Hierarchical control-based fault ride-through of VSC-HVDC considering impacts of renewable energy

When a short-circuit fault occurs at the receiving-end grid, the unbalanced power in voltage source converter based high voltage direct current (VSC-HVDC) should be consumed to prevent excessive DC voltage rise, thereby enabling fault ride-through. Existing methods fail to fully utilize the active power capability of the receiving-end converter (REC). The impacts of nearby renewable energy on the power of REC are also neglected. Consequently, excessive DC chopper power is required or DC voltage limit are exceeded during the fault. To address these issues, An equivalent method considering low voltage ride-through control for renewable energy is proposed. The expression for the REC AC bus voltage, in terms of the active and reactive current of REC, is derived by considering the output current of renewable energy. Using the DC capacitor charging equation, the VSC-HVDC DC voltage safety boundary is established. The fault security region of the REC, capturing the impact of renewable energy, is defined by the intersection of the DC voltage and AC current safety boundaries. The reduction in the fault security region area caused by the current variations of renewable energy during faults is analyzed. A method is proposed to calculate the maximum allowable fault duration (MAFD) for which the fault security region exists. Then a hierarchical control-based fault ride-through strategy that minimizes chopper power is developed. The method determines the fault ride-through strategy based on the relationship between MAFD and fault duration and applies specific control strategies at different fault times according to fault development. Simulations demonstrate that the proposed method ensures maximum active power of REC and appreciable reduction in average chopper power during the fault.