Abstract-The intent of the study detailed in this paper is to demonstrate the benefits of inverter var control on a fast timescale to mitigate rapid and large voltage fluctuations due to the high penetration of photovoltaic generation and the resulting reverse power flow. Our approach is to formulate the volt/var control as a radial optimal power flow (OPF) problem to minimize line losses and energy consumption, subject to constraints on voltage magnitudes. An efficient solution to the radial OPF problem is presented and used to study the structure of optimal inverter var injection and the net benefits, taking into account the additional cost of inverter losses when operating at non-unity power factor. This paper will illustrate how, depending on the circuit topology and its loading condition, the inverter's optimal reactive power injection is not necessarily monotone with respect to their real power output. The results are demonstrated on a distribution feeder on the Southern California Edison system that has a very light load and a 5 MW photovoltaic (PV) system installed away from the substation.

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Southern California Edison (SCE) is well into a five-year project to install a total of 500 MW of distributed photovoltaic (PV) ener g y within its utility service territory.Typical installations to date are 1-3 MW peak rooftop PV systems that interconnect to medium-volta g e urban distribution circuits or larger (5 MW peak) g round-mounted systems that connect to medium-volta g e rural distribution circuits. Some of the PV system interconnections have resulted in distribution circuits that have a si g nificant amount of PV g eneration compared to customer load, resultin g in hi g h-penetration PV inte g ration scenarios. The National Renewable Ener g y Laboratory (NREL) and SCE have assembled a team of distribution modelin g , resource assessment, and PV inverter technolo g y experts in order to investi g ate a few of the hi g h-penetration PV distribution circuits. Currently, the distribution circuits being studied include an urban circuit with a PV penetration of approximately 46% and a rural circuit with a PV penetration of approximately 60%.In both cases, power flow on the circuit reverses direction, compared to traditional circuit operation, durin g periods of hi g h PV power production and low circuit loadin g . Research efforts durin g year two of the five-year project were focused on modelin g the distribution system level impacts of hi g h penetration PV inte g rations, the development and installation of distribution circuit data acquisition equipment appropriate for quantifyin g the impacts of hi g h-penetration PV inte g rations, and investi g atin g hi g h-penetration PV impact miti g ation strate g ies. This paper outlines these research efforts and discusses the following activities in more detail: the development of a quasi static time-series test feeder for evaluatin g hi g h-penetration PV inte g ration modelin g tools; the advanced inverter functions bein g investi g ated for deployment in the project's field demonstration and a power hardware-in-Ioop test of a 500-kW PV inverter implementing a limited set of advanced inverter functions.Index Terms -hi g h-penetration PV inte g ration, PV impact, distribution system, power hardware-in-Ioop testin g , PHIL