In comparing the operation of the half-controlled 2-pulse circuit with that of the fully-controlled circuit, which of the following statements are evident?

1. Since half the thyristors are replaced by diodes, a half-controlled converter costs less than a fully-controlled converter.

2. Due to the freewheeling action with a half-controlled bridge-circuit power factor is improved in half-controlled converters.

3. The AC supply current is more distorted due to its zero periods with the half-controlled circuit, compared to a fully-controlled bridge circuit.

Select the correct answer using the code given below :

The correct answer is option 4.

Explanation

A half-controlled 2-pulse converter is also known as 1ϕ semi converter.

When 2 SCR of a 1ϕ full wave converter are replaced by the diodes, then the obtained is known as 1ϕ semi converter.

∴ A half-controlled converter costs less than a fully-controlled converter.

Hence, statement 1 is correct.

In 1ϕ full wave converter, SCR conducts for 180° from α to 180° + α whereas in 1ϕ semi converter. due to the freewheeling action, SCR conducts for 180° - α from α to 180°.

Since the power factor is given by cosα. As α is less in a semi-converter, it has a better power factor.

Hence, statement 2 is correct.

The waveform of the source current in a semi-converter is a quasi wave whereas, in the full converter, the source current is a symmetrical square wave. Hence, the waveform in the semi-converter is more distorted as compared to the full converter.

Hence, statement 3 is correct.