为了产生可变的电压和频率，该设备首先要把三相或单相交流电变换为直流电(DC)。然后再把直流电(DC)变换为三相或单相交流电(AC)，我们把实现这种转换的装置称为“变频器”inverted-In order to produce a variable voltage and frequency, the device must first three-phase or single-phase AC power is converted to DC (DC). Current (DC) and t