Closed-Form Solution for ZVS and Minimum Current of Cascaded Buck + Boost Converters Eliminating Instantaneous Inductor Current Detection

Existing quadrilateral-current-based zero voltage switching (ZVS) control methods of cascaded buck + boost converters (CBBCs) rely on instantaneous inductor current detection, posing a demanding requirement on the bandwidth of current sensors in high-frequency applications with hundreds of kilohertz. Also, with power level increasing, such methods become more sensitive to switching noise. To overcome these issues, this article proposes a closed-form solution for ZVS and minimum rms inductor current operation of CBBCs while eliminating instantaneous inductor current detection. Instead of accurately sensing inductor current and triggering switch
on
/
off
once ZVS condition is satisfied, the quadrilateral inductor current for ZVS is achieved through current ripple prediction combined with average current (dc component) regulation, which mitigates noise susceptibility and eliminates the requirement of wide bandwidth (dc-to-several megahertz) for current sensor. The operation trajectories are analytically derived and generalized covering buck/boost mode and positive/negative power flow, ensuring ZVS of all switches with minimum conduction loss over a wide voltage range. Moreover, the proposed method does not rely on lookup tables, significantly reducing digital implementation efforts. The validity and feasibility of the proposed strategy are verified via a 2-kW CBBC prototype and a maximum efficiency of 98.7% is achieved.