Pulse Modulated Inverter

In this section, the definition of Pulse Modulated Inverter is provided at the beginning. Soon after, it is categorized based on the way it operates and description of each type of inverter is provided along with the output waveform of each type of inverter.

Summary

Things to Remember

1) Pulse Modulated Inverter is the inverter which works on the basis of the characteristics and nature of pulse signal provided to the gate terminal of the switching device.

2) A large number of way exists to vary the inverter gain and frequency. Few of them are listed below and follows as:

Single Pulse Width Modulation
Multiple Pulse Width Modulation
Sinusoidal Pulse Width Modulation

MCQs

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Subjective Questions

Q1:

Write short notes on Anti-helminthic drugs.

Type: Short Difficulty: Easy

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Answer: <h3>Anti-Helminthic Drugs</h3>
Anthelmintic drugs are used to treat different types of worms as roundworm (Ascaris lumbricoides), Hookworm (Ancylostoma duodenale), Whipworm (Trichuris trichura), Tapeworm, Nematode (Roundworm), etc. some of the drugs are as follows :
<ol>
<li>
<h4>Albendazole</h4>
</li>
</ol>
It is a board spectrum, benzimidazoles anthelmintic. It is poorly absorbed from the GIT but rapidly undergoes extensive first pass metabolism.
Mechanism of action
<ul>
<li>It inhibits up taking of glucose and depletion of glycogen stores. Intracellular microtubules in the cells of the worn are gradually lost as a result of which parasites are killed or paralysed slowly and affected parasites are expelled with stools.</li>
</ul>
Indication
<ul>
<li>Single or mixed infestations of all kinds of worms as roundworm, pinworm (Enterobius) or whipworm.</li>
</ul>
Preparation
<ul>
<li>It is usually available in the form of table and suspension such as :</li>
<li>Albendazole Chewable tablet 400mg</li>
<li>Albendazole suspension 200mg/5ml (10ml bottle)</li>
</ul>
Dose
<ul>
<li>A single dose of 400mg for patients over the age of 2 years. For children from 1-2 years, a dose is 200mg.</li>
</ul>
Adverse effect
<ul>
<li>CNS – neurological problem</li>
<li>Blood – leucopenia, agranulocytosis</li>
<li>GIT – diarrhea, abdominal pain, nausea, vomiting</li>
<li>Skin – allergy (exanthema, rash, angioedema), alopecia</li>
</ul>
Drug interaction
<ul>
<li>Dexamethasone increases the plasma level of active metabolite of Albendazole.</li>
<li>Praziquantel increases the plasma concentration of Albendazole.</li>
<li>Contraindication</li>
<li>Child under 1year, the first trimester of pregnancy.</li>
</ul>
 
<ol start="2">
<li>
<h4>Mebendazole</h4>
</li>
</ol>
It is the broad spectrum vermicidal and ovicidal (parasites, egg, and hydrated cysts) drugs. It is poorly absorbed and does not cause systematic toxicity even in patients with malnutrition.
 
Mechanism of action
<ul>
<li>It inhibits up taking of glucose and depletion of glycogen stores. Intracellular microtubules in the cells of the worn are gradually lost as a result of which parasites are killed or paralysed slowly and affected parasites are expelled with stools.</li>
</ul>
Indication
<ul>
<li>Single or mixed infestations of all kinds of worms as roundworm, pinworm (Enterobius) or whipworm.</li>
</ul>
Preparation
<ul>
<li>It is usually available in the form of table and suspension such as :</li>
<li>Mebendazole tablet 100mg</li>
<li>Mebendazole suspension 100mg/5ml.</li>
</ul>
Dose
<ul>
<li>Pinworm : 100mg single dose (it may be repeated after a week)</li>
<li>Roundworm, hookworm: 100mg bid in three consecutive days.</li>
</ul>
Adverse effect
<ul>
<li>CNS – neurological problem</li>
<li>Blood – leucopenia, agranulocytosis</li>
<li>GIT – diarrhea, abdominal pain, nausea, vomiting</li>
<li>Skin – allergy (exanthema, rash, angioedema), alopecia</li>
</ul>
Drug interaction
<ul>
<li>Absorption increased by fatty food.</li>
<li>Phenytoin and carbamazepine have been reported to lower plasma Mebendazole concentrations.</li>
</ul>
Contraindication
<ul>
<li>The first trimester of pregnancy, children under two years.</li>
</ul>
 
<ol start="3">
<li>
<h4>Pyrantel pamoate</h4>
</li>
</ol>
It is a derivative of tetrahydropyridine. It is mainly used in hookworm and schistosomiasis. It is poorly absorbed from the gut. It has neuromuscular blocking property and they cause aseptic paralysis of the helminthic.
 
 
Mechanism of action
<ul>
<li>It depolarizes the neuromuscular junctions of parasites as a result of which they are paralyzed and expelled in faeces by intestinal peristalsis. A single dose is sufficient for its effect.</li>
</ul>
Indication
<ul>
<li>Hookworm infestation, schistosomiasis</li>
</ul>
Preparation
<ul>
<li>It is usually available in the form of tablets such as:</li>
<li>Pyrantel pamoate 750mg (3tables of 250mg)</li>
</ul>
Dose
<ul>
<li>Single dose of 10mg/kg/day for 3days (max. 750mg for adult).</li>
</ul>
Adverse effect
<ul>
<li>CNS – a headache, drowsiness, insomnia, dizziness</li>
<li>GIT – nausea, vomiting, anorexia, diarrhea, tenesmus, abdominal pain.</li>
<li>Skin – rash.</li>
</ul>
Drug interaction
<ul>
<li>It should not be given with Piperazine citrate to prevent from antagonistic effect.</li>
</ul>
 
<ol start="4">
<li>
<h4>Piperazine</h4>
</li>
</ol>
It was introduced in 1950. It is useful for ascariasis (roundworm) and enterobiasis( threadworm). This medicine is safe for pregnancy.
 
Mechanism of action
<ul>
<li>Reduce the formation of succinate in the worm leading to flaccid paralysis of the worm. Patient easily expels the paralyzed worm.</li>
</ul>
Indication
<ul>
<li>Roundworm and threadworm</li>
</ul>
Preparation
<ul>
<li>It is usually available in the form of elixir and tablets such as:</li>
<li>Piperazine hydrate 750mg/5ml</li>
<li>Piprazineadipate 300mg equivalent to 250mg of piperazine hydrate.</li>
</ul>
Dose
<ul>
<li>Ascariasis: a single daily dose of 75mg/kg (maximum 3.5mg) orally for 2 days.</li>
<li>Enterobiasis: a single daily dose of 75mg/kg (maximum 3.5mg) orally for 7 days.</li>
</ul>
Adverse effect
<ul>
<li>Rare effects: nausea, vomiting, diarrhea, dizziness, rash, loss of co-ordination, Stevens-Johnson syndrome, angioedema</li>
<li>CNS – dizziness, loss of coordination</li>
<li>GIT – nausea, vomiting, diarrhea</li>
</ul>
 
Drug interaction
<ul>
<li>It increases the risk of abdominal movement with phenothiazine, and antipsychotic drugs,</li>
</ul>
Pyrantel pamoate and piperazine has an antagonist mode of action.
<ul>
<li>Contraindication</li>
<li>Epilepsy, hepatic, renal failure, a patient with abnormal movement.</li>
</ul>
 
 
<ol start="5">
<li>Niclosamide</li>
</ol>
Niclosamide is a derivative of Salicylamide. It was introduced in 1960.it is not significantly absorbed from GIT. It is safe during pregnancy and with poor health.
 
<ul>
<li>Mechanism of action</li>
<li>Inhibit anaerobic phosphorylation by ADP by mitochondria of parasite and causing energy depletion.</li>
<li>Indication</li>
<li>Tapeworm, hymenolepiasis nana, diphyllobothrium latum</li>
<li>Preparation</li>
<li>Niclosamide chewable tablet of 500mg and 600mg is usually available.</li>
<li>Dose</li>
<li>Adult and child over 6years: a single 2gm dose orally after a light meal.</li>
</ul>
Child 2-6years:1gm
Child under 2years-not recommended.
<ul>
<li>Adverse effect</li>
<li>CNS – drowsiness, light headache</li>
</ul>
GIT – nausea, abdominal discomfort, anorexia, drowsiness
Skin – urticaria, pruritis.
<ul>
<li>Drug interaction</li>
<li>Alcohol may increase the adverse effect of the drugs.</li>
<li>Contraindication</li>
<li>Occasional GI disturbance, skin rashes, itching, drowsiness.</li>
</ul>
Nursing management
<ul>
<li>Health education regarding proper sanitary habits should be given to all the patients.</li>
<li>Do not skip the drugs of Antihelmintic drugs.</li>
<li>Most of the drugs of this group are available in the form of a chewable tablet. The patient should be advised to chew the tablet before swallowing with water.</li>
<li>Mebendazole should not be given to the patient below 2years. Albendazole should not be given to the patient below under one year.</li>
<li>Niclosamide is safe during pregnancy.</li>
<li>Niclosamide must be taken in the early morning or on an empty stomach.</li>
<li>A purgative is necessary after niclosamide therapy.</li>
</ul>

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Anti- Helminthic

Pulse Modulated Inverter

Pulse Modulated Inverter is the inverter which works on the basis of the characteristics and nature of pulse signal provided to the gate terminal of the switching device. In many industrial applications, it is often required to control the output voltage and frequency of inverter:

To cope with variation of DC Input Voltage.
For voltage regulation of Inverter
For constant volt/hertz control

A large number of way exists to vary the inverter gain and frequency. Few of them are listed below and follows as:

Single Pulse Width Modulation
Multiple Pulse Width Modulation
Sinusoidal Pulse Width Modulation

Single Pulse Width Modulation

As there is only one pulse per half cycle, the name Single Pulse Width Modulation is provided and for the variation of the output rms voltage, the width of the pulse which is fed to the gate terminal of the switching device is changed.

The gate signal is generated by comparing the modulating signal and Carrier signal. The control strategy is :

If modulating signal(A_r) > Carrier Signal(A_c), then V_o = +V_dc/2 If modulating signal(A_r) < Carrier Signal(A_c), then V_o = -V_dc/2

The diagram for gate signal generation based on the above logic and the output voltage waveform is provided below;

Important Definitions Associated With It

Modulation Index is defined as the ratio of Peak value of the modulating Signal to the ratio of Peak value of the carrier signal. And the frequency ratio is defined as the ratio of the frequency of carrier signal to the frequency of the modulating signal.

The frequency of inverter output voltage can be changed by varying the frequency of the modulating signal.

The rms value of the inverter output is given by:

$o(rms) = {\mkern 1mu} \sqrt {{1 \over \pi }\int\limits_{\theta 1}^{\theta 2} {{{V_{dc}^2} \over 4}} d\theta } \; = {{Vdc} \over 2}\sqrt {{\delta \over \pi }} \;where\;\delta = \;\theta 2 - \theta 1$

The fourier series of the output waveform is given by;

$Vo(t) = {{4\;Vdc} \over {\pi 2}}\sum\limits_{m\; = \;1,...\infty ,2} {{1 \over m}\;{{\sin (m\delta )} \over 2}\sin (m\omega t)} \;\;\;\;$

Multiple Pulse Width Modulation

The harmonic content can be reduced by using several pulses in each half cycle of the output voltage. The generation of gating signals for turning on and off of transistors are obtained by comparing a reference modulation signal with a high-frequency triangular carrier wave as shown in the figure below.

P = FR(Freqeuncy Ratio)/2 = Number of pulses per half cycle

The rms value of the inverter output voltage is given by:

$Vo(rms) = {\mkern 1mu} \sqrt {{p \over \pi }\int\limits_{{\pi \over p} - {\delta \over 2}}^{{\pi \over p} + {\delta \over 2}} {{{V_{dc}^2} \over 4}} d\theta } \; = {{Vdc} \over 2}\sqrt {{{p\delta } \over \pi }} \;where\;\delta = \;\theta 2 - \theta 1$

The general form of foruier series of output voltage is given by:

$Vo(t) = m\sum\limits_{m\; = \;1,...\infty ,2} {Bm\sin (m\omega t)}$

The coefficient of B_m can be determined by considering a pair of pulses such that the positive pulse of duration δ starts at wt = α_m and the negative one of the same width starts at wt = π + α_m.

The coefficient of B_m for only two pulses is given by

$\eqalign{ & \;\;\;\;\;Bm\; = \;{1 \over \pi }\;\int\limits_{\alpha m}^{\alpha m + \delta } {{{Vdc} \over 2}Sin(mwt)\;dwt\;} - \;{1 \over \pi }\;\int\limits_{\pi \; + \;\alpha m}^{\pi + \alpha m + \delta } {{{Vdc} \over 2}Sin(mwt)\;dwt\;} \; \cr & \;or,Bm = {2 \over {m\pi }}{{Vdc\;\sin (m\delta /2)} \over 2}[\sin (m(\alpha m + \delta /2) - \sin (m(\pi + \alpha m + \delta / \cr}$

Thus for the whole cycle,

$Bm = \sum\limits_{m = 1}^p {{2 \over {m\pi }}{{Vdc\;\sin (m\delta /2)} \over 2}[\sin (m(\alpha m + \delta /2) - \sin (m(\pi + \alpha m + \delta /2)}$

3) Sinusoidal PWM Inverter

Sinusoidal PWM Inverter is very much similar to the multiple pulse width modulation. In this method, sinusoidal signal is used as reference modulating signal instead of rectangular wave that is used in single pulse width modulation and multiple pulse width modulation.

The switching instant of a pair of switching device for a phase are determined by the following logic:

If Modulating signal > Carrier Signal, then V_R = V_S/2

If Modulating signal < Carrier Signal, then V_R = -V_s/2

Thus, these lines can be verified from the waveform provided above.

Lesson

Inverter

Subject

Electrical Engineering

Grade

Engineering

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