Abstract
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 essential 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. However, 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 critically reviews 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. The advanced LVRT control strategies are categorized and analyzed under different types of grid faults. The work categorizes the state-of-the-art LVRT techniques on the basis of the synchronization methods, current injection techniques and dc-link voltage control strategies. It is found that 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.
Highlights
During recent years, the penetration of distributed generation (DG) based grid-connected photovoltaic (GCPV) systems have exponentially increased [1]
Small capacity GCPV system is generally connected to a lowvoltage network and their inverter control action is designed in such a way to give preference to the injection of active power under LVRT due to the small X/R ratio of the low
ACTIVE AND REACTIVE CURRENT INJECTION BASED CONTROL (AARCIBC) The disadvantages of the traditional LVRT control scheme are: 1) It is less effective for low voltage distribution networks (LVDN) as the resistive component is prominent in this type of network
Summary
The penetration of distributed generation (DG) based grid-connected photovoltaic (GCPV) systems have exponentially increased [1]. Other LVRT grid codes require an increased reactive power injection by PVs to provide voltage support to the grid. The operators demand this grid support due to the increasing PV penetration level in the transmission network. This distinction between the German and Chinese grid codes is apparently due to the difference in penetration levels of PV units within these two countries. None of the articles have provided a detailed classification and critically reviewed the recently developed modified inverter control techniques for the LVRT capability of PV systems. Appropriate reactive power is inability to accurately detect the grid voltage dip under injected into the grid based on the specified grid code to unbalanced grid faults
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