Principle of Operation of Single Phase Cyclo-converter And Step-up And Step-Down Single Phase Controller

Description of Single phase CycloConverter is discussed in this section which might be either required to increase or decrease output frequency in compared to the input frequency of system of ac signals.

Summary

Things to Remember

1) A cyclo-converter is a direct frequency changer that converts ac power at one frequency at one frequency to ac power at another frequency to ac to ac conversion without any intermediate dc link.

2) They are classified into Step Up CycloConverter and Step Down CycloConverter.

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Q1:

Write about Replication and Classification of Medically Important Virus.

Type: Short Difficulty: Easy

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Answer: <h4>Replication of virus</h4>
The virus is a cellular so they do not grow through cell division and they used the other organelles and metabolism of a host cell for the multiplication of themselves.
 
Life cycle of the virus differs between species but there are 6 stages in their life cycle:
<ol>
<li>Attachment</li>
<li>Penetration</li>
<li>Uncoating</li>
<li>Replication</li>
<li>Self-assembly</li>
<li>Release</li>
</ol>
 
Attachment- Specific binding between virus capsids proteins and specific receptors on the host's cellular surface. This specificity describes the host ranges of virus e.g HIV infects a limited range of human leucocytes. Attachment to the receptors can induce the virus to envelop protein to undergo changes which result in the fusion of viral and cellular membranes or changes of non-enveloped virus surface protein that allow the virus to enter.
 
Penetration- It occurs after the attachment. Virion( virus particles) enters the cells through receptors mediated endocytosis or also by the fusion of membrane. Also called viral entry.
 
Uncoating- Process by which the viral capsid is removed. It may be by degradation by viral enzymes or host enzymes or by simple dissociation and the end results are the releasing of viral genomic nucleic acid(DNA/RNA)
 
Replication- It involves the synthesis of virus in RNA for early genes, viral protein synthesis,possible assembly of viral proteins, then viral genome replication mediated by regulatory protein expressions. Replication of virus involves primarily multiplication of genomes. Replication is followed for complex viruses with larger genomes by one or more rounds of RNA synthesis.
 
Self- Assembly- Viral parts undergoes self-assembly by following the structures-mediated self-assembly of the viral particles , some modification of proteins often occurs.
 
Release- As the viral parts are assembled to form the virion particles , virus is released from the hosts cells by lysis( a process in which the cells are killed by bursting it membrane and cell wall if present)
<h4>Classification</h4>
By the medical importance, virus can be classified into two groups and they are:
 
<ol>
<li>DNA virus</li>
<li>RNA virus</li>
</ol>
 
DNA virus- DNA virus is the virus which contains the DNA as a genetic material. It is again further divided :
 
<ul>
<li>Double stranded DNA virus- It means the virus which contains the double-stranded DNA protein and lipids i.e smallpox virus, herpes simplex, Epstein-Barr virus.</li>
<li>Single-stranded DNA virus-It means the virus which contains single-stranded i.e parvovirus</li>
</ul>
RNA virus-It is also divided :
<ul>
<li>Virus with single-stranded RNA virus(+)- This RNA function directly as mRNA in host cells and mRNA is contained within an icosahedral capsid e.g poliovirus , rhinovirus</li>
<li>Virus-containing single-stranded RNA virus(-) –This RNA virus serves as a template for synthesis of a complementary strand which acts as the mRNA. It contains helical nucleic cased with a cone of single stranded RNAof (-) type.e.g parainfluenza virus, measles virus, mumps virus etc</li>
<li>Virus-containing double stranded RNA-It consists of icosahedral viruses having a double capsid, no envelope and consists of double-stranded RNA e.g rotavirus , orbivirus</li>
</ul>
Hepatitis virus is also another types of virus which have complex in structure and complex in nuclear material
 
<h4> </h4>

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Virus structure and classification

Principle of Operation of Single Phase Cyclo-converter And Step-up And Step-Down Single Phase Controller

Principle of Operation of Single Phase Cyclo-converter

A cyclo-converter is a direct frequency changer that converts ac power at one frequency at one frequency to ac power at another frequency to ac to ac conversion without any intermediate dc link.

They are classified into:

Single Phase to Single Phase
Three Phase to Single Phase
Three Phase to the Phase

They are again classified as:

Step Up Cyclo-Converter
Step Down Cyclo-Converter

Step Up Cyclo-Converter

P1,P2 -> Positive Group Thyristor

N1,N2 -> Negative Group Thyristor

In Single Phase Step Up Cyclo Converter, during a positive half cycle of supply voltage terminal A is positive with respect to terminal B so that SCRs P₁ and N₂ are forward biased from wt = 0 to wt = π. SCR P₁ is turned on at wt = 0, so that load voltage is positive. At certain instant wt₁, P₁ is forced commutated and N₂ is turned on by providing a gate signal to it and it remains in a conduction state and load voltage is negative.

Similarly, at wt₂, N₂ is forced commutated and P₁ is turned on and load voltage is positive. So, we can repeat this process by turning on and turning off the Positive Group Thyristor in the appropriate time interval. When wt = π, terminal B is positive with respect to terminal A; both SCR P₂ and N₁ are therefore forward biased from wt = π to 2π. In the same way, P2 and N1 are turned on and off in a certain sequence.

Thus, by switching the positive group thyristor and Negative group thyristor in a certain appropriate sequence as mentioned above, the frequency of the output voltage is increased certain times than frequency of input voltage.

Step Down Cyclo-Converter

In this converter, two single phase controlled converters are operated as a bridge rectifier. And they are named as P-Converter and N-Converter where P and N mean positive and negative. Thus P-Converter gives positive output voltage while N-Converter gives negative output voltage. However, their delay angles are such that the output voltage of P-Converter is equal to the output voltage of N-Converter.

From the figure below we observe that the gate signals are provided to the thyristor of the P-Converter from time instant zero to 3π and to the remaining thyristor of N-converter from 3π to 6 π. Thus the frequency of output voltage is fs/3 of the frequency of the source frequency. It is seen that the output voltage isn’t purely sinusoidal and has high harmonic contents in it.

Gating Sequence

During the first period of output frequency T_o/2, P-Converter operates at a delay angle α_p = α i.e by gating T₁ and T₂ at α and T₃ and T₄ at (π + α). During the negative half cycle, T_o/2, N-Converter operating at delay angle of α_n = α i.e by gating T₁^’ and T₂^’ at 3π + α and T₃^’ and T₄^’ at 4π + α.

References

1) locus. ac-to-ac-converter-working-and-supplies. n.d. 15 05 2016. <https://www.elprocus.com/wp-content/uploads/2014/06/1-converter.jpg>.

Lesson

AC Voltage Controller

Subject

Electrical Engineering

Grade

Engineering

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