Electricity: motive power systems – Induction motor systems
Reexamination Certificate
2001-05-25
2003-01-14
Fletcher, Marlon T. (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S432000, C318S433000, C318S434000, C318S800000, C318S807000, C318S809000, C318S811000
Reexamination Certificate
active
06507166
ABSTRACT:
The present invention relates to a control device for a wide speed range induction machine, carrying out a control based upon a flux estimation performed by means of a Luenberger state observer.
The present invention moreover relates to a method for positioning the eigenvalues of a Luenberger state observer implemented in a control device for a wide speed range induction machine in order to perform an estimation of the flux of said induction machine.
BACKGROUND OF THE INVENTION
As is known, direct field-orientation control of induction machines calls for the knowledge of the components of the rotor flux of the induction machines themselves, which can either be measured directly using magnetic sensors or can be estimated on the basis of the values of the quantities present at the machine terminals.
In practical applications, however, recourse is almost exclusively had to the estimation of the rotor flux of the asynchronous machine, using an appropriate mathematical model, in so far as direct measurement presents numerous problems of a technical and economic nature.
One of the most interesting solutions for the estimation of the rotor flux of induction machines is represented by the known Luenberger state observer, which is based upon the dynamic equations of the induction machine itself and upon the measurement of speed in order to reconstruct the state of the induction machine in terms of stator current and rotor flux.
FIG. 1
shows, purely by way of non-limiting example, a general diagram of the circuit of the control of an induction machine
1
, represented for reasons of simplicity by the symbol of a three-phase electric motor, said control being implemented on the basis of the flux estimation performed by means of a Luenberger state observer.
As is shown in
FIG. 1
, the control of the induction machine
1
envisages the use of a power driving device
2
which supplies to the induction machine
1
three control voltages, the so-called three phases of a three-phase system, and is controlled by a control device
4
, typically implemented by means of a digital signal processor, commonly referred to as DSP.
In particular, the control device
4
carries out control of the induction machine
1
on the basis of the estimation of the rotor flux of the induction machine
1
performed by means of the aforesaid Luenberger state observer, and receives at input one or more reference signals, among which a reference speed signal indicating the desired speed of rotation of the induction machine
1
, and a plurality of measurement signals indicating the values of quantities of the induction machine
1
, among which the value of the effective speed of rotation of the induction machine
1
measured by means of a speed sensor (not shown) connected to the induction machine
1
and the values of two of the three phase currents absorbed by the induction machine
1
and measured by means of appropriate sensors (not shown) at the terminals of the induction machine
1
.
FIG. 2
shows the block diagram of a part of the system with which the induction machine
1
and the Luenberger state observer used in the control device
4
are conventionally modelled from the control standpoint.
As shown in
FIG. 2
, the induction machine is schematically represented by a block
1
defined by a state vector x formed by the state variables of the induction machine
1
, of which only one part is physically measured. The block
1
receives at input an input vector u representing input quantities supplied to the induction machine
1
(control voltages supplied by the power driving device) and generates at output a measured output vector y representing measured output quantities supplied to the induction machine
1
(absorbed currents), which, as is known, are selected from among the state variables contained in the state vector x.
As is known, then, the induction machine
1
is defined by the following variable-parameter linear differential state equations:
{
x
.
=
A
(
ω
)
x
+
Bu
y
=
Cx
(
1
)
where:
A is known in the literature by the name of matrix of the induction machine or matrix of free evolution;
B is known in the literature by the name of input matrix;
and
C is known in the literature by the name of output matrix, which enables generation of the measured output vector y starting from the state vector x, i.e., selection, from among all the state variables, of the output variables of the system.
The Luenberger state observer implemented by the control device
4
is instead schematically represented by a block
6
which receives at input the input vector u and supplies at output an estimated output vector {tilde over (y)} representing the output quantities estimated by the Luenberger state observer
6
, and an estimated state vector {tilde over (x)} representing the state variables estimated by the Luenberger state observer
6
.
The measured output vector y and the estimated output vector {tilde over (y)} are then supplied at input to a block
8
which performs the subtraction and generates at output an error vector e supplied at input to the block
10
to carry out feedback.
As is known, then, the measured output vector y, together with the aforementioned reference signals, is supplied at input to a regulator block (not shown), which generates the aforesaid input vector u for regulating the currents and flux of the induction machine
1
, in order to obtain the references required.
The Luenberger state observer applied to the dynamic model of the induction machine expressed as a function of the rotor flux and of the stator current (this being the most convenient form in so far as one of the state variables coincides with the output itself of the system, and the structure of the algorithm is thus simplified), represented on the stationary &agr;&bgr; reference system, is described by the following variable-parameter linear differential state equations and in complex form (the variables marked with the tilde refer to the variables estimated by the Luenberger state observer):
{
x
.
~
=
A
(
ω
)
x
~
+
Bu
-
K
(
y
-
y
~
)
y
~
=
C
x
~
(
2
)
A
=
[
-
1
σ
(
R
s
L
s
+
(
1
-
σ
)
R
r
L
r
)
1
-
σ
σ
L
m
(
R
r
L
r
-
j
ω
)
L
m
R
r
L
r
(
-
R
r
L
r
+
j
ω
)
]
B
=
[
1
σ
L
s
0
]
C
=
[
1
0
]
(
3
)
x
~
=
[
i
~
s
λ
~
r
]
=
[
i
~
s
α
+
j
i
~
s
β
λ
~
ra
+
j
λ
~
r
β
]
u
=
v
s
=
v
s
α
+
j
v
s
β
y
=
i
s
=
i
s
α
+
ji
s
β
(
4
)
K
=
[
k
11
+
jk
12
k
21
+
jk
22
]
=
[
k
1
k
2
]
(
5
)
where:
A, B and C have the meanings specified previously;
K is the feedback matrix of the Luenberger state observer;
R
s
is the stator resistance of the induction machine;
R
r
is the rotor resistance of the induction machine;
L
m
is the magnetization inductance of the induction machine;
L
s
is the stator inductance of the induction machine;
L
r
is the rotor inductance of the induction machine;
&sgr; is the coefficient of dispersion of the induction machine defined as follows:
σ
=
1
-
L
m
2
L
s
L
r
&ohgr; is the equivalent mechanical speed of rotation of the induction machine, corresponding to the mechanical speed of rotation multiplied by the pole torques;
i
s &agr;,&bgr;
are the components of the stator current in the stationary &agr;&bgr; reference system;
&lgr;
r &agr;,&bgr;
are the components of the rotor flux in the stationary &agr;&bgr; reference system; and
&ngr;
s &agr;,&bgr;
are the components of the stator voltage in the stationary &agr;&bgr; reference system.
Note that in equations (2) and (3) there appear the matrices A, B and C of the induction machine in so far as it is assumed that the parameters of the induction machine are known, and hence, in particular,
Barba Giovanni
Maceratini Roberto
C.R.F. Societa Consortile per Azioni
Conley & Rose & Tayon P.C.
Fletcher Marlon T.
Smith Tyrone
LandOfFree
CONTROL DEVICE FOR A WIDE SPEED RANGE INDUCTION MACHINE,... 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 DEVICE FOR A WIDE SPEED RANGE INDUCTION MACHINE,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and CONTROL DEVICE FOR A WIDE SPEED RANGE INDUCTION MACHINE,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3048235