Large photovoltaic systems providing frequency containment reserves

Photovoltaics is replacing an important portion of conventional generation. Therefore, the newest network codes endow utility-scale photovoltaic units (USPVUs) with frequency control functions similar to that of conventional synchronous generation, i.e., frequency sensitive mode (FSM) and inertial response (IR). Moreover, new prequalification rules for energy-constrained units participating in ancillary services market state the sizing of frequency containment reserves (FCR). In this context, the study presents from a previous authors' model an enhanced USPVU model with a V-f control algorithm which coordinates the maximum power point tracking (MPPT) control, the charging and discharging control of an embedded hybrid energy storage system (HESS), and the inverter control. The whole controls working together provide an equivalent V-f control capacity in the USPVU to that of conventional generation. Short-term and midterm simulations based on historic frequency measurements demonstrated the benefits of the added mandatory FSM enhanced with the IR in USPVUs on frequency stability.