For the high voltage and power of traction power supply system of railway

a two-phase three-leg power conditioning unit is designed based on the modular multilevel converter (MMC) to eliminate the harmonic

reactive power

as well as the negative sequence current. The load current characteristic in the synchronous reference frame

and the compensation signal is calculated through second-order generalized integrator (SOGI) and DC integrator. A control system of MMC railway static power conditioner is designed in the stationary frame. Finally

the effectiveness of the algorithm and the compensation performance of the system are testified by real-time simulation and prototype test on the real-time digital simulation system. This work is supported by International Science & Technology Cooperation Program of China (No. 2013DFA60930) and Fundamental Research Funds for the Central Universities (No. 2010JBZ002).