Diode Bridge Rectifier with low THD for Weak Grids

Diode bridge rectifiers are simple means of converting single phase AC to DC. Such converters are widely used in many applications primarily in low cost and low to medium power ranges. Large transportation systems such as ships are operated as microgrids with a variety of loads some of which need rectification. They often form weak grids due to low stiffness of source. The basic diode bridge rectifier deteriorates power quality by introducing unwanted harmonics into the system, which can be detrimental to such microgrids. Addition of an optimum value of capacitance in parallel to the diodes in one leg of the Diode Bridge can reduce THD to upto two-thirds of its nominal value. In this paper a refinement of this approach is proposed using a Diode RC Bridge (DRCB) rectifier which further reduces the THD to less than half of its nominal value. A simple addition of 2 split RC networks to the normal diode rectifier enables this improvement while causing a minimal drop in efficiency. For the specifications chosen in this paper a 59% reduction in THD is reported while ensuring that the reduction in efficiency is no more than 5.3 %. Detailed analysis of the DRCB rectifier is backed by simulations and experimental studies.