JPH05252755A - Inverter controlling circuit - Google Patents

Abstract

PURPOSE:To provide an inverter which can avoid waste time in working and which reduces a risk of being struck by electricity by making the equipment so structured that a discharging circuit for braking is turned on when an a.c. source is turned off. CONSTITUTION:As for a control signal which turns on a discharging circuit for braking, a three-phase source OFF signal which is output after it is detected that a three-phase source is turned off and a PWM shut-off signal which shuts off a main circuit switching element of a power converter are inputted to an AND circuit 21 besides the conventional ON signal and the output signal from the AND circuit 21 is made into a pulse signal of a constant width by a one-shot trigger circuit 22 and the pulse signal is inputted into an OR circuit 23. Besides the conventional braking operation, a braking circuit is turned on by the OR circuit 23 for the specified period time when the three-phase source is turned off. And, electric charge in a smoothing capacitor is immediately discharged by a discharging resistor for braking. As a result, waste time is avoided in the inspection work for a wide-use inverter and danger in the work can be eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a general-purpose inverter for frequency controlling a three-phase induction motor.

[0002]

2. Description of the Related Art FIG. 3 is a schematic block diagram showing a conventional general-purpose inverter. In the figure, 1 is a three-phase power supply, 2 is a three-phase full-wave rectifier, 3 is a smoothing capacitor, 4 is a discharge resistor, and 5 is a discharge resistor. Is an inverse converter for converting direct current into alternating current, 6 is a three-phase induction motor, 7 is a regenerative braking discharge circuit, 8 is a control circuit,
Reference numeral 9 denotes a drive amplifier for an inverse converter and a switching element of a brake discharge circuit, 10 denotes a DC bus voltage detection signal, and 11
Is a three-phase power supply detection circuit, and 12 is a control power supply.

Next, the operation will be described. A general-purpose inverter usually has a structure as shown in FIG. When the three-phase power supply 1 is turned on, the smoothing capacitor 3 is charged through the three-phase full-wave rectifier 2. The direct current charged in the smoothing capacitor 3 is applied to the inverse converter 5, PW generated by the control circuit 8 and amplified by the switching element drive amplifier 9
It is converted into alternating current again by the M signal and supplied to the three-phase induction motor 6.

Next, when the three-phase power supply 1 is turned off, the three-phase power supply detection circuit 11 detects that the three-phase power supply 1 is turned off, the control circuit 8 cuts off the PWM signal, and the inverse converter 5 is turned off. Stops the operation. Therefore, the electric charge charged in the smoothing capacitor 3 is discharged through the discharge resistor 4.
The voltage across the smoothing capacitor 3 (DC bus voltage) is shown in FIG.
As shown in, the time constant is determined by the capacity of the smoothing capacitor 3 and the resistance value of the discharge resistor 4.

In general, the general-purpose inverter causes the regenerative braking discharge circuit 7 to consume regenerative energy generated when the three-phase induction motor 6 is rapidly decelerated. This is because the rise in the terminal voltage of the smoothing capacitor 3 due to the regenerative energy is detected by the DC bus voltage detection signal 10, and when the voltage level set in advance is exceeded, the control circuit 8 sends the regenerative brake ON signal to the switching element. Drive amplifier 9
Then, the switching element drive amplifier 9 operates the regenerative braking discharge circuit 7 to quickly discharge the electric charge charged in the smoothing capacitor 3 through the resistor, thereby consuming the regenerative energy by heat generation of the resistor. It is a thing.

[0006]

Since the conventional general-purpose inverter is constructed as described above, even if the three-phase power supply 1 is turned off to inspect the inside of the general-purpose inverter, the charge of the smoothing capacitor 3 is It takes a long time to discharge (usually, the resistance value of the discharge resistor 4 is several hundred kΩ due to the problem of heat generation,
It takes a few minutes to discharge. ) Work wastes time. In addition, there is a problem in that there is a risk of accidentally touching a charged part and receiving an electric shock immediately after the power is turned off.

The present invention has been made in order to solve the above-mentioned problems, and the electric charge of the smoothing capacitor is discharged in a short time, so that the waste of working time can be saved and the risk of electric shock can be reduced. The purpose is to obtain an inverter device.

[0008]

The inverter device according to the present invention is provided with a control for turning on the brake discharge circuit when the AC power supply is cut off.

[0009]

According to the means of the present invention, the electric charge of the main circuit capacitor is rapidly discharged by the brake discharge resistor by turning on the brake discharge circuit when the AC power is off.

[0010]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a control signal for turning on the brake discharge circuit. In the figure, 21 is A.
ND circuit, 22 one-shot trigger circuit, 23 OR
Circuit.

Next, the operation will be described. In addition to the conventional ON signal, the control signal for turning on the brake discharge circuit includes a three-phase power-off signal that detects and outputs the three-phase power-off and a PWM signal that shuts off the main circuit switching element of the inverse converter 5. The cutoff signal is input to the AND circuit 21, and its output signal is converted into a pulse signal having a constant width by the one-shot trigger circuit 22 and input to the OR circuit 23. With the above circuit, the brake discharge circuit can be turned on for a certain period of time when the three-phase power supply is turned off, in addition to normal braking operation.
Will be done. That is, the electric charge stored in the smoothing capacitor when the three-phase power supply is turned off is discharged by the brake discharge resistance. Since the constant of the discharge resistance for braking is as small as several tens of Ω with respect to several hundred kΩ of the discharge resistance 4, the charged electric charge is promptly discharged. (See Figure 2)

[0012]

As described above, according to the present invention, when the three-phase power supply is turned off, the discharging of the electric charge of the smoothing capacitor is promptly performed by using the discharging circuit for the brakes. There is an effect that it is possible to omit, and to eliminate the danger during work.

[Brief description of drawings]

FIG. 1 is a diagram showing a brake signal circuit according to an embodiment of the present invention.

FIG. 2 is a timing chart of the operation of each signal when the three-phase power supply is cut off.

FIG. 3 is a schematic block diagram of a conventional general-purpose inverter.

FIG. 4 is a diagram showing an operation when a conventional three-phase power supply is cut off.

[Explanation of symbols]

 1 Three-phase power supply 2 Three-phase full-wave rectifier 3 Smoothing capacitor 4 Discharge resistor 5 Inverter 6 Three-phase induction motor 7 Regenerative braking discharge circuit 8 Control circuit 9 Switching element drive amplifier 10 DC bus voltage detection signal 11 Three-phase Power supply detection circuit 12 Control power supply 21 AND circuit 22 One-shot trigger circuit 23 OR circuit

Claims (1)

[Claims] 1. A main circuit converter section for rectifying / smoothing a commercial power source, an inverter section for inversely converting a direct current into an alternating current, and a control power source from a direct current that can be rectified / smoothed from a commercial power source separately from a main circuit converter section. In a general-purpose inverter equipped with a DC / DC converter section for producing, an AC power source detection section for detecting ON / OFF of an AC power source, and a brake discharge circuit for absorbing regenerative energy from a motor, a brake discharge is generated when the AC power source is cut off. Inverter control circuit with control to turn on the circuit.