A 5-level flying capacitor multi-level converter with integrated auxiliary power supply and start-up

This paper presents a 5-level Flying Capacitor Multi-Level (FCML) converter with an integrated auxiliary power converter to supply power to the controller and gate drive circuitry. The auxiliary power converter is sourced from within the FCML converter at a naturally occurring low voltage node, reducing the voltage rating requirements by 75% and thus the size of the auxiliary converter. The auxiliary load current drawn from the FCML converter induces an imbalance in the flying capacitors, which is detrimental to the capacitor and switch ratings if left unchecked. To compensate for this imbalance, an active balancing method is proposed that adjusts the phase and duty cycle of the traditional Phase-Shifted Pulse-Width Modulated (PSPWM) control signals. The active balancing requires a single capacitor voltage measurement, no additional components and proportional control. A start-up circuit is proposed to power the auxiliary power supply and soft-start the FCML converter. Experimental results have been demonstrated with an experimental prototype resulting in excellent flying capacitor balancing and FCML start-up.