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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1. Use analog circuit to measure the temperature of IGBT module NTC temperature sensor: This basic method is based on a voltage divider as a thermistor, as shown in the figure below:
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IGBT parallel connection can be divided into two categories: "hard parallel connection" and "bridge arm parallel connection". (1) "Hard parallel connection" means that the emitter and collector of IGBT are directly connected together, as shown in the lower left figure; (2) "Bridge arm parallel connection" means that the AC output terminals of the IGBT bridge arms are connected together through a current-sharing reactance (the inductance has a certain value), as shown in the lower right figure;
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Factors affecting static current sharing 1. The resistance component of the DC bus side connection point of the parallel IGBT needs to be as symmetrical as possible; 2. There is a difference between the Vce(sat) of the IGBT chip and the VF of the diode chip, so try to use products from the same batch. 3. The temperature difference between the IGBT modules needs to be considered when designing the mechanical structure and air duct; 4. Differences in magnetic fields where IGBT modules are located; 5. The difference in gate voltage Vge.
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Heteroepitaxy is an advanced crystal growth technology. It refers to the process of growing a thin film or epitaxial layer with a different crystal structure or chemical composition from the substrate material on a specific substrate material, that is: on a specific substrate material. A substrate of material grows on another material.
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