Abstract: Harmonic pollution and low power factor in power
systems caused by power converters have been of great concern. To
overcome these problems several converter topologies using
advanced semiconductor devices and control schemes have been
proposed. This investigation is to identify a low cost, small size,
efficient and reliable ac to dc converter to meet the input performance
index of UPS. The performance of single phase and three phase ac to
dc converter along with various control techniques are studied and
compared. The half bridge converter topology with linear current
control is identified as most suitable. It is simple, energy efficient
because of single switch power loss and transformer-less operation of
UPS. The results are validated practically using a prototype built
using IGBT and analog controller. The performance for both single
and three-phase system is verified. Digital implementation of closed
loop control achieves higher reliability. Its cost largely depends on
chosen bit precision. The minimal bit precision for optimum
converter performance is identified as 16-bit with fixed-point
operation. From the investigation and practical implementation it is
concluded that half bridge ac – dc converter along with digital linear
controller meets the performance index of UPS for single and three
phase systems.