Study on time delay effect on a PV power ramp-rate control and a proposed solution

Photovoltaic (PV) power fluctuations produced by cloud passage in large grid-connected PV plants can compromise both the power quality and network reliability. Consequently, new grid-codes have appeared with the aim of reducing the system variability. For fulfilling these regulations, energy storage systems (ESS) are being combined with PV plants. Although several papers have studied control strategies to properly operate a PV plant with an ESS, almost none of them has taken into consideration the effect of the time delay on a real system implementation. This delay could come from many factors, including the measuring time delay, the microprocessor time delay and the time response of the power electronics converters. This paper studies the effect of the whole system time delay on the performance of ramp-rate control in a real system. Special attention should be taken in case of noncompliance with a ramp-rate restriction imposed. The noncompliance percentage is a function of the time delay, the ramp rate limit and the PV plant size. Finally, a solution to overcome the negative impacts of the time delay problems is proposed. This method has been corroborated carrying out several simulations performed with real 5-s one-year data of 5 sections at a 45 MWp PV plant located in the south of Portugal.