Abstract
Power devices are among the reliability-critical components in the Photovoltaic (PV) inverter, whose failures are normally related to the thermal stress. Therefore, thermal modeling is required for estimating the thermal stress of the power devices under long-term operating conditions of the PV inverter, i.e., mission profile. Unfortunately, most of the thermal models developed for the power device are not suitable for a long-term thermal stress analysis (e.g., days to months), and there is usually a trade-off between the model accuracy and the computational efficiency. To address this challenge, a reduced-order thermal model for PV inverters is proposed in this paper, where the model simplification is based on the thermal impedance characteristic and the mission profile dynamics. The modeling accuracy is evaluated by comparing the estimated thermal stress with the experimental results from a PV inverter test-bench, where daily mission profiles with various dynamics are tested. According to the results, the proposed method offers a relatively high model accuracy (similar to the full-order thermal model) while the computational efficiency is improved significantly, making it suitable for long-term thermal stress modeling applications.
Highlights
Thermal stress is a key factor that influences the reliability and robustness of PV inverters [1]–[3]
The thermal model plays an important role in the reliability assessment of the power devices, where the dynamic loading from the mission profile needs to be translated into the junction temperature profile, and applied to the lifetime prediction [9]–[11]
In this paper, a method to simplify the thermal model for long-term thermal stress modeling has been proposed for the power devices in PV inverters
Summary
Thermal stress is a key factor that influences the reliability and robustness of PV inverters [1]–[3]. Different approaches for the model order reduction should be applied for the thermal modeling of PV inverters, where the time-constant of the IGBT power module (and the cooling system) thermal impedance and the mission profile dynamics need to be considered together [38]. This aspect has not yet been addressed in the previous research. SYSTEM CONFIGURATION AND CONTROL STRUCTURE In order to validate the thermal stress modeling, a test-bench for a PV inverter, which allows an experimental measurement of power device junction temperature during mission profile operation is required. The lifetime model in (3) and (4) will be used as a quantitative measure of the deviation in the lifetime modeling process introduced by different thermal stress modeling approaches
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