Three-phase Semi-converter with inductive load

Semi-converter with inductive load

The ac to dc converter schematic with suitable examples and sketches are discuss here advanced. ac to dc converter schematic is needed to read.

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

Single-phase Semi-converter with inductive load

In a semi-converter, thyristor conduction is delayed by angle Ξ± but diode conduction begins at their default points (i.e. zero delay-angle).  For continuous load current (which we assumed), at any time, a thyristor from the upper-half and a diode from the lower-half must conduct the load current πΌπ‘œ, i.e. last two active devices conduct at any point of time.

By varying 𝛼 over 0Β° to 180Β°, we can adjust  𝑉 π‘œ π‘šπ‘’π‘Žπ‘› between  8𝑉𝑝𝑕 πœ‹  and 0.  

In  𝐼𝑠waveform, front-end of current pulse (in each half-cycle) is moved to the right by 𝛼 but rear-end is fixed.  For a given delay angle 𝛼, the width of current pulse is  πœ‹ βˆ’π›Ό .

Note: We assumed continuous load current for all delay angles.  In reality, at higher delay-angles, load current becomes discontinuous.  Then the input current will be different.

There are some other implementations of the single-phase semi-converter, all offering the same input-output performances.

Standard Implementation

Alternative Implementation – 1

Alternative Implementation – 2

Alternative Implementation – 3

Which implementation we want to select is partly our own preference and partly technical /operational requirements.

Thyristors (also diodes) are available as individual devices or multiple devices.  Twin devices are available in common-cathode, common-anode or bridgedleg options.  Selection of the converter configuration may depend on the type of available devices. 

Technically, common-cathode configuration of standard implementation eases the assembly of two gate drive circuits sharing the cathodes.   Threeleg implementation  gives the choice between  semi-converter and fullconverter during operation by making diode D5 in or out.

Self Attempt:ac to dc converter schematic

Draw the output voltage and input current waveforms for the other three configurations of 1-phase semi-converter, and indicate the devices conducting in different intervals of the cycle.

Single-phase Semi-converter with inductive load (With Source Inductance):

Inductance Ls does not allow current Is to make step changes at T-to-T and D-to-D commutation points.  Current changes taking a brief time.  During these brief intervals both the incoming and the outgoing devices conduct simultaneously. This is a conduction overlap.  Conduction overlap angle for thyristor commutation and diode commutation are different, because they occur at different points of Vs.

ac to dc converter schematic

𝑒𝑇 = Thyristor conduction overlap angle 𝑒𝐷 = Diode conduction overlap angle Diode conduction overlap does not influence output voltage, because it occurs during 𝑉 π‘œ is zero.  However it affects the voltage waveform at the PCC. 

Let consider the conduction overlap after triggering 𝑇1. During this interval  𝑇1,𝐷2,𝑇3 all conduct simultaneously, short-circuiting the load, as well as the source. 

ac to dc converter schematic

Reduction of volt-radian area (A) from 𝑉 π‘œ due to the conduction overlap,

ac to dc converter schematic

Reduction in  𝑉 π‘œ π‘šπ‘’π‘Žπ‘› due to conduction overlap,

ac to dc converter schematic

Similarly, let consider conduction overlap at  𝐷4 taking up conduction.  During this interval 𝐷4,𝐷2,𝑇1 conduct, short circuits the load, as well as the source.  Load voltage during this interval is zero, anyway. 

ac to dc converter schematic

The ac to dc converter schematic with suitable examples and sketches are discuss here advanced. ac to dc converter schematic is needed to read.

Reference ac to dc converter schematic

  1. Page ac to dc converter schematic
  2. Page ac to dc converter schematic

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