The shutdown sequence of the IGBT module three-level circuit when it fails In the three-level circuit with a 1-shaped diode clamp, when a short circuit fault or overcurrent fault occurs, the traditional way to shut down the IGBT is that the driver that detects the fault transmits the fault information to the controller, and then the controller shuts down the outer tube first, and then the inner tube. The reason for this specific shutdown sequence is: 1. If the inner tube is turned off first by mistake, the inner tube IGBT will bear the entire bus voltage, so the inner tube will be severely over-voltage and immediately damaged; 2. If the outer tube is turned off first, the voltage of the outer tube will be clamped at half the bus voltage, and there will be no overvoltage, and then the inner tube will be turned off, and the inner tube will be safe. The timing relationship of the traditional shutdown sequence when the three-level circuit fails:
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With the development of power devices, sine wave pulse width modulation (SPWM) technology has been widely used. SPWM control is to chop DC power into a pulse sequence with equal amplitude and width changing according to the sine law within one cycle of the inverter outputting AC power. The width of the pulse sequence is a discrete pulse that changes with the amplitude of the sine wave. After filtering, the sine wave AC power is obtained.
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Regarding the design method of dead time, the formula TD'=TD-(t3+t4)+(t1+t2) is transformed to TD=TD'+(t3+t4)-(t1+t2)=TD'+(t3-t1)+(t4-t2). The rest is how to define the delay of the driver board (t1, t3) and the IGBT delay (t2, t4). The design method is divided into these two parts, the dead time of the IGBT part and the dead time of the HIC part. (1) Dead time of the IGBT part ① Collection of error data of IGBT switching time and calculation of maximum error data Based on the IGBT data of each company, calculate the error data of IGBT switching time (Tj=25℃). Based on σ and X±4σ, calculate X±4σ of each IGBT. (Maximum error) The following is the σ value of Fuji IGBT for reference. ○600V series σ=0.041 (maximum)
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In electronic components (semiconductor modules), the material that separates the live parts from the base is called insulating material. In high-power semiconductor components, ceramic is often used as the base, which is a high-performance insulator.
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When the IGBT is turned off, the collector current has a high rate of decrease, especially in the case of a short-circuit fault. If no soft-off measures are taken, its critical current decrease rate will reach thousands of amperes per microsecond.
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1. Short-circuit protection circuit with increasing UCE when detecting short circuit Figure 5-14 shows a protection circuit based on the principle that UCE increases when IGBT is overcurrent. The circuit uses the IGBT dedicated driver EXB841. The internal circuit of EXB841 can well complete the gate voltage reduction and soft shutdown functions, and has an internal delay function to eliminate false operations caused by interference. If a short circuit occurs, UCE containing IGBT overcurrent information is not directly sent to the IGBT collector voltage monitoring pin ⑥ of EXB841, but quickly turns off the fast recovery diode VD1, so that the U+ voltage of the comparator IC1 (LM339) is greater than the U- voltage, and the comparator outputs a high level, which is sent to the ⑧ pin of EXB841 by VD1, starting the gate voltage reduction and soft shutdown circuit in the internal circuit of EXB841, and the low-speed cut-off circuit slowly turns off the IGBT. This not only avoids the collector current spike from damaging the IGBT, but also completes the IGBT short-circuit protection. The characteristics of this circuit are that it eliminates the difference in shutdown speed caused by the different forward voltage drop of VD1 with different currents, improves the accuracy of current detection, and directly utilizes the gate voltage reduction and soft shutdown functions in the internal circuit of EXB841, so the overall circuit is simple and reliable.
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