Flying Capacitor Voltage Control with Delta-Sigma Modulation to Reduce the Flying Capacitor and the Switching Frequency for a Three-Level Flying Capacitor Topology

This paper presents a flying capacitor voltage control method for a three-level flying capacitor multilevel (FCML) converter where modulation is controlled by an asynchronous delta-sigma modulator (ADSM). The proposed method enables active balancing of the flying capacitor voltage by utilizing signals inherently available within the ADSM structure. By applying the new method, the flying capacitor size and the switching frequency can be reduced depending on the input signal characteristics and the phase angle between the output voltage and output current. A comparison to a conventional pulse-width modulation (PWM) is given. Furthermore, the impact of the proposed control method on the average switching frequency is analytically derived and validated through system-level simulations. The active balancing behavior is demonstrated in the measurements and compared to a standard ADSM.