Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1987-04-10
1989-04-18
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Primary circuit control
318806, 318811, 318759, H02P 540
Patent
active
048230669
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to a three-phase induction motor control method for performing motor drive control and regenerative control based on digital values.
2. Description of the Related Art
Recent control of three-phase induction motors is in many cases performed by a vector control method of controlling the instantaneous value of motor stator current and generating a torque equivalent to that of a shunt DC machine.
Using vector control of this type to perform motor drive control and regenerative control of a three-phase induction motor is disclosed in e.g. Japanese patent application Laid-Open No. 59-14385.
If an induction motor is subjected to vector control in cases where velocity control is performed up to a region of high rotational velocity, as in a spindle motor of a machine tool or the like, or in cases where control is performed to weaken excitation in accordance with a torque command at a constant rpm, the torque command, excitation current, secondary current and slip frequency become non-linear due to such effects as the secondary leakage impedance and core loss of the motor. As a result, the output torque also becomes non-linear with respect to the torque command, so that a linear relationship between the torque command and output torque cannot be accurately maintained.
Furthermore, since the output of an induction motor generally varies in proportion to the square of the voltage impressed upon the motor, the output will fluctuate when the AC input voltage undergoes a large variation. In the vector control method, a measure devised for preventing such a fluctuation in output entails varying the amount of maximum slip in dependence upon the AC input voltage. Nevertheless, satisfactory results are not obtained in terms of holding the output of the induction motor constant.
At time of regenerative braking, moreover, the power-factor fluctuates due to the capacity of a phase advancing capacitor on the input side, and there is an increase in power supply distortion and reactive power.
SUMMARY OF THE INVENTION
The present invention has been devised to solve the foregoing problems and its object is to provide a three-phase induction motor control method in motor drive control and regenerative control based on the vector control method using a power amplifier comprising a converter and an inverter, in which a linear output torque can be obtained with respect to a torque command without using a flux sensor, and in which the output of the three-phase induction motor can be held constant even when there are fluctuations in power supply voltage.
According to the present invention, there is provided a three-phase induction motor control method based on vector control for converting an AC input into a direct current at the time of motor drive control to drive a three-phase induction motor at a variable velocity. The three-phase induction motor is driven by the output of a first inverter to which the converted direct current is applied. In control method an output current of the three-phase induction motor is converted into a direct current at the time of regenerative control to regenerate the output of a second inverter, to which the direct current resulting from the conversion is applied, in an AC power supply. The method includes vector analyzing an excitation current command and secondary current command into an excitation flux direction component and a motor electromotive force direction component, respectively, on the basis of a torque command with respect to the three-phase induction motor and an excitation flux command decided to accommodate the three-phase induction motor. The method also includes determining a primary current command of the motor based on a synthesis of the vector components, and detecting the voltage of a direct current link portion of a circuit for converting the AC input into a direct current. The method further includes correcting the excitation flux command in dependence upon the detected voltage, obtaining a linear torque comm
REFERENCES:
patent: 3899725 (1975-08-01), Plunkett
patent: 4023083 (1977-10-01), Plunkett
patent: 4047083 (1977-09-01), Plunkett
patent: 4490666 (1984-12-01), Tanamachi et al.
patent: 4532464 (1985-07-01), Igarashi et al.
patent: 4620272 (1986-10-01), Fulton et al.
Shinichi Kouno
Tatsuo Shinohara
Yoshiki Fujioka
Fanuc Ltd.
Smith Jr. David
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