The frequency conversion power supply transforms the alternating current through AC → DC → AC to output pure sine wave, and the output frequency and voltage can be adjusted in a certain range. It is different from the variable frequency speed controller used for motor speed regulation and the common AC stabilized voltage power supply. The ideal AC power supply has the characteristics of stable frequency, stable voltage, zero internal resistance and pure sine wave (no distortion). Yidi AC variable frequency power supply is in the leading position in China.