Electricity: motive power systems – Induction motor systems
Reexamination Certificate
1999-12-20
2001-02-06
Masih, Karen (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S723000, C318S722000, C318S724000, C318S132000, C318S434000, C318S254100, C318S801000
Reexamination Certificate
active
06184647
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of detecting the initial magnetic pole position of a permanent magnet type brushless motor and more particularly to a method of detecting the magnetic pole position of a rotor when a sensorless brushless motor is started.
BACKGROUND ART
In conventional brushless motors, use has been made of a method of detecting a magnetic pole position with omission of a magnetic-pole-position detecting sensor which is constituted of a resolver or a Hall-effect device.
When the rotation of a rotor is allowed at the time of starting in reference to a method of the sort mentioned above for detecting a magnetic pole position, it is possible to utilize a technique, as disclosed in Japanese Patent Publication No. 3-239186A, for determining a rotor position (the magnetic pole position) by switching between a synchronous operation mode wherein steady operation is performed and a rotor-position detecting mode wherein the magnetic pole position is detected, rotating the rotor by supplying such a gate pulse as to generate a rotating magnetic field in each three-phase armature coil at the time of starting a brushless motor and then causing a position detecting circuit to detect the voltage induced in the armature coil.
When the rotation of the rotor is not allowed at the time of starting, that is, when the magnetic pole position is estimated with the motor unoperated, there is a technique, as proposed in IEEJ IAS Vol. 116-D, No. 7, pp. 736-742 (1996) for determining the magnetic pole position with the motor unoperated by supplying intermittent pulse-like voltage commands sequentially in a given direction to the extent that the motor is unrotated, and estimating a position angle from a difference of response, which varies in an anti-sinusoidal wavelike manner, of each of the phase currents i&agr;
u
and i&bgr;
u
, i&agr;
v
and i&bgr;
v
, i&agr;
w
and i&bgr;
w
, etc., which are converted into the static coordinates.
However, there still exist the following problems in the aforesaid prior art. The technique disclosed in Japanese Patent Publication No. 3-239186 is not applicable to a motor which makes it a condition that its rotor is at a standstill before the operation of the motor because the motor has to be started by rotating the rotor in order to determine the rotor position.
In the case of the technique made known by the IEEJ IAS Vol. 116-D, No. 7, electrical parameters such as the inductance of the brushless motor, resistance values or the like are needed to obtain the difference of the current response by deriving each of the phase currents i&agr;
u
, i&agr;
v
, i&agr;
w
or the like from a three-phase voltage equation. Consequently, the degree of difference of the current response is unclear in case these parameters remain unknown and since the voltage command is not a stepwise alternating command, overcurrent may flow, depending on the form of the voltage command, or the rotor may be rotated; thus, there arise problems in view of its practical use.
It is therefore an object of the present invention to provide a method of estimating the initial magnetic pole position of a permanent magnet type brushless motor adapted so that even though electrical parameters are not accurately acquired, the initial magnetic pole position of a rotor in the brushless motor can be estimated quickly without allowing overcurrent to flow and without rotating the rotor, namely, without operating the motor.
DISCLOSURE OF THE INVENTION
In order to accomplish the object above, there is provided a method of estimating a magnetic pole position of a permanent magnet type brushless motor comprising the steps of:
setting a given &ggr; axis and a given &dgr; axis in an advanced from the &ggr; axis by an electrical angle of 90°;
forming a closed-loop electric current control system in the &ggr; axis direction while forming an open-loop electric current control system in the &dgr; axis direction;
calculating an interference current generating in the &dgr; axis direction when a current command in the &ggr; axis direction is given as a stepwise alternating current command;
advancing finely the &ggr; axis by an angle of &Dgr;&thgr; when a sign of a product of an integral value of the interference current and a value of the current command in the &ggr; axis direction is positive;
delaying finely the &ggr; axis by an angle of &Dgr;&thgr; when the sign is negative; and
making thereby the &ggr; axis accord with either a d axis as a true magnetic axis or with a −d axis advanced by 180° from the true magnetic axis.
In the method, a characteristic equation with respect to the response of the interference current i
&dgr;
in the &dgr; axis direction under a condition of which the velocity of the permanent magnet type motor is zero is expressed by the following equation (1):
ⅆ
ⅆ
t
[
i
γ
i
δ
]
=
-
R
s
L
d
L
q
[
L
q
+
(
L
d
-
L
q
)
sin
2
θ
e
1
2
(
L
q
-
L
d
)
sin
2
θ
e
1
2
(
L
q
-
L
d
)
sin
2
θ
e
L
d
-
(
L
d
-
L
q
)
sin
2
θ
e
]
[
i
γ
i
δ
]
+
1
L
d
L
q
[
L
q
+
(
L
d
-
L
q
)
sin
2
θ
e
1
2
(
L
q
-
L
d
)
sin
2
θ
e
1
2
(
L
q
-
L
d
)
sin
2
θ
e
L
d
-
(
L
d
-
L
q
)
sin
2
θ
e
]
[
v
γ
v
δ
]
(
1
)
Here,
i
&ggr;
: current in the &ggr; axis direction;
i
&dgr;
: current in the &dgr; axis direction;
v
&ggr;
: voltage in the &ggr; axis direction;
v
&dgr;
: voltage in the &dgr; axis direction;
L
q
: q axis inductance;
L
d
: d axis inductance;
R
s
: stator resistance; and
&thgr;
e
: electrical angular error between the &ggr; axis and the d axis.
In this case, with the formation of an open-loop current system in the q axis direction and the formation of a proportionally-controlled closed-loop current control system, the &ggr; axis-current command value comes to i
&ggr;Ref
, V
&dgr;
=0, V
&ggr;
=K
&ggr;
(i
&ggr;Ref
−i
&ggr;
), whereby the state of which the speed the permanent magnet type motor is zero is expressed by the following equation (2):
ⅆ
ⅆ
t
[
i
γ
i
δ
]
=
-
R
s
L
d
L
q
[
L
q
0
0
L
d
]
[
i
γ
i
δ
]
+
1
L
d
L
q
[
L
q
K
γ
0
]
(
i
γ
Ref
-
i
γ
)
-
R
s
L
d
L
q
[
L
q
+
(
L
d
-
L
q
)
sin
2
θ
e
1
2
(
L
q
-
L
d
)
sin
2
θ
e
1
2
(
L
q
-
L
d
)
sin
2
θ
e
L
d
-
(
L
d
-
L
q
)
sin
2
θ
e
]
[
i
γ
i
δ
]
+
1
L
d
L
q
[
(
L
d
-
L
q
)
K
γ
sin
2
θ
e
1
2
(
L
q
-
L
d
)
K
γ
sin
2
θ
e
]
(
i
γ
Ref
-
i
γ
)
(
2
)
Moreover, the response of i
&dgr;
subjected to the Laplace transform is expressed by the following equation (3):
i
δ
(
S
)
=
K
λ
a
γδ
S
S
2
+
[
K
γ
a
γγ
+
R
s
(
a
γγ
+
a
δδ
)
]
S
+
(
K
γ
+
R
s
)
R
s
(
a
γγ
a
δδ
-
a
γδ
2
)
i
γ
Ref
(
S
)
(
3
)
Here, I
&dgr;
(S) represents a Laplace expression of i
&dgr;
, and I
&ggr;Ref
(S) represents the Laplace expression of i
&ggr;
. Furthermore, a
&ggr;&ggr;
, a
&dgr;&dgr;
and a
&ggr;&dgr;
are indicated by the following equation (4):
a
γγ
=
L
q
+
(
L
d
-
L
q
)
sin
2
θ
e
L
d
L
q
a
δδ
=
L
d
+
(
L
d
-
L
q
)
sin
2
θ
e
L
d
L
q
α
γδ
=
(
L
q
-
L
d
)
sin
2
θ
e
L
d
L
q
(
4
)
Furthermore, the integration ∫i
&dgr;
dt of the interference current i
&dgr;
in the &dgr; axis direction in the case of giving the cur
Kamei Takeshi
Oguro Ryuichi
Kabushiki Kaisha Yaskawa Denki
Masih Karen
Morgan & Lewis & Bockius, LLP
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