Nonlinear Dynamics and Global Bifurcations in a Fixed Duty Ratio DC–DC Boost Switching Converter with a CPL

Cascaded DC–DC converters with source and load converters as their first and last stages are used in wide-ranging applications. Under certain conditions, the load converter behaves as a Constant Power Load (CPL) for the source converter. Due to the negative incremental resistance characteristic of the CPL, the system shows instability. One way to overcome this problem is to add a Loss-free Resistor (LFR) in series with the inductor of the source converter that stabilizes the system without losing global efficiency. Using an averaged model, this paper presents a dynamical analysis of a fixed duty ratio (open-loop) DC–DC boost converter, incorporating such a stabilizing resistor and a CPL. Fold and Hopf bifurcations associated with existence and stability of equilibria are found and the region covered by the basin of attraction of the stable equilibrium is examined. The criteria for choosing the system parameters are exposed accounting for steady-state stability and transient conditions. The analysis is performed first for a bidirectional boost converter admitting only Continuous Conduction Mode (CCM) operation and then extended to a unidirectional boost converter where both CCM and Discontinuous Conduction Mode (DCM) can take place. Theoretical predictions are validated by numerical simulations and experimental measurements.