JPH03143289A - Switching driving system of induction motor - Google Patents

Abstract

PURPOSE:To enable a speed to be controlled at a high speed, and the speed to be controlled at a low speed, and a device to be exactly positioned by setting a switching circuit for switching PWM signal and rectangular wave signal to each other to provide the input to an inverter, and by switching the signals to each other according to the setting of the speed. CONSTITUTION:The input of the rectangular wave signal of respective phases from a rectangular wave generating circuit 2, and PWM signal from a PWM circuit 3, to a switching circuit 4 is provided, and is switched according to output from a switch command circuit 5, and the output of the rectangular wave signal or the PWM signal is directed to the inverter of a motor driving circuit 6. When the actual speed of a motor 7 is a speed lower than a reference speed, then the inverter is controlled by the PWM signal, and the motor 7 is driven in a PWM type, and so the speed of it is exactly controlled, and it is exactly positioned. Besides, when it exceeds the reference speed, then the inverter is controlled by the rectangular wave signal, and the motor 7 is rectangular-wave-driven, and so high-speed rotation control can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a drive system for an induction motor that drives the main shaft of a machine tool.

The spindles of conventional technical machine tools are required to rotate at high speeds, and now spindles of up to 100,000 to 200,000 revolutions (rpm) have appeared. There is a need for speed control over a wide range from a stopped state to this maximum speed.

Conventionally, the spindle speed was 20. A drive circuit for a motor that exceeds H[l r p m is driven by an inverter square wave drive system. With this method, the excitation frequency of the motor can be increased up to the chopping limit frequency of the switching element of the inverter, making high-speed rotation possible.

On the other hand, in a machine tool that automatically exchanges tools, the spindle must be stopped at a fixed position.

Furthermore, when processing a workpiece attached to the spindle, it is necessary to stop the spindle at a fixed position.

In such cases, slow and accurate positioning control is required.

Problems to be Solved by the Invention In order to rotate the main shaft at high speed, it is necessary to use the inverter's rectangular wave drive system, as described above. However, when the main shaft is driven at low speed for positioning, The wave drive method has the disadvantage that accurate positioning cannot be performed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a switching drive system for an induction motor that enables high-speed speed control as well as low-speed speed control and accurate positioning.

Means for Solving the Problems In an induction motor driven by a rotating magnetic field formed based on an inverter output, the present invention provides a PWM circuit that outputs pulse width modulation (hereinafter referred to as PWM) signals for each phase, and a A rectangular wave generation circuit outputs a phase rectangular wave signal, and a switching circuit inputs the above PWM signal or the above rectangular wave signal to an inverter that drives the induction motor. Depending on whether or not the above rectangular wave signal and the above PWM signal are in phase synchronization, the switching circuit is switched, and if the speed is below the set value, the above PwM signal is applied, and if the speed exceeds the set value, the above rectangular wave signal is applied. The above problem was solved by inputting the signal to an inverter to drive the induction motor.

When the operating motor speed exceeds the set value, the inverter is controlled by a square wave signal, so the motor speed can be increased to the speed determined by the chopping limit frequency of the inverter's switching element, making speed control possible in the high-speed range. Make it. On the other hand, since the inverter is controlled by the PWM signal to drive the motor when the speed of the motor falls below the set value, it is possible to accurately control the speed in the low speed range and to perform accurate positioning.

The embodiment diagram is a main part block diagram of an embodiment for implementing the present invention.

In the figure, reference numeral 1 denotes a reversible counter circuit that counts forward rotation pulses +P and reverse rotation pulses -P from a pulse encoder 8 attached to the induction motor 7. It detects the rotational position of the rotor of the induction motor 7, and detects the electrical angle 0. Every time.

Pulses are output at three points: 120 degrees and 240 degrees.

Code 2 indicates electrical angles from counter circuit 1 of 0 degrees, 120 degrees,
The U phase is sent to the inverter of the motor drive circuit 6 that drives the induction motor 7 in response to the 240 degree pulse.

This is a rectangular wave generation circuit that outputs rectangular wave signals of the (2) phase and W phase via the switching circuit 4.

This counter circuit 1. The rectangular wave generation circuit 2 is the same as a conventional induction motor drive circuit that drives an inverter with a rectangular wave signal, and the details thereof will be omitted.

Further, reference numeral 3 is a PWM circuit that outputs PWM signals of each phase. Similar to the conventional servo control system, a current loop is set up based on the feedback pulse from the pulse encoder 8, a position loop, a velocity loop, and a signal from a current detector (not shown).
Two sine waves with a phase difference of 90 degrees are created from the driving frequency obtained by adding a slip frequency proportional to the output of the speed loop to the rotational frequency of the motor 7 obtained from The primary current command is created by multiplying and adding the excitation current components, and converts these two primary current commands into U, V, and W phase current commands, and then outputs the U, V through the current loop.

W-phase current commands 1u, Iv, and Iw are generated. These current commands 1u, Iv, and W are input to the PWM circuit 4,
In the PWM circuit 4, the triangular wave and this current command are compared, and 3
The phase PWM signal is output.

The switching circuit 4 inputs the rectangular wave signals of each phase from the rectangular wave generating circuit 2 and the PWM signal from the PWM circuit, and switches according to the output from the switching command circuit 5 to output the rectangular wave signal or the PWM signal.
The M signal is output to the inverter of the motor drive circuit 6.

The switching command circuit 5 outputs the actual speed of the electric motor 7, U, determined by the feedback pulse from the pulse encoder 8.
Input the rectangular wave signal of the phase and the PWM signal of the U phase, and when the actual speed exceeds the set reference speed or decreases below the reference speed, compare the rectangular wave signal of the U phase and the PWM signal, When the phase becomes the same, a switching signal is output, switching circuit 4 is switched, and when the actual speed exceeds the reference speed,
The rectangular wave signals of each phase from the rectangular wave generation circuit 2 are input to the inverter of the motor drive amount circuit 5 to drive the induction motor with a rectangular wave. Furthermore, when the actual speed is lower than the reference speed, the switching circuit 4 switches to the PWM signal side, and the PWM signal from the PWM circuit 3 is switched to the PWM signal side.
The WM signal is input to the inverter of the motor drive circuit 6, and the induction motor 7 is driven by the PWM method.

In this way, according to the command from the switching command circuit 5, when the actual speed of the electric motor 7 is lower than the reference speed, the PW
The inverter is controlled by the M signal, and the induction motor is controlled by the P signal.
Since it is driven by the WM method, accurate speed control and positioning can be performed. Furthermore, when the reference speed is exceeded, the inverter is controlled by a rectangular wave signal and the induction motor 7 is driven by a rectangular wave, so the induction motor 7 can be controlled to rotate at high speed up to a speed corresponding to the chopping limit frequency of the switching element of the inverter. becomes.

Note that an upper limit value and a lower limit value with a certain width (hysteresis) are set as reference speeds that serve as the reference for the switching command, and when the actual speed of the motor 7 exceeds the upper limit value, the switching command circuit 5
outputs a switching signal and switches the switching circuit 4 to the square wave signal side, and when the lower limit value is exceeded, outputs a switching signal and switches the switching circuit 4 to the PWM signal side to perform smooth switching. Also good.

Effects of the Invention The present invention drives an induction motor by controlling an inverter with a rectangular wave in a high-speed region, so it is possible to perform high-speed rotation and speed control up to the maximum speed determined by the chopping limit frequency of the switching element of the inverter, and in a low-speed region. Since the inverter is controlled by the PWM method to drive the induction motor, accurate speed control and accurate positioning can be achieved even in the low speed range. Furthermore, it also enables constant speed control of the spindle and constant circumferential speed control that keeps the circumferential speed of the workpiece attached to the spindle constant.

[Brief explanation of the drawing]

The drawing shows essential blocks of one embodiment of the present invention. King: Counter circuit, 2: Square wave generation circuit, 3:
... PWM circuit, 4... switching circuit, 5... switching finger current circuit, 6... motor drive circuit, 7... induction motor, 8... pulse encoder. )

Claims (1)

[Claims] In an induction motor driven by a rotating magnetic field formed based on an inverter output, a pulse width modulation circuit outputs a pulse width modulation signal of each phase, a rectangular wave generation circuit outputs a rectangular wave signal of each phase, and an induction motor. An inverter that drives the motor is provided with a switching circuit that switches and inputs either the pulse width modulation signal or the rectangular wave signal. The switching circuit is switched by synchronizing the phase of the pulse width modulation signal, and if the speed is below the set value, the above pulse width modulation signal is input to the inverter, and when the speed exceeds the set value, the above rectangular wave signal is input to the inverter to drive the induction motor. A switching drive system for an induction motor.