A Simplified Real-Time Digital Control Scheme for ZVS Four-Switch Buck-Boos With Low Inductor Current

In this article, the four-switch buck-boost (FSBB) converter is a preferred choice for the dc-dc applications where the step-up and step-down are needed. In order to reduce the inductor size and improve the efficiency, the zero-voltage switch (ZVS) control schemes with four segments inductor current for FSBB have been investigated in numerous publications. Among these ZVS control schemes, the optimized control variable stored as the huge look-up table data achieved minimum root-meansquare (RMS) inductor current, and the complex real-time calculation is avoided. However, for the purpose of matching the wide input and output voltage ranges, an external flash is needed for storing the look-up table data; And the large time consumption for invoking the data hazard the dynamic performance significantly. To reduce the storage device cost and meet the demand of transient, a simplified real-time control algorithm is proposed by dividing the operation into the defined Discontinuous Conduction Mode (DCM) and Continuous Conduction Mode (CCM) operation featuring the minimum RMS inductor current and ZVS operation during the whole voltage range without complex calculation and mode transient. Finally, a 300 W dc-dc prototype is built to verify the theoretical analysis and proposed control scheme with a low-cost real-time digital controller.

Automated summary

This article introduces the advantages of the four-switch buck-boost (FSBB) converter in dc-dc applications that require step-up and step-down. To reduce the size of the inductor and improve efficiency, various zero-voltage switch (ZVS) control schemes for FSBB with four segments of inductor current have been investigated. Among these schemes, storing the optimized control variable as lookup table data achieves the minimum root-mean-square (RMS) inductor current without complex real-time calculations. However, using an external flash to store the lookup table data for wide input and output voltage ranges leads to significant time consumption for data invocation and affects the dynamic performance. To address this issue, a simplified real-time control algorithm is proposed, dividing the operation into defined Discontinuous Conduction Mode (DCM) and Continuous Conduction Mode (CCM) operation, ensuring minimum RMS inductor current and ZVS operation throughout the voltage range without complex calculations and mode transients. A 300 W dc-dc prototype is also built to verify the theoretical analysis and proposed control scheme using a low-cost real-time digital controller.