IGBT stands for Insulated Gate Bipolar Transistor, which is a device composed of MOSFET and bipolar transistor. The input is a MOSFET, and the output is a PNP transistor, combining the advantages of both devices. It features low driving power and high switching speed of MOSFET low saturation voltage and high capacity of bipolar transistors. Its frequency characteristics lie between MOSFET and power transistors and can operate normally within the range of several kHz.
When a positive drive voltage is applied between the gate and emitter of the IGBT, the MOSFET conducts, placing the PNP transistor in a low-resistance state, causing it to conduct. If the voltage between the gate and emitter of the IGBT is 0V, the MOSFET is off, cutting off the base current of the PNP transistor, and causing it to turn off. Like MOSFETs, IGBTs are also voltage-controlled devices, and applying a DC voltage of several volts between the gate and emitter results in only microampere-level leakage current, essentially consuming no power.
I. Common Tests for IGBT Modules
IGBT modules are energy-saving, easy to install and maintain, and have stable heat dissipation. Most of the products sold in the market are modular products, and IGBT usually refers to IGBT modules. As the core device of energy conversion and transmission, known as the “CPU” of power electronic devices, IGBTs are widely used in fields such as rail transit, smart grids, aerospace, electric vehicles, and new energy equipment due to the promotion of energy-saving and environmental protection concepts.
When handling an IGBT module, we should first conduct a routine test. Here’s how:
1. Polarity Determination
Set the multimeter to the R×1KΩ range. Measure with the multimeter; if one electrode shows infinite resistance with the other two electrodes and the same result after switching the test leads, it is the gate (G). Measure the other two electrodes; if infinite resistance is shown initially and lower resistance after switching leads, the electrode connected to the red lead is the collector (C), and the one connected to the black lead is the emitter (E).
2. Testing Functionality
Set the multimeter to the R×10KΩ range. Connect the black lead to the IGBT collector (C) and the red lead to the emitter (E). The multimeter should show zero. Touch the gate (G) and collector (C) simultaneously with your fingers; the IGBT should turn on, and the multimeter needle should move to a lower resistance value and hold. Then touch the gate (G) and emitter (E) simultaneously; the IGBT should turn off, and the multimeter needle should return to zero. This indicates the IGBT is good.
3. Testing Precautions
Any pointer-type multimeter can be used to test IGBTs. Ensure the multimeter is set to the R×10KΩ range, as lower ranges won’t provide sufficient voltage to turn on the IGBT, making it impossible to determine functionality. This method can also be used to test power MOSFETs.
The “inverter” in speed control systems is a complex electronic system susceptible to damage from electromagnetic interference. Continuous operation of industrial systems is crucial to avoid significant economic losses. In special applications such as automation and space systems, nuclear energy, and hazardous chemical plants, preventing inverter failure is essential to avoid catastrophic losses.
II. Common Issues and Solutions
Strictly speaking, any component in a control system composed of an inverter and motor can fail, but inverters are more prone to faults than motors. IGBTs frequently face capacitive or inductive load impacts, potentially causing damage. Causes of IGBT module damage include:
1. Overcurrent Damage
① Latch-up Effect
IGBTs have an internal parasitic thyristor. Within the specified drain current range, the positive bias of the NPN transistor isn’t sufficient to turn it on. When the drain current is high enough, it can turn on the NPN transistor, leading to the saturation of NPN or PNP transistors, activating the parasitic thyristor, causing the gate to lose control, and resulting in latch-up. This increases the collector current, leading to high power consumption and damage.
② Prolonged Overcurrent Operation
IGBT modules running with currents reaching or exceeding the reverse bias safe operating area (RBSOA) limit (due to selection errors or low safety factors) require immediate shutdown before reaching the RBSOA limit to protect the device.
③ Short Circuit Over-time (>10us)
IGBTs must be shut off within 10us if the current exceeds the short circuit safe operating area (SCSOA) limit, such as 4-5 times the rated current. If the voltage also exceeds the rated value, it needs to be shut off even faster.
2. Overvoltage and Static Damage
During shutdown, inductive components in the inverter circuit can generate spike voltages. If these exceed the IGBT’s maximum voltage rating, it can cause breakdown damage. Overvoltage protection usually involves snubber circuits or RCD structures. Voltage clamping, often using Zener diodes, can prevent collector-emitter overvoltage damage.
Dynamic gate voltage control can address high du/dt-induced collector-emitter overvoltage. However, in inductive loads, the rapid voltage rise during freewheeling diode recovery in a half-bridge structure can induce a high du/dt, generating a transient current through the Miller capacitance to the gate drive circuit, potentially causing false turn-on and bridge short-circuits.
3. Overheating Damage
Overheating occurs when the junction temperature exceeds the device’s maximum limit (typically 150°C for NPT technology). Ensure the junction temperature remains below this limit during operation.
4. Main Circuit Voltage Application in G-E Open-State
In an open state between the gate and emitter, applying main circuit voltage can inadvertently turn on the IGBT due to the reverse transfer capacitance charging the gate-emitter capacitance, causing damage. Avoid mechanical switch operations that leave the gate-emitter open with the main circuit voltage applied.
5. Mechanical Stress Damage
Strong external forces or vibrations on IGBT terminals can induce stress, leading to internal electrical connection damage. Secure printed circuit boards to prevent such issues during installation and operation.
These are common checks and troubleshooting methods for IGBT modules. Hope this helps anyone in need, and please feel free to critique or correct any inaccuracies!
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