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AC VOLTAGE REGULATION BY SWITCH MODE PWM VOLTAGE CONTROLLER
P. K. Banerjee 1 and Kaamran Raahemifar 2 Department of Electrical & Computer Engineering, Ryerson University, Toronto, ON, Canada
1 [email protected]@ryerson.ca
ABSTRACT
Voltage sag is an important power quality problem. It mayaffect domestic, industrial and commercial customers. Voltagesags may either be decreasing or increasing due to faults orchange in loads. In this paper a switch mode AC to ACregulator is investigated to maintain constant voltage across thedomestic appliance during the voltage deviation from the rated
value. Such deviation may occur due to change in load orchange in input voltage due to voltage sag of the system itself.The proposed system incorporates insulated gate bipolartransistor (IGBT) with high frequency switching technology.The Pulse Width Modulation (PWM) controls the ON/OFFtime (Duty cycle) of switching devices (IGBTs) of thisregulator. By regulating duty cycle of the control signal, outputvoltage can be maintained almost constant for wide range ofinput voltage variation. Simulation results show constantvoltage can be achieved in either cases of increasing ordecreasing input voltage as long as it is within specified limit.
Index Terms : AC to AC Regulator, Pulse width modulation(PWM) control, Duty cycle (D), Buck-Boost Converter, CûkConverter
I. INTRODUCTION Power lines experience voltage sags due to switching
lines/loads and faults somewhere in the system. Short timevoltage sags may also occur because of nearby momentary
periodic loads like welding and operation of buildingconstruction equipment. Voltage sags are much more commonsince they can be associated with faults remote from thecustomer. Power quality describes the quality of voltage andcurrent [1] and is one of the important considerations indomestic, industrial and commercial applications. Power
quality faced by industrial operations includes transients, sags,surges, outages, harmonics and impulses. Equipment used inmodern industrial plants is becoming more sensitive to voltagesags. Both momentary and continuous voltage sags areundesirable in complex process controls and householdappliances as they use precision electronic and computerizedcontrol. Major problems associated with the unregulated long-
term voltage sags include equipment failure, overheating andcomplete shutdown. Tap changing transformers with SiliconControlled Rectifier (SCR) switching are usually used as asolution to continuous voltage sags [2]. They require atransformer with many SCRs to control the voltage at the loadwhich lacks the facility of adjusting to momentary changes.Some solutions have been suggested in the past to encounter
voltage sag [3-4]. AC to AC voltage regulation system based
on the Cuk converter have been developed by differenttopologies and methods [5-6].
In an AC Buck converter as reported in [1], normally, areduction of input voltage causes a decrease in output voltage.Output voltage is increased to desired value by adding asuitable voltage, which is induced in the transformer secondaryas shown in Fig.1. If the input voltage is increased then outputis increased. But it is necessary to decrease the output voltageto the desired value by subtracting the secondary inducedvoltage from input voltage. It is not possible to achieve this by
buck arrangement. This limitation can be overcome by using
reported AC Buck-Boost configuration [7], where outputvoltage is remained constant for either case of increasing ordecreasing input voltage. The AC Buck-Boost configuration byusing IGBT switches with manual control circuit is shown inFig. 2.The input-output simulation results of uncontrolled AC Buck-Boost voltage regulator for input voltage 250V, 300V and
Figure 1: AC to AC Buck converter schematic
2013 26th IEEE Canadian Conference Of Electrical And Computer Engineering (CCECE)
978-1-4799-0033-6/13/$31.00 ©2013 IEEE
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(a)
(b)
(c)Figure 3: Input- Output waveforms (Buck-Boost manual controlled)
when input Voltage: (a) 250V (b) 300V (c) 400V and output alwaysmaintain =300V
400V (all are peak values ) are shown in Fig. 3(a), (b) and (c)respectively. The output voltage can be remained constantwhen the input voltage level changes from a lower than actualinput voltage level to higher than the actual input voltagelevel by using PWM technique.
These feature have been also established by an automaticfeedback control circuit for AC buck-boost voltage regulator[7] as shown in Fig. 4. It has been observed that althoughoutput always maintains constant voltage in spite of change
Figure 2: AC Buck-Boost converter configuration by using IGBTswitches with manual control circuit
V515Vdc
V4
13Vdc
V3
15VdcV2
TD =0
TF =. 000001msP W =0PER =.25ms
V1 =15V
TR =.249999ms
V2 =0
V1
FREQ=50HzVAMPL= 400V
VOFF =0
U2 A4N47A
U1 A4N47A
V7
15Vdc
V6
15Vdc
Z1
10
0
U3A
AD648A
+3
-2
V +
8
V-4
OUT1
R3
100k
R1
50
R5
1k
R6
100k
R9
.01
R4
500
D3
R2
50
D6 D4C1
200uf
D5
L1
10mH
D2D1 D7
D8
Z3
0
00
0
0
0
0
Figure 4: AC Buck-Boost converter with automatic feedback contro
C1
50uf
Z1
R18
.01
D7
R17
100kR19
1k
Z3
D9
R1
50
2
D1
L1
10mH Ro
50
V6
15Vdc
0
R3
100k
0
R4
500
L1
2mH
0
D2
R5
1k
2
V7
15Vdc
R2
D3
C1
300uf
PWM
V4
D4D6
U2 A4N47A
1
D5
D8
TX1
U1 A4N47A
1
R12
1
vref
vcc-
R15
1k
R710k
vcc-
U10A
LM324
3
2
4
1 1
1
+
-
V +
V -
OUT
D11
UT268
V38Vdc
U4A
LM324
3
2
4
1 1
1
+
-
V +
V -
OUT
V2
15Vdc
Vout
C9
60uvcc-
vcc-
U5A
LM324
3
2
4
1 1
1
+
-
V +
V -
OUT
C3
2u
1
1
vcc+
R9
10k
R16
10k
C5
.1u
V5
TD =0
TF = 490usPW = 10usPER =1ms
V1= 10v
TR =490us
V2= -10v
vcc+
R14
50k
R8
10k
R10
2meg1
R6
10k
R20
10k
1
V115Vdcrun
vcc+
C8
.1u
vcc-
1
U3A
LM324
3
2
4
1 1
1
+
-
V +
V -
OUT
PWM vref
1
vcc+
vcc+
(a)
(b)
(c)Figure 5: Input- Output waveforms (Buck-Boost feedback contr
when input Voltage: (a) 250V (b) 300V (c) 400V and oalways maintain =300V
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in input voltage, the output voltage contains significantripple when automatic feedback control circuit is used. Thesimulation results for controlled AC to AC Buck-Boostregulator for input voltage 250V, 300V and 400V (all are
peak values) are shown in Fig. 5(a), (b) and (c) respectively.Furthermore, it have been seen that input current is very highwith more harmonics and the output current waveform whichcontain significant ripple also. So, it is important to furtherinvestigate removing the ripple from output voltage, outputcurrent and reduce input current and its associatedharmonics. This present work is a continuation of previousresearch to develop a switch mode AC to AC voltageregulator to overcome above drawbacks with improved
performance by using Cûk converter topology.
II. AC-AC CÛK CONVERTER TOPOLOGY Cûk converter is similar to the Buck-Boost converter
with some rearrangement. Cûk converter provides an outputvoltage which is less than or greater than the input voltage,
but the output voltage polarity is opposite to that of the inputvoltage [8]. In Cûk converter, the capacitor C 1 is the mediumfor transferring energy from the source to the load. Theimplementation of AC Cûk converter by two switches isshown in Fig. 6 where output capacitor (C 2) acts as a filter. The circuit operation has been explained in positive andnegative cycle as follows.
During positive half cycle of input voltage when IGBT-1(Z 1) is ON and IGBT-2 (Z 2) is OFF, the current throughinductor L 1 rises and at the same time capacitor C 1 discharges its energy to the circuit formed by C 1 IGBT-1(Z1), C2, the load, L2 . When IGBT-1(Z 1) is OFF andIGBT-2(Z 2) is ON, the capacitor C 1 is charged from the inputsupply and the energy stored in the inductor L
2 is transferred
to the load.The operation of negative half cycle for AC input voltage
is the same like positive half cycle but direction is opposite.So in both cycles we get the output voltage across the load.
It is assumed that the relation between input and outputvoltage is the same as the DC to DC Cûk converter in idealcase. So, the voltage gain of Cûk converter [9] is given by,
1 , 1
and current gain is given by,
1. 2
A Cûk converter can be obtained by the cascadeconnection of the two basic converters: the step down (Buck)converter and the step up (Boost) converter. In steady state,
(a)
(b)
(c)Figure 7: Input- Output waveforms (AC Cûk manual
controlled) when input Voltage: (a) 250V (b) 300V (c)400V and output always maintain =300V
Figure 6: AC Cûk converter configuration by using IGBTswitches with manual control circuit
V5 15VdcV4
4.5V
V3
15VdcV2
TD = 0
TF = .000001msPW = 0PER =.25ms
V1= 15V
TR = .249999ms
V2= 0
V1
FREQ= 50HzVAMPL=250V
VOFF = 0
U2 A4N47A
U1 A4N47A
V7
15Vdc
V6
15Vdc
Z1
APT3
10
0
U3A
AD648A
+3
-2
V +
8
V-4
OUT1
R3
100k
R1
50
R5
1k
R7
150
R6
100k
R4
500
D3
R2
50
D6 D4
C2
200uf
D5D2D1 D7
D8
Z3
APT3
0
00
0
0
0
0
L2
50mH
L1
1mH
C1
250uf
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the output to input voltage conversion ratio is the product ofthe conversion ratios of the two converters in cascade.To calculate the value of filter capacitor (C 2), the followingformula [10] is given by:
18 ∆
. 3
The input-output simulation results of above uncontrolledAC Cûk converter for input voltage 250V, 300V and 400V(all are peak values) are shown in Fig. 7(a), (b) and (c)respectively. In uncontrolled AC Cûk converter, the pulse
width of switching pulses (PWM) are changed manually tomaintain the constant output voltage when the input voltagelevel changes from a lower than actual input voltage level tohigher than the actual input voltage level.
In Fig.8 shows the controlled AC Cûk converter. It is thecombination of AC Cûk arrangement with automaticfeedback control circuit to make proper PWM signal as perrequirement. In controlled AC Cûk converter arrangement,the same feedback control circuit used as of AC Buck-Boostconverter [7]. Let consider the switching frequency is 1Khz.
Figure 8: AC Cûk converter configuration with automatic feedback control circuit
V4
FREQ = 50Hz
VAMPL = 250V
VOFF = 0
U2
A4N47A
U1 A4N47A
V7
15Vdc
V6
15Vdc
Z1
10
0
R3
100k
R1
50
R5
1k
Ro
150
R17
100k
R4
500
D3
R2
50
D6 D4C2
200uf
D5D2D1 D7
D8
Z3
V-
V+
0
0
2
C1
250uf
PWM
12
VoutL1
1mH
L2
50mH -
++-
E1
E
vref
R12
1vcc-
vcc+
run
U10A
LM324
+3
-2
V +
4
V-11
OUT 1
vcc-
R16
10k
Vout
PWM
R6
10k
1
U4A
LM324
+3
-2
V+4
V -
1 1
OUT 1
R710k
vcc+
vcc-
1
R14
50k
vref
U3A
LM324
+3
-2
V+4
V -
1 1
OUT 1
R8
10k
R20
10k
U5A
LM324
+3
-2
V+4
V -
1 1
OUT 1
vcc+
D11
UT268
R15
1k
C9
60u
C32u
vcc-
vcc+
V5
TD = 0
TF = 490usPW = 10usPER = 1ms
V1 = 10v
TR = 490us
V2 = -10v
R9
10k
vcc+
R102meg
C8
.1u
1
1
V115Vdc
1
R11
10k
1
V2
15Vdc
run
C5.1u
vcc-1
V38Vdc
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III. RESULTS OF CONTROLLED AC-AC CÛK CONVERTER
By considering same cicuit parameter values that arealready used in uncontrolled AC Cûk converter the input-output simulation results for input voltage 250V, 300V and315V (all are peak values ) have been observed. It is seen that
output voltage is constant and always maintained 800V- peak value and better ripple free output than Controlled ACBuck-Boost (simulation results are not included in paper dueto page limitation). To achieve the output voltage always300V-peak value (even the input decrease or increase fromits actual value) and overcome the simulation difficultiessome circuit parameter values have been changed randomly.After making these arrangement of parameters value theresults are shown in Fig. 9(a), (b) and (c) for the inputvoltage 250V, 300V and 315V respectively and outputalways 300V-peak value in every cases.
IV. COMPARISON OF RESULTS :BUCK-BOOST
WITH CÛK CONVERTER By comparing Fig. 3(a), (b) and (c) with Fig. 7(a), (b)
and (c) respectively (for manual controlled converter-in caseof AC Buck-Boost and CUK converter), it has been seen thatoutput always maintains constant (300V-peak) by usingPWM technique in both arrangements. However, sometimesoutput is deviated from its constant value in case of AC Cûkconverter (as observed in simulation results).
On the other hand, by comparing Fig. 5(a), (b) and (c)with Fig. 9(a), (b) and (c) respectively (for feedbackcontrolled converter- for both cases), it has been seen thatoutput always maintains constant (300V-peak) in both cases.
However, in case of AC Cûk converter output havemaintained better ripple free waveforms than AC Buck-Boost converter output.
Comparing the harmonics, while considering the inputcurrent, the higher and more harmonics contains in case ofAC Buck-Boost configuration than the AC Cuk arrangementwhich both are shown in Figs. 10 and 11.
Finally, according to output current, AC Cûk convertercontains smooth and ripple free output than AC Buck-Boostconverter as shown in Figs.12 and 13.
V. CONCLUSIONThe simulation results provided in this paper showsfeasibility of the AC-AC switching voltage converter forvoltage sag correction by using Cûk converter topology. ThisCûk arrangement is not able to simulate and to maintainconstant output voltage when input voltage is decrease orincrease beyond the specified limit. So, further investigationand more research and development are needed for thisarrangement to get better output and performance. Somefuture works are recommended: designing output and inputfilter properly to minimize ripple and harmonics, formula
(a)
(b)
(c)Figure 9: Input- Output waveforms (AC Cûk feedback contr
when input Voltage: (a) 250V (b) 300V (c) 315V and respeoutput
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(procedure) considering the right choice of passive elements(instead of random choice), developing feedback controlcircuit properly as per output requirements, considering thelosses of passive elements and switches, formulating thenon-ideal cases, proper selection of switching frequency,considering variety of loads (resistive, inductive, capacitiveor any combination), considering limitation on load changes,
performance analysis and comparison of efficiency, totalharmonics distortion (THD) and compare with differentstandards like IEEE-519 and IEC 1000-3.[
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[8] M. H. Rashid," Power Electronics – Circuits, Devices, and Applications ," Prenctice Hall Englewood Cliffs, Second Edition, 1993, pp.317-387.
[9] Slobodan C û k ,"Basics of Switched Mode Power ConversionTopologies, Magnetics, and Control, ” Modern Power Electronics:Evaluation, Technology, and applications, Edited by B.K. Bose, IEEEPress, 1992, pp.265-296.
[10] Slobodan M. Cûk , " Modelling, Analysis and Design of SwitchingConverter ," Ph.D Thesis, California Institute of Technology,Pasadena, California, 1977 (November 29, 1976) .
Figure 10. Input current waveform of AC Buck-Boost converter
Figure 11: Input current waveform of AC Cûk converter
Figure 12: Output current waveform of AC Buck-Boost converter
Figure 13: Output current waveform of AC Cûk converter