JPH0623159Y2 - Abnormality detection device for three-phase power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an abnormality detection device for a three-phase power supply, which is suitable for protecting equipment such as a welding power supply and particularly for protecting an inverter control power supply for controlling the output on the primary side of a transformer.

In order to reduce the size and weight of power sources for welding machines and the like, commercial power sources are once converted into direct current, and then converted into high-frequency alternating current by an inverter and added to a transformer, whereby the transformer is significantly downsized. Since this type of welder is small and lightweight, it is portable and is used for on-site welding where it is carried out outdoors. In the field of outdoor work, the power supply situation is bad and the commercial power supply voltage is often abnormally high or low. In the drawing, 1 is a commercial three-phase power supply consisting of UVW phase, and 2 is a rectifier circuit for converting commercial alternating current into direct current. An inverter 3 exchanges direct current with high frequency alternating current. 4 is a transformer for high frequency, which is small. 5 is a second rectifier circuit, 6 is a smoothing reactor, and 7 is a welding load. A detection circuit 8 detects the welding output and feeds back to the output control circuit 9. The output control circuit 9 compares and discriminates the feedback signal from the detection circuit 8 with the signal from the reference setting circuit 10, and controls the inverter 3 so as to supply a constant output to the load 7.

Reference numeral 11 denotes a start / stop circuit that generates a start / stop signal for the inverter 3 and is connected to the output control circuit 9.

Inverter-controlled power supply devices generally use many semiconductors such as power transistors as the inverter 3 and perform switching at high speed, so that spike voltage is likely to occur. Since semiconductor products are relatively weak in withstand voltage, when the switching operation is performed when the voltage of the commercial three-phase power supply 1 becomes abnormally high, the voltage rises enough to destroy the constituent elements of the inverter 3 or does not break. In both cases, the element may be stressed and the reliability may be deteriorated. Therefore, it is necessary to detect the abnormal voltage and protect the element from the abnormal voltage. Further, even if one of the three-phase power supplies is not connected, the output of the rectifier circuit 2 becomes direct current and the inverter 3 operates normally. However, at this time, the current per element in the rectifying circuit 2 is √√ times as many due to the single-phase operation, and the element is destroyed. It is necessary to use a large capacity element in order to avoid destruction. Conventionally, it is necessary to provide protection to detect these abnormal phenomena and stop the circuit. In addition, a dedicated relay is provided for open-phase detection to detect normal when the relay is ON and open-phase when the relay is OFF. It was

The present invention eliminates the above-mentioned conventional drawbacks, and overvoltage of a three-phase power supply,
The purpose is to detect abnormalities such as low voltage and open phase with a simple circuit configuration to prevent damage to semiconductor switches and the like.

In order to achieve the above object, in the present invention, a first transformer connected between one phase of a three-phase power source, a second transformer connected between other phases, and the first transformer. Of the secondary side output of the second transformer to a plurality of reference voltages having different levels, a conversion circuit converting the secondary side of the second transformer to the reference voltage, and a comparison voltage from the conversion circuit. A first comparison circuit for comparing with a high level reference voltage from the stabilizing circuit, and a second comparison circuit for comparing the comparison voltage from the converting circuit with a low level reference voltage from the stabilizing circuit; An abnormality detecting device for a three-phase power supply, comprising an abnormality detecting circuit for determining outputs of the first comparison circuit and the second comparison circuit to determine an abnormality of the three-phase power supply.

An embodiment of the present invention will be described in detail below with reference to the drawings. The part enclosed by the broken line in the figure shows the main part of the present invention. A control circuit transformer 12 connects to the VW phase of the commercial three-phase power source 1, and a stabilizing circuit 13 supplies a constant voltage B to the control circuit. 14 is UV
It is a voltage detection transformer connected to the phase and is rectified and smoothed by a diode 15 and a capacitor 16. Reference numerals 17 and 18 denote resistors for dividing the detected voltage, which together with the diode 15 and the capacitor 16 form a conversion circuit for converting into a comparison voltage corresponding to the reference voltage, and output the input signals of the comparators 21 and 24. 19 and 20
Is a voltage dividing resistor that divides the output voltage B of the stabilizing circuit 13 at a predetermined ratio to obtain a high level reference voltage. The comparator 21 is used to detect abnormal voltage (overvoltage: circuit voltage rise),
When the voltage of the- (minus) terminal is higher than the high level reference voltage, it becomes low level, the abnormality detection circuit 25 is activated, and the oscillation of the inverter 3 is stopped.
Generate a signal to. 22 and 23 are voltage divider resistors for stabilizing circuit
The output voltage B of 13 is divided at a predetermined ratio to be a low level reference voltage. The comparator 24 is used to detect an abnormal voltage (low voltage). When the voltage at the + (plus) terminal is lower than the low level reference voltage, the comparator 24 becomes low level and the abnormality detection circuit 25
Is generated and a signal is generated in the start / stop circuit 11 to stop the transmission of the inverter 3. In the normal state, the voltage at the + terminal is high, so the comparison circuit 24 outputs a high level. Further, when the input of the detection transformer 14, that is, the UV phase is lost, the secondary side output of the transformer 14 disappears, so the + terminal of the comparison circuit 24 becomes OV, the output becomes low level, and the abnormality detection circuit 25.
To stop the inverter 3 from oscillating. The same operation is performed when the voltage of the UV phase drops below the setting, and a low voltage can be detected. When the VW phase is open, no voltage is applied to the transformer 12 of the control circuit and the transformer 12 does not operate. Comparison circuit
The output terminals of the comparator 21 and the comparator circuit 24 are constituted by known open collectors, and the open collector output terminals of the comparator circuits 21 and 24 are commonly connected to form a wired OR. Therefore, in a normal state, both the outputs of the comparison circuits 21 and 24 are at the high level and the output of the abnormality detection circuit 25 is also at the high level, but when one of the outputs of the comparison circuits 21 and 24 becomes the low level. , The output of the abnormality detection circuit 25 is inverted and becomes low level. The abnormality detection circuit 25 generates a stop signal according to the conditions of the first and second comparison circuits 21 and 24, but in the above embodiment, the outputs of the comparison circuits 21 and 24 are connected in parallel and connected to the input terminal. Is enough.

The present invention is useful for an inverter circuit power supply or the like using an element such as a semiconductor on the primary side, but is not limited to this, and even in a general welding machine, etc., protection from single-phase operation due to open phase of input voltage and overvoltage Can be used for

As described above, the present invention provides the transformer for detection and the transformer for the reference power supply between the phases of the three-phase power supply, and discriminates the outputs of the first and second comparison circuits for comparing the respective output voltages. Therefore, in addition to the overvoltage and undervoltage of the three-phase power supply, since it is a three-phase power supply abnormality detection device with a simple configuration that can detect the open phase, protection from overvoltage that exceeds the breakdown voltage of the elements constituting the power supply, Excessive current flowing through the element during single-phase operation due to open phase due to prevention of element destruction due to operation at a halfway voltage when the input voltage has a poor contact at the power supply connection or the output of the engine generator, etc. The effect is that protection from destruction due to damage can be ensured.

[Brief description of drawings]

The drawings are block diagrams showing an embodiment of the present invention. 1 …… Three-phase power supply, 2,5 …… Rectifier circuit, 3 …… Inverter, 11 …… Start-stop circuit, 12 …… First transformer, 13 ……
Stabilization circuit, 14 …… Second transformer, 15 …… Diode,
16 ... Capacitor, 17,18,19,20 ... Resistor, 21 ... First comparison circuit, 22,23 ... Resistor, 24 ... Second comparison circuit, 25 ... Abnormality detection circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yoshifumi Yamanaka 2100 Kamiimaizumi, Ebina City, Kanagawa Hitachi Seiko Co., Ltd. (72) Tokio Setoguchi 2100, Kamiimaizumi, Ebina, Kanagawa Pref. 56) References JP-A-58-156864 (JP, A)

Claims (1)

[Scope of utility model registration request] 1. A three-phase power source, a rectifier circuit connected to the three-phase power source, an inverter connected to the rectifier circuit and converting an output from the rectifier circuit into a high frequency alternating current, and a high frequency wave connected to the inverter. In the abnormality detector of the three-phase power supply used for the transformer for electric power and the inverter welding machine which rectifies the high frequency alternating current from the transformer for the high frequency and supplies it to the load, it is connected between one phase of the three-phase power source. A first transformer, a stabilizing circuit for converting a secondary side output of the first transformer into a plurality of reference voltages having different levels, and a second transformer connected between the other phases of the three-phase power source. And a conversion circuit for converting the secondary side of the second transformer into a comparison voltage corresponding to the reference voltage, and comparing the comparison voltage from the conversion circuit with a high level reference voltage from the stabilization circuit. Detect abnormal voltage (overvoltage) A first comparison circuit for comparing the comparison voltage from the conversion circuit with a low-level reference voltage from the stabilization circuit to detect an abnormal voltage (low voltage); An abnormality detection device for a three-phase power supply, comprising an abnormality detection circuit for determining an abnormality of the three-phase power supply based on the outputs of the comparison circuit and the second comparison circuit.