Maximum Available Power Estimation in Solar Photovoltaic Power Plants Using Reference Inverters: A Critical Assessment

With the ongoing displacement of conventional generators in the power systems by renewable energy (RE) sources, the grid operators are increasingly mandating strict grid code requirements on the RE plants to regulate their operation to ensure the frequency and voltage stability of the grid. Estimating the instantaneous maximum available power (MAP) in largescale RE plants is paramount to evaluating their capability to retain active power reserves and participate in frequency regulation. Assessing the MAP for RE plants is challenging due to the intermittency and variability of the resources. For solar photovoltaic power plants (PVPPs), external factors such as changing cloud cover, air temperature and soiling make it more demanding to accurately estimate the MAP, primarily in deloaded operating mode. In this context, the operation of the PV inverters in a master/slave configuration has often been utilized as a potential method for MAP estimation. This paper discusses one such innovative technique for MAP estimation and assesses its effectiveness in the field. A methodology is proposed to determine the optimal number of master (reference) inverters and their estimation interval depending on the plant layout and the forecasted cloud motion and help evaluate the PVPP’s frequency regulation capability with minimum computational complexity.