Flying Capacitor Voltage Imbalance Protection in Multilevel Bidirectional Inverters during Surge

Input voltage surge events due to lightning strike and short-term transients such as input voltage dips are of a significant interest when flying capacitor multilevel (FCML) inverters are considered. During these fast dynamic events charge balance of flying-capacitor(s) can be compromised. This paper presents a time-efficient and reliable surge detection method to prevent FC drift during input voltage transients in FCML single-phase PFC/inverter systems. The effect on flying capacitor(s) voltage is analyzed with the help of an operational bidirectional inverter simulation. The proposed technique is implemented and validated based on a highly efficient and modern 3-level bridgeless totem-pole (BTP) power factor correction (PFC) with bidirectional grid-tied capability.