T-type three-level circuit is a novel clamp topology,which achieves connection of the DC side neutral point and the load through the two-way switch.Compared with the traditional Neutral-Point-Clamp (NPC),the circuit uses fewer components,the device loss is uniform,the operation efficiency is high,and therefore it is widely used in new energy power generation such as photovoltaic power generation.Neutal point voltage balance problem is the inherent problem of this type of circuit,which need to be properly resolved.In this paper,the generation mechanism and influencing factors of T-type three-level midpoint potential are analyzed,and then the mathematical model of midpoint potential is established.An analysis method based on modulation wave voltage instruction partition is proposed,and the analytic expression of the zero sequence voltage to the midpoint potential is established.Based on this,the balance control strategy of midpoint potential is established,and the controller is designed.Finally,the correctness of the theoretical analysis is verified by simulation analysis.