Experimental tests and simulations about the efficiency of commercial hybrid inverters operating at variable power factor

Abstract

The main problems of the non-programmable generation proliferation, mainly photovoltaic, are related to the angle and frequency stability of the power system. Therefore, new rules to make distributed generation participate in network stability are needed. Consequently, national and international grid codes have been updated requiring distributed generators to supply ancillary services, such as the voltage and frequency regulation. Most LV grid connected inverter based systems are only setup to inject power at unity power factor, meaning they only produce active power. However, the Italian Standards, and in particular the CEI 0–21, require to hybrid inverters of residential systems to include the possibility of being able to absorb or supply reactive energy. This allows to limit the over / under voltages problems. In this context, the inverters’ manufacturers have introduced the necessary changes in order to allow residential inverters to set the power factor. These new potentialities have been exploited in order to study the inverter performance with the variation of the power factor, considering both the inductive and the capacitive behaviour. In particular, the presented paper focuses on the experimental tests on a hybrid inverter based system for residential use with the aim of evaluating the dependence of the inverter efficiency on the power factor. Based on measured values, a Matlab/Simulink simulator has been developed for modelling the system with the aim of evaluating the control systems in order to participate in regulation services and to evaluate the inverter efficiency in case of power factor different from the unit.