Abstract
With the development of high power converters, safe operation of IGBT modules with parallel chips is of increasing importance. IGBT can work normally in safe range in the initial operation even if current imbalance is happening. However, if the uneven current state lasts too long, it is difficult to keep a uniform junction temperature, which can further lead to uneven distribution of the power losses. In severe cases, the device and converter may be damaged due to overheating. This paper studies the stability of such an interactive process with mathematical modelling backed by experiment. Because of the opposite sensitivities of switching and conduction losses to temperature under high current injection, the concept of `inflection point frequency characteristic' is introduced to evaluate the trend of junction temperature mismatches between the parallel IGBT chips. The inflection point frequency at different current and temperature levels is tested to verify the model prediction, and the applicability of this approach in multi-chip parallel module is discussed. By establishing the relationship between the switching frequency and the thermal stability limit of parallel IGBTs, it can provide a feasible reference for improving the reliability of multi-chip parallel power devices.
Highlights
High-power Insulated gate bipolar transistor (IGBT) modules are one of the core components in solid state circuit breaker/transformer and frequency converter technologies [1]
According to the above research, when the switch frequency is lower than the inflection point frequency, the parallel IGBTs are in a thermal stability state; when the switch frequency is higher than the inflection point frequency, the parallel IGBTs will enter the thermal runaway state
For the multi-chip parallel IGBT power module, only the switch frequency is lower than the minimum inflection point frequency, it can be in a thermal stable state
Summary
High-power IGBT modules are one of the core components in solid state circuit breaker/transformer and frequency converter technologies [1]. It is important to highlight the effect of junction temperature on the power loss of parallel IGBTs to improve its reliability. VOLUME 8, 2020 on the influence of temperature on power loss focuses on a single IGBT, and very little was found in the literature on the question of interaction between parallel IGBTs. In this paper, taking the IGBT discrete devices as the research object, studies the stability of parallel IGBTs electrothermal interactive process with mathematical modelling backed by experiment. Based on the relationship between switching frequency and temperature difference, the concept of ‘inflection point frequency characteristic’ was proposed to evaluate development trend of junction temperature difference of parallel IGBTs. The inflection point frequency at different current and temperature difference levels is tested to verify the model prediction, and the applicability of this approach in multi-chip parallel modules is discussed.
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