Efficiency Characterization and Impedance Modeling of a Multilevel Switched-Capacitor Converter Using Pulse Dropping Switching Scheme

A pulse dropping switching technique (PDT) has been presented in this paper to accomplish variable conversion ratio (CR) in a multilevel modular capacitor-clamped dc-dc converter in the step-up conversion mode. The switching pattern is generated by comparing a triangular wave with a rectangular wave, and a proper output voltage regulation can be obtained by controlling the relative frequency and amplitude of these two waveforms. A state-space modeling technique has been applied here to estimate the variation in equivalent output resistance (EOR) for different operating conditions of the PDT. The EOR can be varied in a wide range without changing the operating frequency of the converter, and thereby the PDT enhances the degrees of freedom to accomplish voltage regulation in a two-phase switched-capacitor converter. Slow-switching limit of the converter has been derived to define the boundary of the EOR. Different challenges and limitations of the proposed modulation scheme has been discussed in detail, and the proposed analysis has been verified by comparing the analytical expressions with the simulation and experimental results for different switching frequencies, modulation indices, and number of active modules. In addition, variations in the CR, efficiency and ripple voltage for different number of active modules and switching conditions have been described in detail.