Thermal Stress Balancing for Lifetime Improvement of H6 Solar Inverter

The thermal stress of power semiconductor devices (PSDs) of the H6 solar inverter dictates their lifetime. Two existing modulation schemes for H6 inverter are studied, and their thermal stress distribution is analyzed. It is found that unequal stress distribution exists among PSDs for both modulation strategies. This leads to the earlier failure of some PSDs than others. To address this issue, this paper proposes a hybrid modulation strategy and associated thermal controller for the lifetime enhancement of PSDs in the H6 solar inverter. The proposed thermal controller dictates the hybridization angle to equalize the thermal stress of the PSDs. The proposed technique is estimated to achieve up to 26.5% improvement in a lifetime for the selected mission profile. The impact of the proposed thermal controller on the efficiency of the converter is also studied. It is estimated that a 26.5% enhancement in lifetime is achieved for a 0.23% drop in conversion efficiency.