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Phase controlled wave rectifier complete control circuit type with pure cosine power

electronics I

JOSE JEAN CARLOS VALERO 1090520

E-mail: ing.jeanvalero@gmail.com

DANIEL BALLESTEROS 1090655

E-mail:danielvacan_12@hotmail.com

GUSTAVO ADOLFO ROJAS 1090406

E-mail: gadolforojbue@gmail.com

ABSTRACT: I In this report the design of a

single-phase full-wave controlled rectifier,

offset from the signal, investment, and

generating comparison pulses which

activate the gate of SCR bridge rectifier, in

order to control the power shown which is

supplied to the load by varying the

reference. And whose functionality was

reviewed step by step through simulations

with the Orcad software and then checked

with its implementation.

KEYWORDS: Single Phase Rectifier, shot,

inductive, reference, power, control.

1. INTRODUCTION

The development process has allowed the

Power Electronics evolve the functionality

of Power Semiconductor Devices, as the

SCR. By switching of power semiconductor

devices and control processes conversion of

electrical energy in industrial applications

are made. In the thyristor activation

techniques seen so far, the control variable is

the electrical resistance; that is, the firing

angle, voltage and power supplied to the

load is controlled by varying this.

There is, therefore, a control circuit, which

acts on the firing instant of the thyristors

regulates the conversion, although in actual

control system, these methods have limited

application, as few sensors provide

resistance variation to a change in the input

variable. However, it is very common for

sensors provide current and voltage levels,

since this signal conditioning is easier.

A phase controlled thyristor is activated by

applying a short pulse to its gate and

deactivates firing the other thyristor rectifier

during the negative half cycle of the input

voltage. From the knowledge held in

different areas of power electronics design a

single-phase controlled rectifier without

feedback for a highly inductive load, where

its functionality was revised in Orcad

software allowing shown corroborate that

the calculations were correct and then turn to

implementing it. In this practice we analyze

the single-phase circuits and also the control

circuit is by crossing cosine, which is

important to consider some aspects to a good

response in the load. Let's look at the step by

step development of practice.

2. GENERAL PURPOSE

Design and build a circuit for controlling the conduction angle of the SCR of a

single-phase full wave bridge rectifier, by

pure cosine type control. The voltage at

the load to be controlled with a DC signal

that varies between 0 and 10 V.

A resistive-inductive load is used. To reduce the risk of electric shock, a step-

down transformer 120 / 25V is used, 60

Hz, for the power circuit.

3. PRELIMINARY ANALYSIS

2

3.1 Operation phase controlled rectifier bridge.

In this arrangement, the diodes forming the

uncontrolled rectifier bridge are replaced by

thyristors SCR, enabling the phase control

of a full-wave input signal. The circuit can

be seen in Figure 1.

Figure 1. Anonym. Ciar. Single phase bridge controlled rectifier type. Converters AC / DC Rectifiers. Obtained: http://jeissonsaavedraelectronicengineer.files.wordpress.com/2012/09/tema-3-ep-v14.pdf

Thyristors T1 and T4 conduct during the

positive half cycle of the input, and T2 and

T3 thyristors in the negative. That means

that the thyristors will shoot two at a delayed

phase angle from zero crossing of the input voltage. 2 show the waveforms of the

input current and the output voltage of the

rectifier.

Figure 2. Anonym. Ciar. Waveforms fully controlled bridge rectifier with resistive load. Converters AC / DC Rectifiers. Obtained: http://jeissonsaavedraelectronicengineer.files.wordpress.com/2012/09/tema-3-ep-v14.pdf

( ) ( )

( ) ( )

The average component of the waveform is

determined from:

Therefore, the average output current is:

( ) ( )

( ) ( )

The power delivered to the load is a function

of the input voltage, the shooting angle and

load components. To calculate the power in

a resistive load is used , where.

( )

3

The effective current generator is equal to

the effective load current.

With Rl and a discontinuous load current

is required to do a different analysis.

To wt = 0 and no-load current, the SCR T1

and T4 bridge rectifier are polarized directly

and polarize T2 and T3 are reversed when

the generator voltage becomes positive. T2

and T4 were activated when they are applied

gate signals for wt = . When T1 and T4 are on, the charging voltage is equal to the

generator voltage. For this condition is

identical to the circuit controlled half-wave

rectifier function and the current will be:

( ) [ ( ) (

) ( ) ] ( ) To:

Where:

( )

(

)

The function above current becomes zero at

wt = . If

4

Figure 4. . Anonym. Ciar. Curve voltage-current characteristic of a thyristor (SCR). Obtained: http://usuaris.tinet.cat/fbd/electronica/tiristor/tiristor/tiristores.html

Phase Control Thyristors: They operate at

the line frequency and neutralized by natural

commutation also known as SCRs. Used an

amplifying thyristor gate, in which an

auxiliary thyristor is triggered by a gate

signal to the main thyristor.

a. Control circuit cosine crossing

Figure 5. Block diagram circuit cosine cross firing.

The control circuit must provide a linear

control characteristic, so that the control

response does not depend on the operating

point of the converter. The trigger pulse

thyristor is obtained by comparing an

appropriate voltage signal with a control

voltage.

In this project we control the SCR by cross

firing circuit cosine whose block diagram is

shown in Figure 3.

The operating principle is to monitor the

input signal through a step-down

transformer to obtain a sample of the

appropriate phase.

Is derived to obtain a cosine function. We

now have, at the output of the phase shifter:

Where Vm is the magnitude of the input

signal and Vp is the magnitude of the output

signal down transformer.

If the signal of equation (5) is reversed, the

two signals form:

And if the signal Vc control varies only in

the range defined by 0

5

(

) ( )

If the optocouplers defined in turn triggering

the SCR's, and remember that the equation

defining the average value of the output

signal converter is:

( ) ( )

OPTOCOUPLER

Diode LED and Phototransistor

The optocoupler is a device which consists

of a LED diode and a phototransistor, so that

when the LED emits light, illuminates the

phototransistor and drive.

These two elements are coupled in the most

efficient way possible.

The output current of the optocoupler IC

(phototransistor collector current) is

proportional to the input current IF (current

through the LED).

Figure 6. Anonym. (c.2008).Typical with phototransistor circuit. Projects electronics, obtained: http://www.proyectoselectronics.blogspot.com/2008/09/optoacoplador-que-es-y-como-funcionan.html

THE DIFFERENTIAL AMPLIFIER

The differential amplifier has two input

signals (applied to the inverter and non-

inverting terminal), producing a voltage

proportional to the difference between the

input voltages output.

The difference between the input voltages is called differential input voltage Vid.

The differential gain (Ad) is the gain of the amplifier.

The input voltage common mode (VicM) is the average of the input voltages.

Figure 7. Germn Villalba Madrid, Miguel A. Zamora Izquierdo. Circa. Differentiating circuit. University of Murcia. Differential Amplifier Obtained: http://ocw.um.es/ingenierias/tecnologia-y-sistemas-electronicos/material-de-clase-1/tema-6.-amplificadores-operacionales.pdf

4. PLANNING

1. From the proposed block diagram of Figure 4, is asked to design a control

circuit using the cosine crossing method,

using analog discrete components.

6

V (t): cosine signal source or reduced value

ramp synchronized with the AC power

source...

Vc: control DC signal variable between 0

and 10 V, for the driving theoretical angle

varies between 0 and 180 degrees...

a. Adaptation of the signal

For a transformer circuit 120/25 / 12.5 V.

The operational amplifier (084 TL) be

polarized with 15 volt requiring that a

voltage divider is made to ensure maximum

excursion transformer is used, besides the

comparison voltage will vary between 0 and

10.

To achieve the objective it is necessary to

implement the following circuits.

4.1 90 phase shifter circuit

Requires that the cosine signal is therefore

the 90 phase shift to the input through an

RC filter in follower mode is performed.

The following calculations were made:

The value of C = 100 nF is assumed.

Knowing that f = 60 Hz and = 90 , then:

The circuit to implement is as follows:

Figure 8. Phase shifter circuit.

And whose simulation waveform is

obtained:

Figure 9. Waveform phase shift of 90.

4.2 inverter voltage.

As should have two pulses, one 180 out of

phase from the other, you must generate a

positive and a negative signal, ie 180 out

of phase. Therefore it requires an inverter to

the offset.

7

Figure 10. Voltage inverter circuit.

Figure 11. Cosine wave form out of phase 180 .

4.3 comparator circuit

Two comparator circuits, one for tripping on

wt = comparing the output of the phase shifter follower with the reference voltage

and the other for triggering in wt = + , are used. The output voltage is equal to Vcc

during the time when V + is greater than V-,

so that a step signal is generated.

Figure 12. Circuit voltage comparators.

Figure 13. graph obtained from the comparator circuit.

4.4 Control Circuit

To isolate the control circuit used with the

power diodes optocouplers MOC 3010. We

place between gate and cathode of the SCR

to protect it. Furthermore insert a

freewheeling diode in parallel with the load

anti reduction of the negative peak and

ensure the discharge of the coil.

4.5 Coupling step

Way to separate the control stage and the

power stage is through optical coupling.

Four optocouplers, where two of them are

connected together and they reach the output

8

of comparator 1 and the output of

comparator 2 comes to those remaining

optocouplers are used. This means that two

optocouplers operate in a half cycle as the

comparison signal.

Figure 14. optical coupling.

4.6 Power amp

Controlled in the bridge, due to the

properties of the power element, by varying

the firing angle of the SCR, the average output voltage Vdc also change.

Figure 15. Controlled rectifier bridge.

Figure 16. Waveform controlled full wave rectifier with highly inductive load. (German Gallego, power electronics slides)

The average output voltage to a highly

inductive load is:

( )

( )

( )

9

[ ( ) ( )]

[ ( ) ( )

( ) ( ) ( )]

[ ( )]

( )

With reference to the waveforms of source

voltage and load current, the power factor of

the single phase full wave rectifier bridge

type with highly inductive load is:

Figure 17. Voltage waveforms at the source and load current for phase controlled rectifier with inductive load. (German Gallego, power electronics slides)

( )

( ( ( ))

)

( )

( ( )

)

( )

( (

( )

) ( )

)

( )

(

( )

)

( )

([ ] )

( )

( )

( )

The distortion factor and THD is:

10

( )

( )

As the waveform is AC, and is odd signal,

we have:

( )

( )

( )

( )

( )

( )

2. Draw a block diagram that includes all

stages of the control circuit and power

circuit.

Figure 18. Block diagram of the circuit cross firing cosine.

3. Draw the circuit diagram of the power circuit using the transformer 120 / 12.5 /

12.5V, 60 Hz.

Annex 1.

4. SPICE simulation, the operation of the

power circuit for = 30, 60, 90 and 120 degrees.

= 30

Figure 19. graphic to 30.

= 60

11

Figure 20. graphic to 60.

= 90

Figure 21. graphic to 90.

= 120

Figure 22. graphic to 120.

5. EVALUATION

4. Draw the following graphs:

a. Effective load voltage vs voltage control.

The data obtained for the graph are:

Vcontrol= [11 10 9 8 7 6 5 4 3 2 1];

Veffective= [23 22.9 20 16 14.1 11.9 9.10

6.5 5.1 2.2 1.4];

Figure 23. Graph of voltage effective vs control voltage obtained with MATLAB 2012.

b. Shooting Angle vs voltage control.

Angle= [30 50 70 90];

Control= [9.5 7.91 3.48 0];

Figure 24. Graph of Angle vs control voltage obtained with MATLAB 2012.

c. Load voltage for = 30, 60, 90 and 120 degrees. Comparing the waveform obtained

on the oscilloscope with the SPICE circuit

simulation.

= 30

12

Figure 25. Operation of the power circuit for = 30 degrees.

= 60

Figure 26. Operation of the power circuit for = 60 degrees.

= 90

Figure 27. Operation of the power circuit for = 90 degrees.

= 120

Figure 28. Operation of the power circuit for = 120 degrees.

Comparing the waveform obtained on the

oscilloscope with the SPICE circuit

simulation, we see a very similar but with

increasing angle by more than 90 cannot

fully appreciate the present variation.

d. Waveforms of the voltages at the output

of each of the control circuit block.

For the implementation we use the TL084

integrated circuit, consisting of four

operational amplifiers and reduce space on

the breadboard mounting.

Used were the SCR and the optocoupler

MOC3010 S106.

5. CONCLUSIONS

The cross firing circuit allows cosine linearize the relationship of the average

output voltage in a semi converter

powered by this circuit and a voltage

control signal.

For effective control, it is necessary that the control voltage does not exceed the

peak voltage of the cosine signal.

To isolate the power amplifier control stage has used an optical interface using

the integrated MOC3010, as using a

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magnetic interface, required external

components and a large number of

sources.

The inductance when loaded does not provide the necessary current, thus the

energy supplied is not enough to keep lit

thyristors and off.

Observe through the graph of voltage vs. control firing angle high linearity in the

output response, indicating that the phase

control by full wave rectifier cosine

crossing behaves with linear transfer

function and system response to an

increase in the control variable does not

depend on firing angle ; which is a desirable feature.

We proved that the antiparallel diode in the load RL produces a marked decrease

of the negative load voltage zero crossing

after, the process also serves to degauss

coil. Also noteworthy protection diode

connected to the gate of the SCR to

protect it.

At time of connecting the firing pulses to the power circuit, should take special care

in assigning that pulse is connected to

that pair of SCRs, considering the

polarity of the AC signal, as this should

be positive when cathode of the SCR is

positive - pulses, so the anode voltage is

applied. Otherwise control will fail.

Is necessary to invert the control voltage as the output signals of the adders are

displaced negatively, ie with a negative

offset voltage to effect compared

correctly and properly generate the firing

pulses.

When exchanging cables pulses our circuit to each pair of SCRs was evident that he had control of a form, we

conclude that this occurred because it

must take into account the polarity of the

AC signal, as this should be positive

when the pulses, thereby applying the

voltage anode - cathode of the SCR is

positive. Otherwise no control not is held.

6. BIBLIOGRAPHIC REFERENCES

[1] OGATA, Kantsuiko. Control engineering problems using Matlab. Prentice-Hall Iberia.1999

[2] Germn Gallego. Slides Power Electronics I. Unidad IV. unpublished

manuscript.

[3] Converters AC / DC - Rectifiers.Barcelona (2010, Nov 25).

Available in: tec.upc.es/el/TEMA-

3%20EP%20(v1).pdf Date of

consultation:25/11/2014

[4] MUHAMMAD H. RASHID. Power Electronics. Edition. Mxico D.F.

Editorial Prentice Hall, 1993. PAG. 118-

124

[5] Trip circuit thyristorgdcjorgeprueba.wikispaces.com

[6] J. A. Pompilio, Power Electronics ", State University of Campinas,SP - Brasil.

Pag (15)

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ANNEXS

1. ANNEX 1