National Conference on Recent Trends in Engineering & Technology
AC to AC Voltage Controller Using PWM Technique Without DC Link Y. B. Shukla1, S. K. Joshi2, R. J. Makwana3, A.A.Daiya4 2
1 E & C Engineering Department, SVIT, Vasad , e-mail :
[email protected] Department of Electrical Engineering, The M.S.University of Baroda, e-mail :
[email protected] 3 E & C Engineering Department, SVIT, Vasad , e-mail :
[email protected] 4 Associate Prof, Electronics Dept, BVM V.V.Nagar, e-mail:
[email protected]
Abstract—The power factor can be improved and more number of harmonics can be reduced using the pulse width modulation techniques of a voltage waveform. This paper discusses various PWM techniques on the AC/AC voltage controller without DC link. The paper also discusses two configurations of PWM technique for harmonics reduction and improvement of power factor and output voltage. Fast switching device, PWM techniques can be applied to AC/AC voltage controllers for producing variable output voltage with a better input Power Factor. The theoretical results are validated through simulation studies using PSIM software package.
harmonics can be reduced by selecting the number of pulses per cycle.. II.
PRINCIPLE OF OPERATION AND PROBLEM FORMULATION
Figure 1 shows the circuit configuration of PWM AC to AC voltage converter, which is composed of two bidirectional power switches, one connected in series and the other in parallel with load, the series connected switches S1 & S2 regulate the power delivered to the load and the parallel S1' & S2 ' provide a freewheeling path to discharge the stored energy
Keywords-AC to AC voltage converter; PWM; Harmonic; Pulse width control; Carrier frequency;
I.
INTRODUCTION
PWM AC to AC voltage controllers are widely used in UPS and high power flexible AC transmission systems. These systems need switching elements which can bear high voltage. [1-3] AC/AC line-commutated phase angle control or integral cycle control with thyristors technology have been widely used; however, this technique has many drawbacks such as, reduction of power factor at the input side, plentiful lower order harmonics in supplies, and discontinuity of power flow to the load sides.[4] The pulse width control using variable DC based method and the frequency control using carrier frequency based method can theoretically provide high quality output among all PWM methods with simple design approach.
when the series one turned off. The switches are assumed to have bi-directional voltage blocking ability as well as bidirectional current conduction and turn off capability. The present paper uses the switch configuration of inverse parallel connection of two convention IGBT's and two diodes, the two diodes prevent reverse voltage from appearing across switches. Figure 1.
Circuit Diagram of AC to AC Voltage Converter
In PWM control, the converter switches are turned on and off several times during a half cycle and the output voltage can be controlled by varying width of pulse. The lower order
13-14 May 2011
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National Conference on Recent Trends in Engineering & Technology
III.
OVERVIEW OF CONTROL STRATEGY
A. The pulse width control using variable DC method: The gating signals of S1' & S2 ' switches shown in Figure 2 can be controlled by DC reference based or control strategy and these signals are used to control S1 & S2 switching duration respectively. Figure 2.
Gate signal of AC to AC Voltage Converter
When a switching function shown in Figure 2 is applied to AC/AC voltage controller, the output voltage appears in PWM forms at the load terminals.
In this technique, as the reference DC signal vary, output voltage varies proportionally and reduction in harmonics. B. The frequency control using carrier frequency method: Varying the frequency of clock signal can control the no of pulses in gating signals of S1 & S2 switches shown in Figure 2. In this technique, when the no of pulses vary then harmonics are eliminated/reduced and obtained constant voltage. IV.
SIMULATION RESULTS
TABLE I.
SIMULATED CIRCUIT PARAMETERS
Parameter
Symbol
Value
Vm
110 Volt
Rated power
P
1.21 K Watt
Load resistance
R
100 ohm
Load inductance
L
6.1 mh
Maximum Supply Voltage
Figure 3.
Output Voltage Waveform
Fig. 3shows the idealized output voltage waveform from the AC/AC voltage controller. The general Fourier series expression expressed in terms of n switching points variables for the voltage is Where Bn = 0 for n = 1, 2, 3 ….... Due to half wave symmetry of waveform
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A. The pulse width control using variable DC method: Frequency of carrier signal= 250 Hz Simulation summaries of the output voltage and harmonic with DC reference are given in Table II. Figure 4, Figure 6 and Figure 5 shows output voltage with DC reference 1V, 10V and FFT of output voltage, respectively. TABLE II.
VARIATIONS OF OUTPUT VOLTAGE AND HARMONIC WITH DC REFERENCE
Sr. DC Reference No. (Volts)
Output voltage (Volts)
Harmonic Voltage (Volts) I ST
III RD
V TH
1
1
2.08
28.3
6.6
22.4
2
4
2.08
28.3
6.6
22.4
3
6
2.08
28.3
6.6
22.4
4
8
1.8
25.5
2.9
21.3
5
10
1
15.3
3.53
9.75
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology Simulation summaries of the output voltage and harmonic with DC reference are given in Table III . Fig. \ref{fig.7}, Fig.\ref{fig.9}, Fig.\ref{fig.8}and Fig. \ref{fig10}shows output voltage for carrier frequency 150Hz, 450Hz and FFT of output voltage, respectively. TABLE III.
VARIATIONS OF OUTPUT VOLTAGE AND HARMONIC WITH CARRIER FREQUENCY
Figure 4.
Figure 5.
Figure 6.
B.
Output voltage for input DC reference=1 volt
FFT of output voltage with DC reference =1 volt
Sr. No.
Variable Carrier Freq. (Hz)
Output voltage (Volts)
1
150
2
250
3
Harmonic Voltage (Volts) I ST
III RD
V TH
2.08
33.5
21.2
7.6
2.08
28.4
6.6
22.4
350
2.08
27.8
1.19
6.55
4
450
2.08
27.6
0.46
1.16
5
550
2.08
27.1
0.68
0.56
Output voltage for input DC reference =10 volts
The frequency control using carrier frequency method : Input DC reference = 1 volt
Figure 7. Figure 8.
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Output voltage for carrier frequency= 150Hz FFT of output voltage with carrier frequency =150 Hz
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology V.
Figure 9.
Output voltage for carrier frequency= 450Hz
CONCLUSION
The theoretical PWM pattern is found by solving the non linear harmonic equation which described suggested PWM method. The new pattern proposed in this paper has the features of harmonic reduction up to the specified order as well as linear voltage control and requires low orders pulse number. With the proposed pulse width control using DC ref. method, reduction of desired harmonics are attainable and output voltage can be controllable. While with Frequency control using carrier frequency method, reduction of harmonics are attainable and output voltage can be constant. In this method harmonics reduction are more compare to the pulse width control using DC ref. method. The Feasibility and effectiveness of the proposed algorithm is evaluated with intensive simulation studies. Further work should focus on practical real-time implementation of the PWM AC/AC voltage controller. REFERENCES [1]
[2] [3]
Figure 10.
FFT of output voltage with carrier frequency =450 Hz
[4]
[5]
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M. Marzzuccheli, “ Multilevel Converter for high power AC Drives: A Review”, Presented at IEEE International Symposium on Industrial Electronics, ISIE'93, 1993. J. S. Lai and F. Z. Peng, “ Multilevel Converter -- A new Breed of Power Converters”, IEEE Trans. Ind Appl., Vol.32,pp. 509-517, 1996 H. Akagi, “The state-of-the Art of Power Electronics in Japan”, IEEE Trans. Power Electron, Vol. 13, pp 345-356, 1998 Y. Xiao, B. Wu, F. Dewinter, R. Sotudeh, “A Dual GTO Current Source Converter Topology with Sinusoidal inputs for high Power Applications”, Presented at Applied Power Electronics Conference and Exposition, 1997. M. H. Rashid, “Power Electronics: Circuits, Devices and Applications”, 3rd Ed., Upper Saddle River, New Jersy, Prentice- Hall,2005
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