It is an equipment used to control the speed and torque of an induct motor. The DC voltage can become a variable voltage and variable frequency of alternating current by the inverter after using the converter to rectify 1-phase or 3-phase AC power to direct current. For general-purpose AC motor drives, the voltage will be changed with frequency changes. Therefore, the AC motor drive is called VVVF(Variable Voltage Variable Frequency) for short.