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Understanding and Controlling IGBTs: Essential Knowledge for Power Electronics Engineers

Posted on: 08/05/2024

IGBT, or Insulated Gate Bipolar Transistor, is a crucial power semiconductor device widely used in applications such as high-power DC converters, AC inverters, and power transmission. For an electronics engineer, understanding the principles and control methods of IGBTs is essential.

Reverse Conduction Capability

Firstly, it’s important to understand the structure and working principle of an IGBT. An IGBT combines a PN junction and a MOSFET. The PN junction is key to controlling the conduction of the IGBT. When the PN junction is forward-biased, current can flow through it, allowing the IGBT to conduct. Conversely, when the PN junction is reverse-biased, the IGBT cannot conduct. Therefore, a standard IGBT does not have reverse conduction capability.

In practical applications, the reverse conduction capability is usually provided by a parallel freewheeling diode. This diode allows current to flow in the reverse direction when the IGBT is turned off, thus protecting the device and the circuit.

Controlling IGBT Conduction

There are two primary methods to control an IGBT:

  1. Voltage Control (VGE): By adjusting the voltage between the gate and the emitter (VGE), we can control the conduction and cutoff of the IGBT. When VGE exceeds the threshold voltage, the IGBT turns on; when VGE falls below the threshold voltage, the IGBT turns off. This control method is similar to that of a MOSFET.
  2. Current Control (ICE): While the conduction and cutoff of an IGBT are mainly controlled by VGE, the current flowing through the IGBT (ICE) must also be monitored and limited to prevent overcurrent damage. This current control is usually implemented by external circuits, such as current sensing and protection circuits.

Practical Considerations

In practical operation, controlling the IGBT’s conduction and cutoff through pulse signals is common. For instance, in Pulse Width Modulation (PWM) control, the IGBT is switched on and off at high speeds to achieve precise control of voltage and current. It is crucial to ensure that the current and voltage of the IGBT remain within safe limits to ensure stable operation. Additionally, protection circuits such as overcurrent protection and overvoltage protection are typically designed to safeguard the IGBT. These circuits can quickly disconnect the circuit when abnormal conditions are detected, preventing damage.

Advantages and Applications of IGBT

IGBTs offer several advantages, including high efficiency, high power density, and ease of control, making them indispensable in modern power electronics. Their flexible control characteristics and reliability make them perform exceptionally well in various applications. As power electronics technology continues to advance, the use of IGBTs will become more widespread, and their market prospects are very promising.

Conclusion

In summary, IGBTs are crucial devices in the power electronics field. Understanding their working principles and proper control methods is vital for achieving efficient and safe power conversion. By mastering the use of IGBTs, engineers can design and implement more effective and reliable power electronic systems.