Three-phase Semi-converter with inductive load (With source side inductance)

Three-phase Semi-converter with inductive load (With source side inductance)

The conversion of ac to dc with suitable examples and sketches are discuss here advanced. conversion of ac to dc is needed to read as engineer student.

Semi-controlled Converters

Semi-controlled converter is a hybrid between uncontrolled and fullycontrolled converters.  It is also known as β€œsemi-converter”.

Semi-converter offers variable positive DC output voltage only. Regeneration or inverter mode operation is not available

Three-phase Semi-converter with inductive load (With source side inductance)

Each thyristor-to-thyristor commutation involves with a conduction overlap angle 𝑒𝑇, and each diode-to-diode commutation involves with a conduction overlap angle 𝑒𝐷.  Here too, during overlap, the three recently active devices conduct simultaneously and outside overlaps the two recently active devices conduct simultaneously.

Waveforms of output voltage, input current, thyristor-1 voltage and voltage at PCC

Let consider the thyristor-overlap after triggering 𝑇1, during which  𝑇1,𝐷6,𝑇5 conduct simultaneously.  Following the same steps followed in the case of full-bridge before, we can show that,

Similarly, let consider the diode-overlap after  𝐷2  becoming forward biased, during which 𝐷2,𝑇1,𝐷6 conduct simultaneously. Again, following the same steps as in thyristor-overlap, we can show,

Net reduction in  𝑉 π‘œ π‘šπ‘’π‘Žπ‘› due to conduction overlaps is,

As in the case without source-inductance, operating waveforms will be different depending on whether 𝛼 is below or above 60Β°.   For 𝛼 > 60Β°, ο‚· 𝑉 π‘œ has only 3 ripples per AC cycle. ο‚· During every overlap  𝑉 π‘œ = 0 ο‚· Line voltage at the PCC contains 2 notches only, both are down to zero. However, expressions for  𝑉 π‘œ π‘šπ‘’π‘Žπ‘› , βˆ†π‘‰ π‘œ, 𝐷𝑖𝑠𝐹, 𝑒𝑇, 𝑒𝐷 all remain unchanged.

Waveforms of output voltage, input current, thyristor-1 voltage and voltage at PCC for Ξ± >  60Β°

Ex:

 Derive expressions for βˆ†π‘‰ π‘œ,𝑒𝑇 and 𝑒𝐷 for a three-phase semi-converter operating at a delay angle above 60Β°.  Hence verify that they are same as for delay angles below 60Β°.

Ans

Let consider the overlap after triggering 𝑇1.  With respect to operating waveforms given before, 𝑇1,𝐷2,𝑇5 all conduct simultaneously during this interval.

conversion of ac to dc
conversion of ac to dc

Net reduction of   𝑉 π‘œ π‘šπ‘’π‘Žπ‘› occurs due to thyristor-overlaps only, because diode overlaps are occurring while  𝑉 π‘œ is already zero.

conversion of ac to dc

Considering diode overlap after  𝐷4 becoming forward biased, during which  𝐷4, 𝑇1, 𝐷2 all conduct simultaneously,

conversion of ac to dc

Integrating,

conversion of ac to dc

Thus, the expressions of βˆ†π‘‰ π‘œ,𝑒𝑇 and 𝑒𝐷 for 𝛼 > 60Β° are same as those for 𝛼 < 60Β°.

The conversion of ac to dc with suitable examples and sketches are discuss here advanced. conversion of ac to dc is needed to read as engineer student.

Reference conversion of ac to dc

  1. Page conversion of ac to dc
  2. Page conversion of ac to dc

Leave a Comment

Your email address will not be published. Required fields are marked *