O papel de geradores fotovoltaicos na regulação de tensão em redes de baixa tensão residenciais: estudo comparativo de normas e padrões sob a ótica da mitigação da elevação de tensão

Abstract

Photovoltaic based distributed generation has been growing exponentially worldwide over the past decades, and is on its way to becoming a significant energy source for the world. Brazil is still far behind in contrast to the vanguard of this area, but its privileged levels of solar irradiation gives it huge potential to grow. In this context, this work studied different standards, national and international, regarding the role of photovoltaic generation in the voltage regulation in low voltage residential grids, focusing particularly on the voltage rise provoked by the injection of active power into the network. This creates a scenario of reverse power flow in the low voltage distribution system, which was originally designed to operate with power flow from the distribution transformer to the customer installations. The reversion tends to provoke voltage rises, that may go beyond the over voltage limits. This new scenario demands study, to ensure that the electrical system operation is not compromised, but without wasting the great potential of this distributed energy source. To accomplish that, it was used a model of a typical Cemig residential grid, with characteristic daily average load profiles, introducing a significant level of photovoltaic generation, and it was simulated for a series of meteorological scenarios, with real photovoltaic generation data. All the standards were compared and then applied to the photovoltaic installations of the modeled grid, repeating the simulations in order to evaluate the ability of each one to mitigate the voltage rise caused by the photovoltaic generation. The standards studied were Brazilian NBR 16149, German VDE-AR-N 4105, European IEC 61727 and American IEEE 1547. The study showed that the default method of voltage regulation is grid interface inverter power factor control. The exception is the IEEE standard, which proved very unrestrictive, not presenting any power factor restriction. Brazilian standard turned out to be the strictest one, having the biggest number of restrictive parameters, which reflected in the results, allowing a smaller contribution by the photovoltaic unities in the voltage regulation. In general, however, all standards fulfill their purpose of maintaining voltage on the connection point below the limit, and the best adequacy of one or another would depend on the context of use and the need to maintain the voltage more or less far from the limit.