Reactive Power Control of PV for improvement of Frequency Stability of Power systems

The increasing penetration of renewable energy based sources such as photovoltaic (PV) systems has led to deterioration of frequency stability in power systems due to the lack of inherent inertia and frequency support in these generation systems. Therefore, comprehensive studies are required to explore the potentials of PVs to support frequency stability. In this regard, a low-frequency reactive power logic (LFQL) control is proposed in this paper to enable PVs to increase frequency stability of power systems. In this control system, the voltage reference of the PV is reduced according to changes of frequency at the PV terminal which decreases the output reactive power of the PV in the post-disturbance mode. Consequently, the electrical power and deceleration energy of the remaining synchronous generators are reduced after the disturbance, which results in an improvement in system stability. In addition, the reference voltage recovery scheme is derived, allowing PVs to return to the initial operation mode. The performance of the proposed controller is verified for a simple test system and a more realistic test system named reliability and voltage stability (RVS) test system. The results show that the proposed LFQL and its recovery scheme effectively enhance the frequency stability even at high PV penetration levels without deteriorating the critical load voltage level.