Working principle of IGBT series welding machine

The basic working principle of inverter welding machine:

The inverter welding machine is mainly an inverter arc welding power source generated by an inverter, also known as an arc welding inverter, which is a new type of welding power source. It converts the industrial frequency (50Hz) AC power into DC power after being rectified and filtered by a rectifier, and then inverts it into a medium frequency AC power of several kHz to tens of kHz through high-power switching electronic components (thyristor SCR, transistor GTR, field effect tube MOSFET or IGBT), and at the same time, it is reduced to a voltage of tens of V suitable for welding through a transformer, and then rectified again and filtered by an inductor to output a fairly stable DC welding current.

The transformation sequence can be simply expressed as:

Industrial frequency AC (after rectification and filtering) → DC (after inversion) → medium frequency AC (step-down, rectification, filtering) → DC.

That is: AC→DC→AC→DC

Because the AC power after inverter step-down has high frequency, the inductive reactance is large, and the active power in the welding circuit will be greatly reduced. Therefore, it needs to be rectified again. This is the mechanism of the inverter welding machine commonly used at present.

Characteristics of inverter power supply: The basic characteristic of arc welding inverter is high operating frequency, which brings many advantages. Because the potential E of the transformer, whether it is the primary winding or the secondary winding, has the following relationship with the frequency f of the current, the magnetic flux density B, the cross-sectional area S of the core and the number of turns W of the winding: E=4.44fBSW

The terminal voltage U of the winding is approximately equal to E, that is:

U≈E=4.44fBSW

当U、B确定后，若提高f，则S减小，W减少，因此，变压器的重量和体积就可以大大减小。就能使整机的重量和体积显著减小。还有频率的提高及其他因素而带来了许多优点，与传统弧焊电源比较，其主要特点如下：

1. Small size, light weight, saving materials, easy to carry and move.

2. High efficiency and energy saving, the efficiency can reach 80%~90%, saving more than 1/3 of electricity compared with traditional welding machines.

3. Good dynamic characteristics, easy arc striking, stable arc, beautiful weld formation and little spatter.

4. Suitable for combination with robots to form an automatic welding production system.

5. One machine can be used for multiple purposes to complete various welding and cutting processes.

Working principle of IGBT series welding machine

1. Comparison of power switch tubes

Commonly used power switches include thyristors, IGBTs, field effect tubes, etc. Among them, the switching frequency of thyristors (silicon controlled rectifiers) is as low as about 1000 times per second, which is generally not suitable for high-frequency switching circuits.

1. Characteristics of effect tube:

The outstanding advantage of field effect tubes lies in their extremely high switching frequency. They can switch more than 500,000 times per second. Their voltage resistance is generally above 500V and their temperature resistance is 150℃ (tube core). In addition, their on-resistance and tube loss are low. They are ideal switching devices, especially suitable for use as switching devices in high-frequency circuits.

However, the working current of the field effect tube is relatively small, ranging from about 20A at the highest to about 9A at the lowest, which limits the maximum current in the circuit. In addition, due to the packaging form of the field effect tube, the creepage distance of its pins (the surface distance between a conductor and another conductor) is relatively small, and it is easy to be broken down under high environmental voltage, causing conduction between the pins and damaging the machine or endangering personal safety.

2. Characteristics of IGBT:

IGBT is a bipolar insulated effect transistor, and its symbol and equivalent circuit diagram are shown in Figure 11.1. Its switching frequency is between 20KHZ and 30KHZ. However, it can pass large current (more than 100A), and because of the large spacing between the external package pins and the large creepage distance, it can resist the influence of environmental high voltage and is safe and reliable.

1. Characteristics of Field Effect Transistor Inverter Welding Machine

Due to the outstanding advantages of field effect tubes, when field effect tubes are used as switching devices of inverters, the switching frequency can be designed to be very high to improve conversion efficiency and save costs (using high-frequency transformers to reduce the size of the welding machine, making the welding machine smaller and more convenient to use. (For a comparison between high-frequency transformers and low-frequency transformers, see Chapter 3 "Block Diagram of Inverter Arc Welding Power Supply".

However, both arc welding machines and cutting machines require very high working currents. Using one field effect tube cannot meet the current requirements of the welding machine, so multiple field effect tubes are usually connected in parallel to increase the output current of the welding machine power supply. This not only increases the cost, but also reduces the stability and reliability of the circuit.

2. Characteristics of IGBT welding machine

IGBT welding machine refers to arc welding machine that uses IGBT as inverter switching device. Due to the low switching frequency and large current of IGBT, the main transformer, filter, energy storage capacitor, reactor and other electronic devices used in the welding machine are very different from those of field effect tube welding machine. Not only the volume is larger, but also various technical parameters have changed.

3. Working principle of IGBT welding machine:

The working principle of the half-bridge inverter circuit is shown in Figure 11.2

Working principle:

①tl time: switch K1 is turned on, K2 is turned off, the current direction is as shown in the figure ①, the power supply supplies power to the main transformer T and charges the capacitor C2.

②t2 time: switches K1 and K2 are both cut off, and no current flows through the negative electrode (dead zone).

③t3 time: switch K1 is turned off, K2 is turned on, and capacitor C2 discharges to the load.

④T4 time: switches K1 and K2 are both turned off, forming a dead zone. This process is repeated to obtain the current shown in Figure 11.3 on the load, achieving the purpose of inversion.

2. Working principle of IGBT welding machine

① Power supply:

Like the welding machine with field effect tube as inverter switch, the welding machine power is supplied by the mains, which is supplied to the inverter after rectification and filtering.

② Inversion:

Since the operating current of IGBT is large, a half-bridge inverter can be used, with IGBT as a switch, and its opening and closing are controlled by a drive signal.

③ Generation of driving signal:

The drive signal is still in the form of processing the pulse width modulator output signal. The phases of the two drive signals are staggered (with a dead zone) to prevent the two switches from being turned on at the same time and causing excessive current to damage the switch. The midpoint of the drive signal also sinks a certain amplitude to prevent interference from causing the switch to be turned on by mistake.

④ Protection circuit:

IGBT welding machines are also equipped with over-current, over-voltage, over-heat protection, etc. Some models also have current cut-off to ensure the safety of the welding machine and personnel. Its working principle is similar to that of field effect tube welding machines.

Inversion and rectification are two opposite concepts. Rectification is the process of converting AC into DC, while inversion is the process of changing DC into AC. The arc welding power source using inverter technology is called an inverter welder. The inverter process requires high-power electronic switching devices. The inverter welder that uses insulated gate bipolar transistor IGBT as the switching device is called an IGBT inverter welder.

The working process of the inverter welding machine is as follows: the three-phase or single-phase industrial frequency AC power is rectified and filtered to obtain a smoother DC power. The inverter circuit composed of IGBT converts the DC power into AC power of tens of kHz. After the main transformer steps down the voltage, it is rectified and filtered to obtain a stable DC output welding current.

Advantages of inverter welding machine: Since the inverter working frequency is very high, the core cross-sectional area and coil turns of the main transformer are greatly reduced. Therefore, the inverter welding machine can save metal materials to a large extent, reduce the overall size and weight, and greatly reduce power loss. More importantly, the inverter welding machine can adjust the output current within microseconds, so it can achieve the ideal control process required by the welding process and obtain satisfactory welding results.