JPS6348162A - Controlling apparatus for variable-voltage, variable-frequency inverter - Google Patents

Abstract

PURPOSE:To control an inverter stably and safely by feeding a power circuit from both ends of a first capacitor at a DC voltage behind a converter so as to generate a DC power for a control circuit. CONSTITUTION:A commercial power 1 is converted into a variable voltage, variable frequency electric power through a converter 2, a smoothing first capacitor 3, and a pulse width modulation controlling inverter 4 to drive an AC motor 5. Said inverter 4 is controlled by a control circuit 6. In this case, a diode 8, a second capacitor 9 and a voltage sensor 10 are provided and a power circuit 7 generating power supplied from both ends of the second capacitor 9 to the control circuit 6 is added thereto. Thus, a control power for the control circuit 6 of the inverter 4 is fed by the power circuit 7 from a DC power source behind the converter via the diode 8. Also, if a lowering of voltage between both ends of the first capacitor 3 is detected by the voltage sensor 10, a frequency of the inverter 4 is lowered in proportion to a detected value so that an excessive lowering of voltage is suppressed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a control device for a voltage-type variable voltage/variable frequency (VVVF) inverter (hereinafter abbreviated as inverter) using PWM (pulse width modulation). It is.

[Conventional technology]

A conventional single-line connection diagram of this type of inverter is shown in FIG. 3.

In the figure, 1 is an AC commercial power source, 2 is a converter that converts the AC commercial power source 1 to DC, 3 is a capacitor for smoothing the DC, and 4 is a converter that converts DC to variable voltage variable frequency power using PWM control. 5 is an AC motor, 6 is a control circuit that controls the inverter 4, 11 is a transformer that steps down the voltage from the commercial power supply 1, and 12 is a power supply circuit that generates control power for the control circuit 6 from the output of the transformer 11. .

Next, the operation will be explained. First, commercial power supply 1 which is AC
is converted into direct current by converter 2 and smoothed by capacitor 3. This smoothed direct current is converted into VVVF alternating current (usually three-phase) by an inverter, and is applied to the alternating current motor 5. Since the rotation speed of the AC motor is proportional to the applied frequency, the rotation speed of the AC motor 5 can be changed by changing the output frequency of the inverter 4.

The power supply for the control circuit 6 that controls the inverter 4 is stepped down from a commercial power supply 1 to a suitable voltage via a transformer 11, and then converted to a constant voltage DC voltage by a power supply circuit 12.
given to.

The inverter 4 is made up of semiconductors such as transistors, GTO thyristors, and high-speed thyristors, but if the control signals given to these semiconductors are not given with the designed magnitude and accurate timing, the inverter may malfunction. Not only will the function not be maintained, but the semiconductor itself may be destroyed (short circuit between phases), or abnormal torque may be generated in the AC motor 5. Therefore, in order to operate the inverter 4 safely and stably, the power supply circuit 12 must always maintain a constant voltage while the inverter 4 is operating.

[Problem that the invention seeks to solve]

Conventional variable voltage/variable frequency inverter control devices are configured as described above, so if the commercial power supply 1 becomes abnormal due to a momentary power outage or instantaneous voltage drop, the power supply circuit 1
2 cannot supply normal voltage to the control device 6,
There were problems such as the inverter starting to malfunction and causing problems.

This invention was made in order to eliminate the above-mentioned problems, and the power source of the power supply circuit is determined from the voltage across the capacitor, and the commercial power supply 1 due to instantaneous power outage or instantaneous voltage drop, etc.
It is an object of the present invention to provide a control device for a variable voltage/variable frequency inverter that can operate the inverter normally even in the event of an abnormality.

[Means for solving problems]

The variable voltage/variable frequency inverter control device according to the present invention is designed to prevent the control circuit voltage from changing due to instantaneous power outages or instantaneous voltage drops from causing malfunctions in the inverter operation and resulting in accidents. A DC voltage is supplied to the power supply circuit from both ends of the first capacitor to generate a DC power supply for the control circuit.

[Effect]

The control power supply for the variable voltage/variable frequency inverter in this invention generates control power by supplying power from the DC power supply after the converter to the power supply circuit via a reverse blocking diode, so it An excessive voltage drop due to discharge of the first capacitor is suppressed by guaranteeing the stability of the control power source and instructing an inverter frequency drop using a voltage sensor.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the same parts as in FIG. 2 are denoted by the same reference numerals. In FIG. , 7 is a power supply circuit that generates power to be supplied to the control circuit 6 from both ends of the second capacitor 9.

Further, FIG. 2 is a timing chart showing the voltage and frequency command movements of each part in the circuit of the present invention when the commercial power supply 1 is momentarily interrupted. In the fJc2 diagram, a is the voltage of the commercial power supply, b is the terminal voltage of the first capacitor 3, and C
is the terminal voltage of the second capacitor 9, and d indicates that the station wave number command decreases during an instantaneous power failure according to the gist of the present invention.

Next, the operation will be explained.

First, the voltage across the first capacitor 3 is applied from the commercial power supply 1, but the voltage across the AC motor 5 is applied by the operation of the inverter 4.
It will be discharged to. Therefore, a constant voltage is maintained by the supply from the commercial power source 1 and the discharge via the inverter 4. If the commercial power supply 1 drops in voltage due to an instantaneous power outage or instantaneous voltage drop, the power supply will be cut off, and as a result, the voltage across the first capacitor 6 will drop as shown in FIG. The alternating current voltage that is being used will also drop. - direction control circuit 6
Since the power supply circuit 7 that supplies power to the AC motor receives power from the second capacitor 9 which is charged from the first capacitor 6 through the diode 8, if the first capacitor 6 is discharged to the AC motor by the operation of the inverter 4 Even if it is the second
Since the energy of the capacitor 9 is prevented from flowing backward by the diode 8, it is not discharged to the inverter 4 and is reduced by the amount consumed by the power supply circuit 7. Since the power consumption of the power supply circuit 7 is extremely small compared to the energy discharged from the inverter 4, if the capacity of the second capacitor 9 is appropriately selected, it can be controlled even if the voltage of the AC power supply 1 decreases as shown in FIG. The power supplied to the circuit 6 can be maintained normally for a certain period of time. When the voltage of the first capacitor 6 decreases, the AC voltage applied to the AC motor 5 also decreases. The AC motor 5 requires a certain amount of energy when rotating at a certain number of rotations, so when the voltage decreases, the current increases, and the voltage further decreases. Therefore, the voltage sensor 10 detects the voltage across the first capacitor O, and if the voltage drops below a certain voltage, the frequency generated by the inverter 4 is lowered in proportion to the voltage drop, thereby preventing the discharge of the first capacitor O. It can be prevented. If the frequency is further lowered beyond the speed reduction rate of the AC motor, the AC motor 5 will be operated in regeneration mode via the inverter 4 and will supply energy to the first capacitor 6 instead. This can prevent the voltage of the first capacitor 6 from dropping.

〔Effect of the invention〕

As described above, according to the present invention, the control power source of the inverter device can be maintained normally even in the case of a momentary power outage or momentary voltage drop, so the inverter can be controlled stably and safely, and by lowering the frequency command, the first capacitor This has the effect of allowing stable operation to continue when the power is restored, since the discharge can be minimized.

[Brief explanation of drawings]

Fig. 1 is a single-line connection diagram of an inverter showing an embodiment of the present invention, Fig. 2 is a voltage and frequency command time chart of various parts during momentary power failure in the device of this invention shown in Fig. 1, and Fig. 3 is a conventional It is a single line connection diagram of this type of inverter. In the figure, 1 is a commercial power supply, 2 is a converter, and 3 is a first
capacitor, 4 is inno(-ta), 5 is AC motor, 6
is a control circuit, 7 is a power supply circuit, 8 is a diode, 9 is a second
10 is a voltage sensor, and 12 is a power supply circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A first capacitor that converts commercial power into direct current using a converter and is connected in parallel to the output of the converter;
The output of the converter is changed to a variable voltage by an inverter.
In a control device for a variable voltage, variable frequency inverter that converts AC into variable frequency AC and controls an AC motor at variable speed, the first capacitor is connected in parallel from both ends of the first capacitor via a backflow prevention diode. 1. A control device for a variable voltage, variable frequency inverter, characterized in that a second capacitor is provided, and an inverter control power source is obtained by level conversion from both ends of the second capacitor. (2) Guide a command from a voltage sensor that detects the DC voltage applied across the first capacitor to the control circuit of the inverter, and output a frequency drop command to the control circuit when the DC voltage falls below a predetermined value. Claim 1 characterized in that the discharge of the first capacitor is suppressed by
A control device for a variable voltage/variable frequency inverter as described in .