Research on Fault Isolation of MMC-HVDC DC Side Based on Improved Sub-Module
The high-voltage direct current transmission system(HVDC)has a high failure rate in the case of o-verhead lines.At present,the hybrid DC circuit breaker has the problems of small capacity and high cost,which makes the sub-module with fault self-clearing capability the best solution to solve the DC side fault of the system.However,this solution uses more power electronic devices,which brings Loss increases,investment costs increase and other issues.To this end,this paper proposes a new hybrid modular multi-level converter(MMC)sub-module topolo-gy,which reduces the required power electronic devices without affecting the self-clearing fault capability,and im-proves its economy and DC side fault isolation performance.The paper firstly presented the design scheme of reasona-bly collocating the new sub-module with the traditional half-bridge sub-module in the bridge arm.Secondly,the pole-to-pole short-circuit fault ride-through mechanism of the improved topology and the economic optimization of the sub-module construction were discussed.Finally,a double-ended MMC-HVDC model was built based on the PSCAD/EMTDC platform,and the performance of the proposed sub-module and its hybrid MMC were simulated and verified.The results show that the proposed improved sub-module and the corresponding hybrid MMC can quickly block the fault current,have good DC fault isolation ability,better economy,and a good application prospect in practi-cal engineering.
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