Solar Micro Inverter Modeling and Reliability

The demand for cleaner energy technology is increasing very rapidly. Hence it is important to increase the efficiency and reliability of this emerging clean energy technologies. This thesis focuses on modeling and reliability of solar micro inverters. In order to make photovoltaics (PV) cost competitive with traditional energy sources, the economies of scale have been guiding inverter design in two directions: large, centralized, utility-scale (∼500 kW) inverters vs. small, modular, module level (∼300 W) power electronics (MLPE). MLPE, such as microinverters and DC power optimizers, offer advantages in safety, system operations and maintenance, energy yield, and component lifetime due to their smaller size, lower power handling requirements, and module-level power point tracking and monitoring capability [1]. However, they suer from two main disadvantages: first, depending on array topology (especially the proximity to the PV module), they can be subjected to more extreme environments (i.e. temperature cycling) during the day, resulting in a negative impact to reliability; second, since solar installations can have tens of thousands to millions of modules (and as many MLPE units), it may be difficult or impossible to track and repair units as they go out of service. Therefore identifying the weak links in this system is of critical importance to develop more reliable micro inverters.;While an overwhelming majority of time and research has focused on PV module efficiency and reliability, these issues have been largely ignored for the balance of system components. As a relatively nascent industry, the PV power electronics industry does not have the extensive, standardized reliability design and testing procedures that exist in the module industry or other more mature power electronics industries (e.g. automotive). To do so, the critical components which are at risk and their impact on the system performance has to be studied. This thesis identifies and addresses some of the issues related to reliability of solar micro inverters.;This thesis presents detailed discussions on various components of solar micro inverter and their design. A micro inverter with very similar electrical specifications in comparison with commercial micro inverter is modeled in detail and verified. Components in various stages of micro inverter are listed and their typical failure mechanisms are reviewed. A detailed FMEA is conducted for a typical micro inverter to identify the weak links of the system. Based on the S, O and D metrics, risk priority number (RPN) is calculated to list the critical at-risk components. Degradation of DC bus capacitor is identified as one the failure mechanism and the degradation model is built to study its effect on the system performance. The system is tested for surge immunity using standard ring and combinational surge waveforms as per IEEE 62.41 and IEC 61000-4-5 standards. All the simulation presented in this thesis is performed using PLECS simulation software.