JP2619390B2 - Induction motor speed control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to protection and speed control of an inverter control device for driving an AC motor, and more particularly to a speed control device for an induction motor that reduces a voltage rise during motor regeneration.

[Conventional technology]

As described in Patent Application Publication No. 59-220076, a conventional device includes a voltage detection circuit for detecting a rising voltage during regeneration of a motor, a thyristor forward converter for blocking an AC power supply by the voltage detection circuit, An oscillation control circuit that obtains a frequency higher than the current operation frequency is required, which is expensive. In addition, the speed of the electric motor hunts in order to prevent the voltage increase due to the regeneration by the repetition of the electric regeneration.

[Problems to be Solved by the Invention] In the conventional technology, the DC voltage becomes an overvoltage due to regenerative energy due to the deceleration operation of the motor. To prevent this, a voltage detector that detects the voltage on the DC side is provided, and a power generation braking circuit that consumes regenerative energy by deceleration operation through a resistor, or a regenerative converter device that regenerates energy to the AC power supply side It is expensive because it is necessary. In addition, in the method using a transistor with self-extinguishing ability and GTO, overvoltage due to deceleration operation can be prevented by simply shutting off the base or gate signal with a voltage detector, but a voltage detector is required In addition, since the base or gate signal is suppressed at a voltage equal to or higher than a specified voltage, regenerative electric power is repeated during deceleration, so that deceleration is not performed smoothly, which is a problem for the load. SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive device that performs optimal speed control in view of the above problems.

[Means for solving the problem]

The purpose of the above is to prevent the regenerative energy of the motor from being regenerated to the DC side during the deceleration operation of the motor and becoming an overvoltage during the deceleration operation of the motor. Is established by providing a regeneration preventing means for setting the current command value given to the current control system to zero when the device enters the regenerative operation command mode.

[Action]

The regenerative blocking means provided on the output side of the speed regulator that associates the speed command with the speed feedback is such that during acceleration operation, the speed command becomes larger than the speed feedback and the output of the speed regulator that combines the speed command and the speed feedback is: The current is sent to a current control system (vector control system), and speed control is performed to follow the speed command. Since there is a load during the constant speed operation, the speed command becomes larger than the speed feedback, and the output of the speed adjuster that matches the speed command and the speed feedback is sent to the current control system to perform speed control so as to follow the speed command.

On the other hand, during deceleration operation, unlike during acceleration and constant speed operation, the speed feedback becomes larger than the speed command. When the output of the speed regulator, in which the speed command and the speed feedback are matched, is sent to a current control system, the output is regenerative braking, and the energy of the motor is regenerated to the DC side, resulting in an overvoltage. To prevent this, a regeneration preventing means is provided to prevent the output of the speed regulator from being transmitted to the current control system.

By inserting the regenerative blocking means, the frequency of the speed control system is always higher than the frequency of the motor, so that the regenerative braking of the motor is prevented and the DC side is prevented from being overvoltage.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1. A main circuit of the present invention converts an AC power supply into a DC power supply through a wiring shear breaker 2 for turning on / off an AC power supply 2 and an AC-side main circuit contactor 3. The control device includes a converter 4, a smoothing capacitor 5 for smoothing a DC power supply, and an inverter transistor 6 for converting the DC power supply into a variable frequency of an induction motor 8. Adjuster 1
5, forward rotation regenerative blocking diode 12 which is a main part of the present invention
A variable frequency command to be given to the induction motor 8 is issued based on the speed and current of the induction motor 8 detected by the regenerative blocking diode 13 at the time of reverse rotation, the forward / reverse switching circuit 14, the speed detector 9 and the current detector 7,
It comprises a vector control circuit 11 and a logic circuit 10.

The output of the speed setting device 16 is varied with time as shown in FIG. At the time of forward rotation acceleration, the command value of the speed setting unit 16 becomes larger than the feedback signal of the speed detector 9, and the output of the speed regulator 15 is transmitted to the vector control circuit 11 through the forward rotation prevention diode 12. The speed deviation signal transmitted to the vector control circuit 11 is calculated as a feedback signal from the speed detector 9 and the current detector 7, and the speed of the induction motor 8 is controlled by the variable frequency of the inverter transistor 6.

At the time of forward rotation deceleration, the command value of the speed setting unit 16 becomes smaller than the feedback signal of the speed detector 9, and the output of the speed regulator 15 is blocked by the regenerative blocking diode 12 during forward rotation, and the speed deviation command is sent to the vector control circuit 11. Not transmitted. Therefore, during deceleration, the regenerative current of the induction motor 8 is prevented from flowing into the DC side through the inverter transistor 6 as shown by the motor current in FIG. The speed of the induction motor 8 is naturally decelerated by the load as shown by the speed feedback in FIG. Also, a speed setting device during reverse rotation acceleration
The command value of 16 becomes larger than the feedback signal of the speed detector 9 and the output of the speed regulator 15 is transmitted to the vector control circuit 11 through the regenerative blocking diode 13 at the time of reverse rotation. Vector control circuit
The speed deviation signal transmitted to 11 is calculated as a feedback signal from the speed detector 9 and the current detector 7, and the speed of the induction motor is controlled by the variable frequency of the inverter transistor 6.

At the time of reverse rotation deceleration, the command value of the speed setting unit 16 becomes smaller than the feedback signal of the speed detector 9, the output of the speed regulator 15 is blocked by the reverse rotation prevention diode 13 at the time of reverse rotation, and the speed deviation command is not transmitted to the vector control circuit 11. . For this reason, during deceleration, the regenerative current of the induction motor 8 is prevented from flowing into the DC side through the inverter transistor 6 as shown in the motor current in FIG. The speed of the induction motor 8 is naturally decelerated by the load as shown by the speed feedback in FIG.

 The effect of the present invention will be described with reference to FIG.

In the case where the forward rotation regenerative blocking diode 12 of the present invention shown in FIG. 1 is not inserted, the regenerative current from the induction motor 8 shown in FIG. The voltage on the DC side rises, and the voltage on the DC side rises. In order to consume the regenerative energy of the induction motor 8, the voltage detector 17 provided on the DC side and the voltage regulator 19 which compares the voltage command value of the voltage setting unit 20 with the power generation braking. The regenerative energy is consumed as heat by the transistor 18 for deceleration control.

According to the present embodiment shown in FIG. 1, there is an effect that the regenerative energy of the induction motor 8 is consumed by the load without regenerating to the DC side during deceleration, and the speed control can be smoothly performed.

〔The invention's effect〕

According to the present invention, there is no need to provide a regenerative braking unit or a regenerative converter for consuming regenerative energy generated by the induction motor at the time of deceleration. By providing on the output side of the speed adjuster that comes back together, smooth speed control can be performed by natural deceleration due to load or mechanical loss, so that the device can be simplified and an economically inexpensive inverter device can be provided. There is.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of one embodiment of the present invention, FIG. 2 is a speed current waveform diagram illustrating characteristics of the present invention, FIG. 3 is an explanatory diagram of a conventional embodiment, FIG. FIG. 4 is a speed current waveform diagram for explaining the conventional characteristics. 1 power supply 2 shear breaker for wiring 3 AC main circuit contactor 4 converter 5 smoothing capacitor
6 ... Inverter transistor, 7 ... Current detector, 8
... Induction motor, 9 ... Speed detector, 10 ... Logic circuit, 11 ... Vector control circuit, 12 ... Forward regenerative blocking diode for normal rotation, 13 ... Regenerative blocking diode for reverse rotation, 14 ... Forward / reverse switching Circuit, 15 Speed adjuster, 16 Speed adjuster
17 …… Voltage detector, 18 …… Dynamic braking transistor, 19
…… Voltage regulator, 20 …… Voltage setting device.

Claims (1)

(57) [Claims] 1. A converter for converting AC to DC, a capacitor for smoothing the DC output voltage of the converter, an inverter for converting the DC voltage smoothed by the capacitor to AC of a variable frequency variable voltage, and the inverter An induction motor to be driven, speed adjustment means for inputting a deviation between a speed command value and a speed detection value of the induction motor and outputting a current command value based on the speed deviation; and controlling the current command value and the induction motor. Current control means for controlling the inverter by inputting a detected value of flowing current; and regenerative prevention for reducing the current command value given to the current control means to zero when the output of the speed adjusting means enters a regenerative operation command mode of the induction motor. Means, and wherein the current control means inputs the zero current command value so that the motor current flowing through the induction motor becomes zero. Speed control device for an induction motor and controls the output voltage.