High Step-Down Conversion Ratios of DC-DC Converters under Triple PWM Control Schemes

By extending our previous dual PWM control scheme, a novel control scheme, synthesizing triple PWM waveforms, is proposed for obtaining the buck converter with high step-down conversion ratio. Three PWM waveforms including high-frequency signals, middle-frequency signals, and low-frequency signals are utilized to generate desired PWM waveforms in order to attain the efficient step-down voltage gain of the buck converter. The three PWM waveforms are integrated into the single PWM control signal in which there exists multiple switching pulses in the power switch to result in eleven operating modes for the proposed converter. The small-signal analysis is also considered in the proposed converter by including the switched circuit model. Based on the volt-second balance condition, the proposed scheme is capable of generating the voltage conversion ratio which can be represented as the cubic function of the duty cycle if the duty cycles of the three designed PWM waveforms are the same under the continuous conduction mode. The proposed converter appears effective in cost since there is no need to modify the circuit in the traditional buck converter. Finally, the numerical simulations and the hardware experiments are conducted to verify the proposed scheme.