Grid-connected solar inverter system: a case study

Photovoltaic (PV) power systems have many vulnerable components whose lifecycle reliability is prone to relatively high risks. These risk indices generally deal with ambient environments, temperature, and power losses in the system. Meanwhile, the highly variable and uncontrollable solar irradiance, and PV system power input result in high electrical stresses for PV modules, which affect the operational lifecycles and power electronic converters. Consequently, these effects result in low system reliability when compared with the reliability of conventional generating plants. Besides, the high penetration of PV generation into the distribution networks leads to a detrimental effect causing reverse power flow and unacceptable rise in voltage at the distribution feeders. Generally, these overvoltages trigger the protection aspects of the inverter to disconnect from the grid, resulting in islanding operation of the PV system. This further contributes to abrupt voltage fluctuations, load shedding, and sudden changes in power flow. Therefore, the distribution networks associated with high-penetration PV generation have a risk of power outages and in turn increased maintenance costs. This necessitated the tools and methodologies to quantify reliability of the grid-connected PV systems. These reliability analysis tools and methods serve to evaluate the performance of PV systems and generate reliability indices, which further aid in achieving efficient design at the planning stage and determining the reduced cost and improved benefits at the operational phase. A systematic way to evaluate the reliability of grid-connected PV inverters is then presented in this chapter. The reliability analysis is carried out at the 2.2 MW grid-connected rooftop PV system installed in Jamia Millia Islamia, New Delhi, India, considering the variation of input power, and failure rates of PV system components under ambient conditions. The reliability analysis is carried out for inverters at both string level and central level with the site data as a benchmark. A basic reliability indices computation method is adapted to realize the operation of both inverter systems for several risk metrics and quantify their impact on system operation.