Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1989-11-17
1992-09-22
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Primary circuit control
H02P 540
Patent
active
051500299
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for controlling the magnetic flux of an induction motor for use in carrying out a vector control by detecting the torque current component from the voltage and current applied on the motor.
BACKGROUND OF THE INVENTION
A method is known for producing the secondary linkage magnetic flux of an induction motor by using a primary delay circuit with the voltage and current on the motor and a magnetic flux command value as inputs.
For example, in Japanese Laid-Open Patent Publication No. 57-201870 previously disclosed by the present applicant, a method has been employed in which a secondary induced voltage is obtained by reducing the impedance voltage of an induction motor from the terminal voltage thereof, a voltage obtained by adding to the secondary induced voltage a voltage corresponding to the excitation command current producing by an excitation command is derived and the derived voltage is integrated by a primary delay integration.
However, the above conventional method has had the disadvantage that the effect of the parameters of the motor on the magnetic flux operation value, especially that of the primary resistance varying depending on temperatures, becomes large at low-frequencies.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to reduce the increase in phase error with respect to the magnetic flux operation characteristics of an induction motor by re-investigating the characteristics of magnetic flux operation value on the basis of evaluation of a torque current feedback or magnetic flux orientation type torque control employed for carrying out a vector control.
To achieve the above object, the induction motor magnetic flux production method according to the present invention is characterized as follows. That is, in a vector control device in which a primary current is supplied to the induction motor in response to an excitation current command value and a torque current command value and the frequency is controlled on the basis of the magnetic flux operated from the voltage and current applied on the motor, when the magnetic flux is controlled as a function of the voltage, current on the motor and a magnetic flux command signal by using a primary delay circuit, the time constant of the primary delay circuit is set equal to that of the secondary circuit of the motor.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram of one embodiment of the present invention,
FIG. 2 is a block diagram of an example of a magnetic flux operation circuit and
FIG. 3 is a vector diagram of a secondary flux.
DESCRIPTION OF THE PREFERRED EMBODIMENT
One of the first characteristics required for the magnetic flux vector even for the torque current feedback and magnetic flux orientation type vector controls, is the coincidence in phase between the actual secondary linkage magnetic flux and its operation value and the next required characteristic is the coincidence between the magnetic flux amplitudes.
Therefore, in the present invention, effort has been exercised to reduce the phase error of the magnetic flux operation value at low frequencies, particularly by taking notice of the characteristics of magnetic flux operation value in a motor constrained state brought about at a critical low frequency. For example, the torque current it in the torque current feedback type vector control may be operated as follows: flux vector
As will be seen from the equation (1), the primary current i.sub.1 can be directly detected and the magnetic flux can be expressed by .PHI..sub.2 /.vertline..PHI..sub.2 .vertline. showing a favorable phase characteristic of the unit vector.
In the present invention, the characteristics of the operation magnetic flux vector has been investigated especially at low-frequencies at which the operation error increases, so as to improve them and particularly, an attempt has been made to reduce phase error in a motor constrained state.
FIG. 2 is a block diagram of a magnetic flux control cir
REFERENCES:
patent: 4330741 (1982-05-01), Nagase et al.
patent: 4503376 (1985-03-01), Okuyama
patent: 4862343 (1989-08-01), Nomura et al.
Ohtani Tsugutoshi
Watanabe Eiji
Kabushiki Kaisha Yaskawa Denki Seisakusho
Smith Jr. David
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