Sustainable transition to high PV penetration: curtailment retrofit for the already deployed micro-inverters

Increasing photovoltaic (PV) capacity in low voltage networks is limited by occasional congestion, resulting in unacceptable voltage levels. Network managers and policy makers are getting aware of this problem and various technical recommendations are given. Of special interest are ancillary services (reactive power control and active power curtailment) that could be provided by the "smart" inverters. Most PV inverters deployed to date are solely designed to maximize power output. To make the transition towards smart inverters, they either have to be replaced or retrofitted. Retrofit can be a more sustainable option, especially if it can be done only by software intervention ("soft retrofit"). This paper presents a curtailment method suitable for the already deployed micro-inverters without needing to replace them. Sequential module-level tripping is an optimized overvoltage trip scheme that achieves curtailment on a system level, without modifying the functionality of individual micro-inverter unit. The proposed method was simulated for an increased PV penetration scenario for a Dutch LV network. The annual feed-in losses of curtailment were compared against conventional overvoltage protection. Depending on the location of PV in the distribution network, 62-100% less feed-in loss was achieved with the proposed curtailment method.