JP3585031B2 - Induction motor control device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for an induction motor driven by a voltage source inverter.
[0002]
[Prior art]
In a conventional control device that is driven by a voltage-type inverter and controls the induction motor at a variable speed, when a stop command is issued to the motor, the motor is controlled based on a predetermined deceleration time gradient. It is common practice to decelerate and stop.
[0003]
[Problems to be solved by the invention]
For example, when a stop command is issued to an induction motor as a power source such as an elevating device, since it is desired to stop the elevating device quickly and safely, the motor is stopped via a mechanical brake. I have.
[0004]
However, in a conventional control device for an induction motor driven by a voltage source inverter, when a stop command is issued to the motor, the motor is decelerated and stopped based on a predetermined deceleration time gradient. During the period, the elevating device continues the ascending or descending operation, and therefore, when the mechanical brake is operated during this period, an excessive drive torque is generated in the electric motor via the control device, and the brake In order to prevent the wear of the shoe from being accelerated, the operation timing of the mechanical brake is set after the deceleration stop period has elapsed. As a result, there is a problem in stopping the elevating device immediately.
[0005]
An object of the present invention is to provide a control device for an induction motor that solves the above problems.
[0006]
[Means for Solving the Problems]
The present invention relates to a control device for an induction motor for controlling an induction motor driven by a voltage-source inverter at a variable speed, wherein the motor is provided with a free-run stop means for interrupting an output of the voltage-source inverter, and the motor is driven for a predetermined deceleration time. Deceleration stop means for decelerating and stopping based on the gradient, stop method switching means for selecting either the free-run stop means or deceleration stop means when a stop command is issued to the electric motor, and an operation command to the electric motor And a time measuring means for measuring an operating time from when the issuance is issued, wherein the stopping method switching means selects the free-run stopping means when the measured value of the time measuring means is equal to or greater than a preset switching value. When the measured value is less than the switching value, the deceleration stop means is selected.
[0007]
According to the present invention, when used in the control device of the induction motor for driving the lifting device, when the free-run stop means of the motor is operated, the wear of the brake shoe is accelerated even if the mechanical brake is operated at the same time. That is avoided.
[0008]
Further, when the operation time is extremely short, the operation of the deceleration stop unit and the operation of the mechanical brake are performed simultaneously, and as a result, the lifting / lowering device operates the free-run unit to operate the mechanical brake. "Slipping of the lifting device" due to the operation delay can be prevented. Further, when the operation time is long, the operation of the free-run stop means and the operation of the mechanical brake are performed simultaneously. In this case, the ascending or descending distance of the elevating device is sufficiently long. The "fall" distance can be a relatively small value.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a circuit configuration diagram of an induction motor control device according to an embodiment of the present invention, wherein 1 is an AC power supply such as a commercial power supply, 2 is a voltage source inverter formed by a semiconductor power conversion circuit and the like, and 3 is An induction motor 10 driven by the voltage source inverter 2 is a control circuit for controlling the induction motor 3 at a variable speed.
[0010]
The control circuit 10 includes a frequency commander 11 for setting a command value f _S of the frequency output by the voltage-type inverter 2, and a frequency command output from the voltage-type inverter 2 based on an operation command of the induction motor 3 commanded from the outside. a frequency setter 12 for setting a command value f _S ^*, the command value f _S ^* on the basis of increase or decrease the frequency setting value f ^* to be output at a preset acceleration time gradient and deceleration time gradient, finally f An acceleration / deceleration calculator 13 for calculating a frequency set value f ^* that satisfies _S ^* = f ^* , and a frequency / voltage (F / V) converter 14 for deriving a voltage set value v ^* corresponding to the frequency set value f ^*. A PWM calculator for deriving an AC signal of a frequency and a voltage output by the voltage source inverter 2 from the frequency set value f ^* and the voltage set value v ^*, and converting the AC signal into a pulse signal subjected to pulse width modulation (PWM). 15 and the said A driving circuit 16 for generating a driving signal to the voltage source inverter 2 from the pulse signal, a counter 17 for measuring time from when the operation command is issued to when the operation command is dropped, and The time measurement value immediately before being dropped is taken in, the time measurement value is compared with a preset switching value, and a comparator 18 that outputs the comparison result is provided. A logic level “H” signal and a logic level “L” signal are output. And a switch 19 for switching and outputting.
[0011]
Since each control element constituting the above-described control device 10 is formed by a well-known technique, an operation according to the present invention will be described below.
[0012]
First, when the control device 10 and the voltage source inverter 2 shown in FIG. 1 complete the operation preparation, the operation command has been dropped at this time, so that the frequency setting device 12 closes the contact on the lower side of the paper as shown in FIG. Since f _S ^* = 0, and the switch 19 via the comparator 18 described later also closes the contact point on the lower side of the paper as shown in the figure, and outputs a logical “L” level. The drive circuit 16 is in a non-operating state (= the output of the voltage source inverter 2 is cut off).
[0013]
Then, when the operation command is issued, the frequency setter 12 contacts are closed on the upper side, the f _S ^* = f _S becomes also contacts the upper side switch 19 via a comparator 18 to be described later at the same time Are closed, a logic "H" level is output, and the drive circuit 16 is activated. Accordingly, an AC voltage based on the frequency set value f ^* via the acceleration / deceleration calculator 13 and the voltage set value v ^* via the F / V converter 14 is output from the voltage-type inverter 2, and the induction motor 3 is stopped. , The AC voltage corresponding to the command value f _S of the frequency command device 11 is output from the voltage-type inverter 2 and the induction motor 3 enters the constant-speed operation state.
[0014]
When the induction motor 3 of the aforementioned acceleration operating state or constant speed driving state, when the operation command is dropped, the frequency setter 12 is closed contacts the lower side as illustrated, the f _S ^* = 0 becomes An AC voltage based on the frequency set value f ^* via the acceleration / deceleration calculator 13 and the voltage set value v ^* via the F / V converter 14 is output from the voltage-type inverter 2, and the induction motor 3 is in a deceleration operation state. At this time, the comparator 18 compares the measured value of the counter 18 with the switching value, and when the measured value is equal to or more than the switching value, the switching device 19 via the comparator 18 is also shown in FIG. As described above, the contact is closed on the lower side of the drawing to output a logical "L" level, the output of the voltage source inverter 2 is cut off via the drive circuit 16, and the induction motor 3 enters a free-run state. When the measured value is smaller than the switching value, the contact of the switching device 19 via the comparator 18 remains closed on the upper side of the drawing, so that the induction motor 3 shifts to the deceleration operation state, and eventually the command value f _S ^* An AC voltage corresponding to (= 0) is output from the voltage source inverter 2, and the induction motor 3 is stopped.
[0015]
【The invention's effect】
According to the present invention, the control device of the induction motor as a power source such as a lifting device is provided with a function of stopping the motor in a free-run state. Is avoided.
[0016]
Further, according to the present invention, in the elevating device, when the operation time of the electric motor is extremely short, the deceleration stop operation of the electric motor and the operation of the mechanical brake are simultaneously performed to prevent “slipping” of the elevating device. can do. Further, when the operation time is long, the free-run stop operation of the electric motor and the operation of the mechanical brake are performed simultaneously. In this case, the ascending or descending distance of the elevating device is sufficiently long. The "fall" distance can be a relatively small value.
[0017]
In particular, the control device for an induction motor according to the present invention is suitable for a digital control device using a microcomputer in recent years.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram of a control device for an induction motor showing an embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1 ... AC power supply, 2 ... Voltage type inverter, 3 ... Induction motor, 10 ... Control device, 11 ... Frequency commander, 12 ... Frequency setter, 13 ... Acceleration / deceleration calculator, 14 ... Voltage / frequency converter, 15 ... PWM arithmetic unit, 16 drive circuit, 17 counter, 18 comparator, 19 switch.

Claims (1)

In the induction motor control device that controls the induction motor driven by the voltage-type inverter at a variable speed, the motor-based free-run stop means for interrupting the output of the voltage-type inverter and the motor based on a predetermined deceleration time gradient. A deceleration stop unit for decelerating and stopping, a stop method switching unit for selecting either the free-run stop unit or the deceleration stop unit when a stop command is issued to the motor, and an operation command issued to the motor. A time measuring means for measuring a running time from time to time, wherein the stop method switching means selects the free-run stopping means when the measured value of the time measuring means is equal to or greater than a preset switching value, and The controller for an induction motor, wherein the deceleration stop means is selected when is smaller than the switching value.

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