Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2000-02-03
2001-11-13
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S722000, C318S800000
Reexamination Certificate
active
06316905
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of determining the angular velocity of a polyphase machine operated by field orientation without a transmitter and a device for carrying out this method.
BACKGROUND INFORMATION
German Patent Application No. 195 31 771.8 describes a method and a device for determining an angular velocity of a polyphase machine operated by field orientation without a transmitter.
The present invention is based on the finding that under steady-state operating conditions, there is a difference
&Dgr;&ohgr;/&ohgr;
*
={circumflex over (&ohgr;)}/&ohgr;
*
−&ohgr;/&ohgr;
*
{circumflex over (=)}&Dgr;
n={circumflex over (n)}−n
(1)
between a normalized rotational speed {circumflex over (n)} of the model of the machine and a normalized speed n of the polyphase machine.
According to German Patent Application No. 195 31 771.8, in steady-state operation, the following formal relationship exists between normalized rotational speed difference &Dgr;ñ and system deviation {tilde over (&Dgr;)}⊥ at the input of the equalizing controller according to the older German patent application:
Δ
⊥
~
=
u
¨
^
·
(
-
Δ
n
~
)
with
u
¨
^
=
f
(
n
^
s
,
n
^
r
,
σ
^
,
ρ
^
,
T
^
→
*
)
(
2
)
where
n
^
r
is the model rotor frequency
n
^
s
is the model stator frequency
σ
^
=
L
^
σ
/
(
L
^
μ
+
L
^
σ
)
is the leakage factor of the polyphase machine
ρ
^
=
T
^
r
/
T
^
s
=
(
L
^
μ
+
L
^
σ
)
·
R
^
s
/
(
R
^
r
·
L
^
μ
)
is the time constant ratio
T
^
→
is the selected reference space vector
The “~” symbols above notations in the equation indicate that only steady-state operating states are taken into account.
According to equation 2, the magnitude of steady-state transfer factor {umlaut over ({tilde over (u)})} in general changes considerably as a function of stator frequency {circumflex over (n)}
s
and rotor frequency {circumflex over (n)}
r
as operating parameters, which characterize a steady-state operating point of the polyphase machine.
FIG. 3
illustrates this relationship for the case when normalized rotor flux space vector {circumflex over (&psgr;)}
r
is selected as reference space vector
T
^
→
for splitting the stator current model space vector and the stator current real space vector. Stator frequency {circumflex over (n)}
s
and rotor frequency {circumflex over (n)}
r
as operating parameters are linked together via normalized rotational speed n according to the following equation:
ñ
s
=ñ+ñ
r
Normalization to rotor break-down circular frequency &ohgr;
rK
=R
r
/L
94
and the symbol “−” for characterization of steady-state operation are described in the article “Schnelle Drehmomentregelung im gesamten Drehzahlbereich eines hochausgenutzten Drehfeldantriebs” (Fast torque control in the entire rpm range of a highly utilized rotational field drives), printed in the German journal
Archiv für Elektrotechnik
(Archive for Electrical Engineering), 1994, volume 77, pages 289 through 301.
SUMMARY
An object of the present invention is to improve upon the conventional method and device in such a way as to greatly reduce the interfering dependence of the steady-state transfer factor on the rotor frequency as an operating parameter.
Due to the fact that the conjugated complex normalized rotor flux space vector divided by the square of its modulus is provided as the conjugated complex reference space vector, and the stator current model space vector and the stator current real space vector are each processed in regard to angular position and modulus as a function of the operating point before these processed space vectors are transformed into the complex reference system, this achieves the result that the interfering dependence of the steady-state transfer factor on the rotor frequency as an operating parameter is greatly reduced.
In an advantageous method, the model and real stator current space vectors are each normalized, and a differential current space vector is formed from these normalized space vectors, and then is processed as explained above and transformed. This greatly reduces the dependence of the steady-state transfer factor on rotor frequency as an operating parameter and greatly reduces the complexity.
These two methods can be optimized by calculating a complex factor which depends on the rotor frequency as an operating parameter and a leakage factor and/or a time constant ratio as a system parameter.
In another advantageous method, a time integral value of the differential current space vector is formed and is then processed and added to the processed differential current space vector. This achieves the result that the steady-state transfer factor has a constant value of one. Thus, this steady-state transfer factor no longer depends on rotor frequency as an operating parameter and the leakage factor and/or the time constant ratio as a system parameter.
By varying the calculation of the complex factors for processing the differential current space vector and its time integral value, this method can be improved with regard to its dynamic response without altering the steady-state transfer factor.
In another advantageous method, a time derivation of the differential current space vector is formed, and the sum of the processed differential current integral space vector and the processed differential current space vector is added up, and then the sum space vector thus formed is transformed. This further improves the response characteristic in the dynamic operating state.
In one example embodiment of the present invention, a device for calculating complex factors for processing the stator current model space vector, the stator current real space vector, a differential current space vector and a differential current integral space vector is connected downstream from the signal processor, with several multipliers being provided, connected to this device at the input end and at the other end to the elements at whose outputs the signals to be processed are available.
In comparison with the conventional device, an advantageous device additionally has only the device for calculating the complex factors, a comparator device and two additional multipliers. These additional elements may be integrated into the signal processor in an especially advantageous device. In other words, the difference between the device according to the present invention and the conventional device lies in the software rather than the hardware.
REFERENCES:
patent: 5811957 (1998-09-01), Bose et al.
patent: 5834918 (1998-11-01), Taylor et al.
patent: 5903129 (1999-05-01), Okune
patent: 44 33 551 (1996-03-01), None
patent: 195 31 771 (1997-03-01), None
Baader, et al., “Direct Self Control (DSC) of Inverter-Fed Induction Machine: A Basis for Speed Control Without Speed Measurement”, May 1, 1992, IEEE Transactions on Industry Applications, vol. 28, Nr. 3, p. 581-588*.
Maischak, et al., “Schnelle Drehmomentregelung Im Gesamten Drehzahlbereich Eines Hochausgenutzten Drehfeldantriebs (Fast Torque Control in the Whole Speed Range of an Extremely Utilized Three-Phase A.C. Drive)”, Archiv Fuer Elektrotechnik, Bd. 77, 1994, 289-301*.
Ro Bentsu
Siemens Aktiengesellschaft
Young & Thompson
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