Abstract: As a new type of transmission mode, fractional frequency transmission system (FFTS) has great advantages in long-distance wind power transmission scenario. In order to provide a guide for the practical development and operation of M3C, as a key device in the scenario of long-distance wind power transmission system, we first introduce the vital device, scheme, characteristic and topological structure of wind power transformed by FFTS. On this basis, a 35 kV/3 MVA M3C engineering prototype, which is the key device of FFTS, is developed. Tests for the performance of the M3C are implemented and the test results show that the key performance of the M3C such as efficiency, module voltage imbalance, voltage/currenct harmonic distortion rate, frequency regulation deviation on the fractional frequency side, and power step response time of the prototype of the frequency converter under full load conditions all meet the design requirements. Finally, the prospects and benefits of FFTS are analyzed, and the technical challenges faced in the development of FFTS are pointed out.