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ARTICLE
Year : 2011  |  Volume : 1  |  Issue : 1  |  Page : 37-42

Performance Analysis of Symmetric Multistage Voltage Multipliers


1 Department of Electrical and Electronics Engineering, Hirasugar Institute of Technology, Nidasoshi - 591 236, India
2 Department of Computer Science and Engineering, Hirasugar Institute of Technology, Nidasoshi - 591 236, India

Date of Web Publication4-Jan-2011

Correspondence Address:
H R Zinage
Department of Electrical and Electronics Engineering, Hirasugar Institute of Technology, Nidasoshi - 591 236
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0976-8580.74555

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   Abstract 

A performance study of a 3-phase symmetric Cockcroft-Walton (CW)-multistage voltage multiplier (VM) is proposed. It consists of 1 smoothing column and 6 oscillating columns. The oscillating columns are connected to a 3-phase power through center-tap transformers. The capacitors of the smoothing column are charged 6 times per cycle by 6 oscillating columns and are discharged 6 times through the load, unlike the conventional symmetric VM in which they are charged and discharged twice per cycle. The 3-phase symmetric structure completely eliminates the first 5 harmonic components of load-generated voltage ripple. Theoretic analysis indicates that the proposed 3-phase symmetric CW-VM has one-third the voltage ripple and voltage drop of the conventional single-phase symmetric CW-VM. Simulation results of the proposed 3-phase symmetric CW-VM as well as those of the conventional single-phase symmetric CW-VM are presented. A comparison shows that the 3-phase symmetric CW-VM has significantly less voltage ripple, half the voltage drop, and a 4-fold increase in the output power over the conventional single-phase symmetric CW-VM.

Keywords: Oscillating column, symmetric structure, three-phase voltage multiplier, voltage ripple


How to cite this article:
Zinage H R, Gollagi S G. Performance Analysis of Symmetric Multistage Voltage Multipliers. J Eng Technol 2011;1:37-42

How to cite this URL:
Zinage H R, Gollagi S G. Performance Analysis of Symmetric Multistage Voltage Multipliers. J Eng Technol [serial online] 2011 [cited 2019 Aug 24];1:37-42. Available from: http://www.onlinejet.net/text.asp?2011/1/1/37/74555


   1. Introduction Top


Although Cockcroft-Walton voltage multiplier (CW-VM) circuit was developed long time ago in 1932, it is still widely used in many high-voltage low-current applications, such as lasers, accelerators, ultra-high-voltage electron microscopes, and X-ray power generators [1] . The original CW-VM circuit was of half-wave (asymmetric) type and it has large output voltage ripple and voltage drop. A number of modifications of the original CW-VM circuit have been proposed and applied to reduce steady state voltage drop and voltage ripple [2] . However, the circuit asymmetry, especially the asymmetry of the driving voltage may deteriorate the cancellation effect and give rise to the generation of fundamental and higher order odd harmonic of ripple. The fundamental harmonic of ripples increases with the increase in the asymmetry of driving voltage and in the case of low load current it may dominate over the second harmonic. This is due to the reason that at lower load current the peak-to-peak value of load-generated second harmonic of ripples would be smaller than the fundamental harmonic. The fundamental harmonic component was found to be dominant in some lower load current applications, such as some electron microscopes and accelerators. Similarly the fundamental harmonics also affects the quality of output laser beam of continuous wave carbon dioxide gas laser [1],[2],[3] . Some applications, such as ultra-high-voltage electron microscopes, require high stability of the high DC voltage. Such stability is difficult to achieve directly by the single-phase asymmetrical CW-VM [4],[5] . To overcome the problem of asymmetry of driving voltage and to get output voltage free from fundamental and higher order odd harmonics, we have proposed symmetrical CW-VM [6] . The proposed CW-VM has an intrinsic ability to cancel the fundamental and odd harmonic of ripples caused by the driving voltage. In addition to this the proposed voltage multiplier has many advantages over the original CW-VM circuit which is of half-wave (asymmetric) type. These include smaller size, light weight, less component counts, easier implementation, faster transient response, and smaller voltage drop.

A symmetrical CW-VM, which is an improved form of original CW-VM, is presently more popular and is widely used in most of the above-mentioned application [7] . It has significantly smaller output voltage ripple and voltage drop as compared to original CW-VM [8],[9] . This is because the symmetrical structure of symmetrical CW-VM cancels out the fundamental harmonic of ripples caused by driving voltage and stray capacitance [10] . Thus the load-generated second order harmonic is the major ripple component in the DC output of the symmetric CW-VM. The second and higher order even harmonics of ripples are proportional to load current and can be minimized by choosing larger size of smoothing column capacitors [11],[12] .

A 3-phase symmetric CW-VM is proposed to improve the stability of the output voltage. The proposed 3-phase VM consists of 1 smoothing column and 6 oscillating columns. The charging and discharging of the smoothing column's capacitors completes six times a cycle as compared with the conventional single-phase symmetrical CW-CM in which the capacitors are charged and discharged twice per cycle [5] . The proposed 3-phase symmetric CW-VM has been shown to have a much better performance than the conventional single-phase symmetric voltage multiplier. It has significantly less voltage ripple, half the voltage drop and approximately a four-fold increase in power output over a conventional symmetrical CW-VM [13],[14] Simulation results are presented to verify the effectiveness of the proposed 3-phase symmetric CW-VM.


   2. Circuit Description and Principle of Operation Top


[Figure 1] shows a 3-phase symmetric CW-VM circuit, which consists of 6 oscillating (AC) columns and one smoothing column. Phase a is V a (V′a , V′′a ): (C 1a′, C 2a′ -------------- C na′) and (C 1a′′, C 2a′′ -------------- C na′′); Phase b is V b (V b′, V b′′): (C 1b′, C 2b′ -------------- C nb′) and (C 1b′′, C 2b′′ -------------- C nb′′); Phase c is V c (V′c ,V′′c ): (C 1c′, C 2c′ -------------- C nc′) and (C 1c′′, C 2c′′ -------------- C nc′′). Smoothing column (C 1 , C 2 , --------C n ) is common to all the oscillating columns. Phase a is connected to AC voltage source V a = V a (t) = V1sinwt; Phase b to V b = V b (t) = V2sin(wt-120); and Phase c to V c = V c (t)=V 3 sin(wt-240); through high-frequency center-tap transformers T 1 , T 2 , and T 3 , respectively. If R L = ∞, the capacitors of the smoothing column remain fully charged and none of the rectifiers conducts. However, if RL≠ ∞, then the capacitors of the smoothing column discharge due to load current and are recharged to peak value by the oscillating columns. Each of the 6 oscillating columns charges the smoothing column to peak value once in every cycle (ie, each phase charges the smoothing column twice every cycle).
Figure 1: Proposed n-stage 3-phase symmetric Cockcroft– Walton voltage multiplier

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[Figure 2] shows the 6 charging intervals t 1 -t 6 and 6 discharging intervals t d1 -t d6 in each complete cycle. Capacitors of the smoothing column charge to peak value 6 times every cycle through the oscillating columns and discharge through the load. There are 6 different charging modes. In each mode the smoothing column is connected to only 1 phase, and the other 2 are disconnected by the reverse biasing of the respective diodes. These 6 charging modes are presented here.
Figure 2: Key waveforms of 3-phase symmetric voltage multiplier in steady state operation

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2.1 Modes of Operation

0A. Mode 1 ( t 1 )

Voltage V′′b (t) approaches positive peak value, while voltage V′b (t) approaches negative peak value. The capacitors of oscillating column (C 1b″, C 2b′′ -------------- C nb′′) transfer charge through diodes (D 1b′, D 2b′ -------------- D nb′) and (D 1b″″, D 2b″″ -------------- D nb″″) to the oscillating column capacitors (C 1b′, C 2b′ -------------- C nb′) and the smoothing column capacitors, respectively.

B. Mode 2 ( t 2 )

Voltages V′a (t) and V′′a (t) approach positive and negative peak values, respectively. Oscillating column capacitors (C 1a′, C 2a′ -------------- C na′) transfer charge to oscillating column (C 1a′′, C 2a′′ -------------- C na′′) and to smoothing column (C 1 , C 2 , -------- C n ) through diodes (D 1a′′, D 2a′′ -------------- D na′′) and (D 1a′′′, D 2a′′′ … D na′′′), respectively.

C. Mode 3 ( t 3 )

Voltages V′′c (t) and V′c (t) approach positive and negative peak values, respectively. During this mode the charging current flows from oscillating column (C 1c′′¬, C 2c′′… C nc′′) to oscillating column (C 1c′¬, C 2c′ -… C nc′) and to smoothing column (C 1 , C 2 …C n ), through diodes (D 1c′¬, D 2c′… D nc′) and (D 1c′′′′,D 2c′′′′…D nc′′′′) respectively.

D. Mode 4 ( t 4 )

Voltages V′b (t) and V′′b (t) approach positive and negative peak values, respectively. Charging current flows from oscillating column to (C 1b′, C 2b′ -------------- C nb′) oscillating column (C 1b′′ , C 2b′′ -------------- C nb′′) and to smoothing column (C 1 , C 2 , --------C n ), through diodes (D 1b′′′ , D 2b′′′-------------- D nb′′′) and (D 1b′′, D 2b′′ -------------- D nb′′) respectively.

E. Mode 5 ( t 5 )

Voltages V′′a (t) and V′a (t) approach positive and negative peak values respectively. Charging current flows from oscillating column (C 1a′′, C 2a′′ -------------- C na′′) to oscillating column (C 1a′, C 2a′ -------------- C na′) and to smoothing column (C1, C2,-------Cn), through diodes (D 1a′, D 2a′,--------, D na′) and (D 1a′′′′, D 2a′′′′-------------- D na′′′′), respectively.

F. Mode 6 ( t 6 )

Voltages V′c (t) and V′′c (t) approach positive and negative peak values, respectively. Charging current flows from oscillating column (C 1c′, C 2c′-------------- C nc′) to oscillating column (C 1c′′ , C 2c′′ -------------- C nc′′) and to smoothing column ( C 1 ,C 2 ,--------C n ) through diodes (D 1c′′ , D 2c′′ -------------- D nc′′) and (D 1c′′′, D 2c′′′-------------- D nc′′′), respectively.

Here simulation results are presented to verify the effectiveness of the proposed 3-phase symmetric CW-VM [Figure 3],[Figure 4],[Figure 5],[Figure 6],[Figure 7],[Figure 8],[Figure 9],[Figure 10],[Figure 11],[Figure 12]. The performance of the proposed single- and 3-phase CW-VMs are evaluated on the basis of computer simulation/SIMULINK. The 3-phase AC voltage can be obtained by connecting 3 single-phase high-frequency, high-voltage sources in parallel and delaying input signals by 120 with respect to each other. Following are the specifications of the simulation circuits. The frequency of the 3-phase driving voltage (ie, V a , V b , V c ) is 17 kHz; 10 nF capacitors are used in the VM circuits; the turns ratio of the center-tap transformers is 1:1:1; the magnitude of input voltages V′a , V′′a , V′b , V′′b , and V′c , V′′c are 5 kV for the simulation circuits with resistive load of 10 kΩ.
Figure 3: Input voltage waveform of Single-phase symmetric voltage multiplier (Magnitude of input voltage = 5 kV)

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Figure 4: Simulated output voltage waveform of Single-phase symmetric voltage multiplier

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Figure 5: Simulated output current waveform of Single-phase symmetric voltage multiplier

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Figure 6: Simulated voltage waveforms (ripple content in the output voltage) of Single-phase symmetric voltage multiplier

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Figure 7: Simulated current waveform (ripple content in the output current) of Single-phase symmetric voltage multiplier

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Figure 8: Input voltage waveform of 3-phase symmetric voltage multiplier (Magnitude of input voltages = 5 kV)

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Figure 9: Simulated output voltage waveform of 3-phase symmetric voltage multiplier

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Figure 10: Simulated output current waveform of 3-phase symmetric voltage multiplier

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Figure 11: Simulated voltage waveform (Ripple content in the output voltage) of 3-phase symmetric voltage multiplier

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Figure 12: Simulated current waveforms (Ripple content in the output current) of 3-phase symmetric voltage multiplier

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[Table 1] and [Table 2] compare the output voltage, output current, voltage ripple, current ripple, and Total Harmonic Distortion (THD) of the symmetric 3-phase, 3-stage CW-VM with the corresponding values for the symmetric single-phase, 3-stage CW-VM with an ideal voltage source, that is, R = 0 and L = 0. The comparison results show that for given 5 kV, 17 kHz input supply, the output voltage and output current of 3-phase voltage multiplier is higher than that of a single-phase voltage multiplier. The ripple content in the output voltage and current of a 3-phase voltage multiplier is nearly one-third of that of a single-phase voltage multiplier. The THD of the symmetric 3-phase voltage multiplier is also less than that of a single-phase voltage multiplier. Hence the proposed 3-phase symmetric CW-VM has been shown to have much better performance than the single-phase symmetric voltage multiplier.

[Table 3] and [Table 4] compare the output voltage, output current, voltage ripple, current ripple, and THD of the symmetric 3-phase, 3-stage CW-VM with the corresponding values for the symmetric single-phase, 3-stage CW-VM multiplier with practical voltage source, that is, R = 0 and L = 1 mH. The comparison results show that for given 5 kV, 17 kHz input supply, output voltage and output current of 3-phase voltage multiplier is higher than that of a single-phase voltage multiplier. The ripple content in the output voltage and current of 3-phase voltage multiplier is significantly less than that of a single-phase voltage multiplier. The THD of the symmetric 3-phase voltage multiplier is also less than that of a single-phase voltage multiplier. Hence it is clear from the simulation results that the 3-phase VM has twice the output voltage and considerably less ripple than the single-phase VM. Thus the output power of the 3-phase VM is approximately 4 times larger than the single-phase voltage multiplier (as P = V2 /R). Simulated input voltage, load voltage, and load current waveforms in steady state for both 3-phase and single-phase symmetric VMs are also obtained for different stages. The 3-phase VM load current ripple's frequency is of the sixth order of the drive signal frequency, thereby proving that the charging and discharging process of the smoothing column completes 6 times in a drive signal cycle. Thus the sixth harmonic is the most significant ripple component, and the first 5 harmonics are canceled by the 3-phase symmetric structure of the voltage multiplier.
Table 1: Comparison between single- and 3-phase symmetric voltage multiplier circuit with 5 kV, 17 kHz input supply and 10 kÙ load resistance for 3 stages (fed by an ideal voltage source, i.e. R = 0 and L = 0)

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Table 2: Comparison between single- and 3-phase symmetric voltage Multiplier circuit with 5 kV, 17 kHz input supply and 10 kÙ load resistance for 2 stages (fed by an ideal voltage source i.e. R = 0 and L = 0)

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Table 3: Comparison between single- and 3-phase Symmetric voltage Multiplier circuit with 5 kV, 17 kHz input supply and 10 kÙ load resistance for 3 stages (With Associated voltage source inductance i.e. R = 0 and L = 1 mH)

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Table 4: Comparison between single-phase and 3-phase symmetric voltage multiplier circuit with 5 kV, 17 kHz input supply, and 10 kÙ load resistance for 2 stages (with associated voltage source inductance = 0 and L = 1 mH)

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   4. Conclusion Top


A 3-phase symmetric CW-VM is proposed to improve the stability of the output voltage. The proposed 3-phase symmetric CW-VM has been shown to have much better performance than the conventional single-phase symmetric voltage multiplier. It has significantly less voltage ripple, half the voltage drop, and approximately a 4-fold increase in power output over a conventional symmetric CW-VM. Simulation results of the proposed 3-phase symmetric CW-VM as well as of the conventional single-phase symmetric CW-VM are presented with and without source inductance.

 
   References Top

1.S. Iqbal, "A three-phase symmetrical multistage voltage multiplier," IEEE Power Electron, Lett, vol. 3, no. 1, pp: 30-33, Mar, 2005.  Back to cited text no. 1
    
2.S. Malesani, and R. Piovan, "Theoretical performance of the capacitor diode voltage multiplier fed by a current source," IEEE Trans. Power Electron., vol. 8, pp. 147-155, Apr. 1993.   Back to cited text no. 2
    
3.E. Kuffel, and M. Abdullah, "High Voltage Engineering," Oxford: Pergamon Press; 1984.   Back to cited text no. 3
    
4.M. D. Bellar, E. H. Watanabe, and A. C. Mesquita, "Analysis of the dynamic and steady-state performance of Cockcroft-Walton cascade rectifier," IEEE Trans. Power Electron, vol. 7, pp. 526-534, Jul, 1992.   Back to cited text no. 4
    
5.M. D. Bellar, E. H. Watanabe, and A. C. Mesquita, "Analysis of the dynamic and steady-state performance of Cockcroft-Walton cascade rectifier," IEEE Trans. Power Electron, vol. 7, pp. 477-484, Jul, 1990.   Back to cited text no. 5
    
6.P. M. Lin, and L. O. Chua, "Topological generation and analysis of voltage multiplier circuits," IEEE Trans. Circuits Syst, vol. CAS-24, no. 10, pp. 517-530, Oct, 1977.   Back to cited text no. 6
    
7.M. S. Naidu, and V. Kamaraju, "High Voltage Engineering," 3rd ed, New York: McGraw-Hill Company Ltd; 2004.   Back to cited text no. 7
    
8.N. Marium, D. Ismail, K. Anayet, N. Khan, and M. Amran, "Simulation, Design and Construction of High Voltage DC Power Supply at 15 kV Output Using Voltage Multiplier Circuits," American Journal of Applied Sciences, vol. 3, pp. 2178-2183, 2006.   Back to cited text no. 8
    
9.K. Sur, and E. Bloodworth,"Automated topological generation and analysis of voltage multiplier circuits," IEEE Trans. Circuits Syst., vol. 37, no. 3, pp. 432-436, Mar, 1990.   Back to cited text no. 9
    
10.J. S. Brugler, "Theoretical performance of voltage multiplier circuits," IEEE J. Solid-State Circuits, vol. SC-6, pp. 132-135, 1971.   Back to cited text no. 10
    
11.Vishay Semiconductors application note," Using Rectifiers in Voltage Multiplier circuits," Document number 88842, Jul, 2002.   Back to cited text no. 11
    
12.H. Zhang, A. Takaoka, and K. Ura, "A Numerical analysis Approach to Cockcroft-Walton circuit in Electron Microscope", Journal of Electronic Microscope, Vol. 43 No. 1, pp. 25-31, 1994.   Back to cited text no. 12
    
13.S. Ray, "An Introduction to High Voltage Engineering," Oxford: Pergamon Press; 1984.   Back to cited text no. 13
    
14.S. Iqbal, "A bipolar Cockcroft-Walton voltage multiplier for gas lasers," American journal of applied sciences, vol. 4, pp. 795-801, 2007.   Back to cited text no. 14
    

 
   Authors Top


Prof (Mrs). H. R. Zinage obtained her BE (E and EE) and M.Tech. (Power systems) from Karnataka University, Dharawad, and Shivaji University, Kolhapur, INDIA, respectively. She is life member of ISTE. She is presently working as a Senior Lecturer in Electrical and Electronics Engineering department. Her research interests include AI applications to Power systems and Electrical Harmonics. She has published 2 papers in International Journals and 3 papers in Conferences.




Prof. S. G. Gollagi obtained his BE (CSE) and M.Tech. (Computer Engineering) from Karnataka University, Dharawad, and University of Pune, INDIA, respectively. He is life member of ISTE. He is presently working in HIRASUGAR INSTITUTE OF TECHNOLOGY, NIDASOSHI, INDIA, as Assistant Professor. His research interest includes Security in Wireless Network, AI application to power system, Algorithms, and Image processing. He has published 4 papers in International Journals and 5 papers in Conferences.


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]


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