Three Phase Converter I

Summary

This NPTEL lecture delves into advanced power electronics and control, focusing on three-phase converters. It contrasts single-phase converters with three-phase ones, highlighting their importance in high-power applications, particularly for DC motors. The lecture explains the operation of three-phase half-wave uncontrolled rectifiers, detailing the conduction process through diodes and the resulting output voltages. It also touches on the issues of transformer saturation and the need for controlled rectifiers, providing a foundation for understanding the principles behind power conversion in three-phase systems.

Takeaways

• 🔌 The lecture introduces three-phase converters, emphasizing their importance in high-power applications, particularly for DC motors.
• 📈 The three-phase half-wave uncontrolled rectifier is explained, detailing how diodes conduct based on the phase voltages and the RL load.
• 🌐 The script describes the conduction sequence of diodes in a three-phase system, showing how each diode blocks and allows voltage at different intervals.
• 📊 The waveforms for voltage and current are discussed, highlighting the third harmonic oscillations and the continuous conduction mode due to the RL load.
• ⚙️ The lecture mentions the issue of transformer saturation in three-phase half-wave uncontrolled rectifiers and the preference for full-control devices.
• 🔄 The three-phase full-wave uncontrolled rectifier with an RLE load is explored, explaining the conduction pattern of diodes and the resulting output voltage.
• 🔗 The concept of nomenclature for diodes in full-wave rectifiers is introduced, with a focus on the sequence of conduction and the voltages involved.
• 📚 The script encourages students to calculate RMS values and average values for voltage and current, providing a foundation for understanding power conversion.
• 🛠️ The lecture discusses the three-phase full-wave controlled rectifier, explaining the use of Thyristors and the impact of the delay angle on the output voltage.
• 🔋 The importance of load current continuity is highlighted, especially in the context of battery and load side inductance in RLE loads.
• 🏗️ The lecture concludes with a discussion on the three-phase half-controlled rectifier, emphasizing the difference between diodes and Thyristors and the control over the rectifier operation.

Q & A

What is the primary application of a three-phase converter as discussed in the lecture?

The primary application of a three-phase converter, as discussed in the lecture, is for high power applications, particularly for DC motors, where it is used to convert three-phase AC power directly to DC.

What type of rectifier is used in the three-phase converter discussed in the script?

The script discusses the use of both three-phase half-wave uncontrolled rectifiers and three-phase full-wave uncontrolled rectifiers in the three-phase converter.

How does the conduction of diodes occur in a three-phase half-wave uncontrolled rectifier?

In a three-phase half-wave uncontrolled rectifier, conduction occurs in a 180-degree mode for a 360-degree cycle. The most positive phase conducts at any given time, and the diodes block the voltage when another phase becomes more positive.

What is the role of the RL load in the operation of the three-phase converter?

The RL load in the three-phase converter ensures continuous conduction mode operation. It helps maintain a constant load current, which is essential for the converter's operation and prevents the input transformer from saturating.

Why is the three-phase half-wave uncontrolled rectifier configuration not preferred?

The three-phase half-wave uncontrolled rectifier configuration is not preferred because it can lead to saturation of the input transformer and has a low rate of power conversion. It also results in a discontinuous current, which can cause power quality issues.

How does the three-phase full-wave uncontrolled rectifier differ from the half-wave rectifier in terms of diode conduction?

In a three-phase full-wave uncontrolled rectifier, one diode from the upper leg and another from the lower leg conduct simultaneously, with each diode conducting for a period of 120 degrees, whereas in a half-wave rectifier, only one diode conducts at a time for the entire 180-degree cycle.

What is the significance of the delay angle alpha in a three-phase controlled rectifier?

The delay angle alpha in a three-phase controlled rectifier is significant because it determines the point at which the thyristors are triggered. This angle allows for control over the output voltage and current, providing a means to regulate the power flow.

How does the input power factor (IPF) in a three-phase converter system relate to the RMS values?

The input power factor (IPF) in a three-phase converter system is calculated using the formula IPF = (V_avg * I_avg) / (3 * V_RMS * I_RMS), where V_avg and I_avg are the average voltage and current, and V_RMS and I_RMS are the RMS values of the input voltage and current, respectively.

What is the effect of an RC load on the output voltage waveform in a three-phase full-wave uncontrolled rectifier?

In a three-phase full-wave uncontrolled rectifier with an RC load, the output voltage waveform will have a ripple that depends on the load current and the size of the capacitor. The capacitor filters out the ripple, providing a more constant DC voltage.

Why is the three-phase half-controlled rectifier preferred over the full-wave uncontrolled rectifier in certain applications?

The three-phase half-controlled rectifier is preferred over the full-wave uncontrolled rectifier in certain applications because it offers control over the output voltage through the triggering of thyristors. This control is beneficial in applications requiring adjustable speed drives and where power quality and efficiency are critical.

Outlines

00:00

🔌 Introduction to Three-Phase Converters

The lecture begins with an introduction to three-phase converters, following up on the discussion of single-phase converters. It emphasizes the prevalence of three-phase power supplies in high-power applications, particularly for DC motors. The three-phase half-wave uncontrolled rectifier is introduced, which is suitable for applications requiring direct conversion from three-phase AC to DC. The lecture explains the conduction process through diodes, assuming an RL load, and how the load voltage changes depending on the phase voltages. The conduction of diodes D1, D2, and D3 is detailed, showing how each diode blocks or allows voltage across the load, resulting in different voltages across the load at various points in the cycle. The explanation includes a discussion of the 180-degree mode of conduction and the three different voltages that can be obtained.

05:05

🔄 Conduction and Output Voltage Analysis

This section delves into the continuous conduction mode of the converter due to an RL load, explaining how the diode only conducts when the phase voltage is maximum. The waveform analysis shows the DC component of the phase current, which contributes to AC saturation on the transformer's AC side. The lecture then compares the three-phase half-wave uncontrolled rectifier with the single-phase version, discussing the phase voltages and output voltages. It provides a formula for calculating the RMS and average values of the output voltage, leaving the calculation to the students. The input power factor is also discussed, with a formula for calculating it based on the RMS input voltage and current. The section concludes with a mention of the preference for full-controlled devices over the half-wave uncontrolled rectifier due to its inefficiency and potential for transformer saturation.

10:08

🌀 Three-Phase Full-Wave Uncontrolled Rectifier

The lecture shifts focus to the three-phase full-wave uncontrolled rectifier with an RLE load, explaining the conduction pattern of diodes in the upper and lower legs. The nomenclature for the diode pairs is introduced, and the conduction sequence is detailed, showing how each pair conducts for 60 degrees, while a single diode conducts for 120 degrees. The waveform for the load voltage and input current is described, highlighting the stepped square wave pattern of the input current. Key parameters such as RMS voltage and current are discussed, with formulas provided for their calculation. The lecture also touches on the input power factor and the active power output.

15:12

🔌 Three-Phase Full-Wave Uncontrolled Rectifier with RC Load

This part of the lecture discusses the application of the three-phase full-wave uncontrolled rectifier with an RC load, which is common in adjustable speed drives. The role of the capacitor in filtering out ripples and providing a near-constant DC voltage is explained. The lecture describes the behavior of the circuit when the input voltage is higher or lower than the capacitor voltage, leading to choppy current profiles that can cause power quality issues. The focus is on the unique challenges posed by such loads and the importance of addressing these issues in modern industrial applications.

20:15

🛠 Three-Phase Half-Wave Controlled Rectifier

The lecture introduces the three-phase half-wave controlled rectifier, explaining the difference between diodes and thyristors and the need for triggering the thyristors based on voltage conditions. The conduction sequence of the thyristors is detailed, with each thyristor conducting for 120 degrees and the load voltage profile being influenced by the delay angle alpha. The lecture discusses the input current pattern and the potential issue of transformer saturation, which is avoided in this configuration. Calculations for RMS and average values of voltage and current are mentioned, with an invitation for students to perform these calculations using integration methods found in textbooks.

25:17

🔄 Three-Phase Full-Wave Controlled Rectifier and Half-Wave Controlled Converter

The final part of the lecture covers the three-phase full-wave controlled rectifier, where thyristors in the upper legs and diodes in the lower legs allow for control over the triggering of the thyristors. The conduction pattern and the resulting voltage across the load are described, with an emphasis on the control over the output voltage through the delay angle. The lecture also discusses the half-controlled rectifier or converter, where the upper legs are thyristors and the lower legs are diodes, providing a comparison of the conduction patterns and the resulting waveforms. The summary concludes with a mention of the mathematical analysis to be covered in the next class.

Keywords

💡Three-phase converter

A three-phase converter is a type of power electronic device used to convert three-phase AC power to DC power. In the context of the video, it is discussed as a more efficient alternative for high power applications, particularly for DC motors, compared to single-phase converters. The script mentions that most supplies are three-phase, making this type of converter suitable for such systems.

💡Half-wave uncontrolled rectifier

A half-wave uncontrolled rectifier is a type of rectifier that allows current to flow in only one direction during half of the AC cycle. The video script explains how this rectifier is fitted with diodes and assumes an RL load. It is used in three-phase systems to convert AC to DC directly, and the script describes the conduction process of diodes during different phases of the supply.

💡Conduction

Conduction in the context of the video refers to the process by which diodes allow current to flow through the circuit in a rectifier. The script describes how diodes like D1, D2, and D3 conduct during different intervals of the three-phase supply, blocking voltage when not conducting and allowing voltage to be applied across the load when conducting.

💡RL load

An RL load is a type of electrical load consisting of both resistance and inductance. The video script assumes an RL load for the three-phase half-wave uncontrolled rectifier, which influences how the diodes conduct and the shape of the output voltage waveform. The RL load is crucial for the continuous conduction mode operation of the converter.

💡DC motor applications

DC motor applications are mentioned in the script as a primary use case for three-phase converters. The conversion of three-phase AC to DC is directly beneficial for powering DC motors, which require a constant DC voltage or current to operate. The script emphasizes the importance of this application in high power scenarios.

💡Voltage blocking state

The voltage blocking state refers to the condition when a diode in a rectifier does not allow voltage to pass through it. In the script, it is explained that diodes block voltage when they are not conducting, which is essential for the correct functioning of the three-phase converter and the formation of the output voltage waveform.

💡Continuous conduction mode

Continuous conduction mode is a mode of operation for a rectifier where the load current does not become zero during the operation. The script mentions that the converter operates in this mode, assuming a high load current, which is typical for high power applications like DC motor drives.

💡Input power factor

Input power factor is a measure of how effectively electricity is being used in an AC electrical system. The script discusses calculating the input power factor for the three-phase converter, which is an important parameter in assessing the efficiency of the power conversion process.

💡Full-wave uncontrolled rectifier

A full-wave uncontrolled rectifier is a rectifier that converts the entire cycle of an AC waveform into DC. The video script contrasts this with the half-wave rectifier, explaining that in a full-wave rectifier, both halves of the AC cycle are utilized, which can be more efficient and provide a smoother output voltage.

💡Thyristor

A thyristor, also known as a silicon-controlled rectifier (SCR), is a four-layer, three-terminal semiconductor device that can conduct electricity when a voltage is applied to the gate. The script discusses how thyristors are used in controlled rectifiers, allowing for the regulation of the output voltage by controlling the firing angle.

Highlights

Introduction to three-phase converter concepts following the discussion of single-phase converters.

Explanation of the preference for three-phase systems in high power applications, particularly for DC motors.

Description of the three-phase half-wave uncontrolled rectifier and its components.

Conduction mechanism of diodes in a three-phase rectifier under RL load conditions.

Voltage conduction sequence across diodes D1, D2, and D3 during different phases of the three-phase supply.

Analysis of the three-phase voltage waveforms and the conduction angles for each phase.

Discussion on the third harmonic oscillations and their impact on the system.

Calculation of the RMS and average output voltage for the three-phase half-wave uncontrolled rectifier.

Introduction to the three-phase full-wave uncontrolled rectifier and its operational differences.

Explanation of the conduction sequence in a full-wave rectifier with RLE load.

Impact of the load current on the input power factor and its calculation.

Discussion on the limitations of half-wave uncontrolled rectifiers and the reasons for their reduced usage.

Introduction to the three-phase half-wave controlled rectifier and its operational principles.

Explanation of the triggering mechanism for thyristors in a controlled rectifier and the role of the delay angle.

Analysis of the load voltage and current waveforms in a controlled rectifier under different triggering angles.

Calculation of RMS and average values for voltage and current in a controlled rectifier.

Discussion on the three-phase full-wave controlled rectifier and its applications in highly inductive loads.

Explanation of the nomenclature and conduction sequence for thyristors in a full-wave controlled rectifier.

Impact of the delay angle on the output voltage and current waveforms in a controlled rectifier.

Conclusion and预告 of the next class focusing on mathematical analysis of three-phase half-controlled rectifiers.

Transcripts

Welcome to our NPTEL lectures on advance power electronics and control. Today we are going

to discuss three phase converter. We have discussed in details with a single phase converter

now we are discussing with the three phase converter. We have we started with the same

fashion as we have started the single phase converter.

Since actually most of our supply is three phase three wave or four wave system and it

makes sense for the high power applications for the dc motor mostly this kind of applications

we convert directly three phase to dc. So this is the application part of it so we use

this is basically three phase half wave uncontrolled rectifier fitted through the diodes and it

is fitting data I assume that RL load.

So what happened? you can see that how conduction takes place. So the D1 will actually when

it will conduct basically that would about to stop across it would be 0 and then you

will get a voltage of Van across this diode RL. If D2 is conducting, then at that time

basically it will block the voltage when D2 is conducting D1 will black the voltage of

Vba it would be negative voltage and similarly it will block the voltage of the Vca.

So similarly when diode 2 was conducting so the third diode will block Vac sometime Vbc

and once actually diode 3 is conducting then load will get the voltage Vcn. So load will

get the voltage depending on the 180 degree mode of conduction for 360 degree Van Vbn

and Vcn most positive phase will conduct so accordingly you will get the three different

voltages.

So let us see how it works this is the actually the three phase voltages and our starting

point will be actually this point where the voltage A actually a crossover the voltage

C and thus voltage A become the actually most positive. You can see till this region that

when actually pi/6 to 150 degree actually most positive phase is Van. So definitely

this will conduct for actually pi/6 to 150 degree so this will conduct. Similarly, after

that you know Vb actually at this point crossover takes place

so since there is only a single diode in upper limb so crossover takes place and it will

we have a crossover at this point where V phase becomes most positive place and thus

it well conduct in this point. Similarly, Vc will conduct after actually the period

to 70 degree and so on. So till this time D1 conduct till this time D2 conduct till

this time D3 conduct and thereafter till this time D3 conducts and this is the output voltage.

We will have a third harmonic oscillations we can find it out by analysis.

And this is actually the voltage blocking state or the different diode and this is VD1.

VD1 will conduct actually this point to this point so it will be blocking the voltage red

one. Similarly, VD2 will have this kind of fashion so and same way VD3 so it will conduct

when actually at this instant so you will get a negative. So phase a or red phase will

conduct for pi/6 to 150 degree for another 20 phase b and another 20 degree phase c.

So thus due to the RL load the converter operates in a continuous conduction mode if you assume

that load current is quite high. As diode blocks the negative voltage the diode only

conducts in that phase where the phase of voltage is maximum of these three. As shown

in the wave form the phase current has DC component which flows to that AC source and

makes DC saturation in the ac side of the transformer.

For this you know this kind of configuration we do not prefer so it may lead to the saturation

of the input transformer. So three phase halfwave uncontrolled rectified we can see that what

are the different values what we have seen in the say actually single phase.

So we have actually Van Vbn Vcn these are basically phase voltages and so output voltages

you can see that from pi/6 to 5 pi/6 that means actually 30 degree to 150 degree. It

will get a voltage of Van and so write the Van and you calculate over it similarly you

can calculate actually output RMS voltage that is basically you get three such cycle

so it does multiply by 3 same way for RMS value actually multiply by 3 pi/6 to 5 pi/6

root 2v sin omega t square dt.

So you can get this actually the values for this RMS value as well as the average value

you can calculate I had left it to the student to calculate. So similarly you can have the

load current so that is V average/R similarly i RMS = it should be same input RMS that will

be same for since it is a balanced system Ia Ib Ic should be same and we can find it

out that it tell value will be actually i0/root 3.

So input power factor that is active power output which we have shown also in a single

phase system by RMS input. So that is basically IPF actually voltage average*current average/3*Vi*RMS

so from there you can calculate physically the IPF.

Now, since we are discussed that this mode of the actually configuration is not preferred

because it leads to the saturation of the transformer and the rate of the conversion

of the power is very low generally use full control devices. The three phase full wave

uncontrolled actually rectifier with let us consider the R L E load. Now in this condition

one diode from the upper leg and another diode from the lower leg will conduct.

And will actually since or one diode will conduct for the period of 120 degree so we

have a different way to actually nomenclature it. Since D1 will conduct after 180 degree

of its conduction so for this is and you know actually nomenclature will have a difference

of 3. So that is D1 and D2 that is D1 and D4 will be the first leg and similarly D3

and D6 will be the second leg and D2 and D5 will be the 6 legs the combination is the

odd combination will be up.

So D1 D3 D5 and D4 D6 D2 if you do like that then you will find that actually this sequence

will come. If you name it this way actually this sequence will come. So first phase 60

degree so of course we start from the point where actually phase A and C get intersects

at this point and we have waited from this point for 60 degree intervals. So it is it

starts from pi/6 to pi/2 so what happened in that configurations.

Diode D1 and D2 conducts and when diode D1 and D2 conducts for this is you can see that

these are 0 so and there and it is the ones actually there after what happened diode D2

D3 conducts there after D4 D3 conducts D4 D5 conducts D5 D6 conducts and then D6 D1

conducts then after D1 D2 conducts. So this will actually be the column you will get 0s

so here D1 D2 conducts therefore D3 D4 start conducting it is blocking the voltage of vba

and vca.

Then it is blocking the voltage of actually vca and vcb and so on. So these are the pair

of voltages that you continue to block. And accordingly you can actually find it out which

voltage it is blocking and you can get the output voltage accordingly. So for this you

know in load voltage will be delivered for this first 120 degree by actually D1 and D2

for 60 degree D1 and D2 and thus you get a voltage of actually PSE>

Similarly, you know when D2 D3 conducts you will get a voltage of bc. then after when

D3 D4 conducts you get ba when actually D4 D5 conducts you get ca. When D D6 conducts

again you will get actually reverse cb then when D6 D1 conducts you get ab and so on.

So this cycle will continue and one pair of actually diode will conduct a 60 degree and

thus one single diode will conduct for the period of 120 degree.

So this is actually a wave form so we consider the RLE load represents the DC mode or the

battery and the load side inductance is quite high to keep the load current continuous.

So we have a ripple but actually this is a Idc value and the load current assumed to

be continuous one diode from the upper side is D1 D3 D5 and another diode from the lower

side will conduct at a time. But no two diodes from the same leg will conduct simultaneously

Otherwise it surely leg shorting will take place ultimately no voltage will be delivered

at right to the load. So it has 6 different diode mode of conduction these are D1 D2 D3

D4 and so on. Each diode conducts for as I told you 120 degree and a pair of diode will

conduct for the 60 degree. So this is the wave form so D1 will conduct actually thereafter

D3 will come into the picture thereafter D5 thereafter D1 again.

Similarly, at this time D1 and D2 will conduct thereafter after actually at this point you

know D2 will be actually D1 will be the outgoing Thyristors at 60 degree and D2 will be conducting

and D3 will be the inductance. So similarly it will conduct like that and since there

is a 6 such changes in 360 degree so you will have a 6 phase wave form and this value is

given by under root of 2 VL and we assume that load current to be constant.

And this will be the pattern of the input current. Input current will be the stepped

square wave so since actually this time D1 conducts so for this what will happen current

will be positive. There after interval you can see that D4 once start conducting at this

region so we will get a negative pulse from phase A. Again there is another pulse of 60

degree again it will pick up. So in a cycle of 360 it will conduct within positive or

negative cycle for mode of 120 degree there will be a assume of in between 60 degree.

So there is sufficient time to actually commute similarly this is a current for phase B and

phase C and this is the wave form drawn this is a fundamental of the input line currents.

Now few parameters comes into the pictures now for as we start from this actually pi/3

to 2 pi/3 and AC is the amount of the voltage coming into the picture. So output voltage

will be given by 3 pi/ 3 to pi 3 VL sin omega t from there we can get this basically the

value of the RMS voltage. RMS voltage you can find it out at this 1+3 root 3/2 pi*VL.

So from there of course you know you have a RMS voltage just divide by the you can find

it out the current.

So current will be basically root 2/3 * which is assumed to be cost term that is output

load current and the output load current is given by this basically Vab so that is the

average voltage that is root 3/2 /pi *Vl -E /R. So from there we can calculate the RMS

voltage as well as the RMS current. so input power factor for IPF will be the active power

output/RMS power input.

So now let us see that what happen if this actually three phase full wave uncontrolled

rectifier fitting in RC load that is quite common you know actually most of the application

nowadays are adjustable speed drive. In case of the adjustable speed drive actually you

can have a variable kind of load and what happen you know you fit to an inverter to

run it in the drives in a different manner.

And for this kind of wave form is quite common in case of this actually in different kinds

of industrial applications and this capacitor essentially actually filtered out the ripple

and gives you more or less a constant DC voltage. So similarly this is a three phase wave form

as we have discussed so here what will happen till the input voltage this input voltage

Van is more than Vac that will not conduct.

So output voltage you know tit will hold by the capacitor this will have this kind of

value you will have a ripple that depends on the load current as well as the size of

the capacitor. So due to that what will happen if so till this voltage is more than this

voltage diode will not be forward by us and thus no current will flow and thus diode current

might be picky. So it will conduct or the D1 D2 will conduct for this pretty small internal

on time.

Let us see that it is alpha +2 beta similarly you know current will have this kind of choppy

profile and it is quite disturbance and it is a unique problem to be solved for the this

is one of the issues with the power quality because you can see that actually it gives

a choppy current and you have an actually a sinusoidal voltage. So this is a problem

once you have an actually artsy kind of load and nowadays its prevalence

Now let us come to the three phase half-wave controller rectified. Now since most of the

application we required are constrained source in DC kind of application for this is an we

prefer to have a control rectifier.

So there is a Thyristor iT1 and there is no difference in between the diode and the Thyristor

we required to trigger the forward most forward Thyristor depending on the voltages and automatically

other Thyristor will naturally commutate it. Because if this let us say that previously

b phase was the most positive and Thyristor T2 was actually conducting the moment actually

F has become more positive.

Or definitely the reverse bias will be applied and the thyristor will commute. So for this

what we required to do let us assume let us start from the point where actually am is

a most positive phase and it has been given at an angle delay angle alpha. So it will

trigger at an angle alpha so that is the point where actually T1 will be triggered on it

will continue till conduction there after you know when it is actually you see that

actually most positive phase is actually T2 phase b.

Then T2 decode so each thyristors will conduct for a period of the same wave 120 degree and

so this will be the profile of the load voltages and like that you know controlled rectifier

you get since it is a we assumed that actually this load is RL type of load for this is the

negative portion of that load voltage will come into the picture and we assume and since

this is a lot current is assumed to be constant so we will have a input current will be given

by like this.

And but problem of this halfwave rectifier or the converter is same because you can see

that and actually this load current is positive in input side and that leads to the saturation

of the transformer so for this is an it is not at all used when most of them we are phasing

out it same way we have a calculations, we can do the calculations that is a 3 pulses

360 degree cycles.

So it is alpha+ pi/6 to alpha +5 pi/6 from there we can calculate the vRMS and IRMS and

ultimately from there we can divided it by R to calculate the average current and IRMS

you will find that I0/root 3 by simple calculations since it is a square. So similarly we can

calculate the input power factor that is V output average/ I output average *3*Vrms*Irms.

So let us come to the more practicable solutions of the three phase.

And where load is assumed to be highly inductive three phase full wave rectifier and same the

nomenclature we have used in case of the diode that is T1 T3 T5.

So since it will be conducting and one pair of Thyristor will be conducting for the period

of 60 degree phi/3 and 1 thyristor itself will be conducting for the period of 120 degree

and what will happen here in this case essentially we will have a same kind of actually nomenclature

that is T1 T3 T5 are the upper thyristors and T4 T6 T2 are the lower thyristors. So

you trigger the point where phase A and phase C are crossing over.

So given a delay angle alpha so you will start from this point so T5 will be the outgoing

Thyristor from the top and so T6 and T1 is conducting. So you will get phase A B across

the load. Similarly, there after T1 T2 is conducting and you get AC to the load there

after you get T2 T3 is conducting you get CB to the load so on and frequently you will

get so you can see that here it is inactive so you get Van into the load.

Similarly, you know you triggered this load Thyristor here there after you get Vbm to

the load then you will get Vcn to the load. So here if you start from here so first you

get Vab there after you get Vac across the load there after you get Vbc thereafter you

get Vba there after Vca there after Vcb and this will continue. So this is the configuration

of that full control bridge rectifier

So here it is same as we have discussed in case of the diodes so it is triggered for

an angle alpha to pi/6 before T1 is turn on T1 and T6 is conducting T6 is already conducting

and T5 was the outgoing Thyristors. So the period alpha actually it is alpha + pi/6 to

alpha + pi/2 where the point T1 T6 is conducting and this is the actually the configurations

so you get cb there after ab and consequent voltages.

At alpha +pi/2 T6 gets turned off due to the reverse bias condition conduction and T2 get

triggered. From this period actually alpha+ pi/2 to alpha +2 pi/3 T1 and T2 both are conducts.

So Thyristors are according to be triggered in the sequence T1 T2 T3 T4 T5 T6 and so on

and this is basically assuming that is a constant load current so this is the current through

the thyristor T1.

And this is the current through the thyristors T4 that is the lower leg of the phase a and

thus load current source current will be this and load current will be this since it is

a positive or negative cycle so it can be used in case of the transformer also.

So it does not lead to the saturation on the transformer similarly we required to calculate

that actually the Vrms and the average voltages. So students are requested to calculate this

value you know actually this is a simple integrations and it is available in normal any textbook.

So this is the pattern same way we have discussed in case of the diode now this is for half

controlled rectifier or converter. So here upper legs will be Thyristors and lower legs

will be diode. So you have a control over triggering the thyristor and automatically

actually negatives phase will be triggered depending on the actually which phase is most

negative. So thus what you can see that let us see that again nomenclature will be the

same.

As used in case of the full control converter so it is D4 D6 D2 I so when T1 an D1 is conducting

so voltage across the thyristors 1 is 0 and will continue till 60 degree that it is blocking

the voltage Vab and ultimately what will happen though these are the voltage they will be

blocking throughout it and so similarly when D2 is basically conducting and it will be

conducting for the period of 120 degree.

So it will conduct till 30 degree to 150 degree thereafter other voltage will follow like

that. So again it will be conducting here. Similarly, you can see that D3 will be conducting

for the period here as well as here. So this is the case will be continue and its matrix

will be actually featured him and accordingly it get a voltage.

So this will be the pattern so T1 will be conducting for this period as shown here and

we can apply a delay to it and output voltage since we can change the delay so output voltage

can be changed depending on the profile and assuming that load current is almost constant

and so this will be the actually the input current and this will be the fundamental.

Same way if you have actually this wave form where have a large delay angle?

So then what will happen? so you can see that this will be the pattern first it will trigger

with the T5 thereafter T3 T1 thereafter T3 thereafter T5 and but what will happen then

you can find that actually lower half will continue as per the sequence so ((for this

reason)) (28:10) this leads to the actually a discontinuous voltage we had talked about

discontinuous current. So we will have a discontinuous voltage when actually it will be discontinuous.

If the triggering angle will be more than 90 degree in case half controlled converter

three phase half controlled converter. And this will be that this kind of way for full

control this will be the continuous form. So pattern of the wave form will change till

alpha =0 to 30 degree and thereafter alpha more than 90 degree. We shall continue our

discussions with the three phase half controller with his mathematical analysis in our next

class. Thank you.