International Conference on Control, Automation and Systems 2008
Oct. 14-17, 2008 in COEX, Seoul, Korea
Hybrid Robotic Wheelchair with Photovoltanic Solar Cell and Fuel Cell
Yoshihiko Takahashi, Shogo Matsuo, and Kei Kawakami
Department of System Design Engineering/Vehicle System Engineering,
Kanagawa Institute of Technology, Kanagawa, Japan
(Tel : +81-46-291-3195; E-mail: ytaka@sd.kanagawa-it.ac.jp)
Abstract: A hybrid robotic wheelchair powered by three energy sources, a battery, a photovoltanic solar cell, and a
hydrogen fuel cell is proposed in this paper. The advantage of using a photovoltanic solar cell (a solar panel) is that it
produces power without requiring use of fossil fuels. The advantage of using a fuel cell is that a hydrogen tank may be
changed quickly and easily. We also propose an energy control system which is able to select the energy source
optimally according to the operating conditions. The control system ideally gives priority to the photovoltanic solar
cells before the fuel cell. When conditions allow for abundant sun light, the photovoltanic solar cell is used. When solar
energy is not available, the fuel cell is used. Finally, when the hydrogen is depleted, the battery is used. This paper
explains the concept of the hybrid robotic wheelchair, the mechanical design, the energy control system, and the
experimental results on the energy source selection.
Keywords: Hybrid robotic wheelchair, Photovoltanic solar cell, Fuel cell, Energy control.
1. Introduction
People bound to wheelchairs have limited mobility
reliant on how much battery life is available. Battery life
only allows for short distances to be traveled between
charges. In addition, recharging batteries is time
consuming. The aim of this paper is to propose a system
which will increase the moving distance of the electrical
wheelchair by adding photovoltanic solar cells (solar
panels) and fuel cells. The advantage of using a
photovoltanic solar cell (a solar panel) is that it
produces power without requiring use of fossil fuels.
The advantage of using a fuel cell is that a hydrogen
tank maybe changed quickly and easily.
A hybrid electrical robotic wheelchair with three
energy sources, a battery, a photovoltanic solar cell, and
a fuel cell is proposed in this paper. We also propose an
energy control system which is able to select the energy
source optimally according to the operating conditions.
When conditions allow for abundant sun light, the
photovoltanic solar cell is used. When solar energy is
not available, the fuel cell is used. Finally, when the
hydrogen is depleted, the battery is used. Our objective
is that the proposed robotic wheelchair will enable users
to enjoy more independence when they are outdoors.
This paper will explain the concept of the hybrid
robotic wheelchair, the mechanical design, the energy
control system, and the experimental results on the
energy source selection.
2. Concept of energy control system
Fig.1 illustrates the system configuration of the
energy control system. The energy control system
changes the energy sources optimally in relation to
running condition. The voltages of the photovoltanic
Solar panel
Voltage
detection
circuit
Fuel cell
DC/DC
converter
24V
Voltage
detection
circuit
Battery
Power
supply to
substrate
Energy control board
Signal
Power supply
Motor x2
Current
detection
circuit
Power
supply to
substrate
Electrical wheelchair
drive board
Fig.1 System configuration of energy control
cell, the fuel cell, and the motor drive current are
detected by a micro computer. The detected voltages
and current are compared with preset values, and
optimum energy control is conducted. The control
system will ideally give priority to the photovoltanic
solar cells (the solar panels) before the fuel cell. When
enough sun light is available, the photovoltanic solar
cell will be used. When it is limited, the fuel cell will be
used. Finally, when the hydrogen is depleted, the battery
is used. The energy control system is designed using a
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micro computer, and the energy source is quickly
changeable.
A cascade connection of two solar panels of 17.4 V
and 43 W is utilized as the solar energy source, and the
output voltage is lowered to 24 V using a DC-DC
converter. Additionally, a fuel cell of 24 V and 100 W is
used as the hydrogen fuel cell energy sources. The
voltages of the solar panel and fuel cell, and the driving
current are detected by a detection circuit, and are
entered into the micro computer via an A/D converter.
The detected values are analyzed by the micro computer
software. A Nickel Hydrogen battery of 24 V is used as
the battery energy source. The detection circuit of the
battery is omitted.
The purpose of our study is to confirm the
performances of our energy selection system.
Thereafter, we did not store the battery power from the
solar panel, and also did not use a MPPT (Maximum
Power Point Tracker).
Solar panel
38[V] or more
ON
Motor current
i=0[A]
Battery
OFF
OFF
Solar panel
38[V] less
OFF
Fuel cell
25[V] or more
ON
Solar panel
38[V] less
OFF
Fuel cell
25[V] less
OFF
Battery
OFF
Battery
ON
Fig.2 Example of energy control condition (Part 1)
Solar panel
30[V] or more
ON
3. Energy selection architecture
The software architecture of energy selection is
explained in Figs.2 to 5.
Fuel cell
Motor current
0[A]＜i≦2[A]
Condition (a) (Fig.2):
The electric wheelchair is stopped. If the motor current
is zero, while voltage of the solar panel is over 38.0 V,
the solar panel is used. If the motor current is zero,
while the voltage of the fuel cell is over 25.0 V, the fuel
cell is used. If the voltages of the solar panel and the
fuel cell are less than the preset values, the battery is
used.
Fuel cell
Battery
OFF
OFF
Solar panel
30[V] less
OFF
Fuel cell
24[V] or more
ON
Solar panel
30[V] less
OFF
Fuel cell
24[V] less
OFF
Battery
OFF
Battery
ON
Fig.3 Example of energy control condition (Part 2)
Condition (b) (Fig.3):
The electric wheelchair is stopped. The motor current is
over zero and less than 2.0 A, the voltage conditions for
the solar panel and fuel cell are reduced to 30.0 V, and
24.0 V, respectively. Priority order remains unchanged.
Solar panel
OFF
Fuel cell
24[V] or more
ON
Battery
OFF
Motor current
2[A]＜i≦4[A]
Condition (c) (Fig.4):
Solar panel
The motor current is over 2.0 and less than 4.0 A, the
solar panel is not used because the current value is over
the solar panel limitation. When the voltage is over 24.0
V, the fuel cell is used.
OFF
Fuel cell
24[V] less
OFF
Battery
ON
Fig.4 Example of energy control condition (Part 3)
Condition (d) (Fig.5):
The motor current is over 4.0 and less than 20.0 A, the
solar panel and the fuel cell are not used because the
current values are above the limitations of the solar
panel and the fuel cell.
Motor current
4[A]＜i≦20[A]
Solar panel
Fuel cell
Battery
OFF
OFF
ON
Fig.5 Example of energy control condition (Part 4)
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Illumination sensor
Solar panel
PC for illumination
measurement
Measurement apparatus
Energy control board
and battery
Hydrogen tank
Fig.6 Fabricated hybrid electric wheelchair
Fig.7 Energy control board
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Fuel cell
4. Fabricated hybrid robotic wheelchair
R un
Fuel cell voltage
[V]
50
[W]
We conducted the experiments on the energy
source selection between the solar panel, the fuel cell,
and the battery. Fig.3 shows the experimental results of
the proposed system.
0
Fuel cell power
5. Experiments
S to p
［A］
Fuel cell current
Fig.6 displays the fabricated hybrid robotic
wheelchair. A YAMAHA JW-1 was reinforced, and used
as the main body of the experimental set up. In this
configuration, the photovoltanic solar cells (the solar
panel), the fuel cell, and the battery are installed on the
top, on the back, and under the wheelchair, respectively.
The energy control system and hydrogen tanks are
installed on the back of the wheelchair. Fig.7 shows the
expanded photograph of the energy control board.
T u rn
S to p
8 .0
0
120
0
0
50
T im e [ s]
95
Fig.9 Experimental results of electric wheelchair movement
using fuel cell (low speed mode, low)
Run
Stop
Motor Current
Solar Current
Stop
T u rn
8 .0
[V]
Solar power
[W]
0
100
50
[W]
Solar voltage
[V]
50
0
-20
S to p
R un
0
Fuel cell voltage
0
S to p
［A］
Fuel cell current
Turn
Fuel cell power
Current ［A］
8.0
0
120
0
0
50
T im e [s ]
94
Fig.10 Experimental results of electric wheelchair movement
(high speed, high)
4
Solar radiation
[mW/m2]
10
120
100
50
Time [s]
100
80
145
P[W]
0
0
Fig.8 Experimental results of electric wheelchair movement
using solar panel and battery
60
40
20
0
-20
20
V[V]
Fig.11 Experimental results of P-V characteristics of fuel cell
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The conditions of “low speed mode” and “low” (Fig.9):
When the electric wheelchair was running straight, the
driving current and power were approximately 2.4 A
and 50 W. When the wheel chair was turning, the
current and power were increased to 4.5 A and 90 W.
The condition of “high speed mode” and “high”
(Fig.10):
Motor
Solar
Fuel cell
Current ［A］
4.0
5.3 Energy selection experiments
Fig.12 exhibits the experiments of the energy
source selection. Here, four test patterns were
conducted;
(1) “Low speed mode”, “low”, approximately 1.4 km/h,
(2) “Low speed mode”, “high”, approximately 2.4 km/h,
(3) “High speed mode”, “low”, approximately 3.0 km/h,
(4) “High speed mode”, “high”, approximately 3.4
km/h.
The results of (1)-(4) are displayed from top to bottom
in Fig. 12.
The experimental results show that the wheelchair
was able to run using the solar panel under the
experimental conditions of (1), (2), and (3), however
was not able to run under the condition of (4).
Turn
Stop
0
Current ［A］
-2.0
0
8.0
Turn
6.0
50
stop
100
Turn
Motor
Stop
Solar
Fuel cell
Run(H)
4.0
119
Stop
2.0
0
-2.0
0
8.0
Turn
6.0
50
Motor
Stop
Solar
Fuel cell
Stop Run(L)
4.0
Turn
96
Stop
2.0
0
-2.0
0
8.0
6.0
50
Turn
stop
100
Motor Stop Turn
Solar
Fuel cell
Run(H)
4.0
Stop
2.0
0
-2.00
At the beginning of running, the driving current and
power were over 5.0 A and 100 W.
Fig.11 shows the experimental results of P-V
characteristics of the fuel cell. The experimental results
show that the power was reduced as the voltage was
increased. It was confirmed that the wheelchair was able
to run at the low speed mode.
Stop
2.0
Current ［A］
5.2 Experiments of fuel cell
Figs.9 and 10 show the experimental results of the
fuel cell. Here, “low speed mode” and “high speed
mode” are the prepared selection modes of the
YAMAHA JW-1. In each mode, a user can change its
speed by inclining the joy stick. “low” condition in
figures means that the joy stick was inclined
approximately 10 degrees, and “high” condition means
that the joy stick was inclined completely.
8.0
6.0 Run(L)
Current ［A］
5.1 Experiments of solar panel and battery
Fig.8 displays the experimental results of the
selection of the solar panel and the battery. The
experimental results show that the motor driving current
was between 0.0 to 2.5 A. The solar panel current was
approximately the same value as the driving current.
When the current was over 2.5 A, the battery was used.
It was therefore confirmed that when the current was
small, the solar panel energy was used as the main
energy source, and when the current was large, the
battery was used.
Time[s]
50
78
Fig.12 Experimental results of electric wheelchair movement
using solar panel, fuel cell, and battery
5.4 Discussions
We confirmed that the robotic wheelchair was able
to run using the proposed energy control system. The
speed of the wheelchair was low therefore further
improvements will be required.
6. Conclusions
A hybrid robotic wheelchair powered by three
energy sources, a battery, a photovoltanic solar cell, and
a hydrogen fuel cell is proposed in this paper. We also
propose an energy control system which is able to select
the energy source optimally according to the operating
conditions. It is confirmed from the experimental results
that the hybrid robotic wheelchair is able to run using
the proposed energy control system. However, the speed
of the wheelchair is low, and improvements will be
required. The design of the energy control system using
a power capacitor must be addressed in future research.
This work was supported by MEXT.HAITEKU 2007.
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