基于DMMC的海上风电DRU多端直流系统故障处理方案OA

To address the high cost of fault isolation in multi-terminal direct current(MTDC)systems integrating offshore wind power via diode rectifier units(DRUs),a fault handling scheme based on a receiving-end diode-type modular multi-level converter(DMMC)is proposed.First,for bipolar short-circuit faults in DC submarine cables,the passive blocking of the receiving-end diodes and the coordinated isolation mechanism at the offshore end are clarified;for mono-pole-to-ground faults,the adaptive fault ride-through mechanism in a pseudo-bipolar configuration is analyzed.Then,the coupling process between diode natural turn-off and transient traveling waves in submarine cables is investigated.An equivalent short-circuit discharge circuit model is established,and an analytical expression for the maximum reverse overvoltage across the diode is derived based on the quarter-wavelength resonator theory.Finally,a±500 kV/6 GW four-terminal DC collection electromagnetic transient model is built in PSCAD/EMTDC to validate the proposed scheme.The results show that,under a bipolar short-circuit fault,the series-connected diodes can achieve rapid current ze-ro-crossing and passive blocking within 50 μs,while the DC bus voltage remains above 0.9 pu during the fault transient.Under a monopole-to-ground fault,uninterrupted system ride-through can be realized.