Download A Multi-Mode Charging Circuit for Rechargeable Batteries

The 2005 International Power Electronics Conference
A Multi-Mode Charging Circuit for Rechargeable Batteries
Yao-Ching Hsieh*
Chi-Kang Wu**
Chin-Sien Moo**
To facilitate various battery charging profiles, a multi-mode charging circuit is proposed. This circuit provides not only
four fundamental charging functions, such as constant-voltage, constant-current, pulse current and reflex charging; but also
the multi-stage charging with hybrid charging modes. The desired charging profile can easily be accomplished by selection of
the software control programs. A digital signal processor (DSP) with the associated interface circuits are used as the control
kernel. An experimental circuit was built and tested. Experimental results show that the circuit is able to execute the charging
functions of various tentative charging strategies with hybrid charging modes.
Keyword : multi-stage charging, hybrid charging modes, rechargeable battery
listed
1. Introduction
(8)
« etc; however, pulse or reflex charging has never
been above. On the other hand, there are many proposed
Many kinds of portable electronic devices are getting
multi-stage charging strategies, such as CC-CV, or CV-CV
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mobile phones or even (hybrid) electric vehicles. Since
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reasonable to adopt rechargeable batteries as power source
of these applications. However, there are still a lot of
obstacles that hinder the applications of rechargeable
batteries, such as low capacity, low power density, long
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be revolutionarily improved, charging technology will be an
important topic for research. Besides reducing charging
time, the usable capacity after charging and impact on cycle
life should also be taken into account. Therefore, there are
several aspects of considerations for charging batteries.
Although there are several frequently mentioned
charging
modes,
such
as
constant-current (CC)
(1)
reflex charging (RX)
(5) (6) (7)
constant-voltage
, pulse charging (PS)
(CV),
(2) (3) (4)
, and
, it is not clearly identified
which charging mode is the best among the considerations
*
**
considered into multi-stage charging strategies.
In this paper, a DSP-based charging circuit able to
implement several charging modes is proposed. This circuit
can easily implement four different charging modes, that is,
constant-voltage, constant-current, pulse charging, and
reflex charging. In addition to carrying out each charging
mode alone, the controller can also be programmed to
perform multi-stage charging with combinational modes.
The charging scenario can be customized by the researchers,
such as which charging modes to be adopted, the mode
transition points, or the charging intensities. This circuit can
serve as a good facility for the subsequent research on
charging strategies. A testing circuit was built in laboratory
to carry out the basic charging modes and to verify the
feasibility of this circuit configuration. Besides, two
multi-stage multi-mode charging experiments were
performed, and found out that this circuit can exactly
follow the commands to execute the desired charging mode
at correct charging energy and transit at the pre-defined
points.
2. Multi-mode charging circuit
Department of Electrical Engineering, Kao-Yuan Institute of
Technology, [email protected], 1821, Chung-Shan Rd.,
Lujhu, Kaohsiung County 821, Taiwan
Department of Electrical Engineering, National Sun Yat-sen
University, [email protected], 70, Lien-Hai Rd.,
Kaohsiung 804, Taiwan
Fig. 1 shows the circuit configuration of the proposed
multi-mode charging circuit. This circuit consists of three
parts, that is, energy supplying part, mode-managing part
and control unit. Energy supplying part is the unit to
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The 2005 International Power Electronics Conference
Mode managing part
CS2
D2
iCS2
LS
D3
Energy supplying part
C1
VS
Vrec
C2
Q A DA
D4
T1
QB DB
NS
C3
NS
NP
DSP
controller
Fig. 1
D1
CS1
iC S1
vgs
S1
B1
iB1
DS2
RS
current
feedback
Control unit
LO
DS1
SR
voltage
feedback
Proposed multi-mode charging circuit
process the charging energy. The line in AC power is be
duty-ratio for the energy-supplying part; and decides the
switching states of the switches in mode-managing part.
rectified into DC voltage, through a half-bridge inverter to
sliced into high-frequency voltage wave to feed the
3. Charging modes
step-down transformer, T1. The output of the transformer is
rectified and filtered to provide a constant-current or
constant-voltage DC source for the mode-managing part at
The proposed circuit can perform four different charging
modes. The circuit topologies are described in detail in the
following for each charging mode.
a customized level. Moreover, the charging energy can be
regulated by adjusting the duty-ratios of the switches, QA
and QB in the half-bridge inverter during the charging
3.1 Constant-current charging mode
process to meet the requirement for multi-stage charging.
A constant and stable charging current should be
provided for constant-current charging mode. Fig. 2 shows
the circuit topology at this charging mode. The active
switch S1 keeps at off state; therefore, the charging current
will flow through diode D1 to feed the battery. The energy
supplying part should be gated to provide constant current
at this charging mode. The charging current flowing
through the battery is sensed via the resistor Rs. The control
unit will sense the current and control the duty-ratios of
switches QA and QB in the half-bridge inverter to maintain a
constant charging current.
The mode-managing part is a revised version of the
non-dissipative reflex charging circuit (9). By controlling the
active switches in the mode-managing part, charging
current path can be altered to fulfill the particular charging
mode. As switch S1 remains turned off, the circuit will
perform constant-current charging. While S1 is continuously
switched, and SR remains turned off, pulse charging
waveforms can be obtained; otherwise, the circuit executes
reflex charging mode.
The control unit contains a DSP controller and sensing
3.2 Constant-voltage charging mode
interface circuits. The charging current and battery voltage
are monitored continuously by the DSP controller.
The circuit topology of constant-voltage charging mode
is the same as constant-current mode in Fig. 2. The
difference is on the energy output of energy supplying part.
According to the programmed pre-defined charging
scenario, the controller calculates to obtain the required
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The 2005 International Power Electronics Conference
CS2
CS2
D2
iCS2
D2
iCS2
LS
LS
D3
D4
IO
qpxfs
tvqqmzjoh
qbsu
VS
Fig. 2
RS
SR
D1
vgs
S1
D3
CS1
D4
IO
iCS1
iB1
qpxfs
tvqqmzjoh
qbsu
VS
B1
Circuit topology of constant-current and
constant-voltage charging modes
Fig. 3
RS
SR
CS1
iCS1
D1
vgs S1
iB1
B1
Circuit topology of pulse charging mode
B1-Cs1-Ls-Cs2-S1. The working behavior of energy supplying
In this charging mode, the control unit reads the battery
part and active switch S1 are the same as in pulse charging
terminal voltage through voltage feedback path. According
mode. At the instant of S1 turned on, the battery discharges
to the difference between the measured battery voltage and
through the resonant path to produce the negative pulse.
desired voltage, the control unit will regulate the energy
The resonant pulse can only flow unilaterally, since the
flowing into the battery by adjusting duty-ratios of the
returning path is blocked by diode D3. After the negative
half-bridge inverter. While the battery terminal voltage is
pulse ceased, the battery is left rested. Until the switch S1
maintained at a fixed level, the battery current will decrease
turns off, the charging current flows into the battery; in the
gradually. By this charging mode, battery overcharging can
meantime, the energy stored in capacitors Cs1 and Cs2 is
be avoided; therefore, this is a good choice for the last stage
returned back to the battery. Therefore, the energy of
of battery charging.
negative pulses is not wasted, and the energy efficiency is
promoted.
3.3 Pulse charging mode
In pulse charging, the charging current is a square-pulse
The control unit can be programmed to control the power
wave. The idea is to render the battery a short rest period to
supplying part and the associated switches to perform a
eliminate the undesirable polarization effect. Therefore, a
specified charging scenario. The charging profile can be
switch is needed to produce an intermittent charging current.
one of the four charging modes. Moreover, multiple
Fig. 3 shows the circuit topology of pulse charging mode.
charging modes can be combined together to charge
Control unit will open-circuit the switch SR, and therefore
batteries within one charging cycle. If multiple charging
disable the resonant path of Cs1, Ls and Cs2. In the same
modes are adopted to charge batteries, the control unit will
time, switch S1 will be gated at a specified frequency and
monitor the terminal voltage of the batteries to decide the
duty-ratio to produce the desired pulse current. The
transition point for next charging stage.
intermittent current will flow through diode D1 to charge
CS2
the battery. In this mode, energy supplying part will output
D2
iCS2
a constant DC current at a specified level.
LS
D3
3.4 Reflex charging mode
D4
This charging mode also provides the battery with an
intermittent charging current. However, for reflex charging,
the positive charging pulse is followed by a very narrow
negative pulse. Consequently, the circuit will be more
complicated in this mode than the other modes discussed
previously. Fig. 4 shows the circuit topology. The switch SR
is turned on to short-circuit the resonant path of
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IO
qpxfs
tvqqmzjoh
qbsu
VS
Fig. 4
RS
D1
vgs S1
SR
CS1
iCS1
iB1
Circuit topology of reflex charging mode
B1
The 2005 International Power Electronics Conference
Table II
4. Circuit implementation
On designing the power supplying part, the transformer
turn ratio should be carefully selected to supply appropriate
voltage output for the next stage. The turn ratio can be
obtained from (1).
Np
D max ˜ V rec
««««««... (1)
2V o , max
Ns
Here, Vo,max is chosen as 30V, in order to provide a wider
range of voltage or current output. From the inference of [9],
negative impulse intensity, I, and duration, T can be
calculated by (2) and (3).
I
T
V B1
Settings
Value
CC
Charging current
1A
CV
Charging voltage
14V
Charging current magnitude
2A
Charging pulse frequency
100Hz
Charging pulse duty-ratio
50%
Table III
Experimental results of the four charging modes
CC
CV
PS
RX
77
321
56
57
Input capacity(Ah)
1.28
3.38
0.93
0.95
Output capacity(Ah)
1.15
2.46
0.95
0.93
Results
Charging time(min)
Stabilized battery voltage
12.24 13.08 12.19 12.21
after charging (V)
CS
««««««..........(2)
2 LS
charging waveforms are shown in Fig. 5(a) and 5(b)
respectively.
LS C S
««««.(3)
2
The four basic modes of charging experiments were
carried out to compare their performances. Except
constant-voltage charging, the others are terminated when
average battery loaded voltage reached 14V; while
constant-voltage would stop at battery current reduced to
100mA. On discharging phases, all experiments discharged
with constant 1A current until battery loaded voltages fell to
10V. The charging experiment settings are listed in Table II.
S
Z0
S
The important circuit parameters are listed in Table I.
5. Experimental results
A prototype multi-mode charging circuit was built in
laboratory, and the controller was programmed according to
the charging modes. A 12V Yuasa YB4L-B lead-acid battery
with rated capacity of 4Ah is to be charged in the
experiments. Before starting a charging experiment, the
charging waveforms should be inspected. Pulse and reflex
Table I
Mode
PS, RX
where Np and Ns are the turn numbers on primary and
secondary windings, Dmax is maximum duty ratio, Vo,max is
the maximum required voltage at secondary side of
transformer.
Experiment settings of the multi-stage charging
Circuit parameters
Parameter
Value
Input AC voltage
110V
Turn ratio (Np/ Ns)
2.4
Switching frequency of QA, QB
25 kHz
Maximal duty ratio of QA, QB
45%
Negative pulse magnitude, I 5A
Negative pulse duration,
T
A multi-stage charging experiment with all the charging
modes was performed. The charging starts with
constant-current mode, and followed by pulse, reflex and
finally constant-voltage charging modes. Table IV
enumerates the charging parameters and stage transition
conditions. Fig. 6 shows the experimental results. The
battery voltage and current data were transferred from DSP
11 Ps
Inductance, Ls
8.64 PH
Capacitance, Cs
3 PF
Table III is the experimental results of the charging
experiments. Constant-voltage charging spent the longest
time, and pulse charging was the shortest. However, by
further examining the results, all charging modes but
constant-voltage actually fully charging the battery;
therefore, the results give no accurate judge to which mode
is the best. Furthermore, excluding constant-voltage
charging, multi-stage charging is necessary to fully charge a
battery. If single-stage charging is adopted, the charging
current should be kept at a very low value, and at the
expense of longer charging time.
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The 2005 International Power Electronics Conference
Table IV
Experiment settings of CC-PS-RX-CV charging
Stage
Settings
Value
Charging current
3A
Mode transition voltage
13.75V
Charging current magnitude
3A
Mode transition voltage
13.75V
Charging pulse frequency
100Hz
Charging pulse duty-ratio
50%
Charging current magnitude
1.5A
Mode transition voltage
14V
Charging pulse frequency
100Hz
Charging pulse duty-ratio
50%
Charging voltage
14V
Charging ending current
100mA
CC
PS
(a) Pulse charging waveform
RX
CV
(b) Reflex charging waveform
until the charging current reduced to 100mA, and then the
charging process stopped. The total charging time is 411
min.
(1: VBǺ2V/div, 2: IoǺ5A/div, 4: IBǺ5A/div, TimeǺ2ms/div)
Fig. 5
Charging waveforms
controller to computer and were recorded every 15 seconds.
The experiment begins with constant-current mode. After
the battery voltage reached the transition point, that is,
13.75V, charging mode changed into pulse charging mode.
Since duty ratio of the charging current waveform is 50%,
the average charging current reduced; hence, the battery
voltage decreased. At the instant, battery voltage touched
13.75V again; it turned into reflex charging mode. Due to
Another multi-stage charging marked CC-RX-CV was
also performed, with the experiment settings listed in Table
V. The experimental results of both of the multi-stage
charging are calculated and show in Table VI. From the
results, it seems CC-RX-CV is better than CC-PS-RX-CV.
However, this is not the final conclusion. There are a lot of
combinations of multi-stage charging, and much more study
on transition point selections. Many experiments are to be
carried out to find out the best charging strategy.
the reduction of the current magnitude, the battery voltage
fell. While the battery voltage climbed to 14V, the final
6. Conclusion
mode, constant-voltage mode started. This mode continued
A multi-mode charging circuit for rechargeable batteries
is proposed in this paper. This circuit is composed of an
Charging current (A)
Battery voltage (V)
3.5
15
Battery voltage
Table V
3
14
2.5
13
2
12
1.5
Charging current
11
Stage
CC
1
0.5
RX
0
10
0
Fig. 6
100
200
300
400 Time (min)
CV
Battery voltage and current in a multi-stage
charging experiment
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Experiment settings of CX -RX-CV charging
Settings
Values
Charging current
2A
Mode transition voltage
13.4V
Charging current magnitude
1A
Mode transition voltage
14V
Charging pulse duty-ratio
50%
Charging voltage
14V
Charging ending current
100mA
The 2005 International Power Electronics Conference
Table VI
(3) J. C. M. Chen, ³Rapid Charging of Battery by Applying
Alternating Pulsed Large Current Without A High
Temperature,´ U. S. Pat. No. 6060865, May 09, 2000.
Experiment results of multi-stage chargings
CC -RX-CV CC-PS-RX-CV
Results
Charging time(min)
284
411
Input capacity(Ah)
3.17
3.48
Output capacity(Ah)
2.96
2.84
Stabilized battery voltage
after charging (V)
13.25
13.23
(4) ) % 'LQL] / ( 3 %RUJHV DQG % GH % 1HWR ³$
Comparative Study of Pulsed Current Formation for
3RVLWLYH 3ODWHV RI $XWRPRWLYH /HDG $FLG %DWWHULHV´
Journal of Power Sources, Vol.109, No.1, June 2002,
pp. 184-188.
(5) L. Jun, M. Edward, W. Jack, and K. Paul, ³7KHEffects
of Pulse Charging on Cycling Characteristics of
Commercial Lithium-Ion Batteries,´ -RXUQDO RI Power
Sources, Vol. 102, No.1-2, Dec. 2001, pp. 302-309.
adjustable energy supplying part and a revised reflex
charging circuit proposed earlier. By this charging circuit,
four basic charging modes can be implemented; they are
constant-voltage, constant-current, pulse charging and
reflex charging. The controller can be programmed to
perform solely one of the four charging modes, or even to
charging the batteries with hybrid charging modes within
one charging cycle. A multi-stage charging experiment with
hybrid charging modes was carried out to verify the
feasibility of this proposed circuit. By making use of this
multi-mode charging circuit, charging strategy can be
intensively investigated. It is expected that a more efficient
charging strategy can be exploited out to conform to the
necessity of modern lifestyles.
(6) K. C. Tseng, T. J. Liang, J. F. Chen, and M. T. Chang,
³+LJK)UHTXHQF\3RVLWLYH1HJDWLYH3XOVH&KDUJHUZLWK
Power )DFWRU &RUUHFWLRQ´ 7KH rd IEEE Power
Electronics Specialists Conference, PESC2002, pp.
671-675.
(7) P. H. Cheng and C. L. Chen, ³High Efficiency and
Nondissipative Fast Charging Strategy,´ IEE
Proc.-Electr. Power Appl., Vol. 150, No. 5, Sep. 2003,
pp. 539-545.
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1574
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