Question

Find the expression for average output voltage at R for the below given configuration. Take firing angle as α = 15°, transformer ratio as 1:1:1 and Vmp as the maximum value of phase voltage at the supply.

(a) (3Vmp/2π) x cosα

(b) (3√3Vmp/2π) x cosα

(c) (3√3Vmp/2π) x sinα

(d) (3Vmp/2π) x sinα

The question was asked during an online exam.

Asked question is from Three Phase Converters-1 in section Converters of Power Electronics

Answer 1

The correct answer is (b) (3√3Vmp/2π) x cosα

To explain I would say: The circuit is that of a three-pulse M-3 connection. The firing angle is less than 30°. Therefore, each device conducts for an angle of 120°.

Vo = 3 x [ 1/2π ∫ Vmp sin⁡ωt d(ωt) ]

Where, the integration runs from α+π/6 to α+5π/6.

Vo = (3√3/2π) x Vmp x cosα.