Question

A three phase fully controlled bridge converter is feeding a load drawing a constant and ripple free load current of 10 A at a firing angle of 30° The approximate total harmonic Distortion (%THD) and the rms value of fundamental component of input current will respectively be_
1. 31% and 6.8 A
2. 31% and 7.8 A
3. 66% and 6.8 A
4. 66% and 7.8 A

Answer 1

Correct Answer - Option 2 : 31% and 7.8 A

RMS current \({I_a} = \sqrt {\frac{2}{3}} \times 10 = 8.16\ A\)

Fundamental current \({I_{{a_1}}} = \frac{{\sqrt 6 }}{\pi }{I_o} = 0.78 \times 10 = 7.8\;A\)

\(\begin{array}{l} THD = \sqrt {\frac{1}{{D{F^2}}} - 1} \\ DF = \frac{{{I_{{a_1}}}}}{{{I_a}}} = \frac{{0.78 \times 10}}{{0.816 \times 10}} = 0.955\\ THD = \sqrt {{{\left( {\frac{1}{{0.955}}} \right)}^2} - 1} = 31\% \end{array}\)