On the Necessity of DCM Operation for Buck Converters Between Constant Voltage Buses

Electric vehicles, among other application fields with battery energy storage systems, rely on power electronics to transfer power between different voltage buses. Applications such as charging and active balancing of battery packs utilize converters between DC buses with constant voltage sources and loads, and their reliable design and operation has been a key focus of ongoing research. In this work, a specific focus is made on the non-isolated buck converter, although the results can be generalized to other converters. A key result is to demonstrate that discontinuous conduction mode (DCM) is necessary between constant voltages. A procedure is detailed for the derived formulas in open-loop operation to calculate the duty ratio in DCM and relate it to practical setpoint variables and sizing the inductor. Moreover, the derivations are included in detail to facilitate a better understanding of these results, allow for their extension to other converters, and enable their inclusion as a reference in power electronic textbooks. Additionally, in practice, the procedure allows for the open-loop duty ratio in DCM to be used as a feed-forward term in controlled converters speeding up their convergence and aiding in the converter’s design process.