A Comprehensive Review of Control Strategies to Overcome Challenges During LVRT in PV Systems

Due to the high penetration of grid-connected photovoltaic (GCPV) systems, the network operators are regularly updating the grid codes to ensure that the operation of GCPV systems will assist in maintaining grid stability. Among these, low-voltage-ride-through (LVRT) is an important attribute of PV inverters that allows them to remain connected with the grid during short-term disturbances in the grid voltage. Hence, PV inverters are equipped with control strategies that secure their smooth operation through this ride-through period as per the specified grid code. During the injection of reactive power under LVRT condition, various challenges have been observed, such as inverter overcurrent, unbalance phase voltages at the point of common coupling (PCC), overvoltage in healthy phases, oscillations in active, reactive power and dc-link voltage, distortion in injected currents and poor dynamic response of the system. Several strategies are found in the literature to overcome these challenges associated with LVRT. This paper provides a critical review on the recent challenges and the associated strategies under LVRT conditions in GCPV inverters. The drawbacks associated with the conventional current control strategies are investigated in MATLAB/Simulink environment and each category of the advanced LVRT control strategy is analyzed under different types of grid faults. Moreover, this work categorizes different state-of-the-art LVRT techniques on the basis of synchronization methods, current injection techniques and dc-link voltage control strategies. It is found that the state-of-the-art control strategies like OVSS/OCCIDGS provides improved voltage support and current limitation which results in smooth LVRT operation by injecting currents of enhanced power quality.