JPS59209088A - Controller of ac motor - Google Patents

Abstract

PURPOSE:To enable to stably operate a motor even at a low frequency operating time by correcting the voltage set value by the variation of the output voltage of an inverter, thereby enabling to set the output voltage to the set value even when the phase of a load current is varied. CONSTITUTION:The output voltage Vi of an inverter 5 is detected by a voltage detector 15, a voltage controller 15 receives an output of the detector 15 and an output of a voltage pattern generator 9, compares the both outputs, corrects the voltage set value Vd by the output voltage variation of the inverter thereto, and inputs it to a multiplier 12. When a lower power factor is deteriorated so that the output voltage Vi of the inverter 5 becomes higher than the set voltage value vd, the voltage set value side input of the multiplier 12 decreases corresponding to the variation of the output voltage Vi. Accordingly, the peak of a sinusoidal wave signal Vdf decreases, and the output voltage Vi is controlled toward the voltage set value Vd.

Description

[Detailed description of the invention] The present invention relates to a control device for an AC motor.

1) i of AC motor using WM controlled inverter
A conventional control device for controlling iJ transmission is shown in FIG. In the figure, ■ is a commercial type -/J (i, 2 is a rectifier, 3 is a flat 11) reactor, 4 is a flattened condenser, and 15 is an inverter. The inverter 5 is constructed by connecting switching elements 5a to 5 (in this example, I-run listers) in a bridge manner, as shown in FIG.

p4 of inverter 5. ('+:l is the AC motor. 7 is the speed setting device, 8 is the extension 21 signal generator, 9
is a voltage pattern generator for determining the output voltage of the inverter 5, and is a speed command value VS generated by the speed setting device 7.
Outputs the voltage El-set value Vd corresponding to the voltage El-set value Vd.

10 is a quasi-sine wave generator for determining the frequency of the inverter 5, and generates a sine wave voltage vr of frequency f corresponding to the speed command (iiljVs). 11 is a triangular wave generator, which generates an iE sinusoidal wave. A triangular wave signal Vr with a constant wave height is generated in synchronization with the electric current f and with a frequency that is an integer multiple. 12 is a multiplier which generates a wave 1 proportional to the voltage command value Vd output by the voltage pattern generator 9. Generates a five-value sine wave signal Vdf 6 [3 is a comparator, which compares the triangular wave (d signal Vr) generated by the triangular wave generator 11 with the sine wave signal Vdf, and outputs when df>Vr. (1) Generate a WM multiplied signal. That is, f in the pulse corresponding to the speed setting value VS.
Generate i-. Reference numeral 14 denotes a pulse distributor, which distributes the above-mentioned 1) WM multiplied signal and supplies on-off signals to the switching elements 5a to 5 of the inverter 5. In Figure 2,
The operating waveforms of each part of this device are shown.

In order to prevent a short circuit between the +E (P) and negative (N) arm elements near the switching time of these switching elements, the +E (P) and negative (N) arm elements r, that is, the Swiss Chinku Sachiko 5a, 5t+, 5C
and 5 +1.5e and 5f on-signal line inter-U
The turning time ΔL is set to 1 to prevent them from turning on at the same time. For this reason, the output type 11 (Vi) of the inverter 5 fluctuates as shown in FIG. 2 due to a change in the phase of the negative current.

In the PWM-controlled inverter 5, the output voltage v1 and frequency f are controlled simultaneously, and during low frequency L5Ji fault operation,
Output weight: It is necessary to increase Vi to , the switching interval of the switching element becomes smaller, and the output voltage Vi is controlled to the voltage setting value Vd, as the time difference Δ1 is less than the output voltage Vi. There was a problem in that 21f became low, making stable operation of the AC motor 6 difficult.

This invention was made to address the above-mentioned conventional problems, and by adding a voltage control loop (=j) that controls the voltage setting value by the inverter output fluctuation, −C can also be stabilized in the low frequency region. It is an object of the present invention to provide a control device for an AC motor that can perform IIJ speed change control of an AC motor more frequently than in the past.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

3 differs from the one in FIG. 1 in that a voltage control loop has been added, and the same components as those in FIG.

15 is a voltage detector, which detects the output voltage v of the inverter 5
1 is detected. Reference numeral 16 denotes a voltage regulator i+Ill, which receives the output of the voltage detector 15 and the output of the voltage vacuum generator 9, compares both outputs, and compensates the voltage setting value Vd by the inverter output voltage fluctuation corresponding to this. Then, the passenger I-equipment 12 is manually operated.

In this configuration, when the load power factor becomes 1 and the output voltage Vi of the inverter 5 becomes higher than the voltage setting value Vd,
Since the voltage setting value side input of the multiplier 12 decreases in accordance with the variation of the output voltage Vi, the wave 1 of the sine wave 1r+signal Vdf
and the output voltage Vi is controlled towards the voltage j-ig set value Vd.

Therefore, by adjusting the control cane of the pressure control loop including this voltage controller 16, fluctuations in the inverter output pressure in the low frequency region can be eliminated and the voltage setting (
1q V d.

As described above, according to the present invention, the voltage setting value is corrected by the inverter output cuff'-iJ and the pressure change Wtb. Since the inverter output pressure can be controlled to the set value even when the AC motor is operated at a low frequency, the AC motor can be operated stably and the control system can be improved.

[Brief explanation of the drawing]

FIG. 11 (al is a block diagram of a conventional AC motor control device, FIG. 1 is a circuit diagram of an inverter connected to the control device, FIG. 2 is a waveform diagram of each part of the control device, and FIG. 3 is a block diagram of a conventional AC motor control device. The figure is a block diagram of an embodiment of the control device for an AC motor according to the present invention.
7-speed 1-! Σ setting device, 9-voltage pattern generator, 10
゜=-ノ, j;
vessel. In addition, in the figure, the same and ↑qs indicate the same or equivalent parts. Agent Masu Oiwa 151 Figure 1 (α) 49 Figure 2 (b) Figure 2

Claims (1)

[Claims] A control 11111 device that performs OJ speed change control of an AC motor by PWM control of an inverter and an output of the inverter, corrects the voltage setting value corresponding to the speed setting value by 7 + li by the inverter output fluctuation. A control device for an AC motor, characterized in that: