CCM Noninverting Buck-Boost Converter With Fast Duty-Cycle Calculation Control for Line Transient Improvement

A continuous-conduction mode (CCM) noninverting buck-boost (NBB) converter with a fast duty-cycle calculation (FDCC) control and duty-cycle locking strategy is proposed in this paper. Utilizing auxiliary and adjustable slopes of the modulation signal, the FDCC control not only rapidly determines an accurate duty cycle but also keeps the compensator output constant when the input voltage changes. The theoretical dc value of the numerator of the closed-loop line-to-output voltage transfer function is equal to zero whether the CCM NBB converter operates in boost or buck mode. It indicates that adopting the FDCC control can achieve ideal feedforward compensation for CCM buck and boost operations. Consequently, the output transient ripple of the CCM NBB converter with FDCC control can be eliminated significantly regardless of the unit-gain bandwidth of the NBB converter. To alleviate pulse skipping and to avoid changing buck and boost modes frequently, a duty-cycle locking method is adopted in the transition region of the buck and the boost. Hence, the duty-cycle locking method enhances power conversion and maintains the output voltage. The experimental results demonstrate that the proposed control schemes not only effectively reduce the line transient ripple but also obtain high efficiency in a wide range of input voltage.