Study on Electric Wheelchair System Using Fuel Cell
Chan Anyapo, Kazuo Saito, and Toshihiko Noguchi
Department of Electrical Engineering, Nagaoka University of Technology, JapanAbstract

This paper shows an electric wheelchair system using a PEM fuel cell. The system also has
an EDLC bank as an energy buffer, and a newly designed four-quadrant DC chopper which drives two DCmotors mounted on the wheelchair. Essential characteristics of the PEM fuel cell and drive performance ofthe wheelchair are investigated by experiments. Consequently, it is cleared that the PEM fuel cell is
adaptable to the electric wheelchair system, and the wheelchair is satisfied with required operations.

Keywords: electric wheelchair, PEM fuel cell, DCmotor, four-quadrant DC chopper, EDLC

1. Introduction
Recently, discussions on fuel cells have been
increased amazingly [1], [2]. For problems of the
global environment and exhaustion of harmful gases,
to study on application of fuel cells is noteworthy.
Besides, several types of electric vehicles using fuelcells have been developed by car manufactures andinstitutes [3]. Therefore, combination of fuel cells andelectric vehicles or wheelchairs is notable subject [4].
Furthermore, there is a big problem of the aging
society in Japan. From that viewpoint, development of
new type wheelchair is meaningful topic [5].
This paper shows an electric wheelchair systemusing a PEM (Proton Exchange Membrane) fuel cell.
The system also has an EDLC (Electric Double Layer
Capacitor) bank as an energy buffer, and a fourquadrant DC chopper which drives two DC motors.
The motors are mounted on both the wheels, andspeed detectors are installed on both the tires.
Characteristics of the fuel cell and drive performanceof the electric wheelchair are investigated [6]-[10].

power supply is replaced by the PEM fuel cell stackwith the hydrogen storage alloys, which are seen in
Fig. 2 (front side: the PEM fuel cell stack).
The two DC motors are driven by the newly
designed four-quadrant DC chopper, and the EDLC
bank is employed as the energy buffer controllingenergy flow of the system.
The major specifications of them are as follows;

Fig. 1 Electric wheelchair

2. Structure of Wheelchair System
Figure 1 shows a photograph of the electricwheelchair which originally has the following
specifications; the diameter of each wheel is 22 inches,the maximum speed is 6km/h, the output power of
each DC motor is 90W, and the power supply is aLi-ion battery (25.9V/6Ah). The electric wheelchair
has been improved on several points. In particular, theFig. 2 PEM fuel cell and hydrogen storage alloys

(1) PEM fuel cell: 200W-24V (output),(2) Hydrogen storage alloys: 500ℓ (capacity of H2),
(3) DC motor: 90W (output power each),(4) EDLC: 1350F-2.7V (capability/ 1 piece).
Figure 3 shows the relationship among the main
devices of the electric wheelchair system. A user
should only handle a joy-stick which can select any
drive modes (forward, backward, right/left turn, andpivot). The energy control and motor drive circuit
work depending on signals from the joy-stick. Then,the two DC motors mounted on both the wheels aredriven by the chopper for commanded drive mode.
Figure 3 also indicates that the PEM fuel cell is thepower supply, EDLC is the energy buffer, and the two
DC motors drive the wheels of the wheelchair.
Control of energy flow and the motor drive
circuit of the system are illustrated in Fig. 4. In termsof the PEM fuel cell, hydrogen is supplied from thehydrogen storage alloys, and oxygen in the air isinhaled using a blower DC motor.
The EDLC bank is charged or discharged
depending on drive conditions of the system. For
example, the EDLC supplies energy to the two motors

when the output power of the fuel cell lacks for motor
drive. When regeneration of the motors occurs,normally the EDLC is charged. Figure 5 illustratestwo kinds of examples of energy flow; (a) indicatesthe energy flows from the fuel cell to the motors, anda part of the energy can charge the EDLC. Figure 5 (b)shows the regeneration mode; the energy flows fromthe motors to the EDLC (condition 1), or adischarging resistor (Rd) works to dissipate the energy
if the EDCL is fully charged (condition 2).

Fig. 3 Relationship among main devices

Fig. 4 Control of energy flow and motor drive circuit(a) Motoring mode(b) Regeneration mode

Fig. 5 Examples of energy flow among main devices

3. Characteristics of Fuel Cell
200Voltage

25

Output power (W)Output voltage (V)30Power150

20100Temperature: 23 C

1550Humidity: 81%

00501510

Output current (A)Fig. 6 Characteristics of PEM fuel cell

120
100

Output power (W)Several types of fuel cells have been developedand applied on a lot of fields, above all things, PEM
fuel cells are the most suitable for electric vehicles orelectric wheelchairs, because PEM fuel cells can beused at room temperature and the sizes are small. Thehydrogen storage alloys is connected with the PEM
fuel cell as illustrated in Fig. 4. This figure also shows
the flow of hydrogen and oxygen by the arrows. Effectof chemical reaction, only water vapor is exhausted.
Figure 6 demonstrates the characteristics of thePEM fuel cell obtained by experiments. As load
(output current) increases, output voltage droops
gradually. Meanwhile the maximum output power
reaches around 200W.
Figures 7 and 8 show the experimental results forthe output power of the PEM fuel cell, when theforward mode and the left turn mode are carried out.
As shown in Fig. 7, the maximum output power
reaches at 100W, and the steady state value of it isabout 55W. For Fig. 8, the correspondent values are
105W and 45W, respectively. Besides, the output
power is about 30W when the two motors don’t work(indicated “Stop” in Figs. 7 and 8). The reason of it isoperation of the blower, i. e., the PEM fuel cell is also
used as the power supply of the blower motor which
inhales oxygen from the air.
These data assures that the PEM fuel cell hasenough capability for the electric wheelchair system.

80604020000.5

1.0

1.5

2.0Time(s)StopForward

StopFig. 7 Output power of PEM fuel cell (Forward)120

4. Drive Performance of Wheelchair

4.1 Four-Quadrant DC Chopper
The four-quadrant DC chopper has a combined
structure of two full-bridge choppers. Hence, thenumber of switching device can be reduced from eight
to six, as illustrated in Figs. 4 and 9.
Figure 9 illustrates the operating condition of theDC chopper at the forward mode. Thick arrows
indicate the current path of the two DC motors and theswitching devices (MOSFETs). For the forward mode,
Q1 & Q5 and also Q4 have PWM switching condition.

100Output power (W)The electric wheelchair has several drive modes;
forward, backward, right/left turn, and pivot mode.
The motors mounted on both the wheels are driven by
the four-quadrant DC chopper which is designed tosimplify the motor drive circuit. While, to measure thevelocities of the wheels, speed detectors are installed
on both the tires.

8060
40
2000

0.5

1.0

1.5

2.0Time(s)StopLeft turnStopFig. 8 Output power of PEM fuel cell (Left turn)Figure 10 shows the waveforms of the DC
chopper at the forward mode. PWM switchingfrequency of Q1, Q2, Q5, and Q6 is 10kHz, on the other
hand, that of Q3 and Q4 is 1kHz. When Q4 is ON
condition and Q1 & Q5 are in switching operation, thetwo DC motors rotate in forward direction at once.

Q1

D1

Q3+

D3-

M

Q5-Left Motor

M+

Right Motor

Q4

Q2
D2

D5

Figure 10 also describes the voltage waveformsof the left motor (VL(ave)) and the right motor(VR(ave)) of the wheels, when chopper operation isacting. Thus, the electric wheelchair moves forward.

Q6D6D4Fig. 9 Operation of DC chopper (Forward)(V)
5Q105Q24.2 Speed Characteristics of Wheelchair
Figure 11 shows the wheelchair speeds for theforward and the backward modes under both theconditions of load (a user who weighs 75kg) andno-load. From these data, it is known that the speeds
increase linearly as the switching duty ratios of Q1 &Q5 (for the forward mode) or Q2 & Q6 (for thebackward mode) get higher. According to theseexperimental results, basic speed characteristics of theelectric wheelchair have been assured.

5. Conclusions

05Q305Q405Q505Q6024VL(ave)VL024VR(ave)VR0Fig. 10 Waveforms of DC chopper (Forward)

In this paper, the electric wheelchair systemusing the PEM fuel cell is discussed. The additional
points of the system are utilizing the EDLC bank as
the energy buffer, and the newly designed fourquadrant DC chopper which drives the two DC motors.
Essential characteristics of the PEM fuel cell anddrive performance of the wheelchair have been
investigated by experiments.
As a result, it is proved that the PEM fuel cell is
adaptable to the electric wheelchair system, and basic
operations of the wheelchair have been achieved.
The authors expect the ideas and technologies
which are examined by this study will contribute to
not only electric wheelchairs but also future electricvehicles and transportation.

Acknowledgements
2.5

2Wheelchair Speed( km/h )No-Load
1.5

ForwardBackward

ForwardBackward

Load

1References

0.5

060

We would like to thank Power Systems Co., Ltd.
for providing the EDLCs, and QM Soft Co., Ltd. for
informing us on the PEM fuel cell and the hydrogenstorage alloys. We also acknowledge Mr. Pitak
Kamjitjam who is an exchange student from PIT for
carrying out some experiments.

708090
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