JPS6192125A - Discharge circuit for frequency changer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a discharge circuit for a frequency conversion device for controlling the rotational speed of an electric motor or the like. .

Conventional configuration and its problems In recent years, in order to steplessly control the rotational speed of an AC motor, there are many devices called frequency converters that convert the frequency input to the motor, which are made up of three main circuits. It is configured.

Next, FIG. 2 shows a discharge circuit of a conventional frequency wedge device.

A is a frequency conversion device 5, and this frequency conversion device is
It is equipped with a rectifier circuit 1 that rectifies the AC input power supply voltage, and a field current prevention resistor 2 that suppresses inrush current when the input power is turned on. And 3 is the relay contact, common contact a
and a normally open contact signal are connected to both ends of the resistor 2, respectively,
The normally closed contact is not used, and although it is not shown in the figure, a control circuit is added that controls the relay coil to close the normally closed contact several seconds after the power supply is turned on.
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4 is the rectifying area 7. This is a capacitor that smoothes the rectified voltage. 6 is when the input power supply voltage is cut off,
This is a discharging resistor for discharging the charge stored in the capacitor 4, and is connected in parallel with the capacitor 4. 6 is a main circuit element of the frequency converter A, which applies an arbitrary frequency and voltage to the electric motor 7 at the subsequent stage.

In the conventional discharge circuit having the above configuration, when the AC input power is turned on, the relay contact 3 changes to the normally closed contact C.
Since the current is rectified by the rectifier circuit 1, the current is passed through the inrush current prevention resistor 2 to the capacitor 4 and the discharge resistor 5, so that the capacitor 4 and the discharge resistor 5 are charged.

After a few seconds, the normally open contact of the relay contact 3 operates to close after charging is completed, but since the discharging resistor 5 is always connected in parallel with the capacitor 4, the frequency converter is still operating. Since current flows through the discharge resistor 6 during the
This had the problem of high power loss.

Structure of the Invention In order to achieve this object, one end of the discharge resistor is connected to a normally closed contact of a relay contact that controls the inrush current prevention resistor.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, B is a frequency converter, and 1 and 2 are a rectifier circuit and a rush current prevention resistor, as in the conventional example. 3
' is a relay contact, the common contact a is connected to the capacitor 4 and one end of the resistor 2, and the normally open contact a is connected to the other end of the resistor 2. The closing contact C is connected to one end of the discharge resistor 6', and like the conventional example, although not shown, the relay coil is controlled to close the normally closed contact C several seconds after input power is turned on. A control circuit is added. 6 and 7 are main circuit elements and electric motors as in the conventional example.

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With the above configuration, when the input power is turned on, the relay contact 3 is connected to the normally closed contact C, so the current rectified by the rectifier circuit 1 passes through the inrush current prevention resistor 2 to the capacitor 4.
The current flows through the discharge resistor 6', but since the discharge resistor 6' is set to a high resistance, most of the current flows through the capacitor 4.
1 (shown as a solid line in the relay contact diagram). After this, when charging is completed after a few seconds have passed, relay contact 3
Since the normally open contact 6' operates to close, the discharging resistor 6' is disconnected from the circuit (as shown by the broken line in the relay contact diagram).

After this, the control section (
(not shown), the signal is transmitted to the main circuit element 6.
Current flows from the rectifier circuit 1 to the normally open contacts.

Common contact a, capacitor 4. A current flows through the main circuit element 6, but no current flows through the discharge resistor 6', and any frequency and voltage are transmitted to the motor 7, making it possible to vary the rotational speed. When the input power is cut off, a signal is sent from the control section to switch the relay contact 3' to the normally closed contact C, and the charge in the capacitor 4 is discharged through the discharging resistor 6' as in the conventional case.

Effects of the Invention As is clear from the above explanation, the present invention provides relay contacts that control the resistance that suppresses inrush current when input power is turned on.
By using a normally closed contact, which was previously unused, and connecting it to the discharging resistor, power loss that would occur continuously in the discharging resistor during operation of the conventional frequency converter is reduced until the capacitor is fully charged. The power loss is limited to a very short period of time, and the efficiency of the frequency conversion device can be increased without increasing the price.

[Brief explanation of drawings]

FIG. 1 is a discharge circuit diagram of a frequency converter according to an embodiment of the present invention, and FIG. 2 is a discharge circuit diagram of a conventional frequency converter. 1... Rectifier circuit, 2... Inrush current prevention resistor, 3'... Relay contact, a...
Common contact, b... Normally open contact, C... Normally closed contact, 4... Capacitor, 5'9.・・・・・・
Discharge resistor, 6... Main circuit element.

Claims (1)

[Claims] a current circuit that rectifies the input voltage, a capacitor that smoothes the rectified voltage, a main circuit element that outputs an arbitrary frequency and voltage, a rush current prevention resistor connected in series between the rectifier circuit and the capacitor, and the One end of each of the rectifier circuit and the inrush current prevention resistor is a normally open contact, one end of the capacitor and the other end of the inrush current prevention resistor are a common contact, and one end of the discharge resistor for discharging the charge of the capacitor. A discharge circuit of a frequency converter having a relay contact connected to a normally closed contact.