Electro-Thermal Modelling and Lifetime Evaluation of Power MOSFETs and Converters
- Publication Type:
- Thesis
- Issue Date:
- 2022
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Due to the ongoing pursuit of high-density power supplies, thermal management has become one of the most critical issues to consider for stable and efficient operation. Therefore, this thesis implements a series of thermally related investigations.
Firstly, two electro-thermal modelling techniques are proposed for a converter. Significant efforts have been made in developing electro-thermal models (ETMs) for components individually. However, very few have considered building an ETM for a whole converter to make it more realistic in terms of converter design. Hence, in this thesis, an ETM and an electro-thermal averaged model are proposed for a boost converter as examples. Experimental results illustrate that both the solutions have an improved electrical performance estimation and fairly accurate temperature prediction.
Secondly, a concise but comprehensive MOSFET model that enables electro-thermal modelling, aging, and lifetime estimation on an LTspice® circuit simulator is proposed. This work is motivated by the fact that MOSFETs are relatively less reliable, and their aging impacts are not considered in most reported works. Based on these concerns, this model is proposed. The reported result verifies the accelerated aging trend of a MOSFET in the long-term mission profile simulation, which agrees with the theory. Moreover, the fast simulation speed indicates that the model is a good simulation/analytical tool to implement reliability assessment.
Thirdly, a circuit-based rainflow counting algorithm is elaborated aiming to improve the thermal cycle counting accuracy for the MOSFET model proposed above. The rainflow counting algorithm is gaining popularity for its low relative error in fatigue analysis, however, its offline operation limits the device under study in considering other parameters. This work proposes to tackle the issue and integrate it into a circuit simulator. Results show that the method improves the accuracy, with an averaged error of 3.5% over that of the half-cycle counting which is 24.4% under different loads, and it can be improved still further.
Finally, thermal performances and reliabilities of Wye (Y)-and Delta (∆)-connected 5-level cascaded H-bridge converter-based three-phase systems are investigated. It is due to the most recent studies have only compared the electrical power balancing capability of these two systems. This work verifies that even though the ∆-connection can handle more severely unbalanced power, it will not only lead to an unequalled stress distribution among phases but may also overstress devices. However, the Y-configuration does not have this issue. Consequently, there is a trade-off when selecting the configuration to deal with power imbalances.
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