Effects of non-ideal current sensing on subharmonic oscillation boundary in DC-DC switching converters under CMC

This paper discusses the influences of non-ideal current sensor on the stability and subharmonic oscillation boundaries in current mode controlled switching converters. First, a general-purpose simplified model is built applicable to any switching converter working in continuous conduction mode. Then, a steady-state asymptotic Fourier-series-based method is applied to obtain a boundary condition in the frequency domain and expressed in terms of the system state-space matrices. Using the Poisson sum formulae, this condition is transformed into the time-domain. The approach is applied to dc-dc switching converters with current mode control (CMC) taking into account finite current sensor bandwidth. Design-oriented equations describing the occurrence of subharmonic oscillations are derived for any single-switch dc-dc converter. These equations are expressed explicitly in terms of operating converter parameters and duty cycle making them directly applicable for design purposes. Some problems with influence of the limited bandwitdh of the current sensor on the ramp compensator design and system dynamics are discussed, along with some proposed solutions.