Emergency Support Scheme for Sudden Voltage Drops in Low-Voltage Distribution Networks

Introduction: With the continuous increase in the penetration rate of distributed generation (DG) in distribution networks, the pressure on energy supply has been effectively alleviated. However, its impact on the voltage of distribution networks is gradually becoming apparent, and traditional reactive power voltage support methods are struggling to meet the requirements for fast and flexible voltage regulation in modern distribution networks with high DG penetration.To accommodate the integration of DGs with high penetration rates and enhance the voltage support capability of the distribution network, an emergency voltage support scheme is proposed. The proposed scheme takes into account the impedance properties of the distribution network and focuses on low-voltage distribution networks. Methods: This paper proposes a voltage support scheme for low-voltage distribution networks, taking into account the resistive characteristics of distribution lines. Based on the distribution network impedance ratio (R/X), the optimal active and reactive current reference values are estimated. A voltage support strategy is planned according to the severity of the voltage drop, providing coordinated voltage support by simultaneously delivering active and reactive power during voltage sags and fault conditions. Results: A digital-physical hybrid experimental platform and a simulation model of the low-voltage distribution network were established to validate the effectiveness of the proposed scheme. The results indicate that the voltage support capability of the proposed scheme is superior to that of traditional reactive power voltage support methods. Discussion: The simulation results demonstrate that the proposed method can effectively provide voltage support at the point of common coupling in low-voltage distribution networks during voltage faults, thereby preventing system instability. However, under severe fault conditions, the voltage support capability remains constrained by the converter's rated capacity limitations, preventing perfect voltage restoration. Conclusion: The low-voltage distribution network voltage support scheme proposed in this paper considers the distribution network impedance ratio to calculate the required injected active and reactive power, thereby providing maximum support to the voltage. In addition, the active and reactive currents are adjusted according to the severity of the voltage drop using a droop curve. The effectiveness of the proposed method on the operation of the distribution network is validated through simulations. The scheme can effectively provide voltage support during voltage dips in the distribution network, preventing voltage instability.