Journal of Asian Electric Vehicles, Volume 7, Number 1, June 2009

Development of an Electric Wheelchair System Using PEM Fuel CellKazuo Saito 1, Chan Anyapo 2, Pitak Kamjitjam 3, and Toshihiko Noguchi 4
1

Department of Electrical Engineering, Nagaoka University of Technology, saito@vos.nagaokaut.ac.jp
Department of Electrical Engineering, Nagaoka University of Technology, chan@stn.nagaokaut.ac.jp
3
Department of Electrical Engineering, Nagaoka University of Technology, pitak_ohho@hotmail.com
4
Department of Electrical Engineering, Nagaoka University of Technology, tnoguchi@vos.nagaokaut.ac.jp
2

Abstract

This paper describes an electric wheelchair using a fuel cell and its speed characteristics. The wheelchair system has a PEM fuel cell stack as a power supply, an EDLC bank as an energy buffer, and a newly designed fourquadrant DC chopper which drives two DC motors. Drive performance of the wheelchair and essential characteristics of the fuel cell are investigated by experimental results. Consequently, it is shown that the wheelchairsatisfies basic driving operations, and also the PEM fuel cell has sufficient capability for the wheelchair system.
Therefore, the ideas and technologies which are applied to the system will be able to contribute to future electricvehicles and transportation.

Keywords

electric wheelchair, PEM fuel cell, DC motor, fourquadrant DC chopper, EDLC
1. INTRODUCTION
Recently, discussions on fuel cells have increased significantly. Regarding problems of the global environment and exhaustion of natural resources, the study ofan application of fuel cells is noteworthy [Hoogers,2003; Larminie, 2003]. Besides, several types of electric vehicles using fuel cells have been developed by
car manufacturers and institutes [Iizuka, 2006]. Therefore, a combination of fuel cells and electric vehicles
or wheelchairs is a meaningful topic [Yamaguchi andIkemoto, 2007].
Furthermore, there is an increasing problem of the aging society, especially in Japan. From this viewpoint,
the study of wheelchairs is both important and in urgent need.
This paper introduces an electric wheelchair that uses
a PEM (Proton Exchange Membrane) fuel cell. Thewheelchair system has an EDLC (Electric DoubleLayer Capacitor) bank as an energy buffer, and a fourquadrant DC chopper which drives two DC motors.
The motors are mounted on both of the back wheels,and speed detectors are installed on both of the backtires. Essential characteristics of the PEM fuel cell andthe electric wheelchair system are investigated in thispaper [Anyapo et al., 2006; Saito et al., 2006; Kamjitjam et al., 2007; Saito et al., 2008].
2. STRUCTURE OF WHEELCHAIR
Figure 1 shows a photograph of the electric wheel-chair which originally has the following specifications; the diameter of each back wheel is 22 inches,the maximum speed is 6 km/h, the output power of
each DC motor is 90 W, and the power supply is a Li-Fig. 1 Electric wheelchair

Fig. 2 PEM fuel cell and hydrogen storage alloys1185

K. Saito et al.: Development of an Electric Wheelchair System Using PEM Fuel Cellion battery (25.9 V-6 Ah). The electric wheelchair has
been improved on several points. In particular, thepower supply is replaced by the PEM fuel cell stackwith the hydrogen storage alloys, which are seen inFigure 2 (front side: the PEM fuel cell).
The two DC motors are driven by the newly designed
four-quadrant DC chopper, and the EDLC bank is employed as an energy buffer managing energy flow ofthe system. Their major specifications are as follows;(1) PEM fuel cell: 200 W-24 V (output),(2) Hydrogen storage alloys: 500 L (capacity of H2),
(3) DC motor: 90 W (output power each),(4) EDLC: 1350 F-2.7 V (capability/1 piece).
Figure 3 shows the control system of the electric
wheelchair system. A user of the wheelchair handles
only a joy-stick which can select a drive mode (forward, backward, right/left turn, and pivot). The energy
control and motor drive circuit work depending on
signals from the joy-stick. Then, the two DC motors
mounted on both of the back wheels are driven by thechopper for the commanded drive mode. Figure 3 also
indicates that the PEM fuel cell is the power supply,
EDLC is the energy storage device, and the two DC
motors drive the wheels of the wheelchair.

from the hydrogen storage alloys, and oxygen in the
air is inhaled using a blower DC motor.
The EDLC bank is charged or discharged dependingon the drive conditions of the wheelchair system. For
example, the EDLC supplies energy to the two motors when the output power of the fuel cell lacks formotor drive. When regeneration of the motors occurs,normally the EDLC is charged. Figure 5 illustrates
two examples of energy flow; (a) indicates the energy
flows from the fuel cell to the motors, and a part of theenergy can charge the EDLC. Figure 5 (b) shows theregeneration mode; the energy flows from the motors
to the EDLC (condition 1), or a discharging resistor(Rd) works to dissipate the energy if the EDCL is fully
charged (condition 2).

(a) Motoring mode(b) Regeneration mode
Fig. 5 Examples of energy flow among the main devices

Fig. 3 Control system of the electric wheelchair
Management of energy flow and the motor drive circuit of the wheelchair system are illustrated in Figure
4. In terms of the PEM fuel cell, hydrogen is supplied

3. CHARACTERISTICS OF FUEL CELL
Several types of fuel cells have been developed andapplied in many fields; above all things, PEM fuelcells are the most suitable for electric vehicles or electric wheelchairs, because PEM fuel cells can be usedat room temperature and the sizes are small.
The hydrogen storage alloys are connected with thePEM fuel cell, as illustrated in Figure 4. This figure
also shows the flow of hydrogen and oxygen by theFig. 4 Management of energy flow and the motor drive circuit
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Journal of Asian Electric Vehicles, Volume 7, Number 1, June 2009200

Voltage25

Output power (W)Output voltage (V)

30

Power

150

20100
Temperature: 23 C

1550

Humidity: 81%

00051015

Output current (A)Fig. 6 Characteristics of the PEM fuel celluse of arrows. By the electrochemical reactions, onlywater vapor is exhausted.
Figure 6 demonstrates the characteristics of the PEM
fuel cell obtained by experiments. As load (output current) increases, output voltage gradually drops. Meanwhile, the maximum output power reaches around 200W.
Figure 7 and Figure 8 show the experimental results
for the output power of the PEM fuel cell, when theforward mode and the left turn mode are carried out.
As shown in Figure 7, the maximum output power
reaches 100 W, and the steady state value is about 55

W. In Figure 8, the correspondent values are 105 Wand 45 W, respectively. In addition, the output poweris about 30 W when the two motors do not work (indicated “stop”). The reason for this is that the blower
is working, i.e., the PEM fuel cell is also used as thepower supply of the blower motor which inhales oxygen from the air.
These data assure that the PEM fuel cell has sufficientcapability for the electric wheelchair system.
4. PERFORMANCE OF WHEELCHAIR
The electric wheelchair has several drive modes; forward, backward, right/left turn, and pivot mode. Themotors mounted on both of the back wheels are driven
by the four-quadrant DC chopper which is designed tosimplify the motor drive system. To measure the velocities of the wheels, speed detectors are installed on
both of the back tires.
4.1 Four-quadrant DC chopper
The four-quadrant DC chopper, which drives the two
DC motors, has a combined structure of two fullbridge choppers. Therefore, the number of switching
devices can be reduced from eight to six, as illustrated
in Figure 4 and Figure 9.

Q1120+

Output power (W)

100Q3M

D2D5Q5-M+Right Motor

Q4Q260

D3-Left Motor80

Q6D6D440

Fig. 9 Operation of the DC chopper (Forward)

20000.5
Stop

1.0

1.5

2.0Time(s)ForwardStopFig. 7 Output power of the PEM fuel cell (Forward)
120100

Output power (W)

D180
60
40
20000.5
Stop

1.0
Left turn

1.5

2.0

Time(s)StopFigure 9 illustrates the operating condition of the DC
chopper in the forward mode. Thick arrows indicate
the current path of the two DC motors and the switching devices (MOSFETs). In the case of the forward
mode, Q1 & Q5 and also Q4 have PWM switching conditions.
Figure 10 shows the waveforms of the DC chopper inthe forward mode. The PWM switching frequency ofQ1, Q2, Q5, Q6 is 10 kHz, and that of Q3, Q4 is 1 kHz.
When Q4 is ON condition and Q1 & Q5 are in switching operations, the two DC motors rotate in a forward
direction at once. Figure 10 also describes the voltage
waveforms of the left motor (VL (ave)) and the rightmotor (VR (ave)) of the wheels, which are working
in chopper operation. Thus, the electric wheelchair
moves forward.

Fig. 8 Output power of the PEM fuel cell (Left turn)1187

K. Saito et al.: Development of an Electric Wheelchair System Using PEM Fuel Cell(V)
5ONSw .signal

Q105Q205Gate signal

Q305Startcommand

Q405

Starting time

Q5

90%

05

Q6
Speed

024

10%

VL(ave)Rise time

VL

Fig. 12 Definition of starting time and rise time

024VR(ave)

VR0

2.5

54
32
1

No-LoadForwardBackward

ForwardBackward

Load

Speed ( km/h )021.5

Voltage ( V )Fig. 10 Waveforms of the DC chopper (Forward)Wheelchair Speed( km /h )Switch signal

6202.546Speed (left wheel)

2108Time ( s )Starting time: 1 s

Duty 90%1.5
10.5
0012468Time ( s )10Fig. 13 Switch signal and wheelchair speed (Forward)

0.5

3060

708090D uty ratio ( % )100Load2.5Fig. 11 Wheelchair speed to switching duty ratio

1188

Rise time (s)4.2 Speed data by experiments
Figure 11 shows the wheelchair speeds for the forward
and the backward modes under both the conditions ofa load (a user who weighs 75 kg) and no-load. From
this data, it is shown that the wheelchair speeds increase linearly as the switching duty ratios of Q1 & Q5
(in the case of the forward mode) or Q2 & Q6 (in thecase of the backward mode) become higher.
In order to investigate a smooth start drive, which enables the wheelchair to move slowly, the starting time
and the rise time are defined as indicated in Figure 12.
When a switch signal is sent from the joy-stick, a startcommand rises gradually so that a sudden movement
does not occur. Then, the wheelchair speed increases

Backward
2Forward

1.5

1Backward

Forward0.5

N o-Load

000.5

1

1.5

Starting time (s)Fig. 14 Rise time to starting time2

Journal of Asian Electric Vehicles, Volume 7, Number 1, June 2009

Q1

Q3

Q4

Speed ( km/h )

Q6

2.5
2
1.5
1
0.5
0-0.5
0-1
-1.5
-2-2.5

2.5
2
1.5
1
0.5
0-0.5
-1
0-1.5
-2-2.5

Speed ( km/h)

smoothly, where the time between 10 % and 90 % of
the constant speed is defined as the rise time.
Figure 13 shows an experimental result of a switch
signal and a wheelchair speed when the starting timeis 1 s. Before the speed rises, the delay time (0.35 s)
is observed, which is caused by friction between thetires and the ground. In this case, the conditions are
as follows; forward mode, no-load, and the switching
duty ratio of Q1 & Q5 is 90 %.
The rise time at the load condition is larger than theno-load one, which is caused by the difference ofinertias. For drive feeling, the starting time is better
between 0.5 s and 1.0 s. The relation between the risetime and the starting time is shown in Figure 14. The
rise time increases gradually with the starting time under all conditions.
Figure 15 and Figure 16 describe the gate signals of
Q1, Q3, Q4, and Q6 under the conditions of the rightturn mode and no-load. Figure 15 shows the case of
Q1 = 90 % and Q6 = 0 %. On the other hand, Figure
16 shows the case of Q1 = Q6 = 90 % (the two motors rotate in contrary directions to each other). As forthe turning radius, the case of Figure 15 is 58.2 cm

Q1Left wheel

1234567891078910Time ( s )Right wheel

123456Time ( s )Fig. 16 Gate signals of MOSFETs and wheel speed(Switching duty ratio: Q1 = Q6 = 90 %)Q3

and that of Figure 16 is 35.9 cm, respectively. Thesefigures also indicate the speed data of the left and theright side wheels. In Figure 16, the speed of the rightside wheel is low compared to the left side one; thereason for this is larger friction of the right side tire
when the wheelchair turns right.
According to these experimental results, basic speed
characteristics of the electric wheelchair have been
examined. Then, it is assured that the wheelchair system fundamentally has satisfactory performance.

Q4Speed ( km/h )

Q6

2.5
2
1.5
10.5
0-0.5 0-1

Left wheel

12

3

45

67

891078910Time ( s )-1.5-2-2.5

2.5

Speed ( km/h )2
1.5

Right wheel

1
0.5
0-0.5
0-1-1.5
-2

123

45

6Time ( s )-2.5Fig. 15 Gate signals of MOSFETs and wheel speed(Switching duty ratio: Q1 = 90 %, Q6 = 0 %)5. CONCLUSIONSIn this paper, the prototype electric wheelchair using the PEM fuel cell is discussed. The points of thewheelchair system are also utilizing the EDLC bankas an energy buffer and the newly designed four-quadrant DC chopper which drives the two DC motors.
Basic drive performance of the wheelchair has been
examined by experimental results, considering the essential characteristics of the PEM fuel cell.
As a result, it is shown that the PEM fuel cell can beadapted to the electric wheelchair system, and basic
operations of the wheelchair have been achieved.
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K. Saito et al.: Development of an Electric Wheelchair System Using PEM Fuel Cell

The next stage of this subject is to examine the management of energy flow among the PEM fuel cell, theEDLC bank, and the two DC motors.
The authors hope that the ideas and technologies
which have been investigated in this study will contribute to not only electric wheelchairs but also future
electric vehicles and transportation.

Acknowledgements

We would like to thank Power Systems Co.,Ltd. forproviding the EDLCs, and QM Soft Co.,Ltd. for informing us about the PEM fuel cell and the hydrogenstorage alloys.

References

Anyapo, C., K. Saito, and T. Noguchi, Developmentof electric wheelchair using fuel cell, Proceedingsof Niigata Branch of IEEJ, IV-6, 56, 2006.
Hoogers, G., Fuel cell technology handbook, CRC
Press, 2003.
Iizuka, S., Possibility of fuel cell cars and electric vehicles, Grand Prix Publisher, 2006.
Kamjitjam, P., K. Saito, and T. Noguchi, Speed controlof electric wheelchair using fuel cell, Proceedingsof Niigata Branch of IEEJ, II-7, 25, 2007.
Larminie, J., Fuel cell systems explained (2nd Edition), John Wiley & Sons, 2003.
Saito, K., C. Anyapo, and T. Noguchi, Development ofelectric wheelchair using PEM fuel cell, Proceedings of The International Workshop on Mechatronics, 44-46, 2006.
Saito, K., P. Kamjitjam, and T. Noguchi, Speed characteristics of electric wheelchair using PEM fuelcell, Proceedings of The 2nd Technology and Innovation for Sustainable Development Conference,
03_024_2008I, 347-351, 2008.
Yamaguchi. S., and T. Ikemoto, Electric wheelchairusing Ni-MH battery aided by fuel cell, Journal of
Asian Electric Vehicles, Vol. 5, No. 2, 1049-1053,2007.
(Received November 4, 2008; accepted December 17, 2008)

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