Autonomous control of series-connected low voltage photovoltaic microinverters

This paper considers a photovoltaic (PV) system architecture based on series-connected low-voltage microinverters. The approach is similar to the dc optimizer PV architecture, except that ac instead of dc outputs are connected in series and tied to the ac grid directly, without the need for high-voltage dc wiring, or additional string or central inverters. In contrast to standard microinverters, the low-voltage ac (LVAC) microinverters do not require a high step-up conversion stage, and can therefore have improved efficiency and reduced cost. The paper is focused on distributed autonomous control of LVAC microinverters, which is one of the challenges associated with this architecture. Using fast output power control loop and slow input voltage control loop, it is shown how a controller operating autonomously, based on local sensing only, results in stable operation and appropriate ac voltage sharing across LVAC microinverters. The control approach is verified by simulations and experimental results on a scaled-down system consisting of three series-connected LVAC microinverters.