Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2000-08-01
2002-06-04
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S434000, C318S606000, C318S608000
Reexamination Certificate
active
06400107
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor control device, and particularly a motor control device which can drive a synchronous motor formed of a rotor provided with magnets with high efficiency and high reliability.
2. Description of the Background Art
In recent years, environmental issues have become an object of public concern, and great attention has been given to saving of energy. Particularly, in the field of electric motors, it has been desired to produce a motor having small sizes as well as high efficiency and high output power in view of saving of energy.
Motors such as a dielectric motor and an SPM (Surface Permanent Magnet) motor, which is provided with permanent magnets fixed to a surface of a rotor, are typical examples of the motors in the prior art, and these motors are superior in mass productivity.
Further, motors having structures different from the conventional structures have been developed. Among these motors, an attention has been given to an IPM (Interior Permanent Magnet) motor, in which permanent magnets for further increasing the efficiency are embedded in a rotor for utilizing a reluctance torque in addition to a Fleming torque.
FIG. 35
shows an example of a structure of the IPM motor. The IPM motor shown in
FIG. 35
includes a rotor formed of a rotor core
131
, which is formed of an iron core having a high magnetic permeability or layered ferrosilicon plates, and permanent magnets
132
embedded in rotor core
131
. The IPM motor shown in
FIG. 35
is a four-pole motor, in which four permanent magnets
132
are arranged such that N- and S-poles are arranged alternately to each other in the circumferential direction, although
FIG. 35
shows only half a section.
In
FIG. 35
, a reference number
134
indicates a unit around which a coil is wound, a reference number
135
indicates a stator and a reference number
136
indicates teeth. According to this structure, a difference occurs between an inductance Ld in a direction of a d-axis extending from a center of permanent magnets
132
to a center of a rotor core
131
and an inductance Lq in a direction of a q-axis shifted by an electrical angle of 90 degrees from the d-axis. Thereby, a reluctance torque Tr occurs in addition to a Fleming torque Tm.
The relationship between them is analyzed in “Rotary Machine Employing Reluctance Torque” (Nobuyuki Matsui, et al., T. IEE Japan, Vol. 114-D, No.9, 1994), which will be referred to as a “reference 1” hereinafter. According to the reference 1, the relationship between Fleming torque TM and reluctance torque Tr satisfies the following formula (1).
Tt
=
Tm
+
Tr
=
Pn
·
φ
a
·
ia
·
cos
β
+
Pn
·
1
/
2
·
(
Ld
-
Lq
)
·
ia
2
·
sin
2
β
(
1
)
where Pn represents a number of pair of poles, &phgr;a represents a flux linkage, Ld indicates an inductance in the d-axis direction, Lq represents an inductance in the q-axis direction, id represents a current in the q-axis direction, &bgr; represents a current phase and ia represents a magnitude of a current vector.
As current phase &bgr; changes, Fleming torque Tm, reluctance torque Tr and a total torque Tt change as described below with reference to FIG.
36
. As shown in
FIG. 36
, Fleming torque Tm takes on a maximum value when current phase &bgr; is 90 degrees, decreases as current phase &bgr; changes from 90 degrees, and becomes equal to 0 degrees when current phase &bgr; is 180 degrees. In contrast to this, reluctance torque Tr takes on a maximum value when current phase &bgr; is 135 degrees. Therefore, total torque Tt which is a sum of reluctance torque Tr and Fleming torque Tm takes on a maximum value when current phase &bgr; is equal or close to 115 degrees although it depends on a torque ratio. Accordingly, the IPM motor which effectively utilizes reluctance torque Tr can issue a higher torque than the SPM motor operating only with Fleming torque Tm, if these motors use the same current.
A motor drive controlling method is a major factor for determining a magnitude of the torque of the motor. In a conventional current drive method, 120° rectangular wave drive is generally performed. According to this 120° rectangular wave drive method, a current is supplied to two among three (U, V and W) phases of motor coils so that the currents joined at every 120 degrees form a direct current, and thereby an inverter is controlled. According to the 120° rectangular wave drive, an unconduction period is provided for every phase, and an induced voltage which is generated in the stator coil by rotation of a rotor magnet during this unconduction period is detected for controlling the rotor rotation. In the IPM motor utilizing reluctance torque Tr described above, the conduction timing is important conditions that can maximize the torque. In the IPM motor, therefore, the 120° rectangular wave drive is performed, and the induced voltage is detected during the unconduction period for calculating the rotor phase.
In contrast to this, a 180° sinusoidal drive method in which the conduction width is set to 180 degrees in electrical angle may also be employed as a motor drive control method for improving the motor efficiency. According to “Method of Controlling Driving of Brushless DC Motor, and Apparatus Therefor, and Electric Machinery and Apparatus Used Therefor” (International Laying-Open No. WO95-27328), which will be referred to as a “reference 2”, the conduction width is set to 180 degrees in electrical angle in a motor provided with embedded permanent magnets, and positions of magnetic poles are detected based on differences between a first center point potential of the motor coil and a second central point potential attained by a bridge circuit which is electrically parallel to the motor coil.
A brushless DC motor control device disclosed in the reference 2 will now be described with reference to FIG.
37
.
FIG. 37
schematically shows a structure of a motor control device disclosed in the reference 2. In
FIG. 37
, an inverter is formed by employing three switching transistor pairs
212
u,
212
v
and
212
w,
each of which is connected in series between terminals of a DC power supply
211
, and the voltage on the connection line between the switching transistors in each pair is applied to corresponding one of Y-connected stator windings
213
u,
213
v
and
213
w
of the respective phases in the brushless DC motor. The voltage on the connection point between the switching transistors in each pair is also applied to corresponding one of Y-connected resistances
214
u,
214
v
and
214
w.
A voltage on a neutral point
213
d
is applied to an inverted input terminal of an amplifier
215
via a resistance
215
a,
and a voltage on a neutral point
214
d
of the Y-connected resistances is applied to a noninverted input terminal of amplifier
215
. By connecting a resistance
215
b
between an output terminal and the inverted input terminal of amplifier
215
, the structure can operate as a differential amplifier. A voltage En0 on neutral point
213
d
among stator windings
213
u,
213
v
and
213
w
is equal to a sum of an inverter output waveform and a 3n-th (n: integer) harmonic components contained in the motor induced voltage waveform. A voltage on neutral point
214
d
among Y-connected resistances
214
u,
214
v
and
214
w
is determined only by the output waveform of the inverter. Therefore, the 3n-th harmonic components contained in the motor induced voltage waveform can be taken out by obtaining the difference between voltage En0 on neutral point
213
d
and the voltage on neutral point
214
d.
By the foregoing manners, the motor induced voltage waveform, i.e., the rotor position can be detected without using the magnetic pole position sensor, and therefore the 180°-drive method can be achieved.
“Controller for Electric Vehicle” (Japanese Patent Laying-Open No. 10-341594, which will be referred to as a “reference 3” hereinafte
Nakatani Masaji
Ohtsuka Hideshi
Conlin David G.
Dang Khanh
Edwards & Angell LLP
Jensen Steven M.
Sharp Kabushiki Kaisha
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