Operation of Flying Capacitor Multilevel Converters At and Above Resonance

The flying capacitor multilevel (FCML) converter has shown promise for high step-up/down conversion ratio applications due to its relatively low switch stress and small inductor volume. For higher level-count $(N\geq 3)$ variations of this topology, there is limited research on resonant mode operation, despite its potential to yield considerable performance benefits for fixed conversion ratio applications. When operating resonantly, the decreased inductance requirement compared to regulated operation can further reduce the magnetic volume and improve transient response, while also allowing for zero-voltage/zero-current switching (ZCS/ZVS). This work presents and analyzes a clocking scheme required to operate an $N:\boldsymbol{1}$ FCML converter both at-resonance and above-resonance, while maintaining mini-mum current ripple for reduced losses. A complete derivation is presented, enabling the calculation of precise phase durations as a function of switching frequency. Moreover, a 5:1 FCML hardware prototype is demonstrated, verifying intended operation both at-and above-resonance, in addition to highlighting the achievable loss reduction with the proposed switching scheme.