This document analyzes and designs an LCL resonant converter as a constant current source for capacitor charging applications. It proposes the LCL resonant converter topology, analyzes its operation mathematically, simulates its performance, and discusses the design process. The key findings are that the LCL resonant converter can provide a load-independent output current and behave as a true constant current source for capacitor charging when certain design parameters are met. Simulation results confirm the converter's ability to smoothly charge a capacitor with a constant output current.

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IJECET
© I A E M E
ANALYSIS AND DESIGN RESONANT CONVERTER AS CONSTANT
CURRENT SOURCE FOR CAPACITOR CHARGING
Elmokhtar. A. Elhamruni*, Dr. A. K. Bhardwaj**
*Research Scholar, Department of ECE, Sam Higgin Bottom Institute of Agriculture, Technology
Sciences Deemed University Allahabad, (India
**Department of EE, Sam Higgin Bottom Institute of Agriculture, Technology Sciences Deemed
University Allahabad, (India)
ABSTRACT
In the past, resonant converters have generally been analyzed and characterized for constant
output voltage power supplies. When applied to power supplies, in which output current is regulated,
the topological requirements of a resonant converter differ. This means, a resonant converter
topology not suitable for constant voltage power supplies may become attractive for constant current
power supplies. This paper proposed analysis, simulation and design LCL resonant converter as
constant current for charging applications.
Keywords: Resonance, dc-dc Converters, Constant Current Power Supply, Capacitor Charging.
1- INTRODUCTION
The Resonant Concept
Like switch mode dc-to-dc converter, resonant converters are used to convert dc-to-dc
through an additional conversion stage: the resonant stage in which dc signal is converted to high
frequency ac signal [1, 2 3].
The potential advantage of resonant converter include the natural commutation of power
switches, resulting in low switching power dissipation and reduced component stresses, which in
turns results in increased power efficiency and increased switching frequency; higher operating
frequencies results in reduced size and weight of equipment and results in faster responses; possible
reduction in EMI problems[7, 8 9].Since the size and weight of the magnetic components
(inductors and switching frequency, many power converters have been designed at progressively
higher frequencies in order to reduce excessive size and weight and obtain fast converter transients[2
6]. In recent years, the market demand for wide applications that need variable speed drives,

2. International Journal of Electronics and Communication Engineering Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 7, July (2014), pp. 25-31 © IAEME
highly regulated power supplies, uninterruptible power supplies, and the desire to have smaller size
and lighter weight power electronics systems has been increased [4],[5].
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2- PROPOSED MODEL AND ANALYSIS
The circuit diagram for the proposed converter is shown in fig 1.
Fig 1: Proposed Converter
The circuit consists of inverter to convert DC to high frequency AC, LCL acts as resonant
tank and convert voltage to current through L2 then the output is rectified, filterd and then charge the
load capacitor.
The output voltage of the inverter is square wave and the current is sinusoidal wave to
simplify the analysis fundamental ac analysis method is used.
Rac =8Zl /2 n2, Vin r.m.s = 22 Vd/
The resonant frequency and normalized switching frequency are:
W0=, l1c1 wn = w / w0
The characteristic impedance (ZN ) is
Zn = l1/C1
The Qality factor ( Q) is
Q = n2 w0 l1/Zl = n2 Zn /zl
The ratio L1/L2 = .
The voltage gain M = nVO /Vd
The current gain H = nIO Zn / vd

3. International Journal of Electronics and Communication Engineering Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 7, July (2014), pp. 25-31 © IAEME
Then the voltage and current gain of the converter are:
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M=

4. H=

5. When wn = 1
Hwn=1 =
Then the expressions for normalized rms current through l1,l2,C1 and the voltages across them
are derived as shown below
Il1N =

6. .....................(1)
Il2N=

7. Ic1N =

8. Vl1N =

9. Vl2N =

10. Vc1N =

11. When = 1 (1) can be simplified as
Il1N =

12. And the phase angle between vin and il1 is:
!#=1 = tan-1 $

13. %
When Ø = 0 then # and =1 and l1 =l2 then the converter acts as constant output current source.

14. International Journal of Electronics and Communication Engineering Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 7, July (2014), pp. 25-31 © IAEME
The plot of H and Ø for different values of Q and g=1 are shown in fig2a, fig2b.
The plots of Fig. 3.2(b) show the variation of Ø as a function of n for different values of Q
and for g=1. H is seen to be load independent at n =1 for all values of Q. It can also be noted that
f = 0 at n = 1 for all values of Q and the converter will operate as constant current source under
these conditions.
Fig2a Fig 2b
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3- DESIGN CONCEPT
The values of n and g assumed to be =1. As necessary condition for the converter to operate
as constant current source [10],and since the value of Q has effect on rating of reactive components
which increase the size of the converter and its value is chosen from the fig3 at Q = Qopt and the
rating of
is minimum, where
Fig 3: kva / kw

15. International Journal of Electronics and Communication Engineering Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 7, July (2014), pp. 25-31 © IAEME
Then select voltage source vd = 5V and IO =2A, RLmin = 0.5, fs = 100kHZ
the value of n is calculated from
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n= vd/Io Rlmin
l1 = l2 =
C1(filter) =
4- SIMULATION AND RESULTS
Simulink is used to simulate the converter as shown in fig 4 with components
Vd =5v ,IL1= IL2= 16.1μH, n=5, C1=0.157μF and Cload = 0.3mF
Fig 4: Simulation circuit
The Simulation results are shown in fig 5a, b, c, d, shows that the output current and voltage
of the inverter are in phase and the circuit behaves as constant current source, the transformer
leakage inductance is observed and the charging profile is smooth
Fig 5: a the voltages across switches Fig 5b: the output voltage of inverter

16. International Journal of Electronics and Communication Engineering Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 7, July (2014), pp. 25-31 © IAEME
Fig 5c: output voltage and current of inverter Fig 5d: output voltage
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5- CONCLUSION
Although analysis of resonant converter has been performed in great detail for voltage
regulator type of applications, a study of their suitability for CC power supply is not reported.
Aresonant converter topology not considered beneficial for a CV power supply may become suitable
for a CC power supply if it exhibits load-independent output current. In this paper, the designed
converter is shown to exhibit current source behavior under variable load condition. The load current
is independent of load resistance, if circuit is suitably designed with low value of Q. Most
importantly, the current source characteristics are exhibited in lagging power factor mode of
operation. This makes LCL converter an attractive topology for a CC power supply with simpler
control. Simulation results confirm the application of LCL converter in CC power supply.
6- REFERENCES
[1] A.C. Lippincott, R.M. Nelms, M. Garbi, and E. Strickland, “A series resonant converter with
constant on-time control for capacitor charging applications”, in Proc. of 5th Annual Conf.
and Exposition APEC '90, 1990, pp. 147–154.1990, Fifth Annual 11–16 March 1990,
pp. 147–154.
[2] R. P. Severns, Topologies for three-element resonant converters, IEEE Trans. Power
Electron., 7, 89–98(1992).
[3] M. Swami and A. Bhat, Analysis of a parallel resonant converter with secondary side
resonance, IEEE Trans. Aero. Electr. Sys., 28, 1042–1055 (1992).
[4] I. Bataresh, Resonant converter topologies with three and four energy storage elements, IEEE
Trans. Power Electron., 9, 64–73 (1994).
[5] A. Bhat, Analysis and design of LCL-type series resonant converter, IEEE Trans. Ind.
Electron., 41, 118–124 (1994).
[6] M. Borage, S. Tiwari and S. Kotaiah, Comparison of three-element V-N-V resonant
converters, Proc. IndiaInt. Conf. on Power Electronics (IICPE), Mumbai, India (2002).
[7] Heqing Zhong, Zhixin Xu, Xudong Zou et al.,“Current Characteristic of High Voltage
Capacitor Charging Power Supply Using a Series Resonant Topology”, in Proc. of the 29th
Annual Conference of Industrial Electronics Society the, V. 1,2–6 Nov, 2003, pp. 373–377.
[8] M.M. McQuage, V.P. McDowell, F.E. Peterkin, and J.A. Pasour, “High Power Density
Capacitor Charging Power Supply Development for Repetitive Pulsed Power”, presented at
the Power Modulator Symp., 2006.

17. International Journal of Electronics and Communication Engineering Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 7, July (2014), pp. 25-31 © IAEME
[9] Y. S. Dow. et.alA Study on Half Bridge LLC Resonant Converter for Battery Charger on
Board, 8th International Conference on Power Electronics - ECCE Asia May 30-June 3,
2011, The Shilla Jeju, Korea.
[10] Mangesh Borage Resonant Converter Topologies for Constant-Current Power Supplies and
Their Applications Ph.D dissertation 2011.
[11] Mohamed HediChabchoub and HafedhTrabelsi, “DC-DC Converter for Ultracapacitor
Boosted Electric Vehicle”, International Journal of Advanced Research in Engineering
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ISSN Online: 0976-6499.
[12] P. Hari Krishna Prasad and Dr. M. Venu Gopal Rao, “DC-Dc Converters For Telecom Power
Supply Applications”, International Journal of Electrical Engineering Technology (IJEET),
Volume 3, Issue 1, 2012, pp. 156 - 166, ISSN Print: 0976-6545, ISSN Online: 0976-6553.
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BIOGRAPHY
Elmokhtar.A.Elhamruni received the BSC degree in communication Engg. from
higher institute of electronics, Beni Waled, Libya in 1989, MSC degree in the field
of electronics from Belgrade University ,Serbia in 2000. He is currently working
toward Ph.D degree at Sam Higginbottom Institute of Agriculture, Technology
Sciences (Formerly AAI-DU) Allahabad. His area of interests power electronics
and insturmentation.
Dr. A.K. Bhardwaj is working as “Associate Professor” in the Department of
Electrical Engg. Faculty of Engineering and Technology of Sam Higginbottom
Institute of Agriculture, Technology Sciences (Formerly AAI-DU) Allahabad,
India from last 9 years after obtaining M. Tech. degree from Indian Institute of
Technology Delhi, India in 2005. He has completed his Ph.D. degree from Sam
Higginbottom Institute of Agriculture, Technology Sciences (Formerly AAI-DU)
Allahabad, India in January 2011.
Earlier he was “Assistant Professor” in department of Electrical and Electronics Engineering,
IMS Engineering College Ghaziabad (U.P.) India in the year 2005. He also worked for 6 years as
faculty with IIT Ghaziabad (U.P.) India.
He is also having practical experience with top class multinational companies during
1985-1998. He has published several research Papers in the field of Electrical engineering as well as
energy management. His research interest includes, power management, energy management,
reactive power control in electrical distribution system.