Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
1999-10-29
2001-02-06
Masih, Karen (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S802000, C318S805000, C318S800000, C318S798000
Reexamination Certificate
active
06184638
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control system for controlling the variable speed of an induction motor without an angular velocity detector.
2. Discussion of the Related Art
FIG. 14
is a circuit diagram showing a conventional control system for an induction motor, which is described in “The institute of Electric Engineers of Japan Trans., D”, Vol. 112, No.9, p901, 1993 (referred to an article 1). In the figure, reference numeral
1
is excitation-current command computing means;
2
is as induction motor;
3
is torque control means;
4
is current detecting means; and
5
is parameter estimating means.
In the conventional induction-motor control system shown in
FIG. 14
, the excitation-current command computing means
1
receives a secondary magnetic flux &phgr;dr* to be output by the induction motor
2
, performs the operation of the following equation (20) in which an AC signal is added (superposed) to a DC signal proportional to the secondary magnetic flux &phgr;dr*, and outputs an excitation-current command ids* of the induction motor
2
.
[Formula 7]
ids*=(
1
+k
1sing(2
&pgr;f
1
t
)+
k
2sing(2
&pgr;f
2
t
)&phgr;
dr* M
(20)
where
t: time
k
1
: amplitude of a first superposing signal
f
1
: frequency of the first superposing signal
k
2
: amplitude of a second superposing signal
f
2
: frequency of the second superposing signal
It is known that the excitation current must contain at least two frequency components in order to simultaneously estimate a rotation angular velocity and a secondary resistance of the induction motor.
The reason for this will be described. A circuit diagram shown in
FIG. 15
is known as a T-type equivalent circuit where an excitation current is fixed in value. In the figure, cos is a slip angular velocity. To estimate a rotation angular velocity of the induction motor is equivalent to estimate a slip angular velocity in the figure since &ohgr;r=&ohgr;−&ohgr;s.
To simultaneously estimate a rotation angular velocity and a secondary resistance of the induction motor from the primary current and the primary voltage of the induction motor, which is controlled at a fixed excitation current, is equivalent to estimate Rr/&ohgr;s in the figure. Therefore, the principle makes it impossible to separate those one from the other.
Where the excitation current is not kept constant, &ohgr; and &ohgr;s are not fixed in value. The &ohgr; contains a plurality of components. The T-type equivalent circuit holds at each of the different slip angular velocities &ohgr;s for each of the components of the &ohgr;. Thus, the induction motor into which the control not keeping the excitation current constant is incorporated can simultaneously estimate the rotation angular velocity and the secondary resistance.
Accordingly, the superposing frequencies f
1
and f
2
sued are different in value, and in the conventional control system described in the article 1, those frequencies f
1
and f
2
are
f1=1 (Hz)
f2=3 (Hz)
In the article 1, the period of the first superposing signal is 1/f
1
, and the rating of the induction motor is 3.7 kw. In this sense, this signal is an AC signal having a period longer than a secondary time constant (=Lr/Rr) of the induction motor
2
.
When a torque command &tgr;m* to be output by the induction motor
2
and an excitation current command ids* from the excitation-current command computing means
1
are input to the torque control means
3
, the torque control means
3
receives three-phase primary currents ius and ivs from the current detecting means
4
, an estimated rotation angular velocity &ohgr; r
0
from the current detecting means
4
, and an estimated secondary resistance Rr
0
from the parameter estimating means
5
, and processes those factors so as that an output torque &tgr;m of the induction motor follows &tgr;m*, and supplies three-phase primary voltages vus, vvs, and vws to the induction motor.
The parameter estimating means
5
includes a measuring unit
6
, a gain computing unit
7
, a rotation velocity estimating unit
8
, a secondary-resistance estimating unit
9
, and a primary-resistance estimating unit
10
.
The parameter estimating means
5
receives the primary voltage commands vus* and vvs* from the torque control means
3
, and the primary currents ius and ivs from the current detecting means
4
, and outputs an estimated rotation angular velocity &ohgr;r
0
and an estimated secondary resistance Rr
0
.
The measuring unit
6
receives the primary current commands vus* and vvs* from the torque control means
3
, the primary currents ius and ivs from the current detecting means
4
, a feedback gain G from the gain computing unit
7
, an estimated rotation angular velocity &ohgr;r
0
from the rotation velocity estimating unit
8
, and an estimated secondary resistance Rr
0
from the secondary resistance estimating unit
9
, and an estimated primary resistance Rs
0
from the primary-resistance estimating unit
10
, and performs the operations mathematical expressions (21), (22) and (23), to thereby produce an estimated primary current Is
0
, an estimated secondary current Ir
0
, a state deviation E, and an estimated secondary magnetic flux &phgr;r
0
.
[Formula 8]
ⅆ
ⅆ
t
(
i
s0
Φ
r0
)
=
A
O
(
i
s0
Φ
r0
)
+
Bv
s
-
G
(
i
s0
-
i
s
)
(
21
)
E
=
i
s0
-
i
s
(
22
)
i
r0
=
1
L
r
(
Φ
r0
-
Mi
s0
)
where
A
O
=
(
-
(
R
s0
σ
L
s
+
(
1
-
σ
)
R
r0
σ
L
r
)
I
M
σ
L
s
L
r
(
R
r0
L
r
I
-
ω
r0
J
)
MR
r0
L
r
I
-
R
r0
L
r
I
+
ω
r0
J
)
B
o
=
(
1
σ
L
s
I
0
)
(
23
)
The gain computing unit
7
produces a feedback gain G, which is given by the equation (24) containing the estimated rotation angular velocity &ohgr;r
0
, which is received from the rotational speed estimating unit
8
.
G
=
(
g
1
I
+
g
2
J
g
3
I
+
g
4
J
)
where
g
1
=
-
(
k
-
1
)
(
ar11
+
ar22
)
g
2
=
-
(
k
-
1
)
ai22
g
3
=
-
(
k
2
-
1
)
(
c
x
ar11
+
ar21
)
+
c
x
(
k
-
1
)
(
ar11
+
ar22
)
g
4
=
c
x
(
k
-
1
)
ai22
c
x
=
σ
L
s
L
r
M
ar11
=
-
(
R
s0
σ
L
s
+
(
1
-
σ
)
R
r0
σ
L
r
)
ar12
=
M
σ
L
s
L
r
R
r0
L
r
ai12
=
-
ω
r0
M
σ
L
s
L
r
ar21
=
MR
r0
L
r
ar22
=
-
R
r0
L
r
ai22
=
ω
r0
k
=
arbitrary
positive
number
(
24
)
The number of poles of the measuring unit
6
is k times as large as that of the induction motor
2
when the feedback gain G given by the equation (24) is used.
The rotational speed estimating unit
8
receives the estimated secondary magnetic flux &phgr;r
0
and the state deviation E from the measuring unit
6
, and computes an outer product E×&phgr;r
0
, and corrects the estimated rotation angular velocity &ohgr;r
0
, which is used in the measuring unit, by use of an equation (25), and outputs the corrected one.
[Formula 10]
ω
r0
=
k
sp
s
+
k
si
s
(
J
Φ
r0
)
T
E
(
25
)
The secondary-resistance estimating unit
9
receives the estimated secondary current ir
0
and the state deviation E from the measuring unit
6
, and computes an inner product E·ir
0
, and corrects the estimated secondary resistance Rr
0
used in the measuring unit
6
by use of the equation (26), and outputs the corrected one.
[Formula 11]
R
r0
=
-
k
r2p
s
+
k
r2i
s
(
E
·
i
r0
)
(
26
)
The primary-resistance estimating unit
10
receives the estimated primary current is
0
and the state deviation E from the measuring unit
6
, and computes an inner product E·is
0
, and cor
Leydig , Voit & Mayer, Ltd.
Masih Karen
Mitsubishi Denki & Kabushiki Kaisha
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