Pre-charge Control Strategy of Three-level Converter Based on Flying Capacitor

For bi-directional converters, a pre-charging strategy based on single switch control for flying capacitor three-level is proposed. By controlling the on-off of the three-level outer tube, the flying capacitor can be pre-charged efficiently and quickly. The pre-charging control strategy is applied to bi-directional converter. The pre-charging of flying capacitor is completed in 1s in Buck mode and 5s in boost mode, after pre-charging, the flying capacitor voltage remains half of the high voltage side voltage, and the input capacitor voltage remains as the input voltage. No additional pre-charging power device is needed, which not only simplifies the topology, but also ensures the reliable and fast pre-charge of flying capacitor.