Current Programmed Mode Control of Multi-Level Flying Capacitor Converter Near Zero-Ripple Current Region

This paper explores the challenges and introduces a solution for near zero-ripple current region operation of multilevel flying capacitor (ML-FC) converters, operating in peak and valley current programmed mode (CPM). Around the zero-ripple region, the triangular inductor current ripple waveform is modified to be trapezoidal using a state machine. Seamless transition between peak and valley is desirable to ensure symmetrical stable operation below and above the duty-cycle yielding zero-ripple current. In both cases, flying capacitor voltage inherent stabilization is achieved. The investigated ideas are verified with a three-level FC buck converter with 5 V output operating at 500 kHz nominal switching frequency near 50% duty-cycle, the zero-ripple current region.