Electricity: motive power systems – Synchronous motor systems
Reexamination Certificate
2002-11-02
2004-11-30
Martin, David (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
C318S132000, C318S254100, C318S560000, C318S434000
Reexamination Certificate
active
06825637
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a control apparatus which controls a synchronous motor without using a position sensor.
BACKGROUND ART
In general, a position sensor such as encoder, a resolver, or a Hall element is required to control a synchronous motor. However, the position sensor is disadvantageously used in a control apparatus for a synchronous motor with respect to cost, reliability of the sensor, cumbersome wiring, and the like. From this viewpoint, a method of controlling a synchronous motor without using a position sensor has been proposed.
For example, as a method of calculating a rotational position and a rotational speed of a synchronous motor based on a mechanical constant such as an inertia, an induced voltage coefficient determined from magnetic flux or the like, and electric constants such as inductance and resistance of the synchronous motor, inventions disclosed in U.S. Pat. No. 5,296,793, U.S. Pat. No. 5,296,794, Japanese Patent Application Laid-Open No. 03-049589, Japanese Patent Application Laid-Open No. 03-049588, and the like are known.
As a method of calculating a rotational position and a rotational speed of a synchronous motor based on an induced voltage coefficient, which is a function of rotor magnetic flux and an electric constant, such as inductance and resistance of the synchronous motor, inventions disclosed in Japanese Patent Application Laid-Open No. 08-08286, Japanese Patent Application Laid-Open No. 09-191698, and the like are known
However, even though these methods are used, a mechanical constant such as inertia is unknown, or controllability is deteriorated when degaussing of a magnet is caused by heat generation from an electric motor.
On the other hand, a control method which can solve the above problem without requiring an induced voltage coefficient which is a function of a mechanical constant, such as inertia or rotor magnetic flux, is proposed in, e.g., “Position and Speed Sensorless Control of Brush-Less DC Motor Based on an Adaptive Observer” The Journal of The Institute of Electrical Engineers of Japan Vol. D113, No. 5 (1993).
FIG. 15
shows a conventional control apparatus for a synchronous motor described in The Journal of The Institute of Electrical Engineers of Japan Vol. D113, No. 5. In this figure, reference numeral
1
denotes a synchronous motor,
2
denotes a current detector,
3
denotes an inverter,
4
denotes a current controller,
5
to
8
denote coordinate converters,
9
denotes an adaptive observer, and
10
denotes a rotational position computing unit.
The synchronous motor
1
has a permanent magnet as a rotor which has a rotor magnetic flux of pdr. An inductance Ld in the direction of the rotor magnetic flux (d-axis direction) is equal to an inductance Lq in a direction (q-axis direction) perpendicular to the direction of the rotor magnetic flux. These inductances are L each. A wire wound resistance of the synchronous motor
1
is R.
As is well known, when a synchronous motor is vector-controlled, an arbitrary value has been given as a d-axis current command id* on a rotational biaxial coordinate axis (d-q axis) in advance. As a q-axis current command iq* on the rotational biaxial coordinate axis (d-q axis), a value which is in proportional to a desired torque of the synchronous motor
1
has been given in advance.
The current controller
4
outputs a d-axis voltage command vd* and a q-axis voltage command vq* on the rotational biaxial coordinate axis (d-q axis) such that detection currents id and iq on the rotational biaxial coordinate axis (d-q axis) rotated in synchronism with a rotational position output from the rotational position computing unit
10
follow the d-axis current command id* and the q-axis current command iq*, respectively.
The coordinate converter
5
coordinate-converts the d-axis voltage command vd* and the q-axis voltage command vq* on the rotational biaxial coordinate axis (d-q axis) into an a-axis voltage command va* and a b-axis voltage command vb* on static biaxial coordinates (a-b axis) based on a cosine cos(th
0
) and a sine sin(th
0
) obtained from the rotational position computing unit
10
.
The coordinate converter
6
coordinate-converts the a-axis voltage command va* and the b-axis voltage command vb* on the static biaxial coordinates (a-b axis) into three-phase voltage commands vu*, vv* and vw*. The inverter
3
applies three-phase voltages to the synchronous motor
1
in accordance with the three-phase voltage commands vu*, vv* and vw* obtained from the coordinate converter
8
.
The current detectors
2
detect a U-phase current iu and a V-phase current iv of the synchronous motor
1
. The coordinate converter
7
coordinate-converts the U-phase current iu and the V-phase current iv obtained from the current detectors
2
into an a-axis current ia and a b-axis current ib on the static biaxial coordinates (a-b axis).
The coordinate converter
8
outputs the a-axis current ia and the b-axis current ib on the static biaxial coordinates (a-b axis) and a d-axis current command id and a q-axis current command iq on the rotational biaxial coordinate axis (d-q axis) based on a cosine cos(th
0
) and a sine sin(th
0
) obtained from the rotational position computing unit
10
.
The adaptive observer
9
outputs an a-axis estimated rotor magnetic flux par
0
and a b-axis estimated rotor magnetic flux pbr
0
on the static biaxial coordinates (a-b axis) and an estimated rotational speed wr
0
based on the a-axis voltage command va* and the b-axis voltage command vb* on the static biaxial coordinates (a-b axis) and the a-axis current ia and the b-axis current ib on the static biaxial coordinates (a-b axis).
The rotational position computing unit
10
calculates the cosine cos(th
0
) and the sine sin(th
0
) of a rotational position th
0
of an estimated magnetic flux vector from the a-axis estimated rotor magnetic flux par
0
and the b-axis estimated rotor magnetic flux pbr
0
on the static biaxial coordinates (a-b axis) according to the following equations (1) to (3),
cos
(
th0
)
=
par0
pr0
(
1
)
sin
(
th0
)
=
pbr0
pr0
(
2
)
pr
0=√{square root over (
par
0
2
+pbr
0
2
)} (3)
FIG. 16
is a diagram which shows the internal configuration of the adaptive observer
9
shown in FIG.
15
. In this figure, reference numeral
11
denotes an electric motor model,
12
and
13
denotes subtractors,
14
denotes a speed identifier,
15
denotes a gain computing unit, and
16
denotes a deviation amplifier.
The electric motor model
11
calculates an a-axis estimated current ia
0
and a b-axis estimated current ib
0
on the static biaxial coordinates (a-b axis) and the a-axis estimated rotor magnetic flux par
0
and the b-axis estimated rotor magnetic flux pbr
0
based on the a-axis voltage command va* and the b-axis voltage command vb* on the static biaxial coordinates (a-b axis), the estimated rotational speed wr
0
, and deviations e
1
, e
2
, e
3
, and e
4
(to be described later) according to the following equation (4),
ⅆ
ⅆ
t
(
ia0
ib0
par0
pbr0
)
=
(
-
R
L
0
0
wr0
L
0
-
R
L
-
wr0
L
0
0
0
0
-
wr0
0
0
wr0
0
)
(
ia0
ib0
par0
pbr0
)
+
(
1
L
0
0
1
L
0
0
0
0
)
(
va
*
v
*
)
-
(
e1
e2
e3
e4
)
(
4
)
The subtractor
12
outputs a result obtained by subtracting the a-axis current ia from the a-axis estimated current ia
0
as an a-axis current deviation ea. The subtractor
13
outputs a result obtained by subtracting the b-axis current ib from the b-axis estimated current ib
0
as a b-axis current deviation eb.
The speed identifier
14
outputs the estimated rotational speed wr
0
based on the Par
0
, pbr
0
, ea, and eb according to the following equation (5),
wr0
=
(
kp
+
ki
s
)
(
ea
·
pbr0
-
eb
·
par0
)
(
5
)
The gain computing unit
15
outputs gains g
1
, g
2
, g
3
, and g
4
based on the estimated rotational speed wr
0
according to the following equations (6) to (9),
g1
=
-
(
k
-
1
)
R
L
(
6
)
g
2
=(
k
−1)
wr
0
(7)
g
3
=kR (
Kaitani Toshiyuki
Kinpara Yoshihiko
Leydig , Voit & Mayer, Ltd.
Martin David
Mitsubishi Denki & Kabushiki Kaisha
Smith Tyrone
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