Application of computer simulation technology in inverter welding power supply

Preface

The manufacturing of welding power supplies has a history of more than 100 years. After entering the 1960s, the emergence of silicon rectifier components, high-power transistors (GTR), field effect transistors ( MOSFET ), insulated gate bipolar transistors ( IGBT ) and other devices, the development of integrated circuit technology and control technology, has provided a broader space for the development of electronic welding power supplies, among which the most eye-catching is the inverter welding power supply.

The inverter welding power supply is small in size, light in weight, energy-saving and material-saving, and has good control performance, fast dynamic response, and is easy to achieve real-time control of the welding process. It has great potential advantages in performance. From a long-term perspective, the inverter welding power supply is the development direction of welding power supplies, and the development of foreign inverter welding machines also fully illustrates this point. At present, in industrially developed countries, manual arc welding, TIG welding, and MIG/MAG welding have widely adopted inverter power supplies. Several major welding machine manufacturers in the world have completed the serialization of inverter welding machine products and use this as one of the symbols of their technical level.

1 Development status of welding inverter power supply

Inverter power supply is called "tomorrow's power supply". Its application in welding equipment has brought revolutionary changes to the development of welding equipment. First, the inverter welding power supply saves 20-30% energy compared with the power frequency welding power supply, and the efficiency can reach 80-90%; secondly, the inverter welding power supply is small in size and light in weight. The weight of the whole machine is only 1/5-1/10 of the traditional power frequency rectifier welding power supply, reducing material consumption by 80-90%. In particular, the inverter welding power supply has the advantage of fast dynamic response speed. Its dynamic response speed is 2-3 orders of magnitude higher than that of the traditional power frequency rectifier welding power supply, which is conducive to the automation and intelligent control of the welding process. All these indicate that the inverter welding power supply has a wide range of application prospects and market potential. At present, among the arc welding machines of Panasonic Corporation and Osaka Transformer Company in Japan, the number of inverter welding machines exceeds 50. The number of inverter welding machines produced by major welding machine manufacturers in the United States has exceeded 30. The development speed of inverter welding power supplies in other industrially developed countries is also very fast.

The research and development of inverter welding machines in my country started in the late 1970s and began to develop in the 1980s. In 1982, Chengdu Electric Welding Machine Research Institute began to study thyristor inverter arc welding rectifiers, and in 1983 developed my country's first commercialized ZX7-250 inverter arc welding power supply, and passed the ministerial appraisal of the project. Subsequently, Tsinghua University, Harbin Institute of Technology, South China University of Technology and Times Company and other units have successively launched inverter welding machines using various switching elements. At present, my country's inverter welding machine power supply has formed 4 generations of products: the first generation is an inverter with thyristor SCR as the main power device; the second generation is a transistor inverter; the third generation is a field effect tube inverter; the fourth generation is an IGBT inverter, which has high inverter frequency, low saturation voltage drop, low power consumption, high efficiency, and no noise. Compared with the first three generations of inverters, it has more obvious advantages.

The broad prospects for the development of inverter welding machines have attracted many colleges and universities and research institutes. However, due to the combination of strong and weak currents in inverter welding power supplies, the use of traditional test methods in research and development not only consumes a lot of manpower, material resources and time, but also some problems are difficult to discover and solve by test methods. Therefore, new design methods and means are needed.

In recent years, the methods of circuit analysis and design have developed rapidly due to the use of computer simulation technology. Circuit design uses computer simulation technology to quickly simulate and analyze different design schemes, and after the circuit form is determined, the sensitivity analysis and tolerance analysis of the circuit component parameters are performed to optimize the component parameters and ensure the design quality. Therefore, the use of computer simulation technology in circuit design can greatly reduce manual labor, shorten the design cycle, and reduce design costs. At present, in the research of power electronic devices, more and more devices use computer simulation technology. For high-power welding inverter power supplies, their working environment and load conditions are very harsh, and the power devices used are very expensive, so the use of computer simulation technology in the design of welding inverter power supplies is more advantageous.

2 Computer simulation technology

2.1 Current status of computer simulation technology development

Computer simulation technology combines modern simulation technology with computer development. By establishing a mathematical model of the system, using computers as tools and numerical calculations as a means, it conducts experimental research on existing or imagined systems. In my country, since the mid-1950s, system simulation technology has been applied in cutting-edge fields such as aerospace, aviation, and military, and has achieved significant results. Since the early 1980s, with the widespread application of microcomputers, digital simulation technology has also been widely used in engineering and technical fields such as automatic control, electrical transmission, machinery manufacturing, shipbuilding, and chemical engineering.

Compared with traditional empirical methods, the advantages of computer simulation are: ① It can provide complete and detailed data on all relevant variables in the entire computer domain; ② No need to conduct system experiments; ③ It can predict the change process and final results of a specific process, so that people can have a deep understanding of the law of process change; ④ It is the only research method when measurement methods are difficult. In addition, digital simulation also has the advantages of high efficiency, high precision and difficult to conduct destructive or dangerous experimental research on actual systems. BR>2.2 Current status of power electronics simulation technology research

The application of simulation technology in power electronic circuits is a very important part of its many applications and has become an indispensable and important tool for conducting research in this area. In the design of power electronic circuits, computer simulation is mainly used to verify design solutions, predict system performance, discover potential problems of new products, and evaluate problem-solving methods. It mainly solves two problems, namely how to establish circuit equations and how to solve circuit equations.

Since the 1970s, the main analysis methods used in circuit simulation include: state variable method, node analysis method, improved node analysis method and state space average method, etc. These modeling methods have their own advantages and disadvantages and their own scope of use. When used in specific situations, the corresponding methods should be used to establish specific simulation models according to specific purposes.

For a switching converter, a highly nonlinear time-varying system, it is often very difficult to accurately analyze its spatial and dynamic performance. Establishing an accurate mathematical model has always been a difficult problem in the field of power electronics. Usually, only by assuming certain conditions and ignoring some minor factors can a mathematical model that is applicable within a certain range be obtained to help analyze and design circuits. There are usually two methods for modeling: ① Establish a physical-electrical model based on the physical laws of carrier motion inside the device; ② Establish an equivalent macro model based on the external behavior of the device.

In the past decade, many scholars at home and abroad have done a lot of work in the modeling of electromagnetic devices. The first problem that needs to be solved is to describe the magnetization characteristics of magnetic materials. Among them, the more practical models include the J-A model with clear physical meaning and the macro model constructed using the general component model. On the basis of the magnetic material model, the magnetic circuit model of the electromagnetic device can be determined by comprehensively applying the three major electromagnetic laws of Faraday, Ampere and Gauss. Then, according to the coupling principle of the circuit and the magnetic circuit, the circuit model of the electromagnetic device can be established.

In short, the modeling, theoretical analysis and computer simulation technology of control circuits are relatively mature, while the practical simulation models of power electronic devices and electromagnetic devices, especially the parameter acquisition technology, need to be further improved.

2.2 Commonly used circuit simulation software

Commonly used circuit simulation software include Pspice, Saber, Simplis and MATLAB. Power supply electronic simulation software is usually divided into two types: simulators that focus on circuits and simulators that focus on solving equations. PSPICE, Saber and MATLAB are representatives of the two types of simulators.

PSPICE is one of the earlier EDA software, launched by MICROSIM in 1985. In terms of circuit simulation, its function can be said to be the most powerful and is widely used in China. PSPICE6.2 is now widely used, working in Windows environment, occupying more than 20 megabytes of hard disk space. PSPICE can perform various circuit simulations, excitation establishment, temperature and noise analysis, analog control, waveform output, data output, and display analog and digital circuits in the same window at the same time. No matter which device or circuit is simulated, including IGBT , pulse width modulation circuit, analog/digital conversion, digital/analog conversion, etc., accurate simulation results can be obtained. For component modules that are not in the library, you can also edit them yourself.

MATLAB5.2 was launched by Mathworks in 1998. The newly added Power System Blockset (PSB) contains component models under certain usage conditions, including power system network components, motors, power electronic devices, control and measurement links, and three-phase component libraries. With the help of other module libraries or toolboxes, in the Simulink environment, power system simulation calculations can be performed, complex control method simulations can be realized, and the execution process of the simulation can be observed. The simulation results are stored in the MATLAB workspace using variables at the end of the simulation.

PSPICE and PSB simulation software each have their own application advantages, and their versions are constantly updated. PSB has now launched version 6.1. PSB is suitable for the simulation of medium-sized circuits and circuit simulation of variable/fixed step size simulation algorithms.

The powerful computing power of MATLAB/SIMULINK is very convenient for post-processing of simulation results. PSPICE is suitable for modeling at the component level of small-scale systems. If the system scale is too large, the simulation execution time will become very long.

3 Application status of computer simulation in welding inverter power supply

At present, computer simulation technology has been widely used in cutting-edge technology fields such as aviation, aerospace, and military, and has played a huge role. In the past few years, welding technology researchers began to introduce it into welding power supplies and achieved certain results, but the research is not very in-depth and there are not many literatures in this area.
From the existing literature, it can be seen that the application of simulation technology in arc welding inverters is relatively mature. The earliest research in this area was conducted by Huazhong University of Science and Technology. The National Natural Science Foundation project "Computer Simulation and Auxiliary Design of Arc Welding Inverter Power Supply Structure and Parameters" undertaken by it is a typical example of the application of simulation technology in welding equipment. With the help of powerful computers, it describes and studies the working process and dynamic response of each part and core component of the new generation of arc welding inverters through comprehensive, systematic and in-depth qualitative and quantitative analysis, develops inverter theory, solves the quality and reliability problems of domestic arc welding inverters, and then realizes the computer-aided optimization design of arc welding inverters, which improves the scientific and automated level of China's electromechanical product design.

There are generally two common arc welding inverter power supply simulation methods: one method is to establish models of each component in the circuit , and then connect them into a circuit for simulation. For example, the literature is based on the existing device model in PSPICE, first establishes a combined model of the insulated gate bipolar transistor ( IGBT ), and uses nonlinear capacitance to characterize the parasitic capacitance of the device. Then, using the established model, the two-terminal full-bridge zero voltage zero current (FB-B-ZVZCS-PWM) soft switching converter is simulated by computer, the switching performance of the device and the energy transmission performance of the converter are analyzed, and the simulation results are verified by experiments, which proves that computer simulation can be an effective means to study arc welding inverter power supply on the basis of establishing a suitable device model; another method is to simulate the entire inverter circuit as a whole. According to the characteristics of the dynamic process of the arc welding inverter power supply, computer simulation technology can be used to establish a nonlinear model of the control system to obtain a direct description of various dynamic processes, and simulation analysis can be performed to provide an effective means for studying the dynamic process of the output current of the arc welding inverter.

Simulation always involves parameter optimization. The literature focuses on the design of the dynamic process of the inverter main circuit, and discusses the design points of the power pulse transformer and its buffer circuit. It qualitatively and quantitatively explores the impact of device parameter changes on the dynamic process of the main circuit, and realizes computer-aided optimization design based on simulation. Shenzhen University R> In addition, relevant personnel have conducted in-depth research on the dynamic arc model of the arc welding inverter, successfully simulated the dynamic characteristic curve of the arc, and analyzed the organic connection between the arc dynamic characteristic curve and the pulse multi-fold curve. Since the stability of the arc is based on the stability of the controller, the stability on the driven characteristic diagram can calibrate the correctness of the power supply design.

The transformer is the heart of the welding machine and is a low-voltage, high-current power device. Its performance directly affects the welding quality of the welding machine. References: The computer-aided design system of the AC arc welding transformer was studied. The design of the arc welding transformer was divided into six parts for separate design, and then integrated together, that is, the total-division-total design scheme was adopted, which not only improved the calculation accuracy and speed, but also reduced the designer's labor intensity and reduced the design cost. In addition, for the circuit magnetic saturation and inverter subversion problems caused by transformer bias magnetism, the researchers proposed a solution to the problem by using a dual-loop feedback control method through the study of the magnetic saturation principle of the full-bridge inverter circuit transformer. After circuit design, simulation and waveform analysis, the feasibility and effectiveness of the scheme were proved from an experimental perspective.

Simulation technology has also been applied to inverter resistance welding machines. The main researchers in this field are Harbin Institute of Technology and some other research institutes and universities. They simulated and analyzed the circuits of inverter resistance welding machines and designed the circuits, thereby reducing the development cost and improving the efficiency of the welding machine. As for the application in other areas, it is relatively scattered and not very comprehensive, and there are not many of them now.

So overall, computer simulation technology is a new thing in the field of welding power supplies, and it will take time for it to develop further.

4 Existing problems and future development directions

From the previous introduction, it can be seen that after computer simulation technology was introduced into the field of welding power supply, it has developed rapidly and played a great role in the design of the main circuit structure of welding equipment and the optimization of parameters. It has greatly reduced the design cost, shortened the design cycle, improved the reliability of the product, and demonstrated its vigorous vitality. However, it is undeniable that due to the particularity of the welding power supply itself, the current combination with computer simulation technology still has the following problems:

(1) The welding power supply system is a highly nonlinear system that combines strong and weak electricity. The interaction between electricity and magnetism is very complex and difficult to understand. It is difficult to find a mathematical equation to describe such a system, so it is not easy to simulate it as a whole using a transfer function. Therefore, most existing simulations focus on the simulation of its specific internal circuit. In this way, it is not convenient to verify the overall effect of the simulated design system.

(2) The accuracy of the component model has a great impact on the final simulation results, so it is crucial to establish an accurate component model. The welding power supply circuit includes a large number of nonlinear high-power switching components and electromagnetic devices. As pointed out in the second part above, the modeling and parameter extraction of high-power components and electromagnetic components have always been difficult and need to be further improved. Therefore, if this bottleneck technology cannot be solved, it is obviously unrealistic to apply the simulated circuit to the actual circuit.

(3) The welding power supply is a key part of the welding machine, but if you want to develop a high-performance, high-reliability welding machine, other auxiliary parts such as the drive circuit and the protection circuit cannot be ignored. However, current simulation studies rarely treat them as a whole. Therefore, this aspect needs to be strengthened.

(4) There are many types of welding machines, including arc welding machines, resistance welding machines, laser welding machines, plasma welding machines, etc., which results in different main circuit parts of their welding power supplies. This brings up the issue of circuit selection when designing a specific power supply.

In conclusion, the author believes that the solution of the above four problems is related to whether the welding power supply simulation technology can be truly promoted, and how to solve these problems will be the research direction for a considerable period of time in the future. Once these problems are properly solved, it is not difficult to imagine its broad prospects in the future. We look forward to my country's welding equipment technology reaching the world's advanced level as soon as possible.