ABSTRACT
Frequency variations in the grid require a response from the photovoltaic (PV) system to ensure the safety of equipment connected to the point of coupling, whether it is a PV system, utility network, or consumer equipment. Generally, interconnecting to existing under-frequency load-shed blocks is avoided; this prevents tripping significant generation along with load. Islanding also causes changes in frequency. Depending on the acceptable or permissible value changes in the real and reactive parts of the apparent power, the frequency changes will move out of the permissible limits. Both the International Electric Commission and the European Union define Electromagnetic Compatibility to cover electromagnetic phenomena from zero hertz. In the low-frequency range, the possible variation of the impedance challenges the design of resonant controllers adopted to mitigate the effect of the grid harmonic distortion on the grid current. In high-frequency range, grid impedance influences the frequency characteristic of the filter, and the design of passive or active damping becomes more difficult.
