlled buck converter are investigated and verified theoretically. Fixed point analysis for slow-scale low-frequency oscillation is also given to verify the dynamics and the coexisting fast-slow scale instability.

This paper reports the slow- and fast-scale instabilities in the parallel-connected single-phase H-bridge inverters and discusses the two types of instabilities from the practical design viewpoint. Simulations show that the slow-scale instability which occurs in the whole line cycle is a type of global instability, whereas the fast-scale instability which occurs around the middle time of each half-line cycle is a type of local instability. In order to reveal the mechanisms of the slow- and fast-scale instabilities, theoretical analyses are carried out through the derived averaged model and discrete-time model, respectively. It is identified that the slow-scale instability is due to the occurrence of Hopf bifurcation, and the fast-scale instability manifests itself as period-doubling bifurcation. Furthermore, stability boundaries in various design parameter spaces considering the mismatches in different system parameters between inverter modules, as well as the effects of the current-sharing control loop on the slow- and fast-scale instabilities are also given. Besides, the influences of the nonlinear load and the control method for parallel system on the two types of instabilities are briefly discussed. These findings can be used to guide the tuning of the paralleled inverter system parameters to ensure stable operation in practice. Finally, experimental results are presented to verify the results of the simulation and theoretical analysis.