The frequency conversion power supply is the AC power in the mains through AC→DC→AC transformation, output to pure sine wave, output frequency and voltage range can be adjusted. It is different from the variable frequency speed controller used for motor speed regulation, and is different from ordinary AC regulated power supply. The ideal AC power supply is characterized by stable frequency, stable voltage, zero internal resistance and pure sine wave (no distortion). Frequency conversion power is very close to the ideal AC power supply, therefore, more and more advanced developed countries will use the frequency conversion power supply as a standard power supply, in order to provide the most excellent power supply environment for the use of electrical appliances, to facilitate objective assessment of the technical performance of electrical appliances. Inverter power supply mainly has two kinds: linear large and SPWM switch type.