JPH0274189A - Speed control device - Google Patents

Abstract

PURPOSE:To prevent transient phenomena in switching a control system by performing the control over an AC induction motor in a high speed region and in a medium and low speed region on the rotating speed set out from a reference value in switching respectively over to a synchronous system and an asynchronous system. CONSTITUTION:The rotating speed of an AC induction motor 1 is detected by a detection means 2 such as a pulse generator, etc. When this detected rotating speed exceeds a reference value, a programmable interval timer 112 outputs synchronizing signal pulse. A corrective means composed of a CPU 9, a computing element 18, etc., corrects the initial synchronizing signal pulse to meet the timing of a asynchronous carrier wave. In accordance with this corrected synchronizing signal pulse the detected rotating speed is switched over to a synchronous carrier wave with a sinusoidal wave. The gain of current command immediately after the switching over to the synchronous carrier wave is controlled in inversely proportional to the rotating speed of the motor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a speed control device that controls the speed of a main shaft driven by an AC motor.

(Prior Art) Some high-speed spindles used in special machine tools require stable speed control over a wide range from standstill to high-speed rotation of 100,000 revolutions or more. In such a spindle speed control device, a PWM (pulse width modulation) control method is effective, in which the peak value of the inverter output voltage is fixed and the average voltage is adjusted by varying the time width. There are two types of PWM control: a synchronous method in which the carrier frequency for switching is changed in synchronization with the inverter output, and an asynchronous method in which switching is not performed.

(Problems to be Solved by the Invention) These two conventional systems each have the following characteristics.

In the asynchronous method, a sine wave that changes in proportion to the rotation speed is compared with a carrier wave of a constant period, and PWM (pulse width modulation)
Because of the conversion, the cost of configuring a circuit increases in order to raise the carrier frequency to a higher frequency.

In other words, in order to control the speed at a position of 100,000 rpm,
A carrier wave having a frequency of 20K) Iz or higher is required, and problems arise in processing losses and heat radiation during switching in the power element.

On the other hand, in the synchronous method, the carrier wave and sine wave are always operated in synchronization regardless of the rotation speed, so in the medium and high speed range,
There is no beat with the carrier wave, and stable control is possible, but
In speed control at low speeds, it is necessary to devise ways to control the current.

Therefore, it is desirable to use a synchronous method in the high-speed region and switch to an asynchronous method for controlling low- and medium-speed rotations. However, when switching from the asynchronous system to the synchronous system when shifting to high-speed rotation, on the other hand, there is a problem in that a smooth IJI +'X signal cannot be obtained, resulting in a transient phenomenon.

The present invention was made to solve the above problems, and
It is an object of the present invention to provide a speed control device that controls a current command when switching to synchronous operation to prevent the occurrence of transient phenomena.

(Means for Solving the Problems) According to the present invention, a sine wave is compared with a carrier wave to form a pulse width modulation command, and a rotating magnetic field formed based on an inverter output speed-controls an AC induction motor. In the control device, a detection means for detecting the rotation speed of the electric motor, a means for outputting a synchronization signal pulse when the detected rotation speed exceeds a reference value, and a first synchronization signal pulse matching the timing of the asynchronous carrier wave. a switching means for switching to a synchronous carrier wave synchronized with the sine wave in accordance with the corrected synchronous signal pulse; and a switching means for changing the gain of the current command immediately after switching to the synchronous carrier wave in inverse proportion to the rotation speed of the motor. It is possible to provide a speed control device characterized in that it is equipped with a control means for controlling the speed.

(Function) In the speed control device of the present invention, control is performed in the high speed region and the medium/low speed region by switching between the synchronous method and the asynchronous method at the rotation speed set by the reference value, and immediately after switching to the synchronous method. In addition, the first synchronization signal pulse is corrected to match the timing of the asynchronous carrier wave, thereby making the current command smooth immediately after the transition.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a speed control device according to an embodiment of the present invention.

In FIG. 1, 1 is an AC motor that drives a spindle, and 2 is a pulse generator such as a resolver, which generates two sine wave signals Pa, Pb, etc. that are proportional to the rotational speed and are out of phase by 90 inches.

3 is a quadrupling circuit which forms a speed pulse train from the sine wave signals Pa and Pb and quadruples its frequency.

4 is a frequency-voltage converter (referred to as an F/V converter) that converts the frequency of the speed pulse train into a voltage.

5 is an arithmetic circuit that calculates the difference between a speed command voltage commanded from a speed command circuit (not shown) and the actual speed voltage from the F/V converter 4, that is, a speed deviation; 6 is an error amplifier.

7 is a voltage frequency converter (referred to as a V/F converter) that forms a pulse train corresponding to the error speed from an error voltage corresponding to the speed deviation. 8 is a programmable interval timer (P I
T). This PIT8 is connected to the CP by the data bus.
U (central processing unit) 9, memory 10 such as ROM, second and third PIT IIs that form synchronization signal pulses to be described later.
I.

112, an I10 boat (input/output device) 12, a driver unit 13, and an A/D converter 14 forming a current and voltage loop.

The memory 10 such as the ROM is used as a control program memory and a data memory to store torque versus amplitude characteristics (T-
It stores digital function tables such as IAI characteristics), torque vs. phase characteristics (T-ψ characteristics), and rotation angle vs. sine value characteristics (sine pattern).

Reference numeral 15 denotes a switching circuit for switching the speed control device between an asynchronous control mode and a synchronous control mode. This switching circuit 15 is supplied with a 3KHz signal, which becomes a carrier wave frequency during asynchronous control, from an oscillation circuit 16 via a frequency divider 17, and is connected to a third PIT 112 that corrects and outputs the synchronization signal pulse. Further, a predetermined carrier wave signal is output to the CPU 9 as an interleaved signal.

18 is an arithmetic unit that adds the slip pulse corresponding to the error output of the error amplifier 6 and the speed pulse from the quadrupling circuit 3, and the result of this addition is given to the 20th PITI 11 to generate a sine wave of a predetermined frequency. is commanded.

FIG. 2 shows an example of the circuit configuration of the switching circuit 15 that forms the carrier wave signal in the above embodiment.

With this switching circuit 15, as shown in FIG.
The period of the synchronization signal pulse output from TI 11 is observed. Then, when the set number of revolutions exceeds, for example, 15,000 revolutions, the CPU 9 sets the second output 0UT2 of the boat 12 to "1", and this is the AND gate G5.
It is input to a gate consisting of G6 and knot gate G7,
Synchronization signal pulse is synchronization side interrupt interlab) - (R3
76,5).

Figures 4(a) to (e) show each signal and the second and third PITll before and after the rotational speed N exceeds 15,000 rotations.
, 112. Further, FIG. 5(a) shows an example of a program routine for switching stored in the memory 10&J@. In other words, the interconnected R5T6.5 is the second output 0U of the boat 12.
When the occurrence occurs after T2 is set, if 60 is set in the second PIT as the addition result of the arithmetic unit 18, the CPU 9 moves to the interrupt routine on the synchronization side and then returns 84, which is the next synchronization point. The deviation (24) from the synchronization # control is calculated and written into the third PITl 12 as a correction value for the first synchronization timing when transitioning to synchronization # control.

A schematic flow of operations in such a synchronization-side interrupt routine is shown in FIG. 5(b). After the synchronization signal pulse and the carrier wave for the asynchronous system (3 to 1 (z signal) are synchronized, set FF to 1. This OFF means that synchronization is performed only the first time after transitioning to the synchronization side interrupt routine. This is a register that corrects the timing of the signal, and from the second time onwards, PrT
“42” is written in 112.

As a result, the CPU 9 outputs the second output of the boat 0UT2.
is set to "1", this is manually input to the gate consisting of AND gates G5 and G6, and NOT gate G7, and the interrupt interrupt for CPU9 is switched to 3KHx (from g to synchronization signal pulse), and for one cycle at that time Since a current command as shown in FIG. 4(f) is formed, control can be smoothly shifted to a synchronous control method from then on.

The above operation of the switching circuit 15 is for transitioning from medium-speed rotation to high-speed rotation, and conversely, the switching when transitioning from high-speed rotation to low-speed rotation is also the same as that shown in FIG. 5(a). It will be executed by a routine.

FIG. 6(a) shows the switching fl according to the current control routine.
It is a flowchart which shows an example of Jal. Here, after switching to the synchronous method, the current value is read by the CPU 9 according to the current control software stored in the memory 1o, but in this case, the speed gradually increases from 15,000 rotations. As the speed increases, the gain is controlled to decrease in proportion to the speed ((b) in the same figure), and reading of the current value is stopped from a certain number of rotations, for example, 20,000 rotations. This reduces the time required for current processing and ensures high-speed control.

In this way, the asynchronous system performs control in the low speed range, and when controlling the AC motor at speeds from 15,000 rpm to 100,000 rpm or more, the system shifts to the synchronous system for speed control. This solves the conventional cost problems and current control processing time problems, and also prevents transient phenomena during transition.

Although this invention has been described in some detail with respect to its most preferred embodiment, the description of the preferred embodiment does not include modifications in the detailed parts of the structure unless they are contrary to the spirit of the invention as described in the claims. It is clear that various modifications or combinations of these can be made.

(Effects of the Invention) As explained above, according to the present invention, it is possible to use a conventional general power element, and therefore it is possible to control the speed of an AC spindle up to high speed rotation at low cost. Providing speed control device:! ! Ru.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a speed control device according to an embodiment of the present invention, FIG. 2 is a circuit configuration diagram showing an example of a switching circuit for forming a carrier wave signal in the same embodiment, and FIG. , Waveform explanatory diagram showing current commands during synchronization and non-synchronization, Fig. 4(a)
~(f) are timing diagrams showing signal waveforms at the time of switching, FIG. 5(a) is a diagram showing an example of a program routine for switching, and FIG. FIGS. 6(a) and 6(b) are diagrams showing an example of switching control to the synchronous method. 1...AC motor, 8,111,112...PTT
, 9...CPU, 15...Switching circuit. Patent applicant Fanuc Co., Ltd. Agent Patent attorney Tsuji Minoru-ku Utsuto 8, ＼＼ ＼

Claims (1)

[Claims] Comparing the sine wave with a carrier wave to form a pulse width modulation command,
In a speed control device that controls the speed of an AC induction motor by a rotating magnetic field formed based on an inverter output, the speed control device includes a detection means for detecting the rotation speed of the motor, and a synchronization signal when the detected rotation speed exceeds a reference value. means for outputting a pulse; correction means for making the first synchronization signal pulse match the timing of the asynchronous carrier; switching means for switching to a synchronization carrier that synchronizes with the sine wave according to the corrected synchronization signal pulse; and the synchronization carrier. A speed control device comprising control means for controlling the gain of the current command immediately after being switched to be in inverse proportion to the rotational speed of the electric motor.