JPH0127436Y2 - - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to an overvoltage absorbing device for a voltage type inverter.

B. Overview of the invention This invention uses regenerative energy generated during regenerative operation, which can occur during light load operation in which only a few motors are driven to rotate, in a large number of motors connected in parallel to the output side of a voltage-type inverter. The overvoltage is suppressed by absorbing it into the resistor installed in the

C. PRIOR TECHNIQUE A voltage type inverter controls the speed of a large number of motors using variable frequency and variable voltage, and during heavy load operation in which the motors are driven in parallel, some of the motors are controlled by these motors. It is often the case that the motor is rotated in the opposite direction by a directly connected load or enters regenerative operation in deceleration mode. If the regenerated energy generated at this time is consumed by another electric motor during power running,
Since there is no need to install a regenerative inverter, system equipment costs can be reduced.

D Problems to be solved by the invention However, during light load operation where one or several motors out of a large number of motors are driven to rotate and the other motors are stopped, it is difficult to understand how many motors are being driven to rotate. When the motor is operated regeneratively and regenerated energy is generated, it cannot be consumed by other electric motors running in power running, and is returned to the inverter via the feedback diode. This regenerated energy is absorbed by the ripple attenuation electrolytic capacitor connected to the inverter, causing the terminal voltage of the electrolytic capacitor to jump, generating an overvoltage. Therefore, there is no problem if a thyristor with a large overvoltage resistance is used, but such a configuration makes the inverter itself very uneconomical, which is not preferable.

In view of the problems of the prior art described above, the present invention has been developed to automatically connect the An object of the present invention is to provide an overvoltage absorbing device for a voltage type inverter that can consume regenerated energy using a resistor.

E. Means and operation for solving the problem The present invention is for controlling the drive of a large number of electric motors connected to the inverter of an inverter. Switching to light load operation with rotary drive is determined by comparing a reference current whose set value is the load current of the number of operating motors during light load operation with a load current detected by the load current detection means using a comparator.
Based on this judgment result, the switch is opened to connect the braking resistor to the inverter DC intermediate circuit. The regenerated energy generated thereby flows to the resistor via the feedback diode of the inverse conversion section and is consumed as heat, thereby preventing the occurrence of overvoltage.

F. Embodiment An embodiment of the inverter overvoltage absorbing device of the present invention will be described below with reference to the circuit diagram shown in FIG.

In Figure 1, inverter I is a commercial power supply
It consists of a forward converter 1 consisting of a rectifier that converts phase alternating current to direct current, an electrolytic capacitor 2 that absorbs ripples in the rectified current, a thyristor and a feedback diode, and converts direct current power to variable frequency, variable voltage alternating current power. The inverse conversion unit 5 is also provided. In addition,
A pulse signal from a pulse phase control circuit (not shown) is input to the gate of each thyristor of the inverse converter 5, and the conduction angle of each thyristor is controlled.

On the output side of the inverse converter 5, there are power line connection points P ₁ ,
Through P ₂ and P ₃ , n units, for example, induction motors M ₁ ,
M ₂ ,...M _o are connected. 6 is inverter I
and electric motors M ₁ , M ₂ ,...M _o , and these switches 6 are opened and closed as appropriate.
Starts and stops the electric motor. 8 is a current detector,
Extracts a signal proportional to the load current flowing through the power line.

Reference numeral 10 is an amplifier, and 11 is a current setting device, which outputs a reference signal having a value corresponding to the load current value of one or several electric motors that are rotationally driven during light load operation. 1
A comparator 2 compares the reference signal from the current setter 11 and the load current from the current detector 8.

3 is a switch, 4 is a resistor with a capacity that can absorb the regenerative energy of one or two electric motors,
The switch 3 is a braking resistor that absorbs the regenerated energy returned to the inverter, and the switch 3 is controlled to open and close by a signal from the comparator 12. Note that this switch 3 is closed when switching from heavy load operation to light load operation, and generates chattering when it is opened when switching from light load operation to heavy load operation, so to prevent this, the switch 3 is closed. Of course, 3 should have a hysteresis characteristic.

The operation of this embodiment having such a configuration will be explained.

First, the set current value of the current setting device 11 is set to a value corresponding to the load current value of one or several electric motors. Then, the inverter I is operated, and variable frequency, variable voltage alternating current power is output from the inverter 5, and the n electric motors M ₁ , M ₂ , . . . M _o are driven and controlled. During such heavy load operation (multiple unit operation), since the load current input to the comparator 12 via the current detector 8 is larger than the reference current value of the current setting device 11, the signal from the comparator 12 is is not output, and therefore switch 3 is open.

When transitioning from such a heavy load operating state (many motors operation) to a light load operating state (small number motors operating) in which one or several electric motors are rotationally driven, the following operations are performed. That is, current detectors 8 to 1
Load currents supplied to one or more electric motors are detected and input to a comparator 12 via an amplifier 10. When this detected current becomes smaller than the reference current value of the current setter 11, the comparator 12 determines that a small number of units are operated, and based on this result, the switch 3 is closed and the resistor 4 is connected to the inverter I.

With the resistor 4 connected to the inverter I in this way, one or several electric motors that are being rotated enter regenerative operation, and the regenerative energy generated thereby is transferred through the feedback diode of the inverter 5. The regenerated energy is returned to the inverter I, flows through the switch 3 to the resistor 4, and is consumed as heat.

Therefore, generation of overvoltage in the inverter DC intermediate circuit can be prevented, and stable operation of a small number of inverters can be performed. In addition, when shifting from a small number of machine operation to a multi-machine operation, as is clear from the above explanation, the signal led from the comparator 12 to the switch 3 is cut off, so that when a large number of machines are operated, some of the motors The regenerated energy is supplied as power running energy to other motors that are running, so not only is the energy used effectively, resulting in an energy-saving system, but no overvoltage occurs in the DC intermediate circuit. .

G. Effect of the invention As explained above, according to the invention, when switching from heavy load operation in which a voltage type inverter is used to rotate a large number of electric motors to light load operation in which one or several electric motors are rotationally driven. Since the reference current value of the current setting device is set to a value corresponding to the load current of the motor during light load operation, this reference current is compared with the load current from the load current detection means. If the switch 3 is opened/closed and a light load condition is determined, the resistor is automatically connected to the inverter, so the regenerative energy generated by the motor's regenerative operation that occurs during light load operation is consumed in the resistor. Also, since the resistor is not connected to the inverter during heavy load operation, the regenerated energy can be consumed by other motors in power running without wasting power during heavy load operation. Since the resistor is connected to the inverter during operation, the power factor can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of an overvoltage absorbing device for a voltage type inverter according to the present invention. I... Inverter, 1... Forward conversion unit, 2... Electrolytic capacitor, 3... Switch, 4... Resistor, 5
... Reverse conversion section, 6 ... Switch, 7 ... Electric motor, 8
...Current detector, 10...Amplifier, 11...Current setter, 12...Comparator.

Claims (1)

[Claims for Utility Model Registration] A voltage-type inverter that has a forward conversion section and an inverse conversion section consisting of a thyristor and a feedback diode, and controls the speed of a large number of motor groups connected to its output side, comprising: a current setting device that outputs a reference signal set to a load current when the motor group is operated with a small number of motors (equivalent to one or several motors); a comparator that compares the load current from the detection means with a reference signal of the current setting device to determine whether the motor group is operated with a large number of motors or a small number of motors; A voltage type inverter that performs opening/closing control such that the circuit is opened during operation and closed when a small number of units are operated, and is equipped with a switch inserted in the inverter DC intermediate circuit, and a resistor connected in series with the switch. overvoltage absorber.