CN109093239B

CN109093239B - Medium frequency inversion resistance welding controller and constant current control method thereof

Info

Publication number: CN109093239B
Application number: CN201811315763.XA
Authority: CN
Inventors: 张云; 朱洪升; 饶华仁; 梁健佶; 沈健
Original assignee: Zhongzheng Zhikong Jiangsu Intelligent Technology Co ltd
Current assignee: Zhongzheng Zhikong Jiangsu Intelligent Technology Co ltd
Priority date: 2018-11-07
Filing date: 2018-11-07
Publication date: 2023-09-26
Anticipated expiration: 2038-11-07
Also published as: CN109093239A

Abstract

The invention belongs to the welding machine control technology, and relates to an intermediate frequency inversion resistance welding controller and a constant current control method thereof. The controller comprises a control unit which can drive and control the IGBT module in the welding main circuit; the detection signal input end of the control unit is connected with the current sensing device; the control unit comprises an IGBT driving circuit and a pulse signal source capable of outputting a fixed pulse width signal, a shaping circuit for processing pulse signal waveforms is sequentially arranged between the pulse signal source and the input end of the IGBT driving circuit, and the control unit further comprises a comparison circuit capable of comparing sampling current detected by the current sensing device with set setting current; the signal output end of the comparison circuit is connected to the shaping circuit, and the on-off of the signal output by the shaping circuit can be controlled according to the comparison result. The invention can improve the control precision of the welding process and has high response speed to the control of welding current.

Description

Medium frequency inversion resistance welding controller and constant current control method thereof

Technical Field

The invention belongs to the welding machine control technology, and relates to an intermediate frequency inversion resistance welding controller and a constant current control method thereof.

Background

The working circuit of the medium-frequency inversion resistance welding generally comprises a full-bridge half-control rectifying circuit, a filter circuit and an inversion circuit formed by IGBT modules, which are sequentially arranged at the output part of a three-phase power supply, and the working principle is as follows: the three-phase power is converted into direct current through the full-bridge half-control rectifying circuit and the filtering circuit, and during welding, the inverter circuit converts the direct current into alternating current pulse wave with the frequency of 1000hz and outputs the alternating current pulse wave to the transformer, so that working voltage is provided for welding electrodes.

In the resistance welding process, the controllability of the current determines the welding quality to a great extent, and the higher the current control precision is, the better the welding quality is. Accuracy is in turn divided into two aspects: on the one hand, the welding process is finished once, usually 40ms to 100ms, and the difference between the set value and the actual effective value is set; on the other hand, when the load resistance changes, the speed of the controller adjusts. With the development of manufacturing industry, more and more special materials are welded, and the requirement on the stability of current in the welding process is also higher and higher. Some materials are sensitive to current, and if the current is large within 1ms, splashing is easy to occur, the current is small, and the firmness of the nugget is not enough. Therefore, a controller capable of rapidly and stably adjusting the current is required. The existing intermediate frequency resistance welding controller is generally a 1000HZ controller, and the existing intermediate frequency resistance welding controller with the highest adjustment speed has a reaction speed of at least half a period. It is difficult to meet the control requirements of higher reaction speeds.

Disclosure of Invention

The invention aims to solve the technical problem of providing a medium-frequency inverter resistance welding controller and a constant current control method thereof, which can improve the control precision of the welding process and have high response speed to welding current control.

The medium-frequency inverter resistance welding controller comprises a control unit which can drive and control an IGBT module in a welding main circuit; the detection signal input end of the control unit is connected with a current sensing device for detecting the primary current of the welding transformer; the control unit comprises an IGBT driving circuit and a pulse signal source capable of outputting a fixed pulse width signal, a shaping circuit for processing pulse signal waveforms is sequentially arranged between the pulse signal source and the input end of the IGBT driving circuit, and the control unit further comprises a comparison circuit capable of comparing sampling current detected by a current sensing device with set setting current; the signal output end of the comparison circuit is connected to the shaping circuit, and the on-off of the signal output by the shaping circuit can be controlled according to the comparison result.

The pulse signal source is a singlechip for sending out pulse signals with fixed pulse width.

The current sensing device is a current transformer or a Hall sensor.

An interlocking circuit which is used for controlling the H bridge formed by the four IGBTs to be incapable of being conducted on one side is further arranged between the pulse signal source and the shaping circuit.

The invention discloses a constant current control method for medium frequency inversion resistance welding, which is based on the controller and specifically comprises the following steps: in the welding process, a singlechip continuously sends a pulse signal with a fixed pulse width to a shaping circuit according to the set current required by welding; meanwhile, the comparison circuit controls the signal pulse waveform passing through the shaping circuit according to the comparison result of the sampling current and the setting current; if the sampling current is larger than the setting current, the IGBT driving signal is cut off, otherwise, the pulse signal is not processed.

The invention has the advantages that: in the welding control process, the singlechip always transmits a driving signal without processing and calculating the pulse width, and the turn-off of the pulse is completely realized by a comparison circuit, so that the calculation amount of the singlechip is greatly reduced, and the reaction speed of the current is greatly improved; in addition, in a half period, the trigger signal can be sent for many times, under certain specific conditions, the transformer consumes too fast current, when the IGBT stops conducting, the current drops instantaneously, at the moment, the conventional controller does not send trigger pulse again, because the pulse width sent by the controller is calculated before sending, in the method of the invention, when the current drops rapidly, the circuit can open the pulse channel, give the IGBT trigger signal again, supplement the current, and ensure the stability of the welding process.

Drawings

FIG. 1 is an overall schematic of an embodiment of the present invention;

FIG. 2 is a functional block diagram of a control unit of an embodiment of the present invention;

FIG. 3 is a schematic waveform diagram of a fixed pulse width driving signal when a set current is greater than a sampling current during control according to an embodiment of the present invention;

fig. 4 is a schematic waveform diagram of a truncated signal inserted state when a set current is smaller than a sampling current in a control process according to an embodiment of the present invention.

Detailed Description

As shown in fig. 1, the intermediate frequency inverter resistance welding controller comprises a control unit capable of controlling a welding main circuit; the welding main circuit comprises a full-bridge half-control rectifying circuit 1, a filter circuit 2 and an inverter circuit 3 which consists of IGBT modules, wherein the full-bridge half-control rectifying circuit 1, the filter circuit 2 and the inverter circuit 3 are sequentially arranged between a three-phase power output part and a welding transformer input part; the control unit can output driving signals to the IGBT module of the inverter circuit, and the detection signal input end of the control unit is connected with the current sensing device 4 for detecting the primary current of the welding transformer. As shown in fig. 2, the control unit includes an IGBT driving circuit and a pulse signal source capable of outputting a fixed pulse width signal, a shaping circuit for processing the pulse signal waveform is sequentially disposed between the pulse signal source and the input end of the IGBT driving circuit, and the shaping electric wave processes the rising and falling edges of the pulse wave more steeply; the comparison circuit is used for comparing the sampling current detected by the current sensing device with the set setting current; the signal output end of the comparison circuit is connected to the shaping circuit, and the on-off of the signal output by the shaping circuit can be controlled according to the comparison result. The pulse signal source is a singlechip for sending out pulse signals with fixed pulse width. The current sensing device is a current transformer or a hall sensor. An interlocking circuit which is used for controlling the H bridge formed by the four IGBTs to be incapable of conducting on one side is further arranged between the pulse signal source and the shaping circuit, namely U1 and U2 cannot be conducted simultaneously, V1 and V2 cannot be conducted simultaneously, and the IGBTs are prevented from being burnt. The control unit is also connected with a touch screen for inputting and displaying control and operation parameters.

In the controller of the embodiment, the singlechip continuously sends a pulse signal with a fixed pulse width to the shaping circuit according to the set current required by welding in the welding process; meanwhile, the comparison circuit controls the signal pulse waveform passing through the shaping circuit according to the comparison result of the sampling current and the setting current; if the sampling current is larger than the setting current, the IGBT driving signal is cut off, otherwise, the pulse signal is not processed.

During the working process of the comparison circuit: and outputting an enabling signal if the set current is larger than the sampling current, otherwise outputting a prohibiting signal if the set current is smaller than the sampling current.

The output signal acts on a shaping circuit which, when enabled, outputs a fixed pulse width pulse of the waveform shown in fig. 3.

When the inhibit signal exists, the signal is partially truncated, the shaping circuit outputs a waveform signal as shown in fig. 4, and when the sampling current I does not reach the set current I, the trigger pulse is normally sent; when the sampling current reaches the set current, the trigger waveform is rapidly cut off; in the area A, when the trigger pulse acts on the IGBT, the current increases, when the trigger pulse reaches a set value, the pulse is rapidly intercepted by the comparison circuit, the current rapidly drops after the trigger pulse is intercepted, and after the trigger pulse exceeds a certain threshold (the threshold is mainly determined by circuit precision and reaction time), the comparison circuit opens a pulse channel again, the IGBT continues to work, and the current is supplemented, so that adjustment can be realized in a half period, which cannot be realized by a conventional controller.

Claims

1. The medium frequency inversion resistance welding controller comprises a control unit which can drive and control an IGBT module in a welding main circuit; the method is characterized in that: the detection signal input end of the control unit is connected with a current sensing device for detecting the primary current of the welding transformer; the control unit comprises an IGBT driving circuit and a pulse signal source capable of outputting a fixed pulse width signal, a shaping circuit for processing pulse signal waveforms is sequentially arranged between the pulse signal source and the input end of the IGBT driving circuit, and the control unit further comprises a comparison circuit capable of comparing sampling current detected by the current sensing device with set setting current; the signal output end of the comparison circuit is connected to the shaping circuit, and the on-off of the output signal of the shaping circuit can be controlled according to the comparison result; the pulse signal source is a singlechip for sending out pulse signals with fixed pulse width.

2. The medium frequency inverter resistance welding controller according to claim 1, wherein: the current sensing device is a current transformer.

3. The medium frequency inverter resistance welding controller according to claim 1, wherein: the current sensing device is a hall sensor.

4. The medium frequency inverter resistance welding controller according to claim 1, wherein: an interlocking circuit which is used for controlling the H bridge formed by the four IGBTs to be incapable of being conducted on one side is further arranged between the pulse signal source and the shaping circuit.

5. The medium frequency inverter resistance welding controller according to claim 1, wherein: the control unit is connected with a touch screen for inputting and displaying control and operation parameters.

6. A constant current control method for medium frequency inverter resistance welding based on the medium frequency inverter resistance welding controller of claim 1, which is characterized in that: in the welding process, a pulse signal source continuously sends a pulse signal with a fixed pulse width to a shaping circuit according to the set current of the welding requirement; meanwhile, the comparison circuit controls the signal pulse waveform passing through the shaping circuit according to the comparison result of the sampling current and the setting current; if the sampling current is larger than the setting current, the IGBT driving signal is cut off, and if the sampling current is smaller than the setting current, the pulse signal is not processed.