Electricity: motive power systems – Synchronous motor systems
Reexamination Certificate
2000-08-04
2002-05-14
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
C318S132000, C318S254100, C318S701000, C318S705000, C318S721000, C318S722000, C318S800000, C318S802000, C318S805000, C318S811000
Reexamination Certificate
active
06388416
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to motor control devices and motor control methods. More specifically, the present invention relates to motor control devices and motor control methods driving without using a sensor a synchronous motor having a plurality of phase windings and used for example for compressors of air conditioners.
2. Description of the Background Art
In recent years, environmental issues have become social issues and energy-saving has become an important issue. In particular, in the field of motors there is an acute need for a small, high-efficiency, high-output motor to save energy, while there has also been provided a motor distinguished in configuration from conventional motors.
FIG. 45
shows a representative configuration of a conventional motor with a rotor and a stator cut in half and thus shown in a 1/2 model. In
FIG. 45
, rotor
121
is provided in the form of a column formed of a stacked steel plates. Rotor
121
is provided at an outer circumference thereof with a permanent magnet
122
arranged with its N pole and S pole alternate circumferencially. Permanent magnet
122
has an outer peripheral surface having fixed thereto a non-magnetic SUS tube
123
to prevent the magnet from scattering while it rotates. Stator
125
is provided with a plurality of protruding poles
126
extending radially. Between protruding poles
126
is formed a slot
127
with a coil (not shown) wound therearound.
This motor is a surface permanent magnet (SPM) motor employing a Fleming torque according to Fleming's rules attributed to a magnetic field created by permanent magnet
122
and a coil current (not shown). It is significantly suitable for mass production.
To enhance efficiency, however, an interior permanent magnet (IPM) motor is also noted. This motor has a permanent magnet embedded in its rotor to employ a reluctance torque in addition to a Fleming torque.
FIG. 46
shows an exemplary configuration of an IPM motor. As shown in
FIG. 46
, the IPM motor includes a rotor
130
with a permanent magnet
132
embedded in a rotor core
131
in the form of a circular column formed of a highly permeable iron core or stacked silicone steel plates.
FIG. 46
shows a 4-pole motor, with 4-pole permanent magnet
132
arranged in rotor
130
, with their N and S poles alternate circumferencially, although in
FIG. 46
the four poles are shown in a 1/2 model. Rotor core
131
is circumferentially provided with a stator
135
having a protruding pole
136
.
Such configuration provides a difference between an inductance Ld along an axis d corresponding to a direction extending between the center of permanent magnet
132
and that of rotor
131
and an inductance Lq along an axis q corresponding a direction rotated relative to axis d by an electrical angle of 90°, and in addition to a Fleming torque caused by permanent magnet
132
a reluctance torque is also caused. Such relationship, as described in
Rotary Machines Employing Reluctance Torque,
Nobuyuki Matsui et al, T. EEE Japan Vol.114-D, No.9, 1994, is provided by the following expression (1):
T=Pn×&phgr;a×iq+Pn×
1/2×(
Ld−Lq
)×
id×iq
(1)
wherein
Pn: the number of pole pairs
&phgr;a: interlinkage flux
Ld: inductance along axis d
Lq: inductance along axis q
id: current along axis d
iq: current along axis q
The
FIG. 45
SPM motor has a permanent magnet substantially equal in permeability to air. Thus, in expression (1) both inductances Ld and Lq have substantially the same value and in expression (1) at the second item no reluctance torque is caused. In the
FIG. 46
IPM motor, however, the inductance along axis d is a direction in which a magnetic flux of the permanent magnet is caused, and the flux along axis d flows through the permanent magnet, which is substantially equal in permeability to air. This would result in an increased magnetic resistance and a reduced inductance Ld along axis d.
In contrast, the inductance along axis q passes through a gap of the permanent magnet, which results in a reduced magnetic resistance and an increased inductance Lq along axis q. Thus, there would be introduced a difference between inductance Ld along axis d and inductance Lq along axis q and passing a current Id along axis d would cause a reluctance torque in expression (1) at the second item.
If the above relationship is seen in terms of flux vector, a Fleming torque Tm is caused by multiplying a magnetic flux &phgr;a by a current Iq flowing in a direction electrically orthogonal. Similarly, a reluctance torque Tr is provided by fluxes Ld·Id and Lq·Iq attributed to inductance and current come by electrically orthogonal currents Id and Iq, respectively. These two torques added together correspond to a total torque Tt.
This total torque varies with a current phase &bgr; input. Herein current phase &bgr; is an representation in electrical angle of a phase of a motor current relative to a positional relationship between the permanent magnet and the coil. If this is considered in expression (1) then an expression (2) is provided:
Tt=Pn×&phgr;a×ia×
cos &bgr;+
Pn×
1/2×(
Ld−Lq
)×
ia
2
×sin 2&bgr; (2)
wherein,
Pn: the number of pole pairs
&phgr;a: interlinkage flux
Ld: inductance along axis d
Lq: inductance along axis q
id: current along axis d
iq: current along axis q
&bgr;: current phase
ia: magnitude of current vector
FIG. 47
represents a relationship between Fleming torque Tm and reluctance torque Tr and the summation thereof or total torque Tt with current phase &bgr; varied. Herein, when the center of the permanent magnet is located at that of the coil (e.g., that of the coil at a phase windings U, the winding's current phase is 90°. Fleming torque Tm is maximized for a current phase of 90°. As the current phase advances Fleming torque Tm is reduced, and for a current phase of 180° it reaches zero.
In contrast, reluctance torque Tr is maximized for a current phase of 135°. As such, the summation of the both torques or total torque Tt, although varying depending on their respective torque ratios, is maximized for a current phase of approximately 115°, as shown in
FIG. 47
by a solid line. As such, if an IPM motor's current is equal to an SPM motor's current, the IPM motor, which effectively uses a reluctance torque, can provide an output with a higher torque than the SPM motor, which only employs a Fleming torque.
The magnitude of a torque is determined depending on various factors, among which is also important is a current drive method.
FIGS. 48A-48D
are waveform diagrams showing one example of 120° rectangular-wave drive corresponding to a conventional current drive method.
FIGS. 48A
,
48
B and
48
C represent their respective current waveforms of phase windings U, V, W, respectively. As shown in
FIGS. 48A-48C
, in the current drive method an inverter is controlled to link current conductions of two of three phase windings (U, V, W) for each 120° to provide a direct current. It can be seen that for each phase winding there is provided a pause period, during which an induced voltage caused at a stator coil as a rotor magnet rotates is detected to control the rotor's rotation.
For an IPM motor employing a reluctance torque, as described above, controlling a timing of conduction is an important factor in obtaining a maximized torque, and conventionally a rotor phase can only be detected by a 120° rectangular-wave drive method employing an induced voltage to detect the rotor phase. This method, however, has a pause period for detecting the induced voltage and is thus disadvantageous in terms of motor efficiency, oscillation and noise.
To overcome such disadvantages, a method has been proposed as described in International Publication No. WO95/27328. In this method, a motor has a permanent magnet embedded therein, with a conduction width set to correspond to an electrical angle of 180°, and a magnetic pole is positio
Nakatani Masaji
Ohtsuka Hideshi
Conlin David G.
Dike Bronstein Roberts & Cushman IP Group
Nappi Robert E.
Sharp Kabushiki Kaisha
Smith Tyrone
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