JPS60213295A - Controller of ac motor - Google Patents

Abstract

PURPOSE:To efficiently operate an AC motor even if the rotating speed of the motor is high by using a vibration wave which vibrates at the constant slope between two threshold values, and generating a pulse width modulation signal by level-comparing the vibration wave with a control signal. CONSTITUTION:A control signal output from a current controller 2 is shifted 90 deg. in phase by 90 deg. phase shifter 11, and the output is supplied to a hysteresis comparator 12 and a comparator 14. The output of an integrator 13 becomes a cut wave signal of a triangular shape vibrating between two threshold values set at the upper and lower levels in the hysteresis width set in the comparator 12 at the signal shifted 90 deg. from the control signal as a center, and the signal is input to the comparator 14. The comparator 14 compares the input two signal levels, and supplies the pulse width modulation signal of the output to a drive circuit 4 of an inverter 5.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an AC motor III control device that controls a motor using pulse width modulation.

(Background of the Invention) Conventionally, a device for controlling an AC motor using pulse width modulation (hereinafter abbreviated as PWM) was disclosed in Japanese Patent Application Laid-Open No.
There is one such as that shown in Publication No. 578208.

Figure 1 shows how to control AC Tanabata using such PWM.
11 is a block diagram illustrating a schematic configuration of a device for carrying out 11 operations. FIG.

The current command value generator 1 is used to realize, in the AC motor 7, an output set by an output setting device (not shown) (which generates settings 110 for the output points of the AC motor such as speed and torque). A command value a of the current to be applied to the AC motor 7 is output.

The current control circuit 2 receives the current command value a and the current detector 6.
1: The detected AC-tough drive current Mid is input, and a control signal is generated and output so that the motor drive current matches the current command value a.

This output control signal +'3b is converted into a voltage signal 7jIL.

The PWM circuit 3 pulse width modulates the control signal C supplied from the current control circuit 2 and supplies the resulting pulse train signal C to the drive circuit 4.

, the inverter 5 is operated by the drive circuit 4 to switch the power conversion elements that form the inverter, and converts the power supply voltage received from the valve 8 into a three-phase alternating current (the AC motor 7 is a 1M combination of three-phase motors). It is converted into AC motor 7 and supplied to AC motor 7.

In the same figure, the current command 1fi a, the control signal, and the PWM circuit output C are omitted for simplicity.
etc. have output for three phases.

FIG. 2 is a diagram illustrating an example of the configuration of the WM circuit 3 described above in 1).

As shown in the figure, the PWM circuit 3 is composed of a comparator 33J3 and a constant voltage generator 31, which compare the levels of the triangular wave Tr from the triangular wave generator 32 and the control signal 15. 33, the signal C is cut by the triangular wave T1, which is supplied as a sine wave, and a pulse width modulated signal C is output.

Note that the amplitude of the above triangular wave -(-r is determined by the constant voltage generator 31
It is kept constant by a constant voltage from

The amplitude of the triangular wave Tr is normally set so that when the AC motor 7 is operated at the rated rotational speed, the rated wave Tr is generated.

However, in the case where the amplitude of the triangular wave Tr applied to the PWM circuit 3 is constant as described above, for example, as shown in FIG. 3(a), the AC motor 7 operates at a relatively low speed. When the control signal is rotating, the frequency of the triangular wave is higher than the frequency of the control signal, so the proportion of the ON time of the output C per cycle of the control signal is The effective type 1 voltage applied to the AC motor 7 with a high voltage can operate in a state close to the maximum effective voltage. - At this point, the rotational speed of the AC motor 7 increases to a high speed.1. , : As shown in Fig. 33 (b ''), the frequency of the control signal 1) and the frequency of the triangular wave ``r'' become close to each other, so that the output voltage C per period of the control signal 1) is
The proportion occupied by the total d1 of N hours decreases, thereby
The effective voltage above is reduced over time.

In order to solve such a phenomenon, for example, a 4r4 configuration may be considered in which the rotational speed of the AC motor 7 is detected and the amplitude of the triangular wave 1-r is variably controlled in accordance with the -C1 rotational speed. To achieve such a configuration, it is necessary to construct a complex circuit configuration.

(Ll aspect of the invention) It is an object of the present invention to provide a device that performs smooth control of an AC motor using pulse width modulation, and to provide efficient operation even when the rotational speed of the AC motor is high. (b) To provide a device that can be realized with a relatively simple configuration.

(Structure of the Invention) To achieve the above object, the present invention provides two threshold values that are set with a predetermined width above and below the control signal based on the control signal generated from the current control circuit. Using a vibration wave vibrating with a constant slope between the two, pulse width modulation No. 18 is generated by comparing the level of the signal obtained by shifting the phase of this control signal by 90 degrees.

(Description of Embodiment) FIG. 4 is a block diagram showing the configuration of an embodiment of the AC Tanabata lli+7 control device according to the present invention. In this figure, the same components as those of the conventional device shown in FIG.

As shown in the figure, the device of this embodiment passes the control signal output from the current control circuit 2 to the 90° phase shifter 1'1 (
The configuration is such that the phase of the signal is shifted by 90 degrees.

The output e of this 90' phase shifter 11 is then supplied to a hysteresis comparator 12 and a comparator 14.

[Hysteresis width] The comparator 12 has a preset hysteresis width and inputs the output (e) of the 900 phase shifter 11, and uses the output f of the hysteresis comparator 12 as its reference signal. Integrator 13
The faith Σsiri obtained by integrating is input.

With this configuration, as shown in FIG. 5 (A>),
The output of the integrator 13) J(I is set up and down by the hysteresis width set in the hysteresis comparator 12, with the signal e obtained by shifting the phase of the control signal S by 906 as the center.
This results in a triangular cut wave signal that oscillates between two threshold values 14o and l-lu. The slope of the signal 9 at this time is determined by the integral constant maintained by the integrator 13, and is constant.

The horn g output from the integrator 13 is output from the comparator 14.
It is input as a reference signal to the comparator 14:J
3 T is cT, (7) Itli wave signal 9 etc. 90 above
A level comparison is made with the zero phase shifter output, l) W
M is performed. The resulting output becomes a pulse train signal 11 as shown in FIG. 5(B).

The PWM output 11 outputted from this output 111 is 90° with respect to the phase of the 90° phase shifter output e inputted to the comparator 14.
0' deviation is I'i' L/T.

Therefore, 1) is output from this comparator 17I.
The peak of the W M output 11 coincides with the peak of the control signal S output from the current control circuit 2.

In this way, the 900 phase shifter 11 has the control [+signal and P
This circuit is for correcting the phase in advance in order to prevent a phase shift from occurring between the WM output 11 and the WM output 11.

When the rotational speed of the AC motor 7 becomes high, the integrator 13 output JQ oscillates between two thresholds 1Fti l-1o and l-lu for one period of the signal e. The number of times decreases, resulting in a waveform as shown in FIG. 6(B), and as a result, as shown in FIG. 6(C),
ON at approximately the same frequency as the 90° phase shifter output e.
A PWM output 11 of 0FFTI is obtained.

In this case, since the rotational speed of the alternating motor 7 is 1fi high, even if the ON/OFF of the PW M +l horn 11 is only one cycle per one cycle of the current command Mia, this PW
The rectangular wave indicated by the M output 11 is the current J41iCf
It can be approximated to the sine wave of a! Kome, Ko>AE
Momo-7's efficiency decrease (Ll is no exception, ShihX also,
1174 Percentage of ON time per period/J- becomes longer and contributes to improving the efficiency of the 3-stroke 1C AC motor 7/
J (I can.

In the device of this embodiment, a change in the WM output J11 (G) in which the rotational speed of the AC motor 7 changes from low to high speed is caused by a change in the current command value signal a (1). X；8
Therefore, it is possible to avoid continuous changes.

Therefore, it is possible to smoothly accelerate and decelerate the AC motor 7 (4T) and operate it efficiently.

(Effects of the Invention) As explained in detail above, the AC motor control device of the present invention solves the problem of efficiency reduction when the AC motor stops at a low speed of one revolution 114, and changes the rotational speed of the AC motor. Also, it becomes possible to always efficiently increase the power of the AC motor by +1'Ji.

Also, this can be achieved with a relatively simple configuration,
It is advantageous in terms of cost and workability.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a conventional AC motor control device 211, Fig. 2 is a block diagram showing the 414 configuration of the PWM circuit in Fig. 1, and Fig. 3 shows when the AC motor rotates at low speed and at high speed. 1 waveform diagram showing the relationship between control signals and triangular waves during rotation; FIG. 4 is a block diagram showing the configuration of an embodiment of an AC motor control device according to the present invention; and FIG. FIG. 6 is a waveform diagram showing a signal, a cutting wave, and a PWM output. FIG. 6 is a waveform diagram showing a cutting wave and a P'WM output when the AC 1JlE motor rotates at low speed and at high speed in the same device. 1... Current command 1lfI generator 2... Current control circuit 4... Drive circuit 5... Inverter 6... Current detector 7... AC motor 11... 906 Phase shifter '12 ... Hisu I-Lysis" Nbarreta '13...
・Integrator 14...21 Inverter a...Current command 1iQ 1)......Control It-]Re...
・・・ J攬 11Ji Wave Patent Applicant 1 San Jidosha Co., Ltd. 31 62 3rd cause 5th cause

Claims (1)

[Claims] (1) A current command value generator that outputs and overrides the current command value given to the current motor in response to an external command: +) 1 AC 7-
a motor drive current detector that detects the motor drive current supplied at the same time; 18 and; ゛Said control υ11
A phase shifter that shifts the phase of the signal by 90 degrees and outputs it: Based on the control signal, two threshold values are set by moving a predetermined width up and down with the center point (ii). A vibration wave generator that outputs a vibration wave that vibrates with a constant slope between: Pulse width modulation (PWM) is performed by comparing the levels of the output of the phase shifter and the output of the vibration wave generator. The AC motor is characterized by comprising: a PWM circuit for performing ?I current to the AC motor; and a drive circuit for driving the electric horn converter by the PWM I! IJ road horn. 8 motor control positions.