Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2002-02-15
2004-03-16
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000, C318S434000, C318S805000, C318S716000, C318S720000, C318S723000, C318S724000
Reexamination Certificate
active
06707265
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotor angle detecting apparatus for detecting the rotor angle of a salient-pole DC brushless motor.
2. Description of the Related Art
In order to energize a DC brushless motor to obtain a desired torque, it is necessary to apply a voltage to the armatures in a suitable phase corresponding to the electric angle (hereinafter referred to as rotor angle) of the rotor which has magnetic poles. Therefore, the DC brushless motor generally has a position detecting sensor for detecting the rotor angle.
The DC brushless motor with the position detecting sensor is required to have a circuit combined with the motor driver unit for receiving a detected signal which is outputted from the position detecting sensor, and wires between the position detecting sensor and the motor driver unit. There have been proposed various attempts to detect the rotor angle without the position detecting sensor so as to reduce the cost of the DC brushless motor and the motor driver unit by dispensing with the position detecting sensor.
According to one of the proposals, the voltage applied to the armatures of the DC brushless motor is divided into voltages on two orthogonal axes, and when a high-frequency alternating voltage is applied to one axis, a current generated on the other axis in response to the application of the high-frequency alternating voltage is detected thereby to detect the rotor angle. However, this approach is disadvantageous in that it takes some time in an initial startup stage before the detected rotor angle reaches an actual rotor angle and it is difficult to correct the rotor angle.
Another proposed technique uses a data table containing stored data representative of a correlation between rotor angles and armature currents when two- or three-phase currents are passed through the armatures of the DC brushless motor. Detected currents flowing through the armatures are applied to the data table, and approximating calculations are made on data in the data table to detect a rotor angle. Problems of this process are that errors tend to occur due to the effect of motor parameters that differ from motor to motor and the approximating calculations.
SUMMARY OF THE INVENTION
Basic principles of the present invention will first be described below with reference to FIGS.
1
(
a
) and
1
(
b
) of the accompanying drawings. As shown in FIG.
1
(
a
), a DC brushless motor
1
comprises a rotor
2
having field magnetic poles provided a permanent magnet and armatures
3
,
4
,
5
in three phases (U, V, W phases). When given alternating currents are supplied to the three-phase armatures
3
,
4
,
5
, the rotor
2
is rotated by a revolving magnetic field which is produced as a combination of the magnetic fields generated by the armatures
3
,
4
,
5
.
The revolving magnetic field needs to be generated in a direction depending on the angle &thgr; of the rotor
2
(in FIG.
1
(
a
), the angle of the rotor
2
as measured clockwise from the U-phase armature
3
, hereinafter referred to as “rotor angle &thgr;”). Therefore, it is required to detect the rotor angle &thgr; for the control of the DC brushless motor.
DC brushless motors generally have a position detecting sensor such as a resolver or the like for detecting the rotor angle &thgr;. However, a rotor angle detecting apparatus for a DC brushless motor according to the present invention is capable of detecting the rotor angle &thgr; without a position detecting sensor and hence dispenses with the need for a position detecting sensor.
As shown in FIG.
1
(
a
), with the salient-pole rotor
2
being used, the magnetic reluctance of a gap between the rotor
2
and the armatures
2
,
3
,
4
varies periodically as the rotor
2
rotates. When the rotor
2
makes one revolution, the magnetic reluctance varies in two cycles, i.e., when the rotor
2
makes one half of a revolution, the magnetic reluctance varies in one cycle. The magnetic reluctance is maximum when the rotor
2
is in a position {circumflex over (
1
)} and minimum when the rotor
2
is in a position {circumflex over (
2
)}.
The magnetic circuit of the DC brushless motor shown in FIG.
1
(
a
) is schematically shown in FIG.
1
(
b
) of the accompanying drawings. If it is assumed in FIG.
1
(
b
) that the magnetic reluctance varies in a unit cosine-wave pattern and the average value thereof in one periodic cycle is 0.5, then the magnetic reluctances Ru, Rv, Rw in the respective phases U, V, W are expressed by the following equations (1) through (3):
Ru=
1−cos 2&thgr; (1)
Rv
=
1
-
cos
(
2
θ
+
2
3
π
)
(
2
)
Rw
=
1
-
cos
(
2
θ
-
2
3
π
)
(
3
)
At this time, the magnetic reluctance Rtu of the gap as seen from the U phase can be determined according to the following equation (4):
Rgu
=
Ru
+
Rv
·
Rw
Rv
+
Rw
=
1
+
cos
2
θ
+
=
1
+
cos
(
2
θ
-
2
3
π
)
+
cos
(
2
θ
+
2
3
π
)
+
cos
(
2
θ
-
2
3
π
)
·
cos
(
2
θ
+
2
3
π
)
2
+
cos
(
2
θ
-
2
3
π
)
+
cos
(
2
θ
+
2
3
π
)
=
1
+
cos
2
θ
+
1
-
cos
2
θ
+
1
2
(
cos
4
θ
+
cos
2
3
π
)
2
-
cos
2
θ
=
8
-
cos
2
3
π
4
-
2
cos
2
θ
(
4
)
Therefore, if it is assumed that the U-phase comprises a unit winding, then the self-inductance of the U phase can be determined according to the following equation (5):
Lu
=
1
Rgu
=
4
-
2
cos
2
θ
8
-
cos
2
3
π
(
5
)
The mutual inductance Muw between the U and W phases and the mutual inductance Muv between the U and V phases can be determined according to the following equations (6), (7), respectively, because of the arrangement of the magnetic circuit:
Muw
=
-
Rw
Rv
+
Rw
Lu
=
-
2
+
2
cos
(
2
θ
+
2
3
π
)
8
-
cos
2
3
π
(
6
)
Muv
=
-
Rv
Rv
+
Rw
Lu
=
-
2
+
2
cos
(
2
θ
-
2
3
π
)
8
-
cos
2
3
π
(
7
)
The self-inductances and the mutual inductances of the V and W phases can similarly be determined. If the DC component of the self-inductance of each phase is represented by
1
, a variation of the DC component
1
by &Dgr;
1
, and the DC component of the mutual inductance between each phase pair by m, then the voltage equation of the DC brushless motor with the salient-pole rotor is given as follows:
[
VU
VV
VW
]
=
r
[
Iu
Iv
Iw
]
+
ⅆ
ⅆ
t
[
1
-
Δ1cos2θ
m
-
Δ1cos
(
2
θ
-
2
3
π
)
m
-
Δ1cos
(
2
θ
+
2
3
π
)
m
-
Δ1cos
(
2
θ
-
2
3
π
)
1
-
Δ1cos
(
2
θ
+
2
3
π
)
m
-
Δ1cos2θ
m
-
Δ1cos
(
2
θ
+
2
3
π
)
m
-
Δ1cos2θ
1
-
Δ1cos
(
2
θ
-
2
3
π
)
]
[
Iu
Iv
Iw
]
+
ω
m
Ke
⌈
sin
θ
sin
(
θ
-
2
3
π
)
sin
(
θ
-
4
3
π
)
⌉
(
8
)
where VU, VV, VW represent respective voltages applied to the U-, V-, W-phase armatures, Iu, Iv, Iw represent respective currents flowing through the U-, V-, W-phase armatures, r represents the electric resistance of each of the U-, V-, W-phase armatures, &ohgr;
m
represents the electric angular velocity of the rotor
2
, and Ke represents an induced voltage constant.
If the electric angular velocity &ohgr;
m
is substantially 0, any effect of changes in the induced voltage and the angular velocity of the rotor
2
are small, and the voltage drop due to the resistance r is negligibly small in level, then the above equation (8) can be regarded and handled as the following equation (9):
[
VU
VV
V
Imai Nobuyuki
Takahashi Yutaka
Arent Fox Kintner Plotkin & Kahn
Honda Giken Kogyo Kabushiki Kaisha
Leykin Rita
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