Active and reactive power regulation in grid-connected PV systems

The high incidence of non-programmable renewable sources and in particular of photovoltaics can create relevant problems on distribution networks. These problems are mainly related to the uncertainty of the solar resource and the fact that photovoltaic systems do not take part in the essential network services. CEI 0-21, Italian technical standard, modifying the conception of the PV system, introduces important changes regarding services of frequency and voltage regulation for systems with rated power greater than 3 kW. In this paper, algorithms for voltage and frequency regulations are developed according to the prescription of CEI 0-21. They, along with a detailed model of a photovoltaic system, allow to study the impact of renewable sources on the distribution networks and the interaction of grid connected systems with the grid in the presence of over/under-voltage or over-frequency phenomena. Both algorithms have been tested numerically and results are reported.