IPOS four-level Boost converter and midpoint potential balance control thereof

The invention discloses an IPOS four-level Boost converter and midpoint potential balance control thereof. The converter comprises a switching tube S1, a switching tube S2 and a switching tube S3, wherein the switching tubes S1, S2 and S3 are intersected with each other by 120 degrees for modulation. From the point of modularized series and parallel connection, the converter can be taken as three Boost converters with the parallel input and series output. A flying capacitor Cf1 and a diode D2 form a unit IV, and a flying capacitor Cf2 and a diode D4 form a unit V. The on/off states of all switching tubes and diodes of the converter are shown in the description under the 120-degree intersection modulation strategy. Based on the above device, the invention also proposes a three-ring control strategy formed through a common voltage outer ring, three current inner rings and two mean voltage rings. The mean voltage rings are put in front the current inner rings, and outputs a current instruction of the current inner rings along with the voltage outer ring. The current inner rings employ proportioning controllers.