Abstract:
A scheme for improving the input current waveshape of a single phase bridge
rectifier has been proposed and analyzed. A bridge rectifier with filter capacitor
connected to reduce ripples of output voltage draws discontinuous and nonsinusoidal
current from the supply. In this work a switching scheme has been
developed which exploits a single MOSFET switch driven by rectangular gate
pulses whose duty cycle is continuously varied over the period of supply voltage.
The switch provides an alternative path for the input current during the periods
when due to the reverse biasing of rectifier diodes input current ceases to flow
otherwise. The variation of duty cycle of the switching pulses has been intuitively
varied like a rectified cosine wave. The switching scheme combined with an input
LC (inductor-capacitor) filter that has a resonating frequency almost equal to that
of supply voltage, has been found very effective in improving the input current
waveshape. Analytical expression for the input current drawn by the rectifier with
proposed switching is derived and detail simulation results are presented which
shows that the rectifier with the proposed scheme draws sinusoidal current at unity
power factor and has high overall efficiency. The Total Harmonic Distortion
(THD) in input current is reduced below 2%. Different combinations of LC filter
elements and switching frequency have been considered to obtain optimum results
in terms ofTHD and overall circuit efficiency.
