Download IMPLEMENTATION OF INTEGRAL SWITCHING CYCLE CONTROL

IJREE - International Journal of Research in Electrical Engineering
ISSN: 2349-2503
IMPLEMENTATION OF INTEGRAL
SWITCHING CYCLE CONTROL USING PIC
16F877A
M. Narayanan1 | R. Vidhya2
1
(Department of EEE, Info Institute of Engineering, Coimbatore, India, [email protected])
(Department of EEE, Info Institute of Engineering, Coimbatore, India, [email protected])
___________________________________________________________________________________________________
2
Abstract— This paper presents the comparison of traditional control strategies like Integral Cycle control (ICC) and Phase Angle
Control (PAC) of ac voltage controller with Integral Switching Cycle Control (ISCC) and implementation of ISCC using PIC 16F877A.
This paper also presents simulation study of all the above control strategies using MATLAB SIMULINK and PROTEUS.
Keywords— AC Voltage Controller;Control Strategies;MATLAB SIMULINK;PROTEUS software
___________________________________________________________________________________________________________
1. INTRODUCTION
The need of customer can be satisfied only when
easily operated, reliable, energy saving, reasonable cost
products are introduced in the market. With these
requirements as the main aim, industries are forced to
know about the development and advancement in the
technology. The loads are made efficient by operating them
for our requirement and to ensure energy savings by
injecting variable ac or dc. So the basic requirement should
be the energy input available in required form.
Applications are operated at fixed ac or dc voltage, variable
ac or dc voltage, variable frequency and others to satisfy
the load demand and energy savings. Keeping a view of all
these requirements there is a need to study electrical
circuits that perform the required conversion and their
control techniques.
The advent of power electronic devices has made the
energy conversions much easy and reliable. The energy
conversion such as AC – DC, AC – AC, DC – DC and DC
– AC is possible without using any rotating devices. This
helps to reduce the cost, losses and maintenance problem
and therefore improves the efficiency of the system [17].
The control strategies available to vary fixed ac to
variable ac in ac voltage controller circuits are [1]:
1.
2.
3.
On – Off cycle control
Firing angle control
Integral cycle switching control
To control the rms output voltage the one of the above
control strategy can be used. Choosing the best can be done
by considering the application and percentage Total
Harmonic Distortion (THD).
The implementation of any converter circuit needs to be
tested before going for hardware. This reduces cost, man
power, time. This is achieved by using simulation
software’s were the same model or topology can be tested
with the real time hardware ratings and device
specifications. One such software for testing power
electronic converter circuit is MATLAB and PROTEUS.
The application of these software’s really proves their
worth through their real time applications [18].
2. PRINCIPLE OF INTEGRAL CYCLE CONTROL (ICC)
Some domestic and industrial applications require
variable ac to perform their operation. For example, the
speed of a ceiling fan can be varied by varying the ac
supply voltage input.
AC voltage controllers are power electronic circuit
that converts fixed voltage, fixed frequency ac supply to
variable voltage, fixed frequency ac supply. By properly
triggering the SCR’s the rms value output voltage from the
converter circuit can be varied.
Fig. 2. Circuit diagram of AC Voltage controller
Fig.1. AC to variable AC converter
IJREE - International Journal of Research in Electrical Engineering
Volume: 03 Issue: 04 2016
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ISSN: 2349-2503
IJREE - International Journal of Research in Electrical Engineering
The advantage of this method is continuous output
voltage control is possible by varying the firing angle and
no commutation circuit is required. Since the sine wave
pattern is getting changed, harmonics will be introduced in
the system and hence %THD will get increased [19].
The expression for rms value of output voltage for resistive
load is given by:
where,
Vs - RMS Value of input supply voltage and is
equal to:
Fig. 3. Input and output waveforms
The basic principle of Integral Cycle control or on-off
control technique is explained with reference to a single
phase full wave ac voltage controller circuit shown below.
The output voltage is controlled by triggering the
SCRs such that the entire cycle appears across the load for
‘n’ number of cycles and load voltage is zero for ‘m’
number of cycles. Hence in this method of control, the
shape of the input waveform is not changed but the input
voltage does not appear across the load continuously.
Therefore in this method the %THD should be less and the
drawback being load has to sustain the voltage variations
i.e., A full supply voltage during the ON period and zero
voltage during the OFF period and output voltage control is
not continuous. Here SCR’s are turned on at zero crossing
and duty cycle (ratio of on-time period to total time period)
can be varied to vary the output voltage [19].
The expression for rms value of output voltage for
resistive load is given by:
Vs =
Vm
2
where,
ton – controller ON time = n x T
toff – controller OFF time = m x T
T – Input cycle time period
To – Output cycle time period
To = tON + tOFF
Vs – rms supply voltage
The expression for duty cycle (k) is given by:
Fig. 4. Input voltage, Output voltage and Gate pulse waveform
4. INTEGRAL SWITCHING CYCLE CONTROL
(ISCC)
The expression for rms value of load current is given by:
where,
Z – Load impedance in ohms
3. PHASE ANGLE CONTROL (PAS)
In this method, the output voltage is controlled by
triggering the SCRs T1 and T2. By varying the firing angle
the rms value of output voltage is varied [4].
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Volume: 03 Issue: 04 2016
Fig. 5. Output voltage and current waveform
This method is the combination of on-off cycle and
phase angle control. The disadvantages of above two
techniques are eliminated in this method [1]. The methods
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IJREE - International Journal of Research in Electrical Engineering
ISSN: 2349-2503
by which output voltage is controlled are: a) Keeping firing
angle constant and varying duty cycle b) Keeping duty
cycle constant and varying firing angle. Thus by this
method both continuous control over output voltage is
achieved and also %THD is reduced compared to phase
angle control [19].
The expression for rms value of output voltage for resistive
load is given by:
Fig. 7. MATLAB circuit simulation diagram of ICC and PAC
Fig. 8. MATLAB circuit simulation diagram of ISCC
Fig. 6. Block diagram of the ISCC
5. SIMULATION RESULTS
Fig. 6 shows the MATLAB circuit simulation
diagram where two SCR’s are connected in anti-parallel to
control the output rms voltage. By varying the firing angle
required rms output voltage can be obtained.
Fig. 7. shows FFT analysis of voltage waveforms for
resistive load with 0.75 duty cycle and alpha = 90 deg in
ICC, PAS and ISCC control modes.
Circuit Parameters for simulation:
MATLAB version: 7.8.0(R2009a)
PROTEUS version: 8
PIC controller: 16F877A
Maximum input voltage = 50V
Frequency = 50Hz
Load resistance = 10 ohms
Time Period = 20ms
Fig. 9. ICC output voltage and FFT waveforms
Fig. 10. PAC output voltage and FFT waveforms
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ISSN: 2349-2503
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Fig. 11. ISCC output voltage and FFT waveforms
TABLE I
S.
No
COMPARISON OF ICC FOR R AND RL LOAD
Duty Cycle
Output voltage
rms
Vo (Volts)
Fig. 12. PROTEUS circuit simulation diagram of ISCC
%THD
R load
RL load
TABLE III
PROTEUS SIMULATION PARAMETERS
S. No
Parameter
Specification
1
0.25
120
0.15
5.19
2
0.5
160
0.15
2.63
1
Input supply
230 V, 50 Hz ac
3
0.75
200
0.15
1.77
2
Triac
Q2025R5
3
Opto coupler
MOC3021
4
Switch
SPST, DIP Switch
5
Transistor
2N3904
6
Controller
PIC16F877A
7
Voltmeter
AC
8
Display unit
Scope
From Table I, the %THD is constant for any values of duty
cycle in the ON –OFF control method for resistive load
since the pattern of the sine wave is not disturbed. While in
the case of inductive load the %THD decreases with
increase in duty cycle.
TABLE II
S.
No
COMPARISON OF PAC AND ISCC FOR R LOAD
Output
voltage
rms (V)
Phase angle control
(PAC)
Integral switching cycle
control (ISCC)
δ = 0.8
α in deg
%THD
α in deg
%THD
1
203
62
39.45
30
15.03
2
160
90
65.2
80
54.6
3
120
110
88.65
105
81.43
Table II shows the comparison of PCS and ISCC control
techniques for R load. From the Table II it is inferred that
ISCC control technique produces %THD less than that of
PCS for same output voltage rms. Here duty cycle is kept
constant (δ = 0.8) and firing angle is varied. As the firing
angle increases rms output voltage decreases [11].
The simulation circuit contains the following modules:
1. Power supply
2. Triac based ac voltage controller
3. Opto coupler
4. Gate drive circuits
5. PIC controller
6. Scope and voltmeter
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Volume: 03 Issue: 04 2016
Fig. 13. ISCC input voltage, gate pulse and output voltage waveforms
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IJREE - International Journal of Research in Electrical Engineering
systems: The limits on voltage harmonics are thus set at
5% for THD and 3% for any single harmonic. However,
keeping low THD values on a system will further ensure
proper operation of equipment and a longer equipment life
span [6].
6. HARDWARE SETUP
Fig. 15. ISCC output voltage waveform for α = 90 deg obtained in
Oscilloscope
Fig. 14. Experimental Setup
TABLE IV
COMPONENT SPECIFICATION
S.
N
o
Component
s
Specificat
ion
Temper
ature
(oC)
Curren
t
(A)
Voltage
(V)
1.
TRIAC
BT136
110
4
600
2.
BJT
2N3904
0.2
40
3.
Opto coupler
MOC3021
0.06
400
Voltage
Regulator
Microcontro
ller
4.
5.
-55 to 150
-40 to
+100
LM7805
0 to 125
1.5
25
16F877A
-55 to
+125
0.3
5.5
RMS output voltage (V)
Theoretical
value
Matlab
Proteus
Experimental
value
30
34.78
34.3
35.02
34
60
31.67
31.6
32.1
31
90
24.95
24.62
25.3
25
120
15.48
15.13
15.7
15
From the comparison done in Table V it is clear that
the output voltage rms obtained through MATLAB and
PROTEUS simulation and experimental setup is
approximately equal with the theoretical value. The above
readings are taken keeping the duty cycle = 0.5 as constant.
The controlled voltage output rms is measured using
an ac voltmeter and the readings are compared with the
MATLAB and PROTEUS simulated output and is given in
the table V.
IEEE Standard 519, “Recommended Practices and
Requirements for Harmonic Control In Electrical Power
Systems” provides suggested harmonic values for power
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Volume: 03 Issue: 04 2016
The ISCC is found to be an efficient control technique
from the comparison made on the basis of %THD. But the
%THD is higher than what IEEE standards 519
recommends. Therefore the future work is based on
working on techniques such as designing a suitable filter,
using Selective Harmonic Elimination method, etc. to
suppress the dominant harmonics present in the system and
to ensure that the %THD for voltage waveform is less
than 5%.
7. CONCLUSION
TABLE V
COMPARISON OF THEORETICAL, SIMULATED
AND HARDWARE VALUES OF RMS VALUE OF OUTPUT
VOLTAGE FOR ISCC CONTROL
Firing
angle
α (deg)
ISSN: 2349-2503
The various control strategies of AC voltage controller
used to control the output voltage is discussed in this paper.
In the ON – OFF cycle control even though the %THD is
less, wide range of voltage control is not possible whereas
in phase angle control smooth voltage variation can be
achieved but %THD is high. So to eliminate the above two
drawbacks, the Integral Switching cycle control (ISCC)
technique can be used in which by setting duty cycle
constant and varying firing angle can lead to get both
smooth voltage variation and reduced %THD.
This paper also discusses the simulation study of AC
voltage controller control strategies using MATLAB
SIMULINK and PROTEUS software. From the MATLAB
SIMULINK it is concluded that ISCC is efficient than ONOFF cycle control (ICC) and Phase angle control (PCS) in
terms of percentage THD. It is also concluded that
PROTEUS software proves its worth for real time
application of ISCC control of AC voltage converter using
PIC 16F877A.
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