Electricity: motive power systems – Induction motor systems
Reexamination Certificate
2001-09-18
2004-07-06
Nappi, Robert (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S434000
Reexamination Certificate
active
06759827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a brush-less motor, a control circuit thereof and the like, relates to a constitution used in a vacuum pump of, for example, a vacuum pump of a magnetic bearing type turbo-molecular pump or the like or a magnetic bearing spindle or the like.
2. Description of the Related Art
Conventionally, starting a brush-less motor is carried out as follows.
There is a brush-less motor having a rotor having a permanent magnet of two poles and three motor phase windings for generating a magnetic field for rotating the rotor at its surrounding.
In such a brush-less motor, there is a constitution in which as a sensor-less brush-less motor control circuit which is not provided with a sensor for detecting positions of magnetic poles, current for driving the motor is made to flow to two motor windings in three motor windings to thereby rotate a rotor, by rotating the rotor, positions of magnetic poles of the rotor are detected from induced electromotive force produced in a remaining one of the motor windings and based on the positions of the magnetic poles, the current of the motor winding is successively switched.
An explanation will be given of an example of the above-described conventional brush-less motor control circuit in reference to FIG.
8
and FIG.
9
.
FIG. 8
is a conceptual view representing a brush-less motor of a three-phase all wave system. A rotor
150
is provided with a permanent magnet of two poles. There are arranged U-phase, V-phase and W-phase motor windings
151
U,
151
V and
151
W around the rotor. Current is made to flow to excite two of the motor windings and the rotor
150
is rotated by attractive force of magnetic force thereof. Excited ones of the motor windings
151
U,
151
V and
151
W are successively switched in accordance with positions of the magnetic poles of the rotor
150
to thereby continue rotating the rotor
150
. The positions of the magnetic poles are detected by detecting voltage induced in a remaining one of the motor windings which is not excited.
As shown by
FIG. 9
, there are six kinds of driving voltage vectors outputted to the motor windings
151
U,
15
V and
151
W of the brush-less motor of the three-phase all wave system.
The driving voltage vector when current is made to flow from the U-phase motor winding to the V-phase motor winding is defined as driving voltage vector
1
, the driving voltage vector when current is made to flow from the U-phase motor winding to the W-phase motor winding is defined as driving voltage vector
2
, the driving voltage vector when current is made to flow from the V-phase motor winding to the W-phase motor winding is defined as driving voltage vector
3
, the driving voltage vector when current is made to flow from the V phase motor winding to the U-phase motor winding is defined as driving voltage vector
4
, the driving voltage vector when current is made to flow from the W-phase motor winding to the U-phase motor winding is defined as driving voltage vector
5
, the driving voltage vector when current is made to flow from the W-phase motor winding to the V-phase motor winding is defined as driving voltage vector
6
and hereinafter, the driving voltage vectors will be distinguished from each other by the numerals.
The numerals of the driving voltage vectors are indicated by circling the numerals in FIG.
9
.
Further, current which is made to flow from the V-phase motor winding to the W-phase motor winding is described as current in V→W direction and the like.
The control circuit of the motor generates one pulse per rotation of the rotor
150
in synchronism with the rotation of the rotor
150
from detected positions of magnetic poles. The pulse is inputted to a PLL (Phase Lock Loop) circuit, not illustrated, and the PLL circuit generates six pulses each having a period six times as much as rotation of the rotor
150
. In synchronism with the six pulses, the above-described six driving voltage vectors are successively switched to thereby continue rotating the rotor
150
. That is, the positions of the magnetic poles of the rotor
150
are detected from voltage of the motor winding constituting conductless phase and the voltage vectors outputted to the motor windings
151
U,
151
V and
151
W are switched while carrying out a feedback by the detected values.
Meanwhile, in order to lock (operate) the PLL circuit, at least about 20 Hertz is needed for a frequency of an input signal. That is, unless the rotor
150
is rotated by about 20 times per second, the PLL circuit cannot be operated.
Conventionally, until the motor is started and a rotational number of the rotor
150
is increased to a rotational number capable of locking the PLL circuit, the respective driving voltage vectors are switched by an open loop. That is, the voltage vectors applied to the motor windings
151
U,
151
V and
151
W are initially switched successively at a low speed near to DC (direct current) without carrying out a feedback operation at all, the switching speed is gradually accelerated and the rotor is made to attract and follow thereto to thereby accelerate the rotor to the rotational number capable of locking the PLL circuit.
As a control circuit of a brush-less motor for switching driving voltage vectors by generating pulses synchronized with a multiplied value of a rotational number of a rotor by using a PLL circuit in this way, there is invention of Japanese Patent Laid-Open No. 47285/1996. According to the invention, positions of magnetic poles are detected by Hall sensors and driving voltage vectors are controlled by a feedback control.
Three Hall sensors are arranged at a surrounding of magnetic poles of a rotor at angular intervals of 120°, when the rotor is rotated at a low speed by which a PLL circuit cannot be locked in starting a motor, driving voltage vectors are controlled by detected signals by the three Hall sensors, when a rotational number of the rotor reaches a rotational number capable of locking the PLL circuit, the PLL circuit generates multiplied synchronized pulses each having a period three times as much as the rotational number of the rotor from the detected signals of one of the Hall sensors and the driving voltage vectors are switched by the multiplied synchronized pulses.
Further, the technology is applicable also by detecting counter electromotive voltage generated at the motor windings and produced by rotating the rotor without using the Hall sensors. That is, the technology is applicable to a motor drive circuit free of Hall sensors using a PLL circuit.
A conventional sensor-less brush-less motor is controlled by a control circuit operated as follows.
The control circuit of the sensor-less brush-less motor controls currents flowing in motor windings by a feedback control while detecting positions of magnetic poles of a rotor. The positions of the magnetic poles of the rotor are detected by detecting voltage induced in the motor windings by rotating the rotor, that is, induced electromotive force. For example, in the case of a three phase brush-less motor, voltage is applied to the two motor windings and voltage induced in the remaining conduct less phase is detected. Further, based on the positions of the magnetic poles detected by the voltage, the two motor windings to be applied with voltage are determined and voltage is applied thereto. At the occasion, the induced electromotive force of the motor winding constituting the conductless phase is detected and the positions of the magnetic poles are detected thereby. The motor is driven by continuously carrying out the process.
FIG. 20
illustrates diagrams indicating timings of detecting the positions of the magnetic poles of the control circuit in the conventional sensor-less brush-less motor. Waveforms
201
a
,
201
b
and
201
c
are waveform diagrams of voltage induced in a certain motor winding. As mentioned later, FIG.
20
(
a
) shows a case in which a phase of a rotating field produced by current of the motor winding is more advanced than a phase o
BOC Edwards Japan Limited
Nappi Robert
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