This paper presents a new method for the accelerated ageing tests of power semiconductor devices in photovoltaic inverters. Mission profiles are analysed: output current and ambient temperature are extracted over several years from multiple photovoltaic plants located in France. It is then proposed to create a particular ageing profile which takes into account not only the different constraints of the application of the photovoltaic inverters (high-frequency switching and sinusoidal-shaped current), but also reproduces a typical profile of the output current of photovoltaic inverters. Similarly, the ambient temperature varies as in the real application. By applying current injections with relatively long durations, the DBC (Direct Bonded Copper) substrates and the coolers are subjected to high temperature swings. This method should show better representation of the thermal behavior of DC/AC inverters used in photovoltaic applications, and is expected to show more representative results than traditional power cycling, thus reducing the favoring of certain failure modes to the detriment of others.
This paper presents a new concept of semiconductor ageing test benches dedicated to photovoltaic inverters. The ageing profile is obtained by analyzing mission profiles of the current and the ambient temperature, extracted over several years from different photovoltaic plants. Accordingly, the ageing test is done by applying power cycling under variable ambient temperature, using power semiconductors in a Pulse Width Modulation inverter and under nominal conditions. The measurement and estimation of power losses and thermal models are then used to choose the ageing profile parameters adapted to the experimental setup. Finally, the preliminary experimental results of the accelerated ageing tests are presented in the case of silicon carbide MOSFETs power semiconductors. These results show a remarkable increase in the gate to source threshold voltage, the leakage currents and the drain to source on resistance.
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