JPS5839295A - Inverter device - Google Patents

Abstract

PURPOSE:To control overcurrent rapidly by reducing the slip frequency supplied to an induction motor when the overcurrent is generated in the induction motor in a frequency region higher than the rated frequency of the induction motor. CONSTITUTION:The command of an overcurrent detecting circuit 10 is inputted to a slip-frequency control circuit 8. When overcurrent is generated in an induction motor 3 in the frequency region higher than the rated frequency of the induction motor 3, the overcurrent is detected by means of the overcurrent detecting circuit 10, the slip frequency is reduced by means of the frequency control circuit 8, and brought close to zero, and the overcurrent is controlled. Reliability can further be improved by jointly using the lowering of output voltage and the reduction of the slip frequency at the same time as the overcurrent is detected in a high-frequency pulse-width modulation region.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter device for driving a three-phase induction motor.

Figure 1 shows the basic configuration of a conventional inverter device, in which DC current input from a power source (1) is converted into three-phase AC in the inverter body (2) to drive a three-phase induction motor (3). . The control circuit (
4), the modulated wave generation circuit (5) and the carrier wave generation circuit (6)
) is compared with the comparator (7) to perform high frequency pulse width modulation. The output of this comparator (7) becomes a thyristor firing signal within the inverter main body (2), and has a pulse waveform approximating a sine wave. In the frequency range below the rated frequency of the inductive motive (3), the frequency of this pulse waveform
The ratio to the voltage applied to the sealing machine (3) is controlled to be constant (variable [
11E variable frequency control) and slip frequency control circuit (8
), the induction wLwJ machine (3) is accelerated with an inversely constant acceleration. Speed range (frequency range) above the rated frequency of the induction motor (3)
In this case, the comparator (7) generates a thyristor firing signal that has a single pulse waveform with 120° energization between lines without performing high-frequency pulse width modulation, and performs variable frequency control to control the induction m.
Accelerate motivation (3). Current detection fl (9) detects the current of the induction motor (3), and in the event of overcurrent, the overcurrent detection circuit CO operates, reducing the peak value of the modulated wave of the modulated wave generation circuit (5) and narrowing down the output voltage. Figure 8@2 shows the principle of high frequency pulse width modulation.

Here, explanation will be given using a sine wave as a modulated wave and a triangular wave as a carrier wave. In the figure, the modulated wave (a) and carrier wave (
In comparison with b), the pulse train (C) is generated during the period when the modulated wave (a) is large. Comparing the pulse train (C) with the pulse train (d) of the other phase shifted by 120°, the line voltage waveform (e
) is obtained. When this waveform (d) is Fourier-developed, it can be seen that components similar to a sine wave occupy most of the waveform (f).

Figure 8 shows the case where the peak value of the modulated wave (a) is lowered when overcurrent is detected, and the output waveform (e) is the waveform (a) in Figure 2.
It is explained that the output voltage of the inverter main body (2) is narrowed down.

Figures 2 and 8 show the narrowing control of the output voltage on the high frequency pulse width modulation side φil+, but in the line spacing 120° through m type control, the output is 120° as shown in Figure 4. ° single pulse waveform (c) (Since (1), M pressure cannot be narrowed down when overcurrent is detected,
This will have an adverse effect on the inverter main body (2) and the induction motor (3).

The present invention has been made in view of the above, and provides a highly reliable inverter device that quickly suppresses overcurrent in high frequency pulse width modulation control or 1206 energization type control.

The figures will be explained below. In Figure 5, (1) ~
αO is the same as the conventional one. A command from the overcurrent detection circuit OQ is input to the slip frequency control circuit (8).

The current I of the induction m-motor (3) is generally expressed by the following formula (0) in a small range of slip frequency fs.

1 = k · (V/f ) · fs - (1) However, in equation (1), ■ is the power supply voltage, and f is the power supply frequency %1 is a proportionality constant.

Therefore, in the configuration shown in FIG. 5, when an overcurrent is detected, the slip frequency control circuit (8) narrows down the slip frequency and brings it closer to zero, thereby suppressing the overcurrent. According to this control, it is now possible to suppress overcurrent by narrowing down the slip frequency in the 120° roundabout control region, where overcurrent could not be suppressed conventionally. Furthermore, in the high frequency pulse width modulation range, reliability can be further improved by simultaneously using output voltage narrowing and slip frequency narrowing at the same time as overcurrent detection.

Although the above embodiment has been explained under the acceleration condition of the induction m-motor (3), similar effects are expected under the deceleration condition (regeneration).

According to this invention, when an overcurrent occurs in the induction motor in a frequency range higher than the rated frequency of the induction motor, the excessive current can be quickly suppressed by narrowing down the slip frequency supplied to the induction motor. , reliability can be improved. Further, when an overcurrent occurs in the induction motor in a frequency range below the rated frequency of the induction motor, the overcurrent can be quickly suppressed by narrowing down the voltage supplied to the induction motor and the slip frequency.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional inverter device, Figures 2 and 8 are explanatory diagrams explaining the principle of pulse width modulation control, @4
The figure is an explanatory diagram illustrating the Pi-type ILI control through the line 120', and FIG. 5 is a configuration diagram showing an embodiment of the present invention. In the diagram, %(2)...Inverter body%(3)...
・Induction motor, (5)...Modulated wave generation circuit, (8)・
...Slip frequency control circuit, 00... Overcurrent detection circuit. Note that the same reference numerals in each figure indicate the same or equivalent parts. Agent Makoto Kuzuno - 1st figure 9 mouth 3rd figure

Claims (2)

[Claims] (1) In the frequency range below the rated frequency of the three-phase induction motor, the induction motor is controlled by variable voltage and frequency using high-frequency pulse width modulation, and in the frequency range above the rated frequency, the induction motor is energized at 120° between the lines. When an overcurrent occurs in the induction motor in a frequency range equal to or higher than the rated frequency of the induction motor in a type of variable frequency control. An inverter device characterized in that the slip frequency supplied to the induction motor is narrowed down. (2) In the frequency range below the rated frequency of the three-phase induction motor, the induction motor is subjected to variable voltage variable frequency control using high-frequency pulse width modulation, and in the frequency range above the rated frequency, the induction motor is energized at 120° between the lines. In the type of variable frequency control, when an overcurrent occurs in the induction motor in a frequency range below the rated frequency of the induction motor, the voltage and slip frequency supplied to the induction motor are narrowed down. Features of the inverter device.