Development of inverter welding power supply

Modern industrial production has gradually entered the digital and network era. Digital and network technologies have been continuously applied and popularized in the industrial field. New welding processes and methods have emerged, which have put forward new requirements for the development of welding power sources. With the deepening of research on arcs and molten pools, various new types of inverter welding power sources have emerged.

Requirements for inverter welding power supply in modern industrial production

At the beginning of the 18th century, arcs were discovered, but at the time the industrial level was low, and it was not possible to provide enough electric energy for the arc. Welding with an electric arc was not possible. With the rapid development of industry, electric energy can not only be provided in large quantities, but also at a lower cost. Therefore, the use of arc welding of metal materials has become a reality, and welding power sources have also been greatly developed. Especially for nearly half a century, the invention of various new welding processes, the rapid development of semiconductor technology, and the emergence of silicon rectifier arc welding power sources suitable for different process requirements. Especially with the advent of IGBT devices, the performance of inverter welding power supplies has been greatly improved. The resulting new welding processes and methods, as well as the application of digitization and network technology in industrial production, in turn put forward higher requirements for inverter power supplies. This requirement is mainly reflected in three aspects: (1) numerical control of welding power output power; (2) flexibility of welding power output characteristics; (3) digitization and networking of welding power control interface.

1 Numerical control of welding power output power

It is well known that the form of droplet transfer is broadly divided into three types: free transition, contact transition, and slag wall transition. In the case of MIG welding, the wire is short-circuited and the arc is repeatedly ignited. This contact transition is also referred to as a short-circuit transition. In order to keep the short-circuit transition welding process stable, not only the welding power source is required to have suitable static characteristics, but also the power source has suitable dynamic characteristics. This mainly includes three aspects: (1) for different wire diameters and specifications, to ensure the appropriate short-circuit current rising speed, to achieve the purpose of reducing splash; (2) to have appropriate short-circuit current peak to ensure the stability of the welding process (3) After the short-circuit process is over, the no-load voltage recovery speed is fast, so as to ignite the arc in time to avoid the occurrence of the arc phenomenon.

The main circuit of the inverter power supply now adopts IGBT device, which has small power loss and high efficiency, and another advantage is that its working frequency is high. The higher the operating frequency, the smaller the ripple of the loop output current and the faster the response speed, so the welder achieves better dynamic response characteristics. In order to regulate the energy output over a wide range in the inverter power supply, the ratio (or duty cycle) of the on-time and off-time of the IGBT trigger pulse must be adjustable. A high duty cycle outputs a higher power, while a lower duty cycle outputs a lower power. This adjustment method is called pulse width modulation (PWM). At present, almost all fully-controlled power switch inverter power supplies use PWM control circuits.

In order to achieve the ideal droplet transfer control, many scientific research institutions and power supply manufacturers have conducted in-depth research and development on this form of control. Nowadays, some excellent welding power supply manufacturers produce inverter welding power supplies that can meet various requirements, and are suitable for short-circuit transition welding, pulse welding, jet transition welding and high deposition rate welding.

2 Flexibility of welding power output characteristics

In the arc welding process, the welding power source acts as a power source, and the arc acts as a load for the welding power source, thereby forming a "power-arc" system. For normal soldering, the system must be stable, that is, the system maintains a long-term continuous arc discharge and maintains a static balance for a given arc voltage and current without external disturbances. Once the system is subjected to transient external disturbances, it will destroy the original static balance and cause changes in welding specifications. But when the interference disappears, the system can automatically reach a new stable balance, so that the welding specification is restored.

For silicon rectified power supplies, the output characteristics of the power supply are determined by hardware parameters such as the component network, and once determined, it is difficult to change. The setting of the output parameters is done by selecting the resistor and capacitor parameters. In this way, the tolerance and drift of the resistance parameter in the analog system will inevitably lead to changes in the controller parameters and affect the stability of the output characteristics.

In the "digital" era, powerful new digital signal processors (DSPs) are used in inverter welding power supplies. The new welding power source truly realizes the flexibility and multi-functional integration of output characteristics, and has the advantages of high control precision, good system stability and good product consistency. For this new inverter welding power supply, the output characteristics are achieved by changing the software. This means that the same set of hardware circuits can achieve different output forms to meet different welding process requirements. Different control strategies and control parameters can be selected for different welding methods and different wire materials and diameters, so that the welding machine can achieve multi-functional integration, and the process effect of each welding process can be greatly improved. When using analog control, we often select the current waveform according to the principle of taking into account the entire process interval, which will inevitably result in unsatisfactory process results in some sections. At present, the new technology of the new welding power supply transitions from E2PROM to FLASH ROM in the memory selection, and the online FLASH ROM programming function is also added in the circuit design. Therefore, the control program upgrade or online debugging modification of this new welding power supply can be completed simply by FLASH ROM programming through the universal RS232 serial communication interface. The new welding power supply has greater stability. In digital control, the signal processing or control algorithm is implemented by software addition/subtraction, multiplication/division, etc., so its stability and consistency are also well guaranteed.

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