Increasing Annual Energy Yield of PV Parks With Inverter Focused Control of On-Load Tap Changers to Enhance AC Power Output and DC Voltage Range

Abstract

Large photovoltaic (PV) parks usually span several voltage levels, separated by stationary transformers. In such parks, inverters face restrictions and losses that originate from varying voltage levels on the ac and dc side. In this article, the option to equip park transformers with on-load tap changers (OLTCs) and control them with the aim of regulating voltage levels on the ac output side of the inverters to increase their effectiveness across several operation points and to lift restrictions in inverter power feed-in is explored. Based on a model of a 105 MVA-park, the operation principle is explained and possible annual increases in energy yield are explored based on a simulation of a specific park setup. Subsequently, requirements for reactive power provision on the park are introduced and varied to study the effects on the results. Next, it is investigated whether the OLTC operation enables a different design choice for a larger inverter capacity for new PV parks to achieve a similar output with fewer units. A concluding economic analysis gives insight into whether the expenses for additional tap-changers can be economically justified for a PV park operator for this setup. Finally, we discuss the implications and potential for implementation of OLTC-based control strategies in utility-scale PV systems.