1. Introduction Power electronics technology plays an irreplaceable role in today's industrial sectors that urgently need energy conservation and emission reduction. IGBTs are increasingly becoming the preferred power switching devices for various main circuits in energy conversion and management applications such as frequency converters and high-power switching power supplies. Therefore, how to safely and reliably drive IGBTs has become a problem that more and more design engineers need to solve. In various main circuits using IGBTs, the high-power IGBT drive protection circuit acts as the terminal interface (interface) for weak current control of strong current. Due to its importance, this circuit can be studied, developed, and designed as a relatively independent "subsystem." High-power IGBT drive protection circuits have developed alongside IGBT technology. Currently, many mature high-power IGBT drive protection circuit products are available on the market, becoming the first choice for most design engineers; many engineers have also independently developed various dedicated high-power IGBT drive protection circuits according to the specific requirements of their circuits. This article classifies these high-power IGBT drive protection circuits, describes some of the functions that the circuit needs to achieve, and finally looks forward to the development of this circuit. Furthermore, the high-power IGBT drive protection circuit described in this article refers to applications where the DC bus voltage is in the range of 650V to 1000V and the AC effective value of the output current is in the range of 100A to 600A. 2. Classification of High-Power IGBT Drive Protection Circuits According to the functions that high-power IGBT drive protection circuits can perform, they can be classified into the following three types: single-function type, multi-function type, and full-function type. 2.1 Single-Function Type A single-function high-power IGBT drive protection circuit generally consists of an optocoupler and a power buffer, such as HCPL-3150, as shown in Figure 1. It converts the TTL/CMOS input level signal of ordinary control signals into IGBT gate drive output levels of ±10 volts, the amplitude of which depends on the isolation power supply. Figure 1 shows the block diagram and pinout of the HCPL-3150. Engineers can equip it with an isolation power supply circuit, dead-time control circuit, logic processing circuit, gate drive resistor, etc., to directly drive IGBTs, forming the simplest high-power IGBT drive and protection circuit. Alternatively, they can add some peripheral circuits to create a multi-functional driver. The biggest advantage of a single-function high-power IGBT drive and protection circuit is its flexibility and low cost. It can be applied to main circuits requiring a single IGBT, such as choppers and boosters, as well as to main circuits composed of multiple IGBTs, such as half-bridge, single-phase full-bridge, and three-phase full-bridge circuits. However, because it requires additional isolation power supply circuits and logic processing circuits, the development workload for design engineers is significant, which is also the biggest disadvantage of a single-function high-power IGBT drive and protection circuit. Here, the logic processing circuit generally refers to power-on sequence logic and various protection processing functions. Furthermore, drivers like the HCPL-3150 have limited driving capabilities, generally below 3A. Driving IGBTs above 600A requires a larger external power buffer circuit or other measures. 2.2 Multifunctional High-Power IGBT Driver Protection Circuits Besides directly driving IGBTs, multifunctional high-power IGBT driver protection circuits also offer comprehensive protection functions, such as HCPL-316J and M57962, as shown in Figures 2 and 3. These typically employ hybrid thick-film packaging technology or integrated packaging technology, and are directly compatible with CMOS/TTL levels. Engineers generally only need to add isolation power supply circuits, dead-time control circuits, logic processing circuits, and gate drive resistors to create a relatively complete high-power IGBT driver protection circuit. Drivers like M57962 and HCPL-316J inherently possess comprehensive protection functions and high integration. Their greatest advantage is simplifying the developer's work, and they offer high reliability, making them very suitable for multi-channel drive applications. However, due to their limited driving capability, driving higher-power IGBTs requires a larger external power buffer circuit. Drivers such as M57962 and HCPL-316J generally provide soft-shutdown functionality. This function is crucial when protecting the IGBT from overcurrent and short-circuit conditions, preventing the IGBT's NPNP four-layer structure from entering the "thyristor latch-up" state. Furthermore, drivers like the HCPL-316J also feature undervoltage lockout protection, greatly simplifying the designer's work. 2.3 Full-Function Type In addition to comprehensive protection functions, all full-function high-power IGBT drive protection circuits invariably include a DC/DC isolated power supply, such as 2SD315AI (Concept), SKYPER™ PRO (Semikron), and 2ED300C17-S (Eupec). These are all internationally renowned full-function drivers. 3 Functions of High-Power IGBT Drive Protection Circuits Depending on different application needs, high-power IGBT drive protection circuits can be composed of multiple functions forming a relatively complete independent subsystem. The main task of this system is to perform the "interface" function: 3.1 Isolation Function. Due to the level difference between the control circuit that generates the waveform logic and the main power circuit, and the very high electromagnetic interference in the main power circuit, signal transmission isolation and power supply isolation are required. There are two signal isolation methods: optocoupler isolation and pulse transformer isolation. The advantage of optocoupler isolation is its simple conversion circuit and ease of application. Since the rise and fall delays are on the order of approximately 500ns, it is suitable for low-frequency applications. If fault feedback to the main control system is required, another optocoupler is needed. For ease of use, there are also products that integrate these two optocouplers into one package, such as HCPL-316J. Currently, the maximum operating isolation voltage VIORM for optocoupler isolation on the market is around 3500V. The conversion circuit for pulse transformer isolation is relatively complex, generally requiring the use of dedicated integrated circuits. However, due to its high operating speed, it is suitable for high-frequency applications, and fault feedback does not require additional windings, making the isolation channel relatively simple. Provided space permits, transformer isolation can be achieved to a very high level due to improvements in winding technology. Furthermore, some applications requiring dynamic isolation demand very high dv/dt withstand voltages in the isolation circuits, which can reach levels exceeding 75kV/μs using pulse transformer isolation. Power supply isolation typically employs non-grounded DC/DC converters, whose transformer isolation withstand voltage is generally more than three times the bus voltage. The secondary side of the converter must be able to provide both positive and negative power. 3.2 Dead-Time Isolation Function Driving The setting of dead-time isolation (see the shaded area in Figure 7) is crucial for half-bridge and full-bridge main circuits. It is generally implemented using an R-C circuit. The advantages of the R-C circuit are its simplicity and strong anti-interference capability; the disadvantages are its susceptibility to temperature fluctuations, higher cost, requirement of valuable PCB board space, and relatively large dead-time adjustment interval. Addressing these shortcomings of the R-C circuit, many users with development capabilities prefer to use a "digital" method to obtain the dead time. Its biggest advantage is good temperature stability; since the adjustment step is only related to the clock signal frequency, it can be very precise, facilitating algorithm and main circuit system optimization. 3.3 Power Buffering Function For IGBTs with a rated output current exceeding 100A, although they are field-controlled devices with high-impedance inputs, the presence of parasitic capacitance and the Miller effect necessitates the input or output of large currents (ranging from hundreds of milliamps to tens of amperes) to the IGBT input terminal within a short time (microseconds or submicroseconds), depending on the parameters of the IGBT and the main circuit. Therefore, ordinary logic circuits and logic buffer circuits are insufficient for this power capacity, requiring specially designed power buffer circuits. These power buffer circuits typically employ totem-pole output stages. Many products use bipolar devices such as the M57962L, while others use unipolar devices such as the 2SD315AI, and still others use hybrid devices, with the upper transistor being a bipolar device and the lower transistor a unipolar device such as the HCIPL-316J. To meet the requirement of instantaneously generating and sinking tens of amperes, the selection and placement of decoupling capacitors are extremely important. Generally, monolithic capacitors with good high-frequency characteristics are chosen, and they should be placed as close as possible to the totem pole during PCB layout. The power supply capacity of the power buffer stage is also very important, depending on the gate charge or gate capacitance parameters of the IGBT and the operating frequency of the main circuit. The power buffer stage circuit is shown in Figure 8. Its isolation withstand voltage level is equivalent to the withstand voltage level requirement of the signal transmission circuit. 3.4 Detection and Protection Functions 3.4.1 Overcurrent Detection and Protection Generally, the indirect voltage method is used. When an IGBT experiences an overcurrent, the Vce saturation voltage drop increases. Therefore, by comparing the detected Vce saturation voltage drop when the IGBT is turned on with the set threshold, it can be determined whether an overcurrent has occurred. In order to improve the anti-interference capability, many reference settings and comparison methods have emerged to avoid frequent "hiccups" or even shutdowns in the power main circuit. In addition, how to safely turn off one or more parallel IGBTs that are experiencing overcurrent also needs to be carefully considered. Currently, most methods use soft turn-off to prevent the IGBT from entering a "lock-up" state. 3.4.2 Undervoltage Detection and Protection Under normal circumstances, an IGBT gate voltage Vge of 15V is required for the IGBT to enter deep saturation. If Vge is below 13V, the excessively high forward voltage drop between the collector and emitter (CE) at high current will cause the IGBT chip temperature to rise sharply. When the gate voltage is below 10V, the IGBT will operate in the linear region and will quickly burn out due to overheating. Therefore, undervoltage detection of Vge is necessary. This function is integrated on the secondary side of full-featured drivers such as the 2ED300C17-S and SKYPER™ PRO. 3.4.3 Temperature Detection and Protection Some IGBT modules manufactured by certain companies also integrate temperature sensors. By simply connecting the signal from this temperature sensor to the corresponding detection circuit of the driver, the driver can detect the IGBT temperature. Because the sensor is placed near the IGBT chip, it can more accurately reflect the actual temperature of the IGBT chip, thus providing more reliable protection for the IGBT module. 3.4.4 Logic processing of protection function Once any of the above faults occurs in the IGBT module, it needs to enter the protection state. Therefore, the logic processing of the protection function is the most critical part and the most difficult part to design. It is usually developed by the design engineer himself. Its processing principle is: when a certain IGBT fails, the protection logic processing is required to: (1) not shut down as much as possible; (2) prevent the accident from escalating further; (3) distinguish between true and false alarm signals. This requires the use of a combination of software and hardware design to realize "intelligent protection logic processing". Different systems require different management and protection logic processing designs. The general measures are: first, safely shut down the "problem IGBT", and then determine whether more IGBTs need to be shut down according to the system requirements, until the system stops. At the same time, each step is required to set a suitable delay in order to filter out false signals. 3.5 Short pulse suppression function During the transmission of the drive signal, some short pulses, also called "glitch", will appear on the drive signal due to interference, calculation errors and other reasons; if the driver performs the corresponding IGBT switching according to these short pulses, the output waveform will deteriorate, so such short pulses must be suppressed. 4 Technical outlook 4.1 The gate drive voltage has been increased. Currently, IGBTs are generally driven by a +15V voltage source. Some researchers have proposed developing a constant current source drive method, believing it can overcome the Miller capacitance effect of IGBTs and make IGBT conduction more reliable. The IGBT turn-off voltage has increased from the initial 0V to around -7V, and -15V is commonly used at low frequencies. 4.2 Currently, most high-power IGBT drive protection circuits use hard turn-off during normal operation, only employing soft turn-off in case of overcurrent. Under inductive load conditions, after the IGBT turns off, a freewheeling diode will inevitably conduct to maintain current continuity. This generates a voltage spike on the parasitic inductance of the power bus: Δv = L × di/dt. Besides the influence of the parasitic inductance L and the magnitude of the turn-off current, a faster hard turn-off (i.e., a smaller dt) results in a higher voltage spike Δv. For high-power IGBTs used at lower frequencies, where currents are in the hundreds of amperes, pulse-by-pulse soft turn-off significantly reduces the voltage spike Δv, greatly minimizing interference and improving system reliability. Some IGBT manufacturers are also developing IGBT chips with soft turn-off characteristics. 4.3 Overcurrent Detection Protection Threshold (Reference Baseline) Setting Methods: Currently, most high-power IGBT drive protection circuits have only one overcurrent detection protection threshold, typically set between 7V and 9V. To prevent false alarms, several different threshold setting methods have emerged. Variable Threshold Setting Method: During the period when the IGBT is transitioning from the off state to the saturation state (approximately a few microseconds to a dozen microseconds), the protection threshold can be reduced from 15V (or higher) to the standard setting value according to a certain curve, avoiding false alarms caused by disturbances during this period. Multi-Threshold Setting Method: To better suit actual operating conditions and reduce downtime, multi-threshold protection can be used. For example, when the IGBT's saturation voltage drop reaches the first threshold, the gate voltage is reduced; only when a higher second threshold is reached is the IGBT completely shut down. 4.4 Closer to the Driven Target: Currently, different high-power IGBT drive protection circuits have been developed for various IGBT applications, such as high-voltage frequency converters, UPS, and inverter welding machines. These drivers share similar principles but are more tailored to their respective driven targets. 4.5 Both high-power IGBT drive protection circuits and IPMs are developing in parallel across different power domains. IPMs integrate drive circuits and only require control signals to operate, primarily used in low-to-medium power applications; while high-power IGBT drive protection circuits are generally used in high-power applications to drive high-power IGBTs. With the continuous advancement and development of IGBT manufacturing processes, silicon wafer technology, and drive technology, both high-power IGBT drive protection circuits and IPMs are developing in parallel within their respective power domains. 5. Limitations on the Development of High-Power IGBT Drive Protection Circuits Cost is the biggest limitation to the development of high-power IGBT drive protection circuits. A good high-power IGBT drive protection circuit faces a wide range of complex problems to solve, while the reliability requirements are extremely high. Therefore, cost factors greatly limit the development of full-featured high-power IGBT drive protection circuits, while moderately priced multi-functional high-power IGBT drive protection circuits are the preferred choice for most engineers. For engineers willing to invest in direct current sampling in the main circuit, single-function drive circuits are their preferred option. 6. Conclusion The development of high-power IGBT drive protection technology is entirely influenced by the development of IGBTs. With the further development of semiconductor technology, the emergence of new devices and even new types of IGBTs, as well as new main circuit topologies, novel drive protection technologies will emerge.