Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2000-09-01
2001-10-09
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S801000, C318S809000
Reexamination Certificate
active
06300741
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a speed controlling method for an induction motor, and more particularly to a technique of vector control without a speed sensor which does not require a speed sensor mounted on a motor and makes it possible to obtain high torque starting from a zero speed range.
As a method of controlling the speed of an induction motor, a method of vector control without a speed sensor is conventionally known.
FIG. 14
shows a configuration of its control system. Reference numeral
1
denotes an induction motor;
2
a power inverter for outputting an output voltage proportional to a voltage command value V
1
*;
3
a coordinate transformer for effecting the coordinate transformation of inverter output currents iu and iw and computing d-axis and q-axis currents id and iq;
4
a voltage computing unit for computing a value of a leak-impedance voltage drop of the motor on the basis of id, iq and an output frequency command value &ohgr;
1
*;
5
and
6
adders for adding the voltage drop value to induced-electromotive-force command values ed* and eq* and outputting d-axis and q-axis voltage command values Vd* and Vq*;
7
a phase reference generator for integrating &ohgr;
1
* and outputting a phase reference &thgr;;
8
a coordinate transformer for outputting an inverter output voltage command value V
1
* (three phase) on the basis of Vd* and Vq*;
9
computing unit for outputting a slip-frequency computed value &ohgr;s
1
on the basis of id and iq;
12
an adder for adding &ohgr;s
1
to a speed command value &ohgr;r* and outputting &ohgr;
1
*; and
13
an electromotive-force computing unit for computing eq* on the basis of &ohgr;
1
*.
It should be noted that “Okuyama, et al.: “Simplified Vector Control System without Speed and Voltage Sensors—Effects of Setting Errors in Control Parameters and their Compensation” The Transactions of The Institute of Electrical Engineers of Japan, Vol. 110-D, No. 5, May, 1990, pp. 477-486 is known as a related document.
SUMMARY OF THE INVENTION
In the above-described configuration, the operating frequency &ohgr;
1
of the motor
1
is controlled in proportion to &ohgr;
1
*, and the drop in the leak impedance is compensated by the action of the voltage computing unit
4
. As a result, the induced electromotive force e of the motor
1
does not change irrespective of the magnitude of the torque. Hence, the magnetic flux of the motor is always kept constant, and a decline in the torque due to a decline in the magnetic flux of the motor is prevented. At this time, since iq is proportional to the slip frequency &ohgr;s, as the computing unit
9
estimates &ohgr;s in accordance with the following Formula (1), and adds it to &ohgr;r* to compute &ohgr;
1
*, the variation of the real rotational speed &ohgr;r due to a change in the slip (torque) is compensated.
&ohgr;
s=
1
/T
2
·iq/id
(1)
However, in cases where actual values r
1
and L &sgr; of the motor parameters vary from reference values r
1
* and L&sgr;* of the motor parameters used in the voltage computing unit
4
, the magnetic flux of the motor varies in correspondence with the torque. Consequently, a decline in the torque occurs (the torque fails to be proportional to the current). In addition, since iq and &ohgr;s are not proportional, Formula (1) is not valid, so that the accuracy of the aforementioned compensation for the speed variation deteriorates.
Generally, a decline in the torque and the deterioration of the speed accuracy are noticeable in the zero speed range and its vicinity.
Accordingly, it is an object of the present invention to provide a speed controlling method for an induction motor which does not undergo a decline in the torque in the zero speed range and is suitable for effecting regenerative operation stably.
To attain the above object, if a speed command value is equal to or less than a predetermined value, a d-axis current id is increased to a value greater than a normal value, and a voltage command value is controlled by being changed in accordance with a q-axis current iq so that iq approaches zero.
REFERENCES:
patent: 4451771 (1984-05-01), Nagase et al.
patent: 5652495 (1997-07-01), Narazaki et al.
patent: 5877607 (1999-03-01), Masaki et al.
patent: 5959430 (1999-09-01), Yuki et al.
patent: 6014007 (2000-01-01), Seibel et al.
patent: 6184648 (2001-02-01), Kato et al.
The Transactions of the Institute of Electrical Engineers of Japan, vol. 110-D, No. 5, May, 1990, pp. 477-486.
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Ro Bentsu
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