Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2000-03-06
2001-08-28
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S727000, C318S804000, C318S807000, C318S808000, C318S809000
Reexamination Certificate
active
06281659
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an induction motor drive, and more particularly, to a vector control of an induction motor.
2. Description of the Related Art
A typical direct field-oriented based induction motor drive system is shown in FIG.
12
.
The vector control of an induction motor is performed by adjusting the torque and magnetic flux of an induction motor
102
fed by an inverter
101
.
FIG. 12
exemplifies an induction motor drive comprising a speed sensor
132
. With the vector control of this system, a speed regulator
105
generates a torque current reference
114
based on a PI (Proportional action and Integral action) control from a speed reference
103
being an instruction to the speed of the motor and a rotation speed
112
of the induction motor
102
, which is detected by the speed sensor
132
as feedback, and outputs the generated torque current reference
114
to a current regulator
104
. The current regulator
104
generates and outputs currents, which are adjusted based on the PI control, from the torque current reference
114
being an instruction to the torque and a flux current reference
113
being an instruction to the flux. Then, a vector rotator
106
transforms these current values into a relative value in a coordinate system (d-q coordinate system) which rotates synchronously with the synthetic vector of the currents, and applies the transformed value to an inverter
101
as a primary voltage command
120
. Note that the flux current reference
113
applied to the current regulator
104
can be set constant in a wide range of operation.
Sensors
130
and
131
respectively detect the voltage value and the current value, which are applied from the inverter
101
to the inductor motor
102
, as a detected voltage
121
and a detected current
122
. After the voltage and the current are transformed into two-phase coordinate system values by 3-2 phase transformers
108
and
109
, they are input to a current and flux observer
110
as space vector values Vs
123
and i
s
124
.
A stator,rotor resistance (Rs,Rr) estimator
500
estimates a stator resistance Rs and a rotor resistance Rr of the induction motor
102
from the stator current
124
output from the 3-2 phase transformer
109
and an observed current
127
and observed flux
128
output from the current and flux observer
110
, and outputs observed values Rs′
503
and Rr′
504
of the resistances Rs and Rr. Then, these values are used by the current and flux observer
110
.
The current and flux observer
110
outputs the observed current
127
and the observed flux rotor
128
from the stator voltage Vs
123
, the stator current i
s
124
, the detected speed
112
of the motor output from the sensor
132
, and the estimated stator and rotor resistance values Rs′
503
and Rr′
504
output from the Rs,Rr estimator
500
.
The vector rotator
106
vector-rotates the flux command
118
and the torque command
119
in a direction of the flux of the rotor based on the observed rotor flux
128
, and outputs the vector-rotated instructions to the inverter
101
as a primary voltage command
120
.
Additionally, the vector i
s
124
is vector-rotated by a vector rotator
107
in the direction of the rotor flux based on the observed flux
128
from the current and flux observer
110
in order to obtain the torque current
126
and the flux current
125
, which are used as feedback signals by the current regulator
104
.
A system without speed sensor, that is a speed-sensorless system, is explained next. In the system comprising no speed sensor, only a stator voltage
121
and a stator current
122
are detected by sensors
130
and
131
. The configuration of this system is shown in FIG.
13
.
Comparing the configuration shown in
FIG. 13
with that shown in
FIG. 12
, a speed observer
111
which estimates the speed of the motor is added, and an Rs,Rr estimator
501
which estimates resistance values Rs and Rr of the stator and the rotor from a stator current
124
, an observed current
127
, observed flux
128
, and a torque command
119
as a replacement of an Rs, Rr resistance estimator
500
.
The speed observer
111
estimates the rotor speed from the stator current i
s
124
, the observed current
127
and the observed flux
128
output from a current and flux observer
110
, and outputs an observed speed
115
both to a speed regulator
105
and to the current and flux observer
110
.
Furthermore, to allow the resistance of the rotor to be observed even in a steady state, a harmonic component
162
is injected in the flux current reference
118
.
In the direct field-oriented control, the flux is typically evaluated using an observer as the one described in:
Ref.
1
—H. Kubota et al. “Speed Sensorless Field-Oriented Control of Induction Motor with rotor Resistance Adaptation,” IEEE Trans. on Ind. Appl., Vol. 30, No. 5, September/October 1994
A conventional mathematical model of the induction motor using a state space notation is as follows:
ⅆ
ⅆ
t
[
i
s
φ
r
]
=
A
·
[
i
s
φ
r
]
+
B
·
v
s
where
i
s
=
[
i
s
α
i
s
β
]
T
:
STATOR
CURRENT
;
φ
r
=
[
φ
r
α
φ
r
β
]
T
:
ROTOR
FLUX
;
v
s
=
[
v
s
α
v
s
β
]
T
:
STATOR
VOLTAGE
;
A
=
[
A
11
A
12
A
21
A
22
]
=
[
-
(
R
s
σ
·
L
s
+
1
-
σ
σ
·
τ
r
)
·
I
L
m
σ
·
L
s
·
L
r
(
1`
τ
r
I
-
ω
r
J
)
L
m
τ
r
I
-
1
τ
r
I
+
ω
r
J
]
B
=
[
1
σ
·
L
s
0
0
0
0
1
σ
·
L
s
0
0
]
T
;
I
=
[
1
0
0
1
]
;
J
=
[
0
-
1
1
0
]
;
R
s
,
R
r
:
STATOR
AND
ROTOR
RESISTANCE
;
L
s
,
L
r
,
L
m
:
STATOR
,
ROTOR
,
AND
MUTUAL
INDUCTANCE
;
τ
r
=
L
r
/
R
r
:
ROTOR
TIME
CONSTANT
;
σ
=
1
-
L
m
2
/
(
L
s
L
r
)
:
TOTAL
LEAKAGE
COEFFICIENT
;
ω
r
:
ANGULAR
ROTOR
SPEED
.
(
1
)
The state equation of a simpler observer is represented by the above provided mathematical model (1). This mathematical model is stable, and the following equation for the current and flux observer
110
is derived from this equation.
ⅆ
ⅆ
t
[
i
s
′
φ
r
′
]
=
A
′
·
[
i
s
′
φ
r
′
]
+
B
·
v
s
(
2
)
where ′ indicates an observed value. For example, a matrix A′ has the same value as that in the matrix A in the equation (1), but it is evaluated using nominal and estimated parameter values instead of actual values.
The observation and observed values in this specification respectively represent observation and observation values in a modern control theory, and indicates the estimation of state variable values from an output, and the estimated values.
Since the values of the resistances Rs and Rr of the stator and the rotor change with the operating temperature of the motor, their values are normally evaluated during normal motor operations, and the observed values are obtained from the evaluation expression.
This evaluation expression is represented as follows according to the above provided Ref. 1.
ⅆ
R
s
′
ⅆ
t
=
-
k
1
(
i
s
-
i
s
′
)
·
i
s
′
(
3
)
ⅆ
R
r
′
ⅆ
t
=
k
2
(
i
s
-
i
s
′
)
·
(
φ
r
′
-
L
m
i
s
′
)
(
4
)
where · indicates a dot product of vectors, and k1 and k2 are positive constants.
FIG. 14
is a block diagram showing the details of the Rs,Rr e
Fuji Electric & Co., Ltd.
Greer Burns & Crain Ltd.
Leykin Rita
Nappi Robert E.
LandOfFree
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