Harmonic overvoltage in the traction network of electrified railways can easily lead to the failure of locomotives and related power supply equipment, and in serious cases will lead to the breakdown of insulation of locomotive high-voltage equipment and the stopping of trains in transit. The 27.5kV harmonic control system uses harmonic real-time monitoring and filtering technology to effectively absorb specific frequency band harmonic currents in the traction network, suppress overvoltage and improve the power quality of the traction network.