Voltage control of common flying capacitors in 5-level converter with capacitor current estimation

In this paper, a new flying capacitor (FC) voltage control method that is suitable for a 5-level converter with common FCs is proposed. The proposed method can control voltage of FCs using the estimated capacitor current and control FC voltage more steadily compared with previous method. The current is calculated from detected phase current and phase voltage reference. This method can be applied to a FC shared with any number of phases without violating the limitation of the switching pattern. An experiment was conducted to verify the control method using 400V, 8 kVA downscaled model.