Electricity: motive power systems – Induction motor systems
Reexamination Certificate
2001-06-19
2003-02-11
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S432000, C318S799000
Reexamination Certificate
active
06518722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an induction motor drive without a speed sensor and/or a rotational position sensor, and more particularly, to an observer for vector-controlling an induction motor drive.
2. Description of the Related Art
A typical vector control system for a direct field-oriented induction motor drive without a speed sensor and/or rotational position sensor is shown in FIG.
1
.
In the system without a speed sensor, only a stator voltage
206
and a stator current
207
are detected by sensors
108
and
109
.
Vector control for an induction motor
100
in this figure is performed based on the torque of the induction motor
100
, which is independently applied, and the magnetic flux fed by an inverter
101
.
With the vector control in the system shown in this figure, a speed regulator
107
generates a torque current reference
202
under PI control (proportional action and integral action control) from a an estimated speed reference
200
being an instruction of the speed of the motor, and an estimated speed
211
from a flux and speed observer
110
as a feedback, and outputs the generated torque current reference
202
to a current regulator
106
. The current regulator
106
outputs a current that is regulated under the PI control from the torque current reference
202
being an instruction to the torque and a flux current reference
201
being an instruction to the magnetic flux. Then, a vector rotator
104
transforms this current value into a relative value in a coordinate system (d-q coordinate system) that rotates in synchronization with a synthesized current vector, and applies the transformed value to the inverter
101
as a primary voltage command
205
. The flux current reference
201
applied to the current regulator
106
can be set to a constant value over a wide operation range while the torque current reference
202
is generated by a PI loop according to the estimated speed
211
.
The voltage and the current values applied from the inverter
101
to the induction motor
100
are detected as the detected voltage
206
and the detected current
207
by the sensors
108
and
109
. After the detected voltage
206
and the detected current
207
are transformed into values represented by a two-phase coordinate system by 3-2 phase transformers
102
and
103
, they are input to the flux and speed observer
110
as space vector values v
s
208
and i
s
209
.
The flux and speed observer
110
obtains an observed rotor flux
210
from the stator voltage v
s
208
and the stator current i
s
209
, outputs the obtained flux
210
to vector rotators
104
and
105
, estimates a rotor speed, and outputs the estimated speed
211
to the speed regulator
107
.
The vector rotator
104
vector-rotates a flux command
203
and a torque command
204
in the orientation of the rotor flux based on the observed rotor flux
210
, and outputs the vector-rotated commands to the inverter
101
as the primary voltage instruction
205
.
Additionally, the vector i
s
209
is vector-rotated by the vector rotator
105
in the orientation of the rotor flux based on the observed flux
210
from the flux and speed observer
110
in order to obtain a flux current
212
and a torque current
213
, which are used as feedback signals by the current regulator
106
.
An MRAS (Model Reference Adaptive System) based on a flux and speed observer was initially proposed by Ref. 1.
Ref. 1: H. Kubota et al. “DSP-based speed adaptive flux observer of induction motor”, IEEE Trans. Industry Applicat., vol. 2, no. 2 pp. 343-348, 1993.
According to Ref. 1, a stator current and a rotor flux are used as an independent set of variables in order to explain an induction motor. Accordingly, an equation for an induction motor, which is demonstrated by Ref. 1, can be rewritten to an equation using a stator flux and a rotor flux as state variables. Since the process of this rewrite is a standard linear transformation, it is omitted here.
A classical representation of an induction machine in a stator oriented reference coordinate system (&agr;-&bgr;) using a state space notation is as follows.
{
ⅆ
ⅆ
t
(
φ
s
φ
r
)
=
(
-
R
s
L
sg
I
R
s
L
m
g
I
R
r
L
m
g
I
-
R
r
L
rg
I
+
ω
r
J
)
·
(
φ
s
φ
r
)
+
(
I
0
)
·
v
s
=
Ax
+
Bu
i
s
=
(
L
sg
I
-
L
m
g
I
)
·
(
φ
s
φ
r
)
=
Cx
(
1
)
where:
&phgr;
s
=[&phgr;
s&agr;
&phgr;
s&bgr;
]
T
, &phgr;
r
=[&phgr;
r&agr;
&phgr;
r&bgr;
]
T
, i
s
=[i
s&agr;
i
s&bgr;
]
T
, v
s
=[v
s&agr;
v
s&bgr;
]
T
are space vectors associated with a stator flux, a rotor flux, a stator current, and a stator voltage respectively.
Other symbols are as follows.
L
sg
=
1
σ
·
L
s
=
L
r
L
s
·
L
r
-
L
m
2
L
rg
=
1
σ
·
L
r
=
L
s
L
s
·
L
r
-
L
m
2
L
m
g
=
1
-
σ
σ
·
L
m
=
L
m
L
s
·
L
r
-
L
m
2
I
=
[
1
0
0
1
]
;
J
=
[
0
-
1
1
0
]
;
0
=
[
0
0
0
0
]
;
R
s
, R
r
: Stator and rotor resistance;
L
s
, L
r
, L
m
: Stator, rotor, and mutual inductance;
&sgr;=1−L
m
2
/(L
s
·L
r
): Total leakage coefficient;
&ohgr;
r
: Angular rotor speed.
Furthermore, according to Ref. 1, observed flux values are represented as follows. Note that observation and an observed value referred to in this specification represent observation and an observed value in modern control theory, and indicate the estimation of a state variable value from an output and its estimated value. In the following equation, observed values are marked with “{circumflex over ( )}”.
{
ⅆ
ⅆ
t
(
φ
^
s
φ
^
r
)
=
(
-
R
s
L
sg
I
R
s
L
m
g
I
R
r
L
m
g
I
-
R
r
L
rg
I
+
ω
^
r
J
)
·
(
φ
^
s
φ
^
r
)
+
(
I
0
)
·
v
s
+
(
k
1
I
+
k
2
J
k
3
I
+
k
4
J
)
·
(
i
^
s
-
i
s
)
=
A
^
x
^
+
B
u
+
K
e
i
i
^
s
=
(
L
sg
I
-
L
m
g
I
)
·
(
φ
^
s
φ
^
r
)
=
C
x
^
(
2
)
An output feedback gain K in the equation (2) is used to modify the dynamic characteristics of an estimation error and its determination.
The speed is evaluated with the following equation.
ⅆ
ⅆ
t
ω
^
r
=
k
ω
·
(
i
^
s
-
i
s
)
×
φ
^
r
=
k
ω
·
φ
^
r
T
·
J
·
e
i
(
3
)
where k
&ohgr;
is an arbitrary gain.
According to Ref. 1, the feedback gain K in the observer equation (2) is used along with a constant of proportionality k in order to obtain four eigenvalues &lgr;
obs
of the flux observer represented by the equation (2), which are proportional to an eigenvalue &lgr;
mot
of the corresponding motor represented by the equation (1).
&lgr;
obs
=k·&lgr;
mot
(4)
The equation (4) is proved in the following document.
Ref. 2: Y. Kinpara and M. Koyama, “Speed Sensorless Vector Control Method of Induction Motor Including A Low Speed Region,” The Journal “D” of the Institute of Electrical Engineers of Japan, vol. 120-D, no. 2, pp. 223-229, 2000.
With a selection method for a feedback gain K, which is proposed by Ref. 2, several unstable operation conditions are imposed on the induction motor. Especially, when a stator frequency approaches “0”, an observer does not converge, leading to inability of the operations of the motor drive.
An unstable region on a torque-speed plane of the induction motor drive depends on the value of the constant of proportionality k in the equation (4). This unstable area converges to a single line corresponding to the primary frequency that is exactly “0” when the constant k converges to “0”. Accordingly, the dynamic characteristics resultant from the flux observer become unacceptably slow for a very small value of
Fuji Electric & Co., Ltd.
Greer Burns & Crain Ltd.
Leykin Rita
LandOfFree
Control system, observer, and control method for a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control system, observer, and control method for a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control system, observer, and control method for a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3160205