THERMAL STRESS MITIGATION OF SINGLE-PHASE SINEWAVE INVERTER BY USING DOUBLE SWITCH H BRIDGE CONFIGURATION

The increasing demand for renewable energies and the ongoing advancement in the industry require continuously evolving power converters in terms of efficiency, power density, and reliability. Furthermore, power converters’ applications in harsh and remote environments such as offshore wind turbines demand robust and reliable designs to help reduce operational costs. Power switch failure is a critical reliability issue that leads to the converter going out of service, causing an unscheduled maintenance event. The main reason behind power switch failure is thermal cycling. Therefore, the first part of this thesis attempts to develop an effective double switch H bridge inverter topology aiming to lessen thermal cycling subjected to power switches, increasing the expected lifetime of power switches, improving the system\u27s overall reliability, and reducing operational costs. Meanwhile, the second focus of the thesis is to develop a visual interpretation of an empirical lifetime estimation model that enables the evaluation of the proposed inverter topology compared to the conventional topology. This is done by producing a novel lifetime improvement evaluation curve based on a common empirical lifetime estimation model using MATLAB®. Moreover, the interpretation of the empirical lifetime estimation models as a lifetime improvement evaluation curve helps to bridge the gap between any thermal condition change and its impact on the expected lifetime. The percentage reduction in the junction’s median temperature %_ and the percentage reduction in the temperature swing %Δ_ are taken as the main contributors to the change in the switch’s estimated cycles to failure . The effectiveness of the proposed topology was verified via simulation of the thermal parameters for the two topologies via PLECS® software. Several test scenarios were performed to illustrate the impact of shifting from the conventional topology to the proposed topology. Following that, numerous loading conditions were considered to perform an extensive comparative analysis between the proposed and the conventional topologies. Three power factor values were adopted at high, medium, and low values; to compare the two topologies while covering an adequate loading range for each power factor value. The assessment indices, namely, Life Prolonging Factor (LPF), and the average LPF (in a temperature range) obtained promising results, especially for high loading levels conditions. The LPF reached values more than ‘2’ under some conditions, indicating a more than double lifetime increase. Furthermore, the average LPF in a specific temperature range indicated promising results in general for common loading conditions with an advantage for higher loading conditions over lower loading conditions