Multi-Path Precharge for GaN Flying-Capacitor-Multi-Level Totem-Pole PFC

GaN flying-capacitor-multi-level (FCML) Totem-Pole power-factor-correctors (PFCs) have been demonstrated with very high density and efficiency in the literature. However, there is still a lack of detailed discussion about flying capacitor voltage precharge during the start-up for GaN FCML Totem-Pole PFCs. To enhance the reliability during start-up, we propose a multi-path and multi-step flying capacitor precharge method. In our proposed method, the bulky DC link capacitor is precharged through the path of the auxiliary line-frequency Si diode half-bridge and the body-diodes of the Si MOSFET half-bridge. The flying capacitors which have much smaller capacitances are precharged through the path of the GaN devices and the body-diodes of the Si half-bridge. The DC link capacitor is more than 100 times higher than the flying capacitor in this topology. Therefore, by splitting the total precharging current into two paths, the precharging current through the GaN devices is almost 100 times lower than that through the body-diodes of Si MOSFETs. As a result, this method protects expensive GaN devices from high inrush current and significantly improves the reliability of the GaN devices during the voltage precharge. Detailed operation principles and experimental verifications are presented in this paper.