Metro traction power supply system mostly adopts the 24-pulse rectifier unit,which is composed of two 12-pulse rectifier unit connected in parallel. If the two 12-pulse rectifier units run unstably,it will generate a lot of job insecurity harmonics,and threat the safe operation of the subway. Therefore,the harmonic analysis is conducted from the aspect of rectifying characteristics of rectifier units,and harmonic control for 24-pulse rectifier unit added threelevel active filter. This paper focuses on topol...