Reliability analysis of grid-interfaced filter capacitors

Growing with the increased adoption of renewable energy for the power generation, the reliable and cost-effective operation of grid-connected inverters is of more and more importance. A filter is interfaced between an inverter and the utility grid to reduce the switching harmonics. According to the modulation scheme and the LCL filter impedance, the electrical stresses of the filter capacitor can be thoroughly investigated. With the help of the electro-thermal model, its long-term thermal stress can be obtained based on the mission profile like wind speed, ambient temperature. The reliability of the filter capacitor bank is obtained based on its individual capacitor reliability curves and reliability block diagram method. A case study on a 2MW wind turbine system demonstrates the relationship between the lifetime of the capacitor bank and the single capacitor. Moreover, the severe voltage and current stresses of the filter capacitors are analyzed during abnormal operations (e.g., fault ride-through) with asymmetrical parasitic parameters.