4-024

平成 21 年電気学会全国大会

Four-Quadrant Operation of Two DC Motors with Three-Leg Full-Bridge Chopper
Incorporated Voltage Boost Function
Chan Anyapo*, Kazuo Saito, and Toshihiko Noguchi (Nagaoka University of Technology)
1. Introduction
D7

This paper proposes a novel chopper circuit and its
operation capable to drive two DC motors at the same time,
which is mainly applied to an electric wheelchair drive. The
key feature of the proposed circuit is reduced counts of theswitching devices without sacrificing a perfectly independent
four-quadrant operation and a voltage boost operation of apower source. Several experimental results are presented toconfirm proper operations of the proposed circuit.

Q1+

Fuel
Cell-+

C

D5-M
Left+

MRightD2

D4D6Q4Q6Fig. 1. Three-leg full-bridge chopper for pair of DC motors.

Figure 1 shows a three-leg structure based full-bridge
chopper to drive independent two DC motors simultaneously,
which was proposed by the authors in the past work (1), (2).
In the circuit, a center leg composed with Q3 and Q4 is operated
at a relatively low-frequency, e. g., 1 kHz, while the other twolegs composed with Q1, Q2, Q5 and Q6 are operated at afrequency approximately ten times of the center leg. Theswitching operation of Q3 and Q4 is complementary with a50-% duty cycle; hence the proposed chopper allows
independent drive of the two DC motors in four-quadrant
operation modes.
However, the 50-% duty cycle switching operation of Q3and Q4 limits the chopper output voltages to half of the powersource. Assuming that a 200-W, 24-V PEM fuel cell is apower supply, the maximum voltages across the two DCmotors are limited to 12 V, which implies that the maximum
speed of the motors is reduced to half of the inherent rated
value. Inserting a boost circuit between the power source andthe three-leg full-bridge chopper may solve this problem,
resulting in increase of the switching device counts andcomplexity of the circuit configuration.
A novel approach to solve the above drawback ispresented in Fig. 2. The two DC motors are driven by thethree-leg full-bridge chopper, which is composed withsuperimposed two full-bridge choppers at the center leg. The
total number of the switching devices is reduced to six. Theswitching frequency of Q1, Q2, Q5 and Q6 is 10 kHz, while thatof Q3 and Q4 is set at 1 kHz.
The most significant point of this configuration is avoltage boost function of the center common leg, where thepower source is connected to the mid node. The voltage boost
ratio must be determined by the duty cycle of Q3 and Q4 tomaintain the DC bus voltage at a constant value even though
the power source voltage varies. Therefore, the duty cycles ofQ1, Q2, Q5 and Q6 are also adjusted in accordance with thevoltage boost ratio of the center leg.

Q1

Q3

Q5

D1+

D3

D5--+

CM
Left+

M
Right

D2

D4Q2

D6Q4Q6

D7 L
FuelCell(200W/24V)

Fig. 2. Three-leg full-bridge chopper with boost function.

Q1

Q3

Q5

D1+

D3+C-

D5-

M
Left

+

M
Right

D2

D4Q4

Q2

D6Q6

D7 L
Fuel
Cell

(a) Forward motion.

Q1

Q3

Q5

D1+

D3+C-

M
Left
D2

3. Operations of Proposed Chopper Incorporated
Voltage Boost Function

Q2

D5-+

M
Right
D4Q4

D6Q6

D7 LIn this section, two basic operations are discussed. One isthe case of a forward motion where both of the two DC motors
are operated in the same direction to move the wheelchair
forward. The other is a right-turn pivot motion where the two
DC motors are operated in the opposite directions with eachother to turn the wheelchair to the right.
北海道

Q5
D3

Q2

2. Three-Leg Full-Bridge Chopper to Drive Two DCMotors

2009/3/17～19

Q3
D1

FuelCell(b) Right-turn pivot motion.
Fig. 3. Basic operations of proposed circuit.

-42(第 4 分冊)©2009 IEE Japan

4-024

平成 21 年電気学会全国大会

Table 1. Electrical parameters of prototype.

Figure 3 (a) and Figure 3 (b) illustrate current paths in thethree-leg full-bridge chopper with voltage boost operation. As
shown in Fig. 3 (a), the forward motion makes Q1, Q4 and Q5
turn on, and makes Q2, Q3 and Q6 turn off. The switching
operation of Q4 allows voltage boost action and provides
current flows through the two DC motors at the same time.
For backward motion of the wheelchair, Q2, Q3, and Q6 areturned on, while Q1, Q4 and Q5 are turned off.
Figure 3 (b) shows the current paths when the right-turnpivot motion is carried out. In this motion, turning on Q3 andQ6 allows the right DC motor rotating in the reverse direction,
while turning on Q1 and Q4 makes it possible to rotate the left
DC motor in the forward direction and to boost the powersource voltage at the same time.
In the case of regeneration from both of the two DCmotors, a diode D7 blocks the power flow back into the powersource, i. e., the PEM fuel cell. The regenerated power of themotors is stored only in a DC bus capacitor C .

Voltage of power supply
Switching frequency (Q1, Q2 , Q5, Q6)
Switching frequency (Q3, Q4)
Capacitor C
Rated power of DC motors
Rated voltage of DC motors

24 V
10 kHz1 kHz
3600uF, 350 V
110 W
72 V

5V/div
Q1

Q3

Q4

4. Experimental System and Results
A prototype of the proposed circuit was designed and set
up, of which principal electrical parameters are listed in Table 1.
Using the prototype, some basic operations were examinedthrough the experimental tests. Figure 4 and Figure 5 show
the gate signal waveforms of the switching devices in theprototype circuit. Figure 4 (a) corresponds to the forward
motion of the wheelchair, and Fig. 4 (b) represents thewaveforms in backward motion.
As described in the previous section, the forward motion
makes Q1 and Q5 operate at 10 kHz and Q4 at 1 kHz with 50-%
duty cycle. As shown in Fig. 4 (b), Q2 and Q6 repeats theirswitching action at 10 kHz according to the motor voltage
command, and Q3 and Q4 keep on operation of 1 kHz with50-% duty cycle.
Figure 5 shows the gate signals when the right-turn pivot
motion is performed. Even in this case, Q3 and Q4 maintain 1kHz, 50-% duty cycle operation, which makes it possible toboost up the power source voltage.

Q5
Time:100us/div(a) Forward motion.
5V/div
Q2

Q3

Q4

Q65. Conclusion
A novel technique to drive independent two DC motors at
the same time was proposed in this paper. The proposed
power circuit consists of three-leg full-bridge chopper, which
has advantage over conventional circuit configuration in thereduced counts of the switching devices. In addition, theproposed three-leg configuration incorporates the voltage boost
function of the power source. This function compensates forthe reduced voltages applied to the motors. This circuit
configuration can be applied to not only electric wheelchairs
but also other traction systems that require multiple pairs of DCmotors.

Time:100us/div(b) Backward motion.

Fig. 4. Gate signals in forward and backward direction.
5V/div
Q1

Q3

References
Q4(1) C. Anyapo, K. Saito, T. Noguchi, “Development of Electric
Wheelchair Using Fuel Cell”, Proceedings of Niigata
Branch of IEEJ, IV-6, p. 56, 2006.
(2) C. Anyapo, K. Saito, T. Noguchi, “Full-Bridge Chopper for
Driving Two DC Motors with Reduced Counts ofSwitching Devices”， Proceedings of Niigata Branch ofIEEJ, IEEE-13，p. 143, 2008.

2009/3/17～19

北海道

Q6
Time:100us/div

Fig. 5. Gate signals in right-turn pivot motion.

-43(第 4 分冊)©2009 IEE Japan