AC-DC Conversion

In most power electronic applications, the power input is in the form of a 50 Hz or 60 Hz sine-wave AC voltage provided by the electric utility, which is then converted to a DC voltage. Increasingly, the trend is to convert the input AC into DC in an uncontrolled manner, using rectifiers and diodes. As such, the power flow can only be from the utility AC side to the DC side. A majority of applications such as switching DC power supplies, motor drives, servo drives, and so on, use such uncontrolled rectifiers. In most of these applications, the rectifiers are supplied directly from the utility source without a 50/60 Hz transformer. The avoidance of this costly and bulky transformer is important in most modern applications. In non-power, factor-corrected applications, the DC output voltage of the rectifier circuit should be as ripple-free as possible. Therefore, a large capacitor is connected as a filter on the DC side. This capacitor gets charged to a value close to the peak of the AC input voltage. The DC link voltage is then converted for use throughout the system.