Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1988-10-25
1990-10-30
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Primary circuit control
318806, 318759, H02P 540
Patent
active
049671332
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a motor control apparatus comprising a discharge circuit for reducing a voltage which is regenerated to a driving circuit from a motor in the braking of an AC servomotor or the like, a protection circuit for protecting the discharge circuit, and means to render the driving circuit to an inoperative state after activation of the protection circuit.
BACKGROUND ART
Generally, in an AC servomotor, when reverse revolution braking (sic) is applied to the motor, a voltage is regenerated from the motor to a driving circuit, and the voltage on a smoothing capacitor provided on an input of the driving circuit rises, and sometimes the voltage exceeds the rated voltage of the capacitor.
Therefore, a method wherein, when the voltage of the smoothing capacitor rises, the voltage is detected and is discharged to a discharge circuit and the voltage rise of the smoothing capacitor is restricted, is known.
Hereafter, referring to the drawings, a conventional motor control apparatus is elucidated.
FIG. 1 shows a configuration of the conventional motor control apparatus. Referring to FIG. 1, numeral 1 designates an alternating current power source, numeral 2 designates a rectifier diode, numeral 3 designates a smoothing capacitor for smoothing an output of the rectifier diode 2, numeral 4 designates a motor driving circuit wherein a terminal voltage of the smoothing capacitor 3 is inputted, numeral 5 designates a servomotor which is driven by an output of the motor driving circuit 4, numeral 6 designates a regenerative voltage detection circuit which is connected to the input of the driving circuit 4, numeral 7 designates a discharge circuit of the smoothing capacitor 3, numeral 8 designates a protection circuit of the discharge circuit 7, numeral 9 designates an overvoltage detection circuit for stopping operation of the motor driving circuit 4 when an input of the motor driving circuit 4 exceeds a predetermined level, numeral 10 designates a voltage drop detection circuit for stopping operation of the motor driving circuit 4 when the input of the motor driving circuit 4 is lowered below a predetermined level during the operative state of the motor driving circuit 4.
Operation of the motor control circuit is hereafter described in more detail.
FIG. 2 shows voltage detecting levels Va, Vb, Vc of the regenerative voltage detection circuit 6, the overvoltage detection circuit 9 and the voltage drop detection circuit 10, respectively. In the same figure, V.sub.DC designates a terminal voltage of the smoothing capacitor 3.
When the motor turns into a braking state, V.sub.DC rises gradually, and when V.sub.DC >Va is attained, the regenerative voltage detection circuit 6 is activated, and the discharge circuit 7 is connected to the smoothing capacitor 3, and thereby the electric charge stored in the smoothing capacitor 3 is discharged through the discharge circuit 7, and V.sub.DC is reduced and returns to a steadystate. When V.sub.DC >Vb is attained by an instantaneous voltage rise, the over-voltage detection circuit 9 is activated, and the driving circuit 4 is caused to suspend operation and V.sub.DC is reduced. Even if the voltage of the smoothing capacitor 3 has become V.sub.DC <Vc while starting of the motor 5, the voltage drop detection circuit 10 stops the driving circuit 4 and serves to prevent drop of the voltage of the smoothing capacitor 3 under a set value.
Hereupon in the conventional apparatus, when the discharge circuit 7 is operated during a long time period, there is a danger of burning out the discharge circuit, and hence the protection circuit 8 for protecting the discharge circuit 7 works, and input to the discharge circuit 7 is intercepted; but there has been a disadvantage that the driving circuit 4 is operational in this state, and a voltage is regenerated from the motor to the driving circuit 4, and thereafter the voltage rise of the smoothing capacitor 3 can not be restricted if the voltage of the smoothing capacitor 3 did not rise until it become
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patent: 3887860 (1975-06-01), Bernhardt et al.
patent: 3947748 (1976-03-01), Klein
patent: 4183081 (1980-01-01), Cutler et al.
patent: 4234917 (1980-11-01), Suzuki et al.
patent: 4545464 (1985-10-01), Nomura
patent: 4667776 (1987-05-01), Nomura
Matsushita Electric - Industrial Co., Ltd.
Smith Jr. David
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