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NON-Microcomputer Ultra Capacitor Charging System

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J. L. Tang
J. L. Tang
J. L. Tang
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S. Q. Shao
S. Q. Shao
S. Q. Shao
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T. T. Sun
T. T. Sun
T. T. Sun
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NON-Microcomputer Ultra Capacitor Charging System
J. L. Tang1, S. Q. Shao1 and T. T. Sun1
1College of Electrical and Information Engineering ,Southwest Minzu University, Chengdu,
Sichuan 610041, China
Keywords: Ultra capacitor. NON-microcomputer. CCLV. CVLC.
Abstract. The conventional ultra capacitor charger uses computer to monitor the ultra capacitor’s
state of charge(SOC) and adopts different strategy to charge the ultra capacitor. It makes the
system expensive and the control method is also inconvenient. For the above problems, a
non-microcomputer ultra capacitor charging system is designed. The proposed system can achieve
two-step charging modes, constant current limiting voltage(CCLV) mode and constant voltage
limiting current(CVLC) mode. Finally, the designed charging system is presented at the last of the
article.
Introduction
Renewable energy resources appear to be the one of the most efficient and effective solutions.
That is why there is an intimate connection between renewable energy and sustainable
development [1-2]. It is urgent to develop renewable energy and related materials. Ultra capacitor
is a kind of electrical energy storage device. The advantages of Ultra capacitor are high power
density, high efficiency, fast charging and discharging speed, long cycle life, wide operating
temperature range and environment friendly [3-4]. It has become an ideal option for high power
applications, such as hybrid power systems, regenerative energy systems and instantaneous backup
power source.
But charging condition of the ultra capacitor is restricted. The chargers are designed typically
around two modes of operation, namely, constant-voltage charging and constant-current charging.
The former utilizes a constant voltage source and an equivalent series resistance to control the
amount of current that flows into the battery. As soon as the battery voltage is raised to the voltage
sources, the converter must limit its current to prevent excessive dissipation. The latter, moreover,
keeps the charging current constant until the battery voltage reaches a designated value[5-7]. But it
adopts microcomputer to detect the ultra capacitor’s SOC that makes the charger expensive and
inconvenient. So we design a simple charger.
In section II, the ultra-capacitor’s characteristic is described. In section III introduces the
designed charging system and the principle of the charging system. Section IV shows the
simulation results. Finally, conclusion is made at last.
The ultra capacitor and its charging characteristic introduction
Ultra capacitor is a high-capacity capacitor with capacitance values much higher than other
capacitors, but lower voltage limits. It bridges the gap between electrolytic capacitors and
rechargeable batteries and stores 10 to 100 times more energy per unit volume or mass than
electrolytic capacitors. The ultra-capacitor can charge and discharge much faster than batteries, and
tolerate many more charge and discharge cycles than rechargeable batteries.
Constant voltage charging is also called as constant potential charging used to maintain the same
voltage input to the ultra capacitor throughout the charging process, regardless of the ultra
capacitor’s state of charge. Constant voltage charging provides a high inrush current to the ultra
capacitor because of the higher potential difference between ultra capacitor and charger. The
charging curve is shown in figure. 1, a.
Constant current charging supplies a relatively constant current, regardless of the ultra
capacitor’s temperature and state of charge. The charging curve is shown in figure. 1, b.
Copyright © 2017, the Authors. Published by Atlantis Press.
This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
601
Advances in Engineering Research (AER), volume 135
2nd International Conference on Civil, Transportation and Environmental Engineering (ICCTE 2017)
a. Constant voltage charging b. Constant current charging
Figure. 1, Ultra capacitor charging curve
The ultra capacitor charging system
We utilize the buck circuit to charging the ultra-capacitor as shown in figure 2 and by
controlling the pulse width of the PWM signal , it can achieve CCLV and CVLC two charging
modes under different SOC condition.
Figure. 2, Ultra capacitor charging circuit
The controlling circuit is shown in figure. 3, ccV is a certain value. According to the
characteristics of the operational amplifier, if CFVF
≠
, one of the amplifier will work at
amplification state and the other will work at negative saturation state. So by changing the value of
VF and CF, the charging circuit can work at constant current state or constant voltage state.
Figure. 3, The control circuit of ultra capacitor charger
The CVLC controlling process is as follow:
①VFUCF
=
<
set ：the error amp1 works and the error amp2 doesn’t work, the system works in
constant voltage mode.
②VFUCF
=
=
set ：when the current feedback increases to the setting value, the error amp1 and the
error amp2 work together and the system works at the constant voltage and constant current mode.
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Advances in Engineering Research (AER), volume 135
③set
UCF
>
：if the load current continues increasing, the error amp2 works and the error amp1
doesn’t work. The system works at limiting current mode. As the voltage of the super capacitor
rises, the VF increases to the setting value and then the system works at constant voltage mode.
The CCLV controlling process is as follow:
①CFUVF
=
<
set ：the error amp2 works and the error amp1 doesn’t work, the system works in
constant current mode.
②CFUVF
=
=
set : when the voltage feedback increases to the set value, the error amp1 and the
error amp2 work together and the system works at the critical constant current mode.
③set
UVF
>
: when the voltage sample exceeds the set-value, the error amp1 works and the error
amp2 doesn’t work. The system works at limiting voltage mode. And the load current increases
until the current sample reaching to the setting value, then the controller will work at constant
voltage mode.
The current sampling circuit is shown in figure. 4. Port in- and port in+ connect to sampling
resistor.
Figure. 4, the current sampling circuit
We choose TL494 as the controlling chip. The system achieves two charging mode according
to the ultra capacitor’s SOC. The charging circuit is shown at figure, 5. In the figure, TG is CMOS
transfer gate and it is controlled by CCLV signal and CVLC signal. When TG1 and TG3 work
together, the system works at CCLV mode. When TG2 and TG4 work together, the system works
at CVLC mode.
Figure. 5, The realization circuit of ultra capacitor charging system
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Advances in Engineering Research (AER), volume 135
The ultra capacitor’s state of charge(SOC) detecting circuit is shown in figure. 6. Comparing
the instantaneous voltage of super capacitor and its rated voltage, digit selector produces CCLV or
CVLC signal.
Figure. 6, The ultra capacitor SOC detecting circuit
The ultra capacitor charging system
The simulation model is implemented in saber sketch. The capacity of the UC is 1400F, the
rated voltage is 2.5V, the initial voltage is 0 and the number of ultra capacitor in series is 1. The
power source and the simulation result are shown in figure. 7.
a, power source
b,charging current c, UC voltage
Figure. 7, The simulation result: c, power source. a, charging current. b, UC voltage
Conclusions
A non-microcomputer ultra capacitor charging system is designed. The control principle and
the control circuit are also presented. It can charge the ultra capacitor in two modes and achieves
two-step charging without microcomputer. Compared to traditional ultra capacitor charger, the cost
of the system is cheaper.
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Advances in Engineering Research (AER), volume 135
Acknowledgements
This work was financially supported by the Fundamental Research Funds for the Central Univ
ersities(2015NZYQN08), Sichuan Provincial Department of Education Project(No.15ZA0391)
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