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Short-Circuit Failure Detection in Series-Connected IGBTs for Reliability Improvements

Javidi, Pourya | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56835 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Kaboli, Shahriyar
  7. Abstract:
  8. In high-voltage power electronics systems where the supply voltage exceeds the maximum voltage these devices can withstand, series-connected IGBTs with TO-247 packaging and simultaneous gate command circuitry are used to create a high-voltage switch with an on and off time equivalent to a single IGBT. By considering voltage protection circuits for the series IGBTs, the large supply voltage is approximately evenly divided among the series switches. The resulting high-voltage switch has smaller conduction and switching losses compared to single high-voltage switches, has a lower finished price, and its turn-on time is much shorter due to their smaller gate-emitter junction capacitance $C_{\mathrm{GE}}$ , making them more attractive in many high-voltage applications. In addition, due to the inherent substitution of this structure, the reliability of the resulting high-voltage switch from series-connected individual switches is higher than that of high-voltage modules. However, like any other power semiconductor device, IGBT switches can fail. The failure of these switches is usually divided into two categories: short-circuit and open-circuit failures. If we can liken any power electronic switch to a controllable impedance by the gate terminal voltage with a dominant real component, then after a failure occurs, the IGBT switches will be similar to a small (short-circuit) or very large (open-circuit) impedance in terms of their collector-emitter voltage characteristic relative to the collector current, and their controllability will be lost. In the series structure, the occurrence of a short-circuit failure is of special importance because after this failure occurs, the switch loses its voltage withstand capability and the large system voltage is distributed over fewer series switches, and therefore the divided voltage on the remaining healthy switches will increase significantly as the number of failures increases. This voltage increase, if less than the maximum withstand of the switch, can reduce the reliability of the healthy switches in the long term due to the higher voltage stress. If the number of failures reaches a certain critical level, the divided voltage on the healthy switches will be greater than their maximum withstands, leading to a cascading failure of the remaining healthy switches. Therefore, the ability to detect short-circuit failures in series switches is of special importance to prevent cascading and consecutive failures of these switches, control gate circuits, and protect them, and by monitoring the failure status of each of the switches along with replacement, enhance their reliability. In this thesis, solutions for detecting short-circuit failures in the structure of series switches are examined and two final solutions are proposed that make it possible to detect short-circuit failures economically. The first method is based on the structure of the simultaneous gate command of the series switches and makes failure detection possible by continuously reading and monitoring the maximum current of the pulse transformer used to command the gates of the switches. The second solution, relying on a systemic view with the analysis of the electrical power consumed by the series switches and their protection circuits by turning them on in a specific sequence, makes it possible to detect short-circuit failures. In addition, in order to achieve the objectives of the thesis, a considerable number of IGBT switches with short-circuit failures have been analyzed experimentally and practically to better understand their interesting electrical characteristics, which have been very little analyzed in the literature and history of this research. Then, through simulation results and experimental tests, the correctness of the proposed methods is presented
  9. Keywords:
  10. Reliability ; Fault Detection ; Short Circuit Current ; Power Supply ; Simultaneous Gate-Command Circuitry ; Insulated Gate Bipolar Transistors (IGBTs) ; Voltage Stress ; Short-Circuit Failure In Semiconductor Switches

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