Active power control of photovoltaic power systems

Historically, electric power system operators have seen photovoltaic (PV) power systems as potential sources of problems due to intermittency and lack of controllability. However, the flexibility of power electronic inverters allows PV to provide grid-friendly features including volt-VAR control, ramp-rate control, high-frequency power curtailment, and event ride-through. These technologies offer power quality improvements and enable wider penetrations of PV systems. Commercially available smart PV inverters can further provide frequency down-regulation by curtailing power, but they are unable to provide true frequency regulation through active power control (APC) because they are unable to increase power on command. The development of inverters capable of APC for primary and secondary frequency regulation without the need for energy storage has the potential to transform the way grid operators view high PV penetration levels. This paper provides a brief tutorial on APC of PV inverters, summarizes state of the art research in the area, and suggests future research directions.