Frequency converter and inverter due to adopt the mode of the ac/dc power supply, the output contains a large number of higher harmonic, voltage waveform distortion, seriously affect the electricity Equipment normal work and life. Sine filter with the method of resonant circuit filter, can effectively extend the electricity equipment to improve and effectively improve waveform, make the output Reach the state of the approximate sine wave filter form so as to improve the power quality and prolong the service life of equipment.