IGBT trong biến tần: cấu tạo, chức năng và cách kiểm tra

Inverter technology is increasingly modern, leading to increasing requirements for accuracy and flexibility in controlling and controlling motor speed. The birth of IGBT has solved two important problems: fast switching and high current load of inverters in industrial environments, contributing to improving the overall reliability and efficiency of the VFD system. In this article, Trường Chu Văn An will introduce to you the structure, functions as well as how to check IGBT in the inverter.

What is IGBT in inverter?

IGBT (abbreviation for Insulated Gate Bipolar Transistor), also known as Insulated Gate Bipolar Transistor, is a high-power semiconductor device, combining the advantages of fast switching of MOSFET and high current tolerance, low saturation voltage of BJT (bipolar transistor). Thanks to that, IGBT is the ideal choice for applications that require fast switching, especially inverters.

More specifically, IGBT plays an important role in AC drives with the ability to adjust the power supplied to electric motors, thereby controlling motor speed and torque.

The presence of IGBT significantly improves the performance of the inverter, allowing precise control and control of motor operation by adjusting the frequency and voltage of the power supply, while saving energy and minimizing heat generation. IGBT also contributes to reducing the weight and size of the inverter, giving this device a more optimal design than many other power switching devices.

Structure and operating principle of IGBT in inverter

Structurally, an inverter IGBT usually consists of 3 poles and 4 stacked semiconductor layers.

3 main poles:

• Gate pole (G): The control pole, isolated from the semiconductor layer by a layer of silicon dioxide (SiO2), is capable of regulating voltage without requiring large currents.
• Extreme autumn (C): Attached to the outer P+ semiconductor layer.
• Emitting pole (E): Attached to the inner N+ semiconductor layer.

4 semiconductor layers:

• Class P+ (Collector): Outermost layer, highest doping concentration.
• Class N− (Drift region): Middle layer, lower doping concentration.
• Class P (Base): Located near the E pole.
• Class N+ (Emitter): Located close to the E pole, the doping concentration is high.

IGBT’s integrated module design facilitates installation and thermal management, ensuring high reliability in voltage regulation.

In addition, some symmetric IGBTs (PT-IGBT (Punch Through IGBT)) also have an additional N+ buffer layer. This padding layer is not available in the Asymmetric IGBT (NPT-IGBT (Non-Punch Through IGBT) series).

Regarding the working principle, through Pulse Width Modulation (PWM) technique, the IGBT in the inverter is turned on/off in sequence to create an output signal similar to the sine wave of the motor. This signal is then used to control motor speed and torque.

The specific operating principle of IGBT in the inverter is as follows:

• OFF state: When there is no voltage applied to terminal G, the IGBT is in a locked state, meaning it does not conduct electricity.
• ON state: When the G terminal of the IGBT is placed at a positive voltage, an electric field will be created, acting as a “channel” allowing electrons to freely move between the C and E terminals. The IGBT is now like a closed switch, allowing current to flow.

The role of IGBT in inverter

The IGBT in the inverter has the main role of converting DC current into AC current with the appropriate frequency and voltage to supply to the motor. Specifically, the role of this department is expressed as follows:

Inverter function

After the input AC power source is rectified into DC power, the system of IGBTs in the inverter circuit will begin the reverse conversion function. Through Pulse Width Modulation (PWM), IGBT generates pulses of different widths from the DC bus, then filters it so that the output voltage has a shape similar to a sine wave, suitable for motor operating requirements. During this process, the IGBT takes on the role of an electronic switch with the ability to convert DC to AC with adjustable frequency and amplitude.

Adjust engine speed and torque

With fast switching capabilities, IGBT inverters help adjust the desired output voltage and frequency, thereby controlling the speed and torque of the motor.

IGBT’s fast switching ability helps the inverter to accurately adjust frequency and output voltage, thereby controlling the speed and torque of the motor. The higher the output frequency, the faster the motor rotates. At the same time, IGBT also helps maintain a constant voltage-to-frequency ratio, helping the motor operate smoothly and efficiently.

Improve conversion efficiency

As a more advanced technology than BJT and MOSFET, IGBT in inverters meets the requirements of higher current and voltage, suitable for harsh applications in heavy industry.

In addition, IGBT’s fast switching ability also minimizes energy loss when switching, contributing to improving the system’s conversion efficiency.

With the above important roles, IGBT in inverters is specially applied to:

• Engine control: This device allows detailed and precise adjustment of motor speed, suitable for applications such as conveyors, conveyors or pumping systems.
• Energy management: Through adjusting the motor speed, the inverter IGBT is capable of managing the motor’s power consumption, ensuring the motor only uses energy when needed.
• Heavy industrial applications: With the ability to handle large voltage and current effectively, IGBT inverters are the ideal solution for the mining, iron and steel production industries…

See more: What is an inverter circuit? Structure and operating principle

Advantages and disadvantages of IGBT in inverters

Advantages of IGBT inverter

• High performance and reliability, enabling precise motor speed control, enhancing the performance of connected machines.
• Reduce energy consumption and operating costs.
• High switching frequency reduces the size of passive components (inductors, capacitors…), helping the inverter to have a smaller and lighter design, suitable for limited installation spaces.
• IGBT has a long lifespan, reducing regular maintenance and repair costs.
• IGBT maintains performance even when subjected to high thermal loads, thereby preventing overheating of the inverter, ensuring continuous machine operation.

Disadvantages of IGBT in inverter

• Operating frequency is lower than MOSFET so it is not suitable for devices operating at high frequency (from 400V or more).
• It is easy to lose voltage when operating at high frequencies, affecting other devices.
• The cost of IGBT is quite high, leading to an increase in the cost of the inverter.

How to measure and test IGBT in inverter

To test the inverter quickly and accurately, the simplest and most common method is to use a multimeter. The steps to measure and check whether the inverter IGBT is alive or dead are performed according to the steps below:

Discharge voltage

It is necessary to discharge the voltage between the 3 terminals G – C – E of the inverter so that the IGBT no longer has voltage applied to the G terminal. This step is carried out in turn: Connect the black measuring lead of the meter to terminal C or E, the red measuring probe connects to terminal G.

Check OFF status

The purpose of this step is to determine whether the IGBT has a short circuit or electric leakage.

Adjust the multimeter to Diode or resistance measurement mode at the highest scale. Then place the red measuring lead on terminal C, the black measuring probe on terminal E. The multimeter needle will not come up at this time.

Continue to reverse the measuring rod, the red rod corresponds to pole E and the black rod corresponds to pole C. At that time, the clock needle will move up close to the maximum line. If the result is between 0 and 1, it proves that the inverter IGBT is working well.

Check ON status

This is the most important step to evaluate the condition of IGBT. First, you need to activate terminal G by placing the black stick on terminal E. Use your finger to touch both terminal G and terminal C at the same time to create a small voltage to activate terminal G.

After activating terminal G, it is necessary to place the red rod on terminal C and the black rod on terminal E. If the meter shows the needle or shows low resistance, the IGBT has been activated. Conversely, if the meter shows infinite resistance, it is likely that terminal G is damaged.

Measure again after locking the IGBT

To lock the G terminal, you need to touch your finger to the G and E terminals at the same time to discharge all the charge that just excited the G terminal. Next, re-measure the IGBT by: placing the red measuring probe connected to the C terminal and the black probe connected to the E terminal.

If the meter shows infinite resistance, the IGBT is locked. If the meter still shows low resistance, the IGBT is likely damaged and cannot be locked.

Check the semiconductor layer between the IGBT terminals

The semiconductor layer of IGBT has a structure quite similar to the semiconductor layer of MOSFET but has an additional collector junction layer, forming a pnp structure, different from the nn structure of MOSFET.

Measure the IGBT conduction layer

• Place the red rod connected to terminal E, the black rod connected to terminal C. If the meter displays the voltage as acbV, the voltage difference between the two semiconductor terminals is still good.
• Place the red rod on terminal C, the black rod on terminal E, if the meter displays 0V, it proves that the conduction layer is stable.

See more: Comparison of inverter and soft starter: Advantages and disadvantages

Some questions about IGBT in inverters

Question 1: How many types of IGBTs are there in inverters?

Reply: IGBT inverters are divided into 3 basic types, including:

• Standard IGBT: The most popular type, capable of balancing switching speed and voltage handling, suitable for general-purpose inverters.
• IGBT penetration (PT): This line has a higher switching speed but has a lower voltage level.
• Non-penetrating IGBT (NPT): Suitable for applications requiring high voltage. However, the switching speed is somewhat limited.

Question 2: What should we pay attention to when choosing IGBT for inverter?

Reply: IGBT directly affects the switching ability of the inverter, so the IGBT selection process requires attention to a number of issues:

• Voltage and current requirements: Each IGBT can withstand specific voltage and current levels. It is necessary to determine these two parameters in specific applications to select the appropriate IGBT.
• Switching frequency requirements: If your system requires high switching frequency, penetrating IGBT is the most suitable choice.
• Thermal performance: IGBTs can operate at high temperatures, but it is necessary to ensure that the device can withstand the thermal limits of the application.
• Compatibility: Ensure the IGBT is compatible with other system components such as control circuits and protection mechanisms.

Question 3: Compare IGBT in inverter with silicon controlled rectifier (SCR)?

Reply: Although SCR can withstand high current and voltage, it is limited in switching ability. This component cannot be turned off on its own, but requires the support of an auxiliary circuit breaker or waits when the current drops to 0. In addition, SCR also causes large power loss and generates a lot of heat.

In terms of current and voltage tolerance, IGBT inverters are usually one power range lower than SCRs. In return, IGBT has the great advantage of fast switching and can be actively turned on/off by voltage signal. IGBT causes less energy loss, thereby increasing the switching efficiency of the inverter.

Above is the important information about IGBT in inverters that we have compiled and introduced to you. Other knowledge related to inverters, you can learn more at: https://etinco.vn/tin-tuc/kien-thuc/kien-thuc-bien-tan/.