1
Phase controlled wave rectifier complete control circuit type with pure cosine power
electronics I
JOSE JEAN CARLOS VALERO 1090520
E-mail: [email protected]
DANIEL BALLESTEROS 1090655
E-mail:[email protected]
GUSTAVO ADOLFO ROJAS 1090406
E-mail: [email protected]
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
13
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