Aiming at the traditional diode clamped three-level rectifier has the problems of switching off over-voltage on the inner side of bridge arm and the deviation of neutral point potential on the DC side, a new type of high-voltage and high-power double-clamp three-level converter is studied in this paper. Its working principle and double clamp mechanism are analyzed, and its mathematical model in rotating coordinate system is deduced. According to the characteristic that the current path cannot be changed abruptly, a double balance modulation method is proposed, which can satisfy the voltage balance of DC side capacitance and clamp capacitance at the same time. Simulation and experimental verification are conducted through MATLAB simulation and DSP+FPGA based controller prototype, and the results show that the double balance modulation method is correct and the new topology can be extended.