1. Main Applications of IGBTs IGBTs are advanced third-generation power modules, operating at frequencies from 1-20kHz. They are primarily used in the main circuit inverters of frequency converters and all inverter circuits, i.e., DC/AC conversion. Examples include electric vehicles, servo controllers, UPS, switching power supplies, chopper power supplies, and trolleybuses. Having been around for over ten years, they have almost completely replaced other power devices, such as SCRs, GTOs, GTRs, MOSFETs, and bipolar Darlington transistors. In low-frequency applications with power up to 1MW, a single element can achieve a voltage of 4.0kV (PT structure) – 6.5kV (NPT structure) and a current of up to 1.5kA, making them a relatively ideal power module. This is because the third-generation IGBT module features voltage-controlled operation, high input impedance, low drive power, simple control circuitry, low switching losses, fast switching speed, high operating frequency, and large component capacity. Essentially, it is a composite power device, integrating the advantages of bipolar power transistors and power MOSFETs. Furthermore, advanced processing technology results in low on-state saturation voltage and high switching frequency (up to 20kHz). These two significant characteristics, coupled with Siemens' recent introduction of a low-saturation voltage drop (2.2V) NPT-IGBT, further enhance its performance. Toshiba, Fuji, IR, and Motorola are also developing new varieties. The development trend of IGBTs aims for high withstand voltage, high current, high speed, low voltage drop, high reliability, and low cost, particularly in the application of high-voltage frequency converters. Simplifying the main circuit, reducing the number of components, improving reliability, lowering manufacturing costs, and simplifying debugging are all closely related to IGBTs. Therefore, major component companies worldwide are actively researching and developing IGBTs, and breakthroughs are expected within the next 2-3 years. Currently, voltage-type HV-IGBTs, IGCTs, and current-type SGCTs are available for high-voltage frequency converters. 2. Turn-off Surge Voltage The instantaneous voltage generated when the current flowing through the IGBT is interrupted during turn-off. It is due to the inductive load (L) of the motor and the leakage inductance (Lp) in the circuit. The total value L*p = L + Lp, then Vp* = Vce + Vp, and Vp = L*p di/dt. In extreme cases, this will generate Vp*Vces (rated voltage), causing damage to the device. Therefore, it is necessary to minimize the inductance (L). The leakage inductance (Lp) in the circuit is determined by the device manufacturing structure, such as reasonable distribution, shortening the wire length, and appropriately widening and thickening. 3. Recovery Surge Voltage The freewheeling diode provides a path for the inductive current in the upper arm freewheeling diode when the lower arm of the IGBT is turned off (at this time, it is forward conducting). It will reduce the di/dt value and prevent overvoltage. However, when the lower arm is turned on, the freewheeling diode reverses and becomes negative and turns off. The current will drop to zero. Due to the presence of Lp, a surge voltage will be generated, preventing the current from decreasing. Especially when a hard recovery diode is used, a high reverse recovery di/dt value will be generated, which can lead to a very high instantaneous voltage. 4. Buffer Circuit Forms This circuit is used to control surge voltage interruption and recovery, reducing module switching losses and transient overvoltage values. Although IGBTs have a strong safe operating area, transient voltage values ​​need to be controlled. The buffer circuit can discharge through the IGBT in each switching cycle, thus generating some power consumption, but ensuring safe operation. [align=center]Figure 1 General IGBT Buffer Circuit[/align] Figure 1-A consists of only a low-inductance capacitor. For small-power single-unit modules, it can be connected between C and E; for six-in-one package modules, it can be connected between P and N. It is effective, simple, low-cost, and suitable for small-power devices in reducing transient voltage. Figure 1-B uses a fast diode, which can clamp transient voltage, thereby suppressing parasitic inductance with the bus and producing a damped oscillation. RC is the time constant, set to 1/3 of the switching period (i.e., τ = T/3 = 1/3fz), suitable for medium-power devices. Figure 1-C is similar to Figure B, but with a smaller loop inductance. It is directly connected to the collector and emitter of each IGBT, and using a small RCD (resistive-capacitive diode) works well to suppress parasitic oscillations in the snubber circuit. Specific recommended values ​​for high-power devices are shown in Table 1. 5. Reducing the Inductance of Power Circuits The energy of surge voltage is proportional to 1/2LpI, therefore reducing Lp is crucial. Multi-layered positive and negative cross-bracing, wide-biased stacked busbars can be used, including connections between IGBTs and with large capacitors. For example, the busbars of high-power frequency converters use this method to reduce the inductance of power circuits. 6. Grounding Loop Forms When the gate G drive or control signal shares a current path with the main current, it can lead to a grounding loop. This may result in a potential value of several volts that should be grounded, causing devices that are supposed to be off to conduct, leading to malfunctions. Therefore, in high-power IGBT applications, or when di/dt is very high, the above phenomenon is unlikely to occur. For devices with different capacities, the following three circuits are shown in Figure 2. [align=center] Figure 2 Avoiding Ground Loop Noise[/align] Figure 2-A has a common ground loop potential problem. Its gate circuit ground wire is connected to the main circuit (I) bus. It is suitable for <100A six-in-one packaged devices, but still requires a high reverse bias voltage of 5-15V. Figure 2-B uses an independent gate power supply for the lower arm device, employing an auxiliary emitter and a nearby drive power supply coupling capacitor, which can best suppress ground loop noise. It is suitable for modules below 200A. Figure 2-C uses separate isolated power supplies for each gate drive circuit in the lower arm to eliminate ground loop noise problems, with better results. It is suitable for modules ≥300A. 7 IGBT Losses This refers to the power loss of the IGBT during the turn-on or turn-off transition process. When the PWM signal frequency is greater than 5kHz, switching losses become very significant. Therefore, correctly selecting the carrier frequency value is crucial when using a frequency converter. For specific selection instructions, please refer to the article "The Basis for Correctly Selecting the Carrier Frequency Value of a Frequency Converter," written by Zhang Xuanzheng, published in the 7th issue of "Frequency Converter World" magazine in 2001. In short, the carrier frequency is related to the switching losses of the components, the heat generated by the components, the waveform of the current, the magnitude of interference, and the noise and vibration of the motor. Therefore, correctly selecting the carrier frequency value based on the motor power and site conditions is a key aspect of frequency converter commissioning. 8. Regarding Junction Temperature: The maximum rated junction temperature of the IGBT module chip is 150℃. This temperature must not be exceeded under any operating conditions, otherwise thermal breakdown will occur, causing damage. Generally, a margin should be allowed. Under the worst conditions, the junction temperature is limited to below 125℃. However, monitoring the junction temperature inside the chip is difficult. Therefore, the IGBT modules in the inverter are equipped with a temperature control switch on the surface of the heat sink, with a value between 80-85℃. When this temperature is reached, the overheat protection will activate, automatically shutting down the system to ensure the safety of the IGBT. Thermistors are also used. 9. Heat Sink Installation: The IGBT module is directly fixed to the heat sink, and the screws must be evenly tightened. The heat sink surface must be flat and clean, with a flatness ≤150μm. Ideally, a torque wrench should be used to ensure a surface finish ≤6μm. Thermal and conductive paste should be applied to the interface, with a uniform coating thickness of approximately 150μm. 10. Reasonable Parameter Selection: A principle for parameter selection is to leave appropriate margins to ensure long-term, reliable, and safe operation. The device is safest under the following conditions: operating voltage ≤50%-60%, junction temperature ≤70-80%. Limiting factors: A) Under turn-off or overload conditions, the IC must be in the safe operating area, i.e., less than twice the rated current value; B) The IGBT peak current is determined based on 200% overload and 120% current ripple rate; C) The junction temperature must be <150℃ under all conditions, including overload. Refer to Table 2 for specific selection. A) A turn-on voltage of 15V ± 10% of the positive gate voltage can achieve complete saturation and minimize switching losses. When <12V, conduction losses increase; when >20V, overcurrent and short-circuit protection are difficult to achieve. B) A turn-off bias of -5 to -15V aims to ensure effective turn-off even in the event of noise and to reduce turn-off losses. The optimal value is approximately -10V. C) IGBTs are not suitable for linear operation; only during extremely fast switching can a lower gate voltage of 3-11V be applied. D. Saturation voltage drop directly affects conduction losses and junction temperature; a lower value is desirable, but this increases the price. Saturation voltage drop ranges from 1.7V to 4.05V in increments of 0.25V-0.3V, with ten levels from C to M. 11. Gate Resistor Rg [align=center]Figure 3 Typical IGBT Gate Drive Circuit[/align] It is connected in series in the gate circuit, as shown in Figure 3. Its purpose is to improve the steepness of the control pulse leading and trailing edges and prevent oscillations, reducing the spike value of the IGBT collector voltage. Since the IGBT's turn-on or turn-off is achieved through the charging and discharging of the gate circuit, the value of Rg has a significant impact on the dynamic characteristics, as detailed below: In cases of high DC bus voltage, it may be necessary to use the buffer circuit shown in Figure IC for these high-current dual-unit modules. In this case, the recommended combination given for the unit modules can be selected. Table 1 Recommended Buffer Circuit and Power Circuit Designs Table 2 IGBT Modules Suitable for AC 460/480V Line Voltage Applications Table 3 Requirements for OC Protection Settings of AC 400V Motor Rated Values ​​Table 4 Series Resistance of the Gate Used A. Small Rg value – Faster charging and discharging, reducing switching time and switching losses, enhancing operational robustness, and avoiding misleading turn-on due to dv/dt. The drawback is lower noise tolerance, susceptibility to parasitic oscillations, increased di/dt during turn-on, and increased surge voltage during FWD recovery. Specific values ​​can be found in Table 4. B. Large Rg value – Performance is the opposite of the above. Gate drive wiring has a significant impact on preventing potential oscillations, slowing gate voltage rise, reducing noise losses, lowering gate voltage, or reducing the efficiency of gate protection circuits. Important considerations include: A. Minimizing the parasitic inductance between the driver output stage and the IGBT. B. The driver board and shielded gate drive circuit must be placed correctly to prevent inductive coupling between the power circuit and the control circuit. C. Use auxiliary emitter terminals to connect the gate drive circuit. D. When a direct connection between the driver PCB board and the IGBT control terminals is not possible, it is recommended to use twisted-pair cable (2 rpm, less than 3 cm long) or strip cable, or coaxial cable. E. The gate clamping protection circuit must be wired with low inductance and placed as close as possible to the gate and emitter control terminals of the IGBT module. F. Since IGBT switching involves mutual potential changes, the lines on the PCB board should not be too close together. Excessive dv/dt will generate coupling noise due to parasitic capacitance. If wiring cannot avoid crossing or balancing, a shielding layer must be used for protection. G. Reduce the parasitic capacitance between components to avoid coupling noise. H. Use an optocoupler to isolate the gate drive signal. Its minimum common-mode rejection ratio (CMRR) should be 10.000V/μS. In addition to the above, to prevent high-voltage spikes in the gate circuit, a resistor Rge is typically connected in parallel between the G and E terminals, followed by two reverse-connected Zener diodes to ensure more reliable, safe, and efficient operation. The Rge value should be between 1000-5000 ohms (see Figure 4). 12 dv/dt and Short-Circuit Protection When the IGBT is turned off, the gate must be reverse-biased. Due to the high gate impedance, this current increases Vge. Under severe conditions, if the current reaches the threshold voltage, the IGBT will turn on, causing both upper and lower arms to turn on simultaneously, resulting in a short circuit in each phase of the bridge arm. To prevent this, the following points should be noted: A. Apply a sufficient negative gate voltage of at least -5V in the off-state. B. Rg should be a low value during turn-off (see Table 4). C. The inductance Lg of the gate circuit should be minimized. When a short circuit occurs, the IGBT must remain within the short-circuit safe operating area. Methods include: A) Current sensor; B) Undersaturation type, but the short-circuit to turn-off time must be measurable within 10μs. Three common methods are: A) Controlled turn-off—reducing the gate voltage (with segmented or ramp-down reduction) to increase channel resistance; B) Vge clamping—for low-power devices below 18V, a Zener diode can be used for clamping between the gate and emitter; C) Reducing tw—shortening the short-circuit duration, but this will increase the turn-off current. 13. Precautions for use: A) The gate must be insulated from any conductive area to prevent electrostatic discharge and breakdown. Therefore, conductive foam should be placed between the gate and emitter during packaging to short-circuit them. Never touch the gate directly with your fingers during assembly until the gate pin is permanently connected. B) Tighten the main circuit with screws. Use a through-hole connector for the control gate (G), avoiding soldering as much as possible. C. Anti-static measures such as using a grounded workbench, grounded ground, and grounded wrist strap should be taken during loading and unloading. D. When measuring with the instrument, connect a 100Ω resistor in series with the G terminal. E. Installation should be performed when there is no power supply. F. When soldering the G terminal, the soldering iron must be powered off and grounded; a constant-temperature soldering iron is most suitable. For manual soldering, the temperature should be 260℃±5℃, the time (10±1) seconds, and rosin flux. For wave soldering, the PCB board should be preheated to 80℃—105℃, and immersed in the soldering solution at 245℃ for 3-4 seconds, using rosin flux. 14. IGBT Series and Parallel Connections : A. Parallel connection aims to increase the operating current, but the devices must be matched, with a Vce difference of < 0.3V between each device. Current reduction is also necessary: ​​10% Ic reduction for 600V, 15% Ic reduction for 1200-1400V, and 20% Ic reduction for 1700V. These values ​​apply to modules ≥200A, and modules with equal or close saturation voltage drops must be selected. The gate control circuits must be separate, addressing both static and dynamic current sharing, and their temperatures must be similar to avoid affecting current distribution balance, as IGBTs are negative resistance devices. B. Series connection aims to increase the operating voltage, with higher requirements than parallel connection, mainly due to static and dynamic voltage sharing issues, especially dynamic voltage sharing, which is quite challenging. Chengdu Jialing Company's capacitive motherboard technology (1+N) with only series dynamic voltage clamping and voltage sharing is already in the industrial experimental stage. If dynamic voltage equalization is poor, it will cause unequal Vce voltages on each device in the series arm, resulting in an overvoltage affecting the entire series in the same arm and causing breakdown. C. In short, series and parallel connections of IGBTs should be avoided as much as possible. Do not attempt to solve high voltage and high current problems by connecting low-voltage, low-current devices in series or parallel; this approach often backfires, increasing the number of devices, decreasing reliability, and complicating the circuit. Exercise caution only when absolutely necessary. Currently, the voltage or current of a single IGBT can basically meet user needs. With the development of technology and circuit improvements, higher voltage and higher current power devices will inevitably emerge. 15 Intelligent IPM Module Intelligent IPM modules have been on the market for ten years, and currently, 110KW modules are available for frequency converters. It is an advanced hybrid integrated power device that integrates IGBTs, drive circuits, and protection circuits. Therefore, it features high speed, high efficiency, low power consumption, optimized gate drive and protection circuits, undervoltage lockout, and superior overcurrent and short-circuit protection using current sensing chips, greatly improving overall reliability. IPMs come in four circuit configurations: single-transistor package (H), dual-transistor package (D), six-in-one package (C), and seven-in-one package (R). Due to their low conduction and switching losses, IPMs allow for smaller heat sinks, thus reducing overall size. They also offer self-protection capabilities, reducing the likelihood of damage under overload conditions during development and use. It is therefore natural that most inverters below 55kW, both domestically and internationally, use IPM modules. With a junction temperature of 125℃ and a gate control voltage between 13.5-16.5V, they can operate safely. IPMs offer comprehensive protection, including short-circuit protection (SC), overcurrent protection (OC), undervoltage protection (UV), overheat protection (OT), and overvoltage protection (OV). Table 3 provides a selection reference. 16. PIM (Power Integrated Module) – A comprehensive integrated power device specifically designed for use in the main circuit of inverters, introduced in the last five years. For example, the 2.5-66A 1200V series and 4-75A 600V series produced by TYCO in Munich, Germany, include a single-phase/three-phase input rectifier bridge, a braking unit (or a PFC power factor correction unit), six IGBT units, and NTC temperature monitoring. However, they do not include the drive circuit. Some specialized manufacturers, such as Fuji, integrate rectification, braking, IGBT, protection, drive, and control into a single module, making it more convenient, safe, and reliable to use. Its characteristics are: A) Integration of all components and circuits; B) Small size, high power, low loss, and relatively stable; C) Optimized internal wiring to reduce parasitic noise; D) Complete self-protection circuitry, providing fast and sensitive protection; E) The only drawback is that if one component fails, the entire module will be damaged, unlike separate modules where only the damaged component needs to be replaced. 17. The Sequence of Applying Vge and Vce to IGBTs As is well known, the electronic components used in the inverter's internal measurement circuits, protection circuits, drive circuits, conversion circuits, isolation circuits, CPU, gate circuits, etc., such as TTL, CMOS, operational amplifiers, optocouplers, etc., are all supplied with different voltage values ​​by the switching power supply. For IGBTs, Vge is provided by the switching power supply at ±5-15V, but Vce is provided by the DC power supply (PN) after filtering by the three-phase rectifier bridge in the main circuit. To ensure the safe use of the IGBT and prevent mis-conduction, the sequence of applying Vge and Vce is required. Vge must be applied first and allowed to stabilize (cutoff bias -15V, conduction bias +15V) before applying Vce. Never apply Vce (several hundred or one thousand volts) when the gate is floating or unstable, because the coupling capacitance between the gate and collector can mis-conduct the IGBT, resulting in excessively high dv/dt causing electrical breakdown and damage. To avoid the above phenomenon, a delay circuit method is generally used to delay Vce by about 0.2 seconds to Vge, which greatly improves the safety and reliability of use, especially for medium and high power devices. 18 Conclusion The overall performance of IGBT is very superior and cannot be replaced by other power devices. Therefore, it has become the main device in DC/AC inverter circuits today, which is also right. Its weakness is that it has low resistance to overvoltage, overheating, impact, and interference. Therefore, it is very important to correctly select the device capacity and have a completely strict protection circuit. It is very important to correctly select various parameter values ​​and protection values ​​according to the product technical performance specifications. Do not be careless, otherwise there will be endless troubles and economic losses. As long as it is carefully designed and operated in a standardized manner, it can ensure the safety and reliability of use. This is also undoubtedly true. Main reference materials: [1] IGBT application manuals of Mitsubishi, Fuji, Hitachi, Toshiba and NEC of Japan. [2] IGBT application manuals of Siemens and Semikron of Germany. [3] Product introduction of TYCO GmbH, Munich, Germany. [4] Selection guide for speed control inverters and supporting equipment. [5] Practical power supply technology manual - power supply component manual. [6] Special article on IGBT related components in Inverter World. [7] Article by Zhang Xuanzheng in Inverter World, Issue 7, 2001, "The basis for the correct selection of inverter carrier frequency value". [8] User manual for Jialing GY series high voltage inverter products.