Study On Pulse Train Controlled CCM Buck Converter

The most obvious difference between pulse train (Pulse Train, PT) control.technique and traditional PWM modulation technique is that, PT control circuit doesn’t need error amplifiers and their compensation netwok, thus has faster response speed. Up to now, the study on PT controlled switching converter almost focuses on the converters operating in discontinuous conduction mode, which severely limiting the power level of the switching converter.The working principle of PT control technique is analyzed in this thesis. Then, the control characteristic of PT controlled discontinuous conduction mode (DCM) and continuous conduction mode (CCM) buck converter is introduced The combination of high and low power pulse of PT controlled DCM and CCM buck converter is analyzed in detail. Simulation model of PT controlled CCM buck converter is constructed to verify the validity of design process and combination. Finally, the problems existing in the PT controlled CCM buck converter in steady state and transient state are presented.A steady state modified scheme is presented for PT controlled CCM buck converter, when the ESR of the output capacitor is very small. Theoretical analysis of the modified scheme is conducted in detail. The presented steady state modified scheme can obviously suppress the low-frepuency oscillation in PT controlled CCM buck converter. Finally, simulation and experimental results are used to verify the feasibility and validity of steady state modified scheme.A transient state modified scheme is presented for PT controlled CCM buck converter in the thesis. The whole design process and theoretical basis of the transient state modified scheme are introduced in detail. The presented scheme can markedly improve the transient characteristic of PT controlled CCM buck converter. At last, simulation and experimental results are provided to demonstrate the correctness and feasibility of the transient state modified scheme.