Non-pilot protection scheme for multi-terminal VSC–HVDC transmission systems

摘要

High-voltage direct current (HVDC) transmission systems are nowadays ideal candidates for interconnecting renewable energy resources to the electrical grids. This study presents a communication-less protection scheme for HVDC transmission systems with a multi-terminal voltage source converter (VSC). The existence of a tie-busbar is also considered, which represents a challenge for protection selectivity functions without the aid of a communication channel. The proposed scheme identifies the faulted segment on either a DC busbar or a line segment based on monitoring the calculated rate of change of the current-to-voltage ratio. This criterion is sensitive to detect the faults as the current increases rapidly in a few milliseconds, while the voltage decreases in the same time frame remarkably. Once the fault detection criterion is satisfied, the faulted section can be identified by checking the summation and direction of all branch currents at each busbar individually without utilising communication links. For investigation purposes, the proposed scheme is tested via a four-terminal HVDC system with two tie-busbars. Different simulation cases are evaluated with a variety of fault conditions using MATLAB/SIMULINK. The results corroborate the reliability, security, and efficacy of the proposed protection scheme for multi-terminal HVDC transmission systems.