SCYR 2010 - 10th Scientific Conference of Young Researchers – FEI TU of Košice
Bi-directional DC/DC Converter controlled by UC3637
1
1,2,3
Tomáš Béreš, 2Martin Olejár, 3 Ľubomír Matis
Dept. of Electrical, Mechatronic and Industrial Engineering, FEI TU of Košice, Slovak Republic
1
tomas.beres@tuke.sk, 2martin.olejar@tuke.sk, 3lubomir.matis@tuke.sk
Abstract— Concept of hybrid battery with bi-directional buckboost DC/DC converter controlled by UC3637 is described in this
paper. The first part of the paper is aimed at concept of hybrid
battery. Design of power circuit and control circuit with UC3637
of converter is described in the second part of the paper.
Experimental results from measuring of converter are mentioned
in last part.
Keywords— Converter control, hybrid battery, pulse width
modulation (PWM),
II. CONCEPT OF HYBRID BATTERY
Hybrid battery (HB) is a name for an improved
topology of secondary voltage power source. Its output power
dynamics and lifetime considerably exceed the recent types of
accumulators. The hybrid battery is in nature a cascade
connection of an ordinary accumulator with an ultracapacitor
via a bi-directional DC/DC converter as it is seen in Fig. 1.
I. INTRODUCTION
The last years are characterized by rapid development of
electronic systems, which uses an accumulator as a basic
power supply. However, presently the accumulators are the
weakest element of the power electronic supply system. It is
caused by low dynamics of input power, temperature
dependence, short lifetime and a lot of other limitations. The
most significant improvement in recent 200 years has been
achieved by developing ultra capacitor (UCAP). The
ultracapacitor has much better electrical parameters than
conventional accumulator. The next table shows comparison
of the features of ultra-capacitor, accumulator and classic
capacitor.
Available
Performance
Charge Time
Discharge Time
Energy (Wh/kg)
Cycle life
Specific Power
Charge/Discharg
e Efficiency
Accumula
tor
1 – 5 hrs
0.3 – 3 hrs
10 - 100
1000
< 1000
0.7 – 0.85
Ultra –
capacitor
0,3 – 30 s
0,3 – 30 s
1 – 10
106
10 000
0.85 – 0.98
Classic
capacitor
10-3 – 10-6s
10-3 – 10-6s
<0,1
>100 000
> 0.95
Tab.1. Parameter comparison of ultra-capacitor with accumulator and
classic capacitor
At present the low energy density is main disadvantage of
ultra-capacitors. One of the possibilities is to fuse the
advantages of ultra-capacitors and high energy density of
accumulators to a hybrid secondary power source.
Fig. 1. Block diagram of hybrid battery
High dynamics of input-output power of the hybrid battery is
achieved due to the ultra-capacitor. It means that high
dynamic parameters of the hybrid battery are given by the
parameters of the ultra-capacitor and static parameters by the
accumulator. Bi-directional DC/DC converter is a main part
of a hybrid battery. The converter has essential influence on
the operational properties and the efficiency. Recuperation
conditions of the bi-directional DC/DC converter are given by
the use of an accumulator in hybrid battery.
III. DESIGN OF DC/DC CONVERTER
The parameters of proposed DC/DC converter are shown
in Table 2.
Parameter
Value
Input voltage Uin
15-30 V
Output voltage Uout
14/24 V
Max. output voltage ripple
∆Uout
Max. output current
5%
10A
Max. current ripple
1A
Switching frequency
50kHz
Efficiency
>80%
Tab. 1. Table of parameters
SCYR 2010 - 10th Scientific Conference of Young Researchers – FEI TU of Košice
A. Power circuit of DC/DC converter
Power circuits of the DC/DC converter are in the Figure 2.
c)
Boost mode (VIN < VOUT)
Transistor Q1 is always ON and Q3 is always OFF during the
period in this mode (D1 = 1). Only Q2 and Q4 are switching
synchronously. In this operation mode the cascaded buckbuck
boost converter works as classic boost converter. Then the
value of VOUT is for boost mode as follows:
VOUT =
VIN
D2
(6)
B. Control circuit with UC3637
Switched mode controller UC3637 is used for control of this
converter. Scheme of control circuit is shown in Figure 4.
Fig.2.Topology of bi-directional buck-boost
boost DC/DC converter
The bi-directional
directional converter consists of two buck-boost
buck
converters connected in cascade. This converters are
interconnected through inductance
uctance i.e. boost converter with
buck converter (Fig.2).
The value of output voltage in general is:
VOUT = VIN
D1
D2
(1)
where:
D1 =
tQ1(ON )
T
D2 =
;
tQ 2(ON )
T
(2)
Fig. 4. Control circuit with UC3637
tQ1(ON) and tQ2(ON) indicate the ON time of the MOSFET
switches Q1 and Q2 respectively, whereas T is the switching
period.
Cascaded buck-boost
boost converter can work in three
operation modes, which will be introduced below.
a)
If:
Buck mode(VIN >VOUT)
Transistor Q2 is always ON and Q4 is always OFF during
this mode (D = 1). Only Q1 and Q3 are switching
synchronously. In this operation mode the cascaded buckbuck
boost converter works as classic buck converter. Then the
value of VOUT is for buck mode as follows:
2
VOUT = VIN .D1
b)
Amplitude of triangle waveform oscillator (+UTH; -UTH) is
set by voltage divider R15, R17, and R20. Value UH and UL is
set by trimmer RP2 and RP3. Changing modes of converter
depend on value UH and UL as follows:
(3)
Buck-boost mode (VIN ≈ VOUT)
UEAO-UL < U-VTH and UEAO+UH < U+VTH
buck mode is set
If: UEAO-UL > U-VTH and UEAO+UH < U+VTH
buck-boost mode is set
If: UEAO-UL > U-VTH and UEAO+UH > U+VTH
boost mode is set
where UEAO is output from voltage PI regulator.
For better understanding the function of controller is shown in
Figure 5.
In this switching mode all four MOSFET’s operate during
the period. The first path (Q1, Q4 are ON) enables charging the
inductor, the second path (Q2, Q3 are ON) allows the energy
stored in the inductor to be delivered to the output capacitor.
This way of switching determines the following relation
between D1 and D2:
(4)
D2 = 1 − D1
By combination of the equations (1) and (4), the following
expression is obtained:
VOUT
D
= VI N . 1
1 − D1
Fig. 5. Function of control circuit
(5)
Voltage uAOUT is input for transistors Q1 and Q3 driver,
voltage uBOUT is input for transistors Q2 and Q4 driver.
Transistors Q1 and Q2 are switched by non-inverted
non
signal and
transistors Q3 and Q4 are switched by inverted signal.
SCYR 2010 - 10th Scientific Conference of Young Researchers – FEI TU of Košice
IV. EXPERIMENTAL RESULTS
The function of the proposed DC/DC converter was
verified on the laboratory model. Principle of signal creation
with controller UC3637 for drivers is displayed on the
following oscillograms.
The first oscillogram (Fig.6) was captured in buck mode
of the converter. Transistors Q1, Q3 are switched. Transistor
Q2 is always ON, Q4 is always OFF in this mode. The second
oscillogram (Fig.7) shows buck-boost
boost mode operation of the
converter. In this mode all transistors are switched in diagonal
pairs.
converter control is shown in this oscillogram. All four
transistors are switched on simultaneously.
Fig. 9. Voltage of transistors Q1-Q4 and current of inductor in buck-boost
buck
mode (UIN=20V, UOUT=20V, IOUT=0,6A)
Experimental model of DC/DC converter is in the Fig.10.
Fig. 6. Control signal creation with UC3637 for drivers in buck mode
(UIN=28V,UOUT=24V)
Fig. 10. Photo of DC/DC converter
V. CONCLUSION
Fig. 7 Control signal creation with UC3637 for drivers in buck-boost
buck
mode
(UIN=25V, UOUT=24V)
Boost mode operation of the converter is displayed in the
third oscillogram (Fig.8). Transistors Q2, Q4 are switched.
Transistor Q1 is always ON and transistor Q3 OFF.
New concept of control method for bi-direction buckboost DC/DC converter is described in the paper. This
concept of control decreases power transistor switching losses
loss
and thus increases efficiency of converter.
ACKNOWLEDGMENT
This work was supported by Slovak Research and
Development Agency under project APVV-0095-07
APVV
and
by Scientific Grant Agency of the Ministry of Education of
Slovak Republic under the contract VEGA
VEG No. 1/0099/09.
REFERENCES
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Fig. 8. Control signal creation with UC3637 for drivers in boost mode
(UIN=18V, UOUT=24V)
[5]
Voltage of transistors Q1-Q4 and inductor current iL in
buck-boost mode is shown in Fig.9.
g.9. Correct function of
[6]
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