Electricity: motive power systems – Induction motor systems
Reexamination Certificate
2001-08-30
2004-03-23
Nappi, Robert (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S254100, C318S434000
Reexamination Certificate
active
06710572
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a drive controller for controlling brushless motors in use as motors for driving discs of audio systems, video tape recorders, and personal computers.
BACKGROUND OF THE INVENTION
This type of controllers for brushless motors is described, for example, in Japanese Patent Laid-Open Publication No. 10-146085. This conventional drive controller has a structure as shown in FIG.
1
. The controller is operated using various control signals as shown in
FIG. 2
controlling various components thereof as will be discussed in more detail below.
In the prior art, a brushless motor M has a permanent magnetic rotor and three-phase armature coils U, V, and W arranged on a circumference of a stator. The stator has rotor-position detectors, one for each of the armature coils, located at the respective armature coils. For brevity, these rotor-position detectors
11
are shown in
FIG. 1
altogether outside the brushless motor M.
As shown in
FIG. 1
, transistor switches for the three-phase motor M consist of P-channel type Metal Oxide Semiconductor field effect (MOS) transistors QUH, QVH, QWH connected to the positive potential source VDD (such transistors hereinafter referred to as positive side transistors), and N-channel type MOS transistors QUL, QVL, QWL connected to the ground (such transistors hereinafter referred to as negative side transistors). The P-channel type and N-channel type transistors are turned ON/OFF by the gate controlling signals supplied to the respective gates of the transistors.
The rotor-position detector
11
may be formed of, for example, hall elements to generates three “positive phase” sinusoidal signals in response to the rotating magnetic field created in the U, V, and W coils, and three sinusoidal “negative phase” signals which are the inversions of the respective positive phase signals. The three phase signals are out of phase with each other by 120° (=360°/3 coils).
A position-detection/phase-shifting circuit
14
takes a difference between the positive and negative outputs contained in the respective three-phase outputs HU, HV, and HW received from the rotor-position detector
11
to eliminate noises that exist in common in the signal lines. Thus, the position-detection/phase-shifting circuit
14
generates six difference signals HU-HV, HV-HW, HW-HU, HV-HU, HW-HV, and HU-HW. From these signals, phase-shifted signals HU
1
, HV
1
, and HW
1
having a phase difference &Dgr;&thgr;=30°, for example, can be generated as shown in FIGS.
2
(
a
)-(
c
). These phase-shifted signals HU
1
, HV
1
, and HW
1
serve as position detection signals. Each of the phase-shifted signals HU
1
, HV
1
, and HW
1
is compared with the inverted version of the respective phase-shifted signals to generate polarity-determination signals UHL, VHL, and WHL for the respective U, V, and W phases, respectively.
The reason for forming three phase-shifted signals HU
1
, HV
1
, and HW
1
is as follows. There is a delay between the point when the armature of the motor M is actuated by a signal received from the rotor-position detector
11
and the point when the armature is actually energized by an energizing current that flows therethrough, due to the inductance of the armature. The delay depends on the time constant, which is determined by the inductance of the armature. Thus, the commutation time of the current through the armature delays behind the normal commutation time, which can harm the driving efficiency of the motor and entail fluctuation of torque.
A full-wave rectifier
15
rectifies the phase-shifted signals HU
1
, HV
1
, and HW
1
received from the position-detection/phase-shifting circuit
14
and generates three full-wave outputs HU
2
(FIG.
2
(
d
)), HV
2
, and HW
2
, which are fed to a comparator
16
. The reference potential of the HU
2
, HV
2
, and HW
2
is taken to be the ground potential Vgnd. Waveforms of the signals HV
2
and HW
2
are not shown in FIG.
2
.
The oscillator
13
includes a built-in triangular signal generation circuit for generating high frequency triangular signals OSC (FIG.
2
(
e
)) in the frequency range above 16 KHz for example, which are fed to the comparator
16
. The triangular signal generation circuit includes an operational amplifier, a constant current power supply, and a condenser. The triangular signals OSC also has a reference voltage equal to the ground potential Vgnd.
The comparator
16
receives rectified full-wave signals HU
2
, HV
2
, HW
2
and triangular signals OSC from the oscillator
13
, and compares them to generate pulse width modulation (PWM) signals UPWM, VPWM, and WPWM from their differences.
Pre-drive circuits
17
U,
17
V, and
17
W provided for the respective three phases receive PWM signals UPWM, VPWM, WPWM from the comparator
16
, and polarity discrimination signals UHL, VHL, and WHL for the respective phases from the position-detection/phase-shifting circuit
14
directly or via the comparator
16
. These pre-drive circuits invert or switches PWM signals UPWM, VPWM, WPWM in accordance with the polarity discrimination signals UHL, VHL, WHL to form gate control signals VUGH, VUGL, VVGH, VVGL, VWGH, and VWGL as shown in FIGS.
2
(
f
)-(
k
), which control signals are supplied to the P-channel type MOS transistors QUH, QVH, and QWH on the positive side, and to the N-channel type MOS transistors QUL, QVL, QWL on the negative side.
As a typical example, take gate control signals VUGH and VUGL for the U-phase. It is seen in
FIG. 2
that in the first half period shown of
FIG. 2
, the positive side MOS transistor QUH is turned ON and OFF by the gate control signal VUGH, while the negative side MOS transistor QUL is turned OFF by the gate control signal VUGL. In the second half period, on the other hand, the positive side MOS transistor QUH is turned OFF by the gate control signal VUGH, while the negative side MOS transistor QUL is turned ON and OFF by the gate control signal VGUL. It is noted that in both the positive side MOS transistor QUH and the negative side MOS transistor QUL, a backward current flows through a back gate contact of the transistor and a parasitic diode associated with it during the OFF periods.
A torque instruction circuit
12
generates control signals for controlling the rotational speed of the motor M by controlling the amplitudes of the phase-shifted signals HU
1
, HV
1
, and HW
1
. This can be done by comparing a measured value Vdet indicative of the actual speed of the motor M and a preset value Vs and controls the amplitudes in accordance with the differences between them.
In this arrangement, if, for example, the measured value Vdet representing the actual speed of the motor M is greater than the preset value Vs (i.e. the motor is faster than the intended speed), the torque instruction circuit
12
supplies the position-detection/phase-shifting circuit
14
with a control signal determined by the difference between them to reduce the amplitudes of the phase-shift signals HU
1
, HV
1
, HW
1
. Accordingly, the rectified full-wave signals HU
2
, HV
2
, HW
2
are output from the full-wave rectifier
15
with a reduced wave height.
The reduction of the height of the rectified full-wave signals HU
2
, HV
2
, HW
2
results in a decrease in the pulse width of the PWM ON-OFF duty pulses UPWM, VPWM, WPWM issued from the comparator
16
, which in turn decreases the current energizing the motor M via the MOS transistors QUH QWL for the respective U, V, and W phases. If the rotational speed is lower than the preset value, the current to the motor is increased by the same mechanism to thereby raise the speed of the motor. In this manner, the motor speed is controlled precisely.
In this conventional drive controller, the gate control signals VUGH VWGL shown in FIGS.
2
(
f
)-(
k
) are supplied to the MOS transistors QUH QWL in the respective phases, such that the negative side MOS transistors are turned OFF while the positive side MOS transistors are turned ON and OFF while PWM controlled in the respective phases. Conversely, the positive side MOS t
McCloud Renata
Nappi Robert
Rohm & Co., Ltd.
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