Electricity: motive power systems – Positional servo systems – Pulse-width modulated power input to motor
Reexamination Certificate
2003-02-19
2004-03-23
Duda, Rina I (Department: 2837)
Electricity: motive power systems
Positional servo systems
Pulse-width modulated power input to motor
C318S254100, C318S811000, C318S432000, C318S434000, C318S434000, C318S132000
Reexamination Certificate
active
06710569
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a technique for driving a motor, and more particularly to a technique for driving a PWM-controlled motor.
U.S. patent application Ser. No. 10/307,986 (filed Dec. 3, 2002) by the same inventors as the present application discloses a motor driving device, which is an example of a technique for driving a motor by energizing motor coils of different phases with PWM control in parallel. A motor driving device of
FIG. 13
, which is one embodiment disclosed in the application, will now be described.
The motor driving device of
FIG. 13
drives a three-phase motor (having U phase, V phase and W phase) by energizing the motor coils with PWM control. This motor driving device includes a plurality of transistors Tr
11
, Tr
12
, Tr
21
, Tr
22
, Tr
31
and Tr
32
(hereinafter referred to collectively as “Tr”) to be switched for appropriately energizing the motor coils, a plurality of diodes D
11
, D
12
, D
21
, D
22
, D
31
, D
32
(hereinafter referred to collectively as “D”) for supplying a regenerative current to the motor coils when the transistors Tr are OFF, a power supply
1
for driving the motor, a Hall signal processing section
2
for producing signals that indicate the rotor position from signals from Hall elements, an energization switching section
3
for switching energized phases at a predetermined cycle, a level shift section
4
for applying the gate voltage of each transistor Tr according to the output from the energization switching section
3
, an oscillation section
5
for producing set pulse signals SP
1
and SP
2
, a torque command signal generation section
6
for producing torque command signals TQ
1
, TQ
2
and TQ
3
from an original torque command signal TQ, a comparison section
7
for comparing a current detection signal DS with the torque command signals TQ
1
to TQ
3
to output comparison results CR
1
, CR
2
and CR
3
, respectively, a masking section
8
for selectively masking or not masking the comparison results CR
1
and CR
2
, and a PWM control section
9
for producing PWM control signals P
1
and P
2
. Note that the current detection signal DS is a signal obtained by amplifying, with an amplifier A, a voltage that is present across the current detection resistor R when the current applied to the motor coil is allowed to flow through the current detection resistor R.
The energization switching section
3
switches the energized phases at a cycle of a period corresponding to 60 electrical degrees in a cycle of a phase current. At the switching, two phases are selected as the energized phases to be energized with PWM control. The remaining one phase is controlled so that the corresponding transistor Tr is fixed to ON for one cycle.
The masking section
8
receives the comparison results CR
1
to CR
3
from the comparison section
7
and the PWM control signals P
1
and P
2
from the PWM control section
9
for selectively masking or not masking the comparison results CR
1
and CR
2
according to the PWM control signals P
1
and P
2
and the comparison result CR
3
.
The PWM control section
9
turns ON the PWM control signal P
1
according to the set pulse signal SP
1
, and turns it OFF when detecting, from the comparison result CR
1
, that the level of the current detection signal DS has reached that of the torque command signal TQ
1
. Similarly, the PWM control signal P
2
is turned ON according to the set pulse signal SP
2
, and is turned OFF when the PWM control section
9
detects, from the comparison result CR
2
, that the level of the current detection signal DS has reached that of the torque command signal TQ
2
.
The operation of the motor driving device of
FIG. 13
having such a configuration will now be described with reference to the drawings.
FIG. 14A
to
FIG. 14C
each illustrate a phase current to be applied to a motor coil by the motor driving device of
FIG. 13
, wherein
FIG. 14A
illustrates a U-phase current,
FIG. 14B
illustrates a V-phase current, and
FIG. 14C
illustrates a W-phase current. Note that each hatched portion in the figures denotes an energized phase to be energized with PWM control, and any other portion denotes an energized phase to be energized while the transistor Tr is fixed to ON.
These phase currents are applied for every 60 electrical degrees according to the torque command signals TQ
1
to TQ
3
illustrated in FIG.
14
D. During a period of 60 electrical degrees, the torque command signal TQ
1
keeps increasing, and the torque command signal TQ
2
keeps decreasing, with the torque command signal TQ
3
being obtained by synthesizing the torque command signal TQ
1
with the torque command signal TQ
2
.
As the energization switching section
3
switches the energized phases at a cycle of a period corresponding to 60 electrical degrees in a cycle of a phase current, the level of each phase current changes as follows. First, in one cycle, the level increases according to the torque command signal TQ
1
. In the next cycle, the level stays constant according to the torque command signal TQ
3
. Then, in the following cycle, the level decreases according to the torque command signal TQ
2
. Then, after the polarity inverts, the level of each phase current undergoes similar transitions. The motor driving device of
FIG. 13
drives the motor by using trapezoidal phase currents as illustrated in
FIG. 14A
to FIG.
14
C.
Next, PWM control with the motor driving device of
FIG. 13
will be described with reference to the timing charts of
FIG. 15A
to
FIG. 15E
, illustrating a portion of
FIG. 14A
to
FIG. 14D
around time t1 in an enlarged manner.
FIG. 15A
illustrates the set pulse signals SP
1
and SP
2
.
FIG. 15B
illustrates the PWM control signals P
1
and P
2
.
FIG. 15C
illustrates the torque command signals TQ
1
to TQ
3
and the current detection signal DS. FIG.
15
D and
FIG. 15E
illustrate the V-phase current and the W-phase current, respectively.
Upon receiving the set pulse signal SP
1
, the PWM control section
9
turns ON the PWM control signal P
1
. Thus, the V-phase current is energized (period A in
FIG. 15B
to FIG.
15
D). Then, upon detecting, from the comparison result CR
1
, that the level of the current detection signal DS has reached that of the torque command signal TQ
1
, the PWM control section
9
turns OFF the PWM control signal P
1
. Thus, a regenerative current flows through the V phase (period A′ in FIG.
15
D). Similarly, upon receiving the set pulse signal SP
2
, the PWM control section
9
turns ON the PWM control signal P
2
. Thus, the W-phase current is energized (period B in
FIG. 15B
, FIG.
15
C and FIG.
15
E). Then, upon detecting, from the comparison result CR
2
, that the level of the current detection signal DS has reached that of the torque command signal TQ
2
, the PWM control section
9
turns OFF the PWM control signal P
2
. Thus, a regenerative current flows through the W phase (period B′ in FIG.
15
E).
When the motor driving device of
FIG. 13
is driving the motor at a low torque, the ON periods of the PWM control signals P
1
and P
2
(period A and period B) do not overlap with each other, and the two phases to be PWM-controlled are controlled fully independently. As a result, it is possible to apply trapezoidal phase currents as illustrated in
FIG. 14A
to
FIG. 14C
, thereby suppressing vibrations of the motor and thus reducing noise from the motor.
On the other hand, when the motor driving device of
FIG. 13
drives the motor at a high torque, the ON periods of the PWM control signals P
1
and P
2
(period A and period B) overlap with each other.
Next, PWM control when the motor driving device of
FIG. 13
drives the motor at a high torque will be described with reference to the timing charts of
FIG. 16A
to
FIG. 16E
, illustrating a portion of
FIG. 14A
to
FIG. 14D
around time t1 in an enlarged manner.
FIG. 16A
illustrates the set pulse signals SP
1
and SP
2
.
FIG. 16B
illustrates the PWM control signals P
1
and P
2
.
FIG. 16C
illustrates the torque command signals TQ
Iwanaga Taishi
Yamamoto Yasunori
Duda Rina I
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
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