An efficient ramp rate and state of charge control for PV-battery system capacity firming

Abstract

This paper proposes an efficient ramp rate control scheme for capacity firming of an integrated Photovoltaic (PV) power system with battery energy storage. This scheme addresses one of the main limitations of PV systems, namely intermittency, making available energy to be non-dispatchable to the grid and cannot be forecasted on a day ahead basis. The paper also proposes a novel state of charge controller which monitors the energy storage State-Of-Charge and adjusts the battery charge and discharge rates so that in the event of a steep variation in the PV power, it doesn't over charge or deep discharges and continues to be available for the next cycle. The combined ramp rate and state of charge control achieves a smooth dispatchable PV profile, keeps the system loss at a minimum, while improving the system reliability and performance by preserving battery life. The controller can be implemented without affecting the normal PV system control and operation. The proposed firming concept has been theoretically explained and simulation results verifies the expected theoretical performance.