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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a drive control apparatus for a brushless DC
motor mounted on a compressor or the like and a method for driving the
brushless DC motor.
2. Description of the Related Art
A brushless DC motor includes a stator having three phase windings and a
rotor having permanent magnets.
When the brushless DC motor is driven, a DC voltage circuit for outputting
a DC voltage and a switching circuit receiving the output voltage of the
DC voltage circuit are used.
The switching circuit has three series circuits each having a pair of
switching elements series-connected on the upstream side and downstream
side with respect to current flow. Each of the connection nodes between
the paired switching elements of the series circuits is connected to a
corresponding one of the phase windings of the brushless DC motor.
The respective phase windings of the brushless DC motor are sequentially
energized by continuously setting one of the upstream side switching
element of one of the series circuits of the switching circuit and the
downstream side switching element of a different one of the series
circuits in the ON state, intermittently turning ON the other switching
element and sequentially changing the switching elements to be turned ON.
Energization of the respective phase windings generates magnetic fields
from the respective phase windings. Interaction between the thus generated
magnetic fields and the magnetic fields created by the permanent magnets
of the rotor rotates the rotor. Switching of the energization of the
respective phase windings is called commutation.
When the rotor is rotated, a voltage is induced in a phase winding which is
not energized. The induced voltage is derived out and the rotation
position of the rotor is detected based on a variation in the induced
voltage. The timing of energization switching (commutation) for each phase
winding is controlled according to the detected rotation position. The
energization switching is repeatedly effected to continuously rotate the
rotor.
One example of the driving control for the brushless DC motor is disclosed
in Japanese Patent Specification No. H.1-13318 and Japanese Patent
Disclosure No. H.2-142383.
In the example in Japanese Patent Specification No. H.1-13318, an inverter
(4) is driven to sequentially energize the respective phase windings of a
brushless motor (5). Then, the rotation position of a rotor (6) is
detected by use of position detectors (71, 72, 73). Energization of each
phase winding is controlled in a period of 120 electrical degrees
according to the detected rotation position. In the energization of the
period of 120 electrical degrees, energization of a front half period of
60 electrical degrees is continuously effected and energization of a
latter half period of 60 electrical degrees is intermittently effected
(subjected to the pulse-width modulation).
In the example in Japanese Patent Disclosure No. H.2-142383, a
semiconductor switching element (2) is driven to sequentially energize the
respective phase windings of a brushless motor (1). Then, a voltage
induced in each phase winding is sampled and fetched by a microcomputer
(5) and processed in the microcomputer (5) so as to detect the rotation
position of a rotor of the brushless motor (1). Energization of each phase
winding is controlled according to the detected rotation position.
At the time of switching of energization of the phase windings of the
brushless DC motor, a counter electromotive force is generated in a phase
winding whose energization is to be interrupted. When the counter
electromotive force is generated, a current will flow from the switching
circuit to the DC voltage circuit. The reverse flow of current reduces the
service life of the electrical parts of the DC voltage circuit and at the
same time reduces the rotation torque of the brushless DC motor. If the
rotation torque of the brushless DC motor is reduced, the operation
efficiency of the brushless DC motor is lowered and large noises and
vibration are generated from the brushless DC motor.
SUMMARY OF THE INVENTION
An object of this invention is to prevent the reverse flow of current from
the switching circuit to the DC voltage circuit so as to increase the
service life of electrical parts of the DC voltage circuit and at the same
time suppress a reduction in the rotation torque of the brushless DC
motor, thereby enhancing the operation efficiency of the brushless DC
motor and suppressing generation of large noises and vibration of the
brushless DC motor.
According to this invention, the above object can be attained by a drive
control apparatus for a brushless DC motor which includes a stator having
three phase windings and a rotor having magnets. The drive control
apparatus comprises a switching circuit including three series circuits
each having a pair of switching elements series-connected on the upstream
side and downstream side with respect to current flow, each of the
connection nodes between the paired switching elements of the series
circuits being connected to a corresponding one of the phase windings; a
DC voltage circuit outputting a DC voltage to the series circuits of the
switching circuit; first control means for sequentially energizing the
phase windings by continuously setting one of the switching element on the
upstream side in one of the series circuits of the switching circuit and
the switching element on the downstream side in a different one of the
series circuits in the ON state, intermittently turning ON the other
switching element and sequentially changing the switching elements to be
turned ON; second control means for forcedly continuously setting the
switching element, which is one of the switching elements to be turned ON
by the first control means and which has been set in the ON state, in the
ON state for a first preset initial period of time and forcedly
intermittently turning ON one of the switching elements which is newly
turned ON for the first preset initial period of time; and third control
means for controlling the ON/OFF duty of the switching element which is to
be intermittently turned ON by one of the first and second control means
to adjust the speed of the brushless DC motor.
According to this invention, the above object can be attained by a method
for driving a brushless DC motor in an apparatus including a brushless DC
motor which includes a stator having three phase windings and a rotor
having magnets, and a switching circuit including three series circuits
each having a pair of switching elements series-connected on the upstream
side and downstream side with respect to current flow, each of the
connection nodes between the paired switching elements of the series
circuits being connected to a corresponding one of the respective phase
windings, comprising a first step of applying a DC voltage to the series
circuits of the switching circuit; a second step of turning ON/OFF the
switching elements of the switching circuit to sequentially energize the
phase windings for a period of 120 electrical degrees; and a third step of
intermittently effecting the energization operation in a first preset
period among the period of 120 electrical degrees in which the
energization of the phase windings is effected in the second step,
continuously effecting the energization operation in a next preset period
among the period of 120 electrical degrees and intermittently effecting
the energization operation in a last preset period among the period of 120
electrical degrees.
Additional objects and advantages of the invention will be set forth in the
description which follows, and in part will be obvious from the
description, or may be learned by practice of the invention. The objects
and advantages of the invention may be realized and obtained by means of
the instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part
of the specification, illustrate presently preferred embodiments of the
invention, and together with the general description given above and the
detailed description of the preferred embodiments given below, serve to
explain the principles of the invention.
FIG. 1 is a block diagram of an electric circuit according to a first
embodiment of this invention;
FIG. 2 is a plan view showing the structure of the brushless DC motor of
one of the first and second embodiments with partly cut-away portion;
FIG. 3 is a plan view showing the structure of a rotor shown in FIG. 3;
FIG. 4 is an exploded perspective view showing the structure of the rotor
of FIG. 2;
FIG. 5 shows the respective phase windings mounted on a stator shown in
FIG. 3;
FIG. 6 is a cross sectional view showing the structure of a compressor
having the brushless DC motor of one of the first and second embodiments
incorporated therein;
FIG. 7 is a block diagram showing a control section in the first
embodiment;
FIG. 8 is a diagram showing the relation between the rotation position of
the rotor in one of the first and second embodiments and the operation
states of transistors;
FIGS. 9a-9g are signal waveform diagrams for illustrating the operation of
the first embodiment;
FIG. 10 is a block diagram showing the control section of FIG. 7 with part
of the main portions thereof removed;
FIG. 11 is a diagram showing the relation between the rotation position of
the rotor in the case of FIG. 12 and the operation states of transistors;
FIG. 12a-12g are signal waveform diagrams illustrating the operation
effected in the case of FIG. 10;
FIG. 13 is a diagram illustrating currents flowing between the switching
elements and the respective phase windings in the case of FIG. 10;
FIG. 14 is a diagram illustrating reverse currents occurring in the case of
FIG. 10;
FIG. 15 is a diagram illustrating currents flowing between the switching
elements and the respective phase windings in the first and second
embodiments;
FIG. 16 is a diagram showing the relation between the current waveform and
the rotation torque of the brushless DC motor in the first and second
embodiments;
FIG. 17 is a diagram showing the relation between the current waveform and
the rotation torque of the brushless DC motor in the case of FIG. 12;
FIG. 18 is a block diagram showing an electric circuit of the second
embodiment of this invention;
FIG. 19 is a concrete block diagram showing a control section in the second
embodiment;
FIG. 20 is a flowchart illustrating the operation of the second embodiment;
and
FIGS. 21a-21f are signal waveform diagrams for illustrating the operation
of the second embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
There will now be described a first embodiment of this invention with
reference to the accompanying drawings.
In FIG. 1, 1 denotes a brushless DC motor having three phase windings Lu,
Lv, Lw connected in the star connection form with a neutral point P set at
the center. The free ends of the three phase windings Lu, Lv, Lw are
respectively connected to terminals Su, Sv, Sw.
A single-phase AC power source 2 is connected to a DC voltage circuit 3.
The DC voltage circuit 3 rectifies the voltage from the single-phase AC
power source 2 to output a DC voltage.
Output terminals of the DC voltage circuit 3 are connected to a switching
circuit 4. The switching circuit 4 has three series circuits of U-phase,
v-phase and W-phase each having a pair of switching elements
series-connected on the upstream side and downstream side with respect to
current flow. Each of the series circuits is applied with a DC voltage
output from the DC voltage circuit 3.
The U-phase series circuit includes a transistor T.sub.u+ which is the
upstream side switching element and a transistor T.sub.u- which is the
downstream side switching element. The V-phase series circuit includes a
transistor T.sub.v+ which is the upstream side switching element and a
transistor T.sub.v- which is the downstream side switching element. The
W-phase series circuit includes a transistor T.sub.w+ which is the
upstream side switching element and a transistor T.sub.w- which is the
downstream side switching element. Flywheel diodes D are respectively
connected in parallel with the transistors.
The connection node between the transistors T.sub.u+ and T.sub.u-, the
connection node between the transistors T.sub.v+ and T.sub.v- and the
connection node between the transistors T.sub.w+ and T.sub.w- are
respectively connected to the terminals Su, Sv and Sw of the brushless DC
motor 1.
The switching circuit 4 has a function of sequentially energizing the phase
windings Lu, Lv, Lw of the brushless DC motor 1 by selectively turning ON
and OFF the transistors.
The output terminal of the DC voltage circuit 3 is connected to a series
circuit of resistors 5 and 6. A voltage occurring across the resistor 6 is
input to the inverting input terminals (-) of comparators 7, 8 and 9 as a
reference voltage Vo. The resistances of the resistors 5 and 6 are so
determined that the voltage occurring across the resistor 6 will be set to
one half the level of the output voltage of the DC voltage circuit 3.
A voltage V.sub.1u induced in the phase winding Lu is input to the
non-inverting input terminal (+) of the comparator 7. A voltage V.sub.1v
induced in the phase winding Lv is input to the non-inverting input
terminal (+) of the comparator 8. A voltage V.sub.1w induced in the phase
winding Lw is input to the non-inverting input terminal (+) of the
comparator 9.
Each of the comparators 7, 8, 9 outputs a logic "0" signal when the level
of the induced voltage V.sub.1u, V.sub.1v, V.sub.1w thereof is lower than
the level of the reference voltage Vo and outputs a logic "1" signal when
the level of an input voltage to the non-inverting input terminal (+)
thereof is equal to or higher than the level of the reference voltage vo.
That is, the level of each of the induced voltages V.sub.1u, V.sub.1v,
V.sub.1w, thereof is compared with the level of the reference voltage vo,
and when the levels thereof cross each other, the logic level of the
output signal of a corresponding one of the comparators 7, 8, 9 is
changed.
The output signals of the comparators 7, 8, 9 are input to a control
section 10. The control section 10 monitors the voltages V.sub.1u,
V.sub.1v, V.sub.1w induced in the phase windings Lu, Lv, Lw via the
comparators 7, 8, 9, detects the rotation position of a rotor 42 of the
brushless DC motor 1, which will be described later based on variations in
the induced voltages V.sub.1u, V.sub.1v, V.sub.1w and creates driving
signals for the transistors of the switching circuit 4 according to the
detected rotation position of the rotor 42. The driving signals are
supplied to the bases of the transistors of the switching circuit 4 so as
to turn ON or OFF the transistors. Two of the phase windings Lu, Lv, Lw of
the brushless DC motor 1 are sequentially energized by the turn-ON/OFF of
the transistors. Switching of the energization of the respective phase
windings Lu, Lv, Lw is called commutation.
Next, the construction of the brushless DC motor 1 is explained.
As shown in FIG. 2, the brushless DC motor 1 includes a stator 41 and the
rotor 42 which is rotatably mounted inside the stator 41.
A large number of (24) slots 41a are formed in the inner peripheral surface
of the stator 41 and slot numbers from "1" to "24" identify the slots 41a.
The phase windings Lu, Lv, Lw are disposed and fixed in the slots 41a with
the positional deviation of 120 degrees set therebetween.
In practice, the phase winding Lu is constructed by a pair of phase
windings L.sub.ua and L.sub.ub which are connected in parallel with each
other. The phase windings L.sub.ua and L.sub.ub are arranged in opposed
positions.
In practice, the phase winding Lv is constructed by a pair of phase
windings L.sub.va and L.sub.vb which are connected in parallel with each
other. The phase windings L.sub.va and L.sub.vb are arranged in opposed
positions.
In practice, the phase winding Lw is constructed by a pair of phase
windings L.sub.wa and L.sub.wb which are connected in parallel with each
other. The phase windings L.sub.wa and L.sub.wb are arranged in opposed
positions.
As shown in FIG. 3, the rotor 42 includes a yoke 44 disposed around a
rotating shaft 43, a plurality of, for example, four permanent magnets 45
disposed around the yoke 44, an annular portion 46 disposed around the
permanent magnets 45, and four coupling portions 47 disposed in gaps
between the permanent magnets 45 to couple the yoke 44 with the annular
portion 46. The coupling portions 47 have a function of magnetically
coupling the yoke 44 with the annular portion 46.
As more specifically shown in FIG. 4, the yoke 44, annular portion 46 and
coupling portions 47 of the rotor 42 are formed by stacking a large number
of circular steel plates 51. Each of the steel plates 51 has insertion
holes for reception of the permanent magnets 45 formed in the peripheral
portions thereof, an insertion hole 53 for reception of the rotating shaft
43 formed in the central portion thereof, and four rivet insertion holes
54 formed in positions (corresponding to the position of the yoke 44)
around the insertion hole 53. End plates 55 are disposed on the end
positions in the stack direction of the steel plates 51. Each of the end
plates 55 also has an insertion hole 53 for receiving the rotating shaft
43 and four rivet insertion holes 54.
Assembling of the rotor 42 is effected by first stacking the steel plates
51 and inserting the permanent magnets 45 into the respective insertion
holes 52. Each of the permanent magnets 45 is formed by solidifying
magnetic particles and has no magnetic polarity when it is inserted into
the corresponding insertion hole 52, and the magnetic polarity thereof is
not determined until the magnetizing process which will be described later
is effected. After this, the end plates 55 are set in contact with the end
portions of the stacked structure of the steel plates 51 and rivets (not
shown) are inserted into the rivet insertion holes 54 of the end plates 55
and the steel plates 51. Then, both ends of the rivets are caulked so as
to fix the whole rotor 42.
Connections of the phase windings L.sub.ua, L.sub.ub, L.sub.va, L.sub.vb,
L.sub.wa and L.sub.wb are shown in FIG. 5.
For example, as shown in FIG. 6, the brushless DC motor 1 with the above
structure is mounted on a compressor 60 for an air-conditioner.
The outer appearance of the compressor 60 is constructed by a casing 61 and
a cover 62 which closes the upper opening of the casing 61. In the casing
61, a compressor 63 is disposed on the bottom portion thereof and the
brushless DC motor 1 is disposed in position above the compressor 63.
A terminal board 64 is mounted on the upper surface of the cover 62 and the
terminals Su, Sv, Sw are provided on the terminal board 64. The terminals
Su, Sv, Sw are connected to the phase windings Lu, Lv, Lw in the casing 61
via an electric cable 65.
The terminals Su, Sv, Sw of the terminal board 64 are connected to the
output terminals of the switching circuit 4 via a connector and electric
cable when the manufacturing process of the compressor 60 is completed.
The control section 10 performs the following functions.
[1 ]The control section sequentially energizes the phase windings Lu, Lv,
Lw by continuously setting one of the upstream side switching element of
one of the series circuits of the switching circuit and the downstream
side switching element of a different one of the series circuits in the ON
state, intermittently turning ON the other Switching element and
sequentially changing the switching elements to be turned ON. More
precisely, in a case where the induced voltage V.sub.1u, V.sub.1v,
V.sub.1w ; generated in one of the phase windings which is set in the
non-energized state varies in a falling direction, the upstream side
transistor is continuously set in the ON state and the downstream side
transistor is intermittently turned ON, and in a case where the induced
voltage V.sub.1u, V.sub.1v, V.sub.1w generated in one of the phase
windings which is set in the non-energized state varies in a rising
direction, the upstream side transistor is intermittently turned ON and
the downstream side transistor is continuously set in the ON state. This
control operation is effected to precisely detect the rotation position of
the rotor 42.
[2] The control section forcedly continuously sets one transistor, which is
one of the transistors to be set into the ON state by the first control
means and which has been kept in the ON state, in the ON state for a
preset initial period (a period of 20 electrical degrees) and
intermittently turns ON one transistor which is newly turned ON for the
first preset initial period.
[3] The control section controls controlling the ON-OFF duty of the
transistor to be intermittently turned ON by the first or second control
means to adjust the speed of the brushless DC motor 1.
[4] The control section detects the rotation position of the rotor 42 based
on a variation in the induced voltage V.sub.1u, V.sub.1v, V.sub.1w
generated in one of the phase windings Lu, Lv, Lw which is set in the
non-energized state when a second preset period (a period of 25 electrical
degrees) has elapsed after the switching of energization of the phase
windings Lu, Lv, Lw was effected by the first control means. More
specifically, the level of the induced voltage V.sub.1, V.sub.1v, V.sub.1w
generated in one of the phase windings Lu, Lv, Lw which is set in the
non-energized state is compared with the level of the preset reference
voltage vo and the rotation position of the rotor 42 is detected as the
reference rotation position when the compared levels cross each other.
[5] The control section also controls the timing of switching of
energization of the phase windings Lu, Lv, Lw according to the rotation
position of the rotor 42 detected by the detection means to set the
energization period of the phase windings Lu, Lv, Lw to a period of 120
electrical degrees.
The block of the control section 10 is shown in FIG. 7.
Outputs of the comparators 7, 8, 9 are input to a position detecting
circuit 20. The position detecting circuit 20 selects one of the output
signals of the comparators 7, 8, 9 based on the count value (corresponding
to the energization mode A, B, C, D, E or F) of an energization mode
counter 23 which will be described later. That is, when the phase windings
Lv, Lw are energized and the phase winding Lu is set in the non-energized
state, the output signal of the comparator 7 corresponding to the phase
winding Lu which is set in the non-energized state is selected. When the
phase windings Lw, Lu are energized and the phase winding Lv is set in the
non-energized state, the output signal of the comparator 8 corresponding
to the phase winding Lv which is set in the non-energized state is
selected. When the phase windings Lu, Lv are energized and the phase
winding Lw is set in the non-energized state, the output signal of the
comparator 9 corresponding to the phase winding Lw which is set in the
non-energized state is selected. Then, the position detection circuit 20
monitors a point of change of the logic level of the selected output
signal (point of change from the logic "0" to "1" or from the logic "1" to
"0") in a period from the time a position detection permitting instruction
from a comparator 36 which will be described later is received until the
count value of the energization mode counter 23 is changed (commutated).
Further, when the logic level of the selected output signal is changed,
the position detection circuit 20 determines that the rotor 42 is set in
the reference rotation position and outputs a position detection signal.
The position detection signal output from the position detection circuit 20
is supplied to a timer counter 21 and control circuit
The timer counter 21 starts a new time counting operation each time the
position detection signal is received. That is, time (electrical angle)
which has elapsed after the reference rotation position of the rotor 42
was detected is measured by the timer counter 21. Further, time T
(corresponding to a period of 60 electrical degrees) from the time the
reference rotation position of the rotor 42 is detected until a next
reference rotation angle is detected is measured. The time count value of
the timer counter 21 is informed to the control circuit 22.
When receiving the position detection signal from the position detection
circuit 20, the control circuit 22 derives the rotation speed of the rotor
42 based on the time count value (time T) of the timer counter 21 and
controls the ON-OFF duty of the ON/OFF signal output from a driving
circuit 25 so as to set a difference between the derived rotation speed
and a preset target speed to zero.
Further, the control circuit 22 derives a value (=T/2; corresponding to a
period of 30 electrical degrees) which is half the time count value (time
T) of the timer counter 21, sets the value into a register 31, derives a
value (=5T/6; corresponding to a period of 50 electrical degrees) which is
5/6 times the time count value of the timer counter 21, sets the value
into a register 32, derives a value (=11T/12; corresponding to a period of
55 electrical degrees) which is 11/12times the time count value of the
timer counter 21, and sets the value into a register 33.
The set value "T/2" (electrical angle of 30.degree.) into the register 31
corresponds to the remaining period from the time the reference rotation
position of the rotor 42 is detected until the switching of energization
(commutation) of the phase windings Lu, Lv, Lw is effected.
The set value "5T/6" (electrical angle of 50.degree.) into the register 32
corresponds to the sum of the remaining period (electrical angle of
30.degree.) from the time the reference rotation position of the rotor 42
is detected until the switching of energization (commutation) of the phase
windings Lu, Lv, Lw is effected and the first preset initial period
(electrical angle of 20.degree.) after the switching of energization.
The set value "11T/12" (electrical angle of 55.degree.) into the register
33 corresponds to the sum of the remaining period (electrical angle of
30.degree.) from the time the reference rotation position of the rotor 42
is detected until the switching of energization (commutation) of the phase
windings Lu, Lv, Lw is effected and the second preset initial period
(electrical angle of 25.degree.) after the switching of energization.
The second preset initial period (electrical angle of 25.degree.) is a
period for inhibiting detection of the induced voltage V.sub.1u, V.sub.1v,
V.sub.1w . At the time of switching of energization of the phase windings
Lu, Lv, Lw, a counter electromotive force is generated in a phase winding
whose energization is to be interrupted. Because the noise by the counter
electromotive force is added to the induced voltage V.sub.1u, V.sub.1v,
V.sub.1w , there may be a possibility that the cross point between the
induced voltage v.sub.1 and the reference voltage Vo cannot be correctly
detected, i.e., that an error occurs in the detection of the reference
rotation position of the rotor 42 may occur. Therefore, detection of the
induced voltage V.sub.1u, V.sub.1v, V.sub.1w is inhibited in the second
preset initial period after the switching of energization.
The set values into the registers 31, 32, 33 are compared with the time
count value of the timer counter 21 by comparators 34, 35, 36,
respectively.
When the time count value of the timer counter 21 has reached the set value
of the register 31, an energization mode switching instruction is issued
from the comparator 34. The energization mode switching instruction is
supplied to the energization mode counter 23.
When the time count value of the timer counter 21 has reached the set value
of the register 32, a pattern switching instruction is issued from the
comparator 34. The pattern switching instruction is supplied to a memory
24.
When the time count value of the timer counter 21 has reached the set value
of the register 33, a position detection permitting instruction is issued
from the comparator 36. The position detection permitting instruction is
supplied to the position detection circuit 20.
The energization mode counter 23 is a six-scale counter whose count value
is sequentially set to one of values of "1" to "6" and counts the number
of energization mode switching instructions issued from the comparator 34.
The count values correspond to the six types of energization modes A, B,
C, D, E and F for the respective transistors of the switching circuit 4
and are informed to the position detection circuit 20 and memory 24.
The memory 24 stores twelve types of driving signal patterns corresponding
to the energization modes A0, A1, B0, B1, C0, C1, D0, D1, E0, E1, F0 and
F1. One of the above memory patterns is read out according to the count
value of the energization mode counter 23 and the pattern switching
instruction generated from the comparator 34 and supplied to the driving
circuit 25.
The driving circuit 25 outputs a driving signal for the transistors of the
switching circuit 4 according to the driving signal pattern read out from
the memory 24 and the instruction issued from the control circuit 22. The
driving signal includes an ON signal for continuously setting the
transistor in the ON state, an ON/OFF signal for intermittently turning ON
the transistor, and an OFF signal for turning OFF the transistor.
Next, the operation of the above construction is explained.
The relation between the energization modes A0, A1, B0, B1, C0, C1, D0, D1,
E0, E1, F0 and F1 and the operation patterns of the transistors of the
switching circuit 4 is shown in FIG. 8. In FIG. 8, ON indicates the
operation of continuously turning-ON the transistor. Further, PWM
indicates the pulse width modulation control, that is, the operation of
intermittently turning-ON the transistor. In FIG. 8, the blank indicates
the operation of turning-OFF of the transistor.
The waveforms of the induced voltages v.sub.1 occurring in the phase
windings Lu, Lv, Lw, the waveforms of currents flowing in the phase
windings Lu, Lv, Lw, and the waveform of a DC current output from the DC
voltage circuit 3 are shown in FIGS. 9a-9g.
First, when the count value of the energization mode counter 23 is "1",
energization of the phase windings from Lu to Lv is effected (energization
modes A0, A1). That is, two corresponding transistors, or the upstream
side transistor T.sub.u+ and the downstream side transistor T.sub.v- are
turned ON and the other transistors are turned OFF.
When the magnetic fields occur in the phase windings Lu, Lv, rotation
torque occurs in the rotor 42 by the interaction between the above
magnetic fields and the magnetic fields created by the permanent magnets
45, thus starting the rotation of the rotor 42. At this time, the induced
voltage v.sub.1w is induced in the phase winding Lw which is set in the
non-energized state by the magnetic action caused by rotation of the
permanent magnets 45.
The induced voltage V.sub.1w in the phase winding Lw is compared with the
reference voltage Vo by the comparator 9. When the level of the induced
voltage V.sub.1w and the level of the reference voltage Vo cross each
other and the logic level of the output signal of the comparator 9 is
changed, the rotation position of the rotor 42 obtained at this time is
detected as the reference rotation position.
When the reference rotation position of the rotor 42 is detected, the
energization mode switching instruction is issued from the comparator 34
when a period of 30 electrical degrees from the detected reference
rotation position has elapsed. The count value of the energization mode
counter 23 is set to "2" in response to the energization mode switching
instruction.
When the count value of the energization mode counter 23 is set to "2",
energization of the phase windings from Lu to Lw is effected (energization
modes B0, B1). That is, two corresponding transistors, or the upstream
side transistor T.sub.u+ and the downstream side transistor T.sub.w- are
turned ON and the other transistors are turned OFF.
When the magnetic fields occur in the phase windings Lu, Lw, rotation
torque occurs in the rotor 42 by the interaction between the above
magnetic fields and the magnetic fields created by the permanent magnets
45, thus causing the rotor 42 to be continuously rotated. At this time,
the induced voltage V.sub.1v is induced in the phase winding Lv which is
set in the non-energized state by the magnetic action caused by rotation
of the permanent magnets 45.
The induced voltage V.sub.1v in the phase winding Lv is compared with the
reference voltage Vo by the comparator 8. When the level of the induced
voltage v.sub.1v and the level of the reference voltage Vo cross each
other and the logic level of the output signal of the comparator 8 is
changed, the rotation position of the rotor 42 obtained at this time is
detected as the reference rotation position.
When the reference rotation position of the rotor 42 is detected, the
energization mode switching instruction is issued from the comparator 34
when a period of 30 electrical degrees from the detected reference
rotation position has elapsed. The count value of the energization mode
counter 23 is set to "3" in response to the energization mode switching
instruction.
When the count value of the energization mode counter 23 is set to "3",
energization of the phase windings from Lv to Lw is effected (energization
modes C0, C1). That is, two corresponding transistors, or the upstream
side transistor T.sub.v+ and the downstream side transistor T.sub.w- are
turned ON and the other transistors are turned OFF.
When the magnetic fields occur in the phase windings Lv, Lw, rotation
torque occurs in the rotor 42 by the interaction between the above
magnetic fields and the magnetic fields created by the per | | |
