During the month-long online external exchange course, I have learned a lot from Professor Francesco Lannuzzo and Professor Arijit Banerjee. At the same time, I searched for relevant reference materials about the reliability of power‐modules gate drivers introduced by Professor Francesco Lannuzzo to read, and briefly summarized a summary report. And the report is as below.
Overview
The key to the research about reliability improvement for power‐modules gate drivers is Insulated Gate Bipolar Transistors (IGBTs). As the working conditions of electrical apparatus becomes more complex, the demanding of higher reliability for IGBTs requires further studies. According to research, semiconductor and soldering failures in device modules account for 34% of failures in a converter system [1]. Therefore, it is necessary to perfect fault detection mechanisms and discover more ways to improve reliability of the IGBTs by ascending reliability of gate drivers.
Gate drivers are usually adopted for IGBT modules, and they are significant interfaces between the modules and microcontrollers. With the increasing switching frequency, switching losses can be seriously influenced by the power circuit and gate driver. Recently, a circuit was proposed to achieve quick turn on and turn off transition times to reduce switching loss and conduction loss in power MOSFETs, the proposed current source gate driver behaves like a nearly constant current source, and the result is that the turn on and turn off times decrease significantly and more importantly, the rise and fall times decrease significantly, which decreases switching loss [2]. With these advantages, this sort of circuit is applied in the gate drivers now. Nowadays, following the power‐cycling operating principles, the fault detection by gate driver is the fastest and most affordable way to perform fault diagnosis on packaged IGBT modules, which helps to ascend the reliability of gate drivers.
Therefore, in this summary report, I mainly discuss about the fault detection and protection methods, as well as the power‐cycling operating principles and standards to follow in the process of strengthening the reliability for the gate drivers.
Fault detection and protection methods
In the online course, the professor briefly introduced four typical fault detection and protection circuits, and I collected the specific information about these circuits after class.
There are four most common types of IGBT fault detection circuits. Each of them is based on a different measurement in the circuit such as collector voltage.
The first detection circuit is the desaturation detection, which is based on the collector voltage. In this circuit, a sensing diode connected to the collector of the IGBT detects the increase of the collector voltage to ensure whether the device is in a fault condition.
The second detection circuit is based on the collector current measured by a current mirror. We can find out the fault current by measuring the voltage drop across a known resistor created by the mirror current.
The third type of detection circuit is based on the change of the gate voltage is sensed. The collector-emitter voltage will change under fault conditions. A current will be applied to the gate resistance through the collector-gate capacitance, changing the gate voltage and tell us whether there is a fault condition.
The fourth also the last technique is based on the induced voltage across the stray inductance between the Kelvin emitter and the power emitter. Collector current change can be detected by measuring the induced voltage. As the induced voltage from a fault current lasts much longer than the one from normal switching, the fault can be detected quickly [3].
Among these various faults, short-circuit operation seems to be the most familiar and serious failure in IGBTs.
The first way which is most commercial to solve short-circuit operation is to measure the on-state voltage drop. During the short-circuit fault, the short-circuit current will rapidly increase, and the collector voltage will also increase. Once the collector voltage is higher than a specific value, the IGBT can be regarded as short-circuit. And in this case, the collector voltage will be reduced to limit the short-circuit current. [4]
Another way to solve the problem is to measure the voltage across the inductance between the power-emitter and the auxiliary-emitter. In this method, we modulate the gate-signal, reduces the gate emitter voltage in order to limit the short circuit current and allows the semiconductor to be operated in the safe operation area.
We can detect the failures precisely by using various types of IGBT fault detection circuits, also we protect the circuits from short-circuit operation by using the methods above, which make it feasible for us to perfect the reliability of the functioning of IGBTs as well as the gate drivers.
Power‐cycling operating principles and standards
Reliability assessment is primarily a study of failures and includes two aspects: where would the failures occur and when would the failures occur. We can make more accurate assumptions about parameters such as the time of failure by constructing mathematical models, like Weibull distribution. And all of these follows the principles of power-cycling operating.
Wear testing of power IGBT and SiC modules is also an important aspect of power-cycling operating principles. The objects to be tested include MW-Scale IGBT modules, molded modules, SiC MOSFETs and other components.
At the same time, there are many power-cycling standards to estimate reliability calculation for electronic components and systems. Among them, FIDES standards are proposed by AIRBUS France, Eurocopter and other six companies. The first aim of the FIDES project was to find a new reliability assessment method for electronic components. The global aim is to find a replacement to the old reference. The second aim was to write a reliability engineering guide in order to provide engineering process and tools to improve reliability in the development of new electronic systems. As a result, these standards are important references for the reliability analysis of IGBTs, gate drivers and many other electrical components. [6] Other power‐cycling operating standards include IEC standards, ECPE Guideline, AEC and VDE.
Conclusion
In summary, by applying the methods of fault detection and protection and following the power‐cycling operating principles and standards, we can achieve the improvement in the reliability of power‐modules gate drivers more easily, which has a significant influence to people’s daily lives.
After a month of study, I have not only learnt more professional knowledge from the professor’s lectures, but also enhanced my ability to find literature and extract useful information, which is invaluable to me.
Sources
[1] M. Ma, B. Ji, J. Han, J. Wang, M. Zhan and N. Xiang, “In-situ health monitoring of IGBT modules of an on-line medium-voltage inverter system using industrial Internet of Things,” in CSEE Journal of Power and Energy Systems, vol. 6, no. 3, pp. 638-648, Sept. 2020, doi: 10.17775/CSEEJPES.2019.01670.
[2] W. Eberle, Z. Zhang, Y. -F. Liu and P. C. Sen, “A Current Source Gate Driver Achieving Switching Loss Savings and Gate Energy Recovery at 1-MHz,” in IEEE Transactions on Power Electronics, vol. 23, no. 2, pp. 678-691, March 2008, doi: 10.1109/TPEL.2007.915769.
[3] F. Huang and F. Flett, “IGBT Fault Protection Based on di/dt Feedback Control,” 2007 IEEE Power Electronics Specialists Conference, 2007, pp. 1478-1484, doi: 10.1109/PESC.2007.4342213.
[4] Haoze Luo, Francesco Iannuzzo, Paula Diaz Reigosa, Frede Blaabjerg, Wuhua Li, Xiangning He, Modern IGBT gate driving methods for enhancing reliability of high-power converters — An overview, Microelectronics Reliability, Volume 58, 2016, Pages 141-150, ISSN 0026-2714
[5] I. Lizama, R. Alvarez, S. Bernet and M. Wagner, “A new method for fast short circuit protection of IGBTs,” IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society, 2014, pp. 1072-1076, doi: 10.1109/IECON.2014.7048635.
[6] FIDES Project. (2006). FIDES Guide Website. https://www.fides-reliability.org/en