A methodological assessment to determine the frequency response of utility-scale deloaded PV under variability

Replacing the traditional synchronous generators with photovoltaic systems (PV) causes an overall reduction in grid inertia. Further, as the newly installed PV plants do not require any rotational mechanism to generate active power, they are not also able to ramp the generation during contingency situations leading to frequency collapse of the grid. To deal with this issue, a portion of peak solar generation can be kept as deloaded reserve which can be released during emergency conditions emulating the conventional system. However, the allocation of deloading as a percentage of PV power can introduce randomness on the expected support as the dispatched PV power varies depending on the irradiance and temperature values. Therefore, it is essential to accurately estimate the frequency support of a given deloading percentage to maintain frequency stability considering PV variability. In this regard, this study presents a generalized approach to determine the frequency response of deloaded support under utility-scale PV integration. To achieve this, linear and quadratic regression are employed to establish a mathematical correlation using the data derived from dynamic simulations conducted on a modified IEEE 39 bus grid at various PV penetration levels. The obtained results indicate a minimum generation of PV power is required to prevent under-frequency load shedding for a fixed deloading percentage. These findings are later verified by comparing them with two other techniques - battery energy storage system and synchronous condenser based on the simulated results achieved from DIgSILENT PowerFactory software. Moreover, this paper provides insights into how this required minimum PV generation changes with the variation in sanctioned deloading percentage. This can aid the grid designers to allow proper deloaded operation depending on the environmental condition.