Power Electronics Lab Experiments

To Study Three Phase Fully Controlled Bridge Converter

Nov 27 2023

Aim

To Study Three Phase Fully Controlled Bridge Converter.

Apparatus Required:

S.No.	Apparatus/Software Used	Specification	Range/Rating	Quantity
1
2
3
4
5

Theory & Formulae Used:

The figure ‘1’ shows the power circuit of three phase fully controlled converter. The load is fed via a three phase half wave connection to one of the three supply lines, no neutral being required. Hence transformer connection is optional. However, for isolation of output from supply source, or for higher output requirement, the transformer is to be connected. If transformer is used, then one winding is connected in delta because the delta connection gives the circulating path for third harmonic current. This circuit consists of two groups of SCRs, positive group and negative group. Here, Scr T₁, T₂, T₃ forms a positive group. Whereas SCR T₄, T₅, T₆ forms a negative group. The positive group SCRs are turned on when the supply voltages are poisitive and negative group SCRs are turned on when the supply voltage are negative

Continuous Conduction Mode:The firing angle of each phasor is varied through a range of 60 degree to 180degree. The minimum firing angle is 60degree and is taken as α=0, at 60degree. When the phasor R-Y is allowed to conduct at α between zero to, π/3 it continues to conduct by 60degree when the phasor R-B is fired. The condition is shifted from SCR T5 to SCR T6. T5 is commutated off by reverse voltage of phase Y and Y across it. The Phasor R-B conducts after another 600 after which it is replaced by phasor (Y-B) when phase Y voltage assumes greater value than B or R. Hence load current is continuous for between 0 to ;π/3 The waveforms are shown in figure.