Enhancing inertia of solar photovoltaic-based microgrid through notch filter-based PLL in SRF control

Synchronous reference frame (SRF) control strategy for solar photovoltaic (SPV) sources is widely used to deliver maximum power to the grid. However, poor inertia support just after a disturbance and improper phase angle tracking in presence of the harmonics and system unbalance are noticed when the conventional phase-locked loop (PLL) based SRF control structure is used. In this study, an inertia enhancement method for inverter interfaced SPV sources is proposed, which adjusts only the PLL parameters with a notch filter (NF) in the SRF controller. NF in PLL is used due to its disturbance rejection potential and accurate phase angle tracking, even during system unbalance. The dynamic equation of pseudo induced voltage (PIV) vector with respect to the point of common coupling is derived. The kinematic equation of the PIV angle vector correlates inertia contribution and inverter terminal voltage. The impact of the change in PLL parameters on inertia enhancement is analyzed by validating the proposed technique on a test system in the real-time digital simulator. The frequency response by the proposed method has been compared with two state-of-art methods to prove the superiority of the proposed approach in enhancing the inertia of the SPV source in a microgrid.