Transient Behavior and Frequency Response of Constant Frequency One Cycle Charge Control Modulator (O3C)

This paper presents a new pulse width modulator capable of adjusting the conversion duty ratio so that the necessary output filter charge will reach its steady-state value in only one switching period, when any disturbance of the input voltage, output current or output voltage occurs. The proposed modulator is based on the calculation of the variation of the electric charge required to restore the steady-state operation in only one switching period, and therefore is designated by one cycle charge control (O3C). The synthesis of the proposed modulator is presented in detail. It will be also shown, theoretically, by simulation and experimentally, that the use of this modulator in a buck converter presents as a major advantage, the fact that the output voltage gain is not limited by the cutoff frequency of the output filter. As a consequence, very low output ripple can be achieved without compromising the dynamic response of the converter. Comparative simulation results considering the presented modulator and the conventional one cycle control, both applied to a buck converter in the same conditions, are also presented.