Question

For a three-phase full controlled converter with R load, the average value of output voltage is zero for

(a) α = 0°

(b) α = 90°

(c) α = 180°

(d) It can never be zero

This question was posed to me in semester exam.

The doubt is from Three Phase Converters-2 in division Converters of Power Electronics

Answer 1

Right option is (b) α = 90°

Best explanation: For α = 90 degrees, the voltage waveform is equally symmetrical about the ωt axis, hence the average value is zero. This can also be found by using the formula for average output voltage,

Vo = (3Vml/π) cos α,

For α = 90°, cosα = 0, Vo = zero.