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EVS25 World Battery,Hybrid and Fuel Cell ElectricVehicle Symposium 1
EVS-25
Shenzhen, China, Nov 5-9, 2010
Design of Power System Control in Hybrid Electric
Vehicle
Van Tsai Liu
Department of Electrical Engineering, National Formosa University, Huwei 632, Taiwan
E-mail: vtliu@nfu.edu.tw
Abstract
This paper proposes a design of power system control in the hybrid electric vehicle. It
adopts the isolated DC/DC power converter as the front-end fuel cell and Lithium-ion
battery to supply constant voltage. By micro-controller to detect the hybrid power output,
and the low-pressure hydrogen storage temperature, and the adjustment of the power output
ratio to provide the energy for loading balance. The results can obtain the overall
performance of electric vehicle. It is important to avoid the excessive usage of hydrogen
fuel which causes the phenomenon of storage tank freezing and fuel cell or Lithium-ion
batteries abnormal situation. Display the working data of hybrid power system can achieve
the capability of instant surveillance. For the loading under consideration, the fuel cell and
Lithium-ion battery can supply stable voltage output. Copyright Form of EVS25.
Keywords: hybrid electric vehicle, fuel cell, push-pull converter, Lithium-ion battery
1 Introduction
Vehicles technology brings convenience in
traffic for humans, but cause serious global
warming, air pollution, depletion of oil
resources and other issues. Therefore, the
hybrid and pure electric vehicles is the most
effective way to reduce emissions of carbon
dioxide, which is about 45% of internal
combustion engine vehicle emissions, or
even non-exhaust emissions [1]. Electric
vehicles system becomes effective solution
to reduce air pollution and fossil fuel [2].
In recent years, power conversion system of
fuel cell has been proposed. The fuel cell is
used in electric vehicles, the most
compelling reason is that fuel-cell electric
vehicles are electric-drive vehicles as a
source, not only will have no exhaust
pollution, and can resolve the problem of
depletion for oil stocks[3]. This structure of
electric vehicle system is based on fuel cells
for energy supply sources, but was limited
by the fuel cell electrochemical reaction rate.
Therefore, vehicles can not provide an
instant start and climbing required output
power, and the batteries or super capacitors
as auxiliary power supply is used to provide
a steady output for the load [4].
2 System structure
Based on hybrid power system and energy
distribution is proposed hybrid electric
vehicle system structure shown in figure 1
[5-9]. This article uses the fuel cell and
lithium-ion battery as power sources, and
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fuel cell power generation process as : The
low-pressure hydrogen storage bottles
provides hydrogen, and through the
appropriate hydrogen pressure regulating
valve to adjust the pressure switch by the
hydrogen fuel cell modules into the house
with the oxygen is electrochemically
converted. Fuel cells and lithium-ion
batteries can not smooth voltage output in
the load change, so must uses the power
converter to output stable voltage for the
motor-driven DC-wheel drive motor. About
power distribution of control design for the
output state that uses the A/D feedback
circuits and pressure sensors to detect the
fuel cell, Lithium-ion battery voltage and
the hydrogen storage bottle pressure. After
the micro-controller via judge that sends
PWM signals to the power distribution
circuit. The power converter controls the
output load ratio of the energy, and
completes the complex the overall design of
power electric vehicles.
Figure 1: Block diagram of hybrid electric
vehicle
3 Design of power converter
Figure 2 demonstrates the power converter
is used for the full-bridge rectifier push-pull
converter. The article uses KA3525 as a
drive control IC to control the power
switches (S1,S2) of the conduction and
cut-off time respectively with two PWM
output circuit. Dead time and frequency of
the speed is series-parallel resistor and
capacitor to control. The secondary side of
isolated power conversion is used
optocoupler feedback circuit. Ratio
converter (CT) is used to detect currents
flowing through the power switch, besides,
protect the switch and prevent circuit
overload. The circuit design is tally with
specifications, such as Table 1.
Figure 2: The circuit of push-pull converter
Table 1: Push-pull converter specification
Input voltage DC 26V-40V
Switch frequency 50 kHz
Output voltage DC 50V
Output current 12A
4 Design of complex power
systems control
The hybrid electric vehicles will be
considered for safe driving that depends on
the electric power distribution systems.
About hybrid power and stability control is
proposed a power distribution system
control structure shown in figure 3.This
structure consists of two parts:
Figure 3: The structure of power distribution
system
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1. A/D detection circuit: Based on the
protection of micro-controllers and A/D
conversion values, which is used the
optocoupler isolated as a complex
dynamic system feedback. The main
pressure sensor to detect the pressure of
conversion values, moreover, the
lithium-ion battery voltage and fuel-cell
voltage is obtained to determine
treatment by the micro-controller for the
output energy distribution of control
signals.
2. PWM driver circuit: The output control
signals are not sufficient to drive power
switches for the micro-controller. High
current through circuits to reflux
prevention of abnormal result, which
give rise to burn for micro-controller.
Therefore, the optically coupled driver
circuit is used to reach power switch
isolation amplified in this article.
This design of approach using the Microchip’s
dsPIC30F4011 in A/D, PWM and LCD display
[10]. The main uses AD-based, and samples the
output voltage in the fuel cell. Lithium-ion
battery output voltage and pressure sensors
convert voltage signals is as a control power
distribution circuit of the PWM signal output.
The signal determines the priority shown in
figure 4. First the fuel cell is No.1 priority, the
next is Lithium-ion batteries, and the last is the
pressure sensor signal. Table 2 is based on the
sampling that designed states of signal control
that has the following five kinds of:
Figure 4: Block diagram of the energy control
strategy for hybrid electric vehicle
1. If the fuel cell voltage is greater than 26V,
the Lithium-ion battery voltage is greater
than 32V, and the pressure sensor
feedback voltage is greater than 36V: The
fuel cell is controlled at 80% to output,
and the Lithium-ion battery is at 20%.
2. If the fuel cell voltage is greater than 26V,
the Lithium-ion battery voltage is greater
than 32V, and the pressure sensor
feedback voltage is less than or equal to
36V: The fuel cell is controlled at 20%
to output, and the Lithium-ion battery is
at 80%.
3. If the fuel cell voltage is less than or
equal to 26V, and the Lithium-ion battery
voltage is greater than 32V: The fuel cell
is stopped to output, and the
Lithium-ion battery is controlled to
output at 100%.
4. If the fuel cell voltage is greater than 26V,
and the Lithium-ion battery voltage is
less than or equal to 32V: The fuel cell is
controlled to output at 100%, and the
Lithium-ion battery is stopped to output.
5. If the fuel cell voltage is less than or
equal to 26V and the Lithium-ion battery
voltage is less than or equal to 32V: The
fuel cell and the Lithium-ion battery is
stopped to output.
Table 2: The state of energy distribution
5 Experiment Results
The input voltage and the output voltage
waveform of the converter are shown in
figure 5. This figure shows the non-pumping
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load conditions of fuel cells and lithium
batteries, because the load current affects
the output voltage level. Therefore, the
power converter needs a stable output
voltage for the load.
This article uses micro-controller to detect
the fuel cell voltage. The Lithium-ion
battery voltage and output pressure
hydrogen storage bottle of hydrogen
through the A/D feedback circuit to judge
hybrid voltage output. Control signals
decided the distribution of electrical energy
in the system, and display distribution
system state of the current power at work, as
shown in figure 6-9.
Figure 5: Input voltage, output voltage, and
output inductor current waveforms. (Step
change from 0 to 600W)
(a)
(b)
Figure 6: At normal state, (a) Power control
signal (b) Status of display
(a)
(b)
Figure 7: At hydrogen lack state, (a) Power
control signal (b) Status of display
(a)
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(b)
Figure 8: At fuel cell abnormality, (a) Power
control signal (b) Status of display
(a)
(b)
Figure 9: At Lithium-ion battery abnormality, (a)
Power control signal (b) Status of display
Figure 10 is the complete with the hybrid
electric vehicle. At various loads and power
status measure the fuel cell and the
lithium-ion battery output power, as shown
in figure 11-14. From the figure could
discover that the fuel cell and lithium-ion
battery power distribution status and the
whole hybrid system are feasible.
Figure 10: Complete diagram of hybrid electric
vehicle
Figure 11: Fuel cell and Lithium-ion battery
power output curve at normal state
Figure 12: Fuel cell and Lithium-ion battery
power output curve at hydrogen lack state
Figure 13: Fuel cell and Lithium-ion battery
power output curve at fuel cell abnormality
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Figure 14: Fuel cell and Lithium-ion battery
power output curve at Lithium-ion battery
abnormality
6 Conclusion
Renewable energy is the new trend of the
times. The green energy vehicles is used by
the national attention in the environmental
awareness and oil rising, which put forward
a number of different electric vehicle
architecture. The power converter is used to
regulation devices for the fuel cell and
lithium-ion battery output voltage in this
article, and completing design of the power
distribution control for hybrid power system
load energy. The hydrogen storage bottle
prevented freeze and increased travel
mileage and safety for this hybrid electric
vehicle architecture. Final, the
micro-controller is used to read the fuel cell
modules, the hybrid power distribution
system and the working conditions
displayed to show in LCD, which
immediately can combine to use of state
power.
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Author
Associate Professor: Van
Tsai Liu
Department of Electrical
Engineering, National
Formosa University
Tel: +886-56315607
Fax: +886-56315609
He is currently an
associate professor in the
department of electrical engineering,
National Formosa University, Yunlin,
Taiwan. His research interests include
intelligent control, high voltage gain
converter, battery management system.
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