Comparison between Three Phase Uncontrolled Rectifiers

• The single phase rectifiers are generally used for low power applications of electronic circuits. 
• They are used for supplying DC loads up to 5 kW. However the single phase rectifier circuit have following advantages.

( 1 ) Low output voltage and current

( 2 ) Low frequency harmonic ripple current

( 3 ) Low efficiency

( 4 ) Very large filter is requires to obtain smooth output DC voltage

The three phase rectifiers mitigated most of these disadvantages. 

• The three phase rectifier does not only supply high power but also produces less ripple in the output voltage and current as compared to single phase rectifiers. 
• The efficiency of the three phase rectifiers is very high as compared to single phase rectifiers.

Comparison between three phase half wave, three phase full wave and Six phase half wave uncontrolled rectifiers

Parameters	Three phase half waver rectifiers	Three phase full wave rectifiers	Six phase half wave rectifiers
Number of diodes	3	6	6
Conduction period of each diode	120o	120o	60o
Average current	Idc / 3	Idc / 3	Idc / 6
Average voltage	0.827Vm 1.17V	0.955Vm 2.34V	0.955Vm 1.35V
Peak inverse voltage ( PIV )	√3 Vm 2.09Vdc	√3 Vm 1.05Vdc	2 Vm 2.09Vdc
Ripple frequency	3f	3f	6f
Ripple factor	0.17	0.04	0.04
Efficiency	97%	99.87%	99.87%
Core saturation of transformer	Yes	No	No

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