Research On Fault And Power Reversal Of Hybrid HVDC With Full-bridge MMC And LCC

The Line Commutated Converter(LCC)has lower cost,and the technology is more mature.But it need to absorb large amounts of reactive power and it has the risk of commutation failure.As one of the newest Voltage Source Converter(VSC)topologies,the Full Bridge Modular Multilevel Converter(FBMMC)can control active and reactive power independently and send power to the passive network.Besides,it don't need to rely on devices in series,and it has flexible operation control characteristics the fault ride-through capability,but its cost is relatively high.The paper presents the Hybrid High Voltage Direct Current with FBMMC as Inverter(FBMMC-IH-HVDC)which combines the economy of LCC and flexibility and controllability of FBMMC.Compared to the general hybrid HVDC,it has the advantages of power reversal and the fault ride-through capability.The paper builds the mathematical model of FBMMC-IH-HVDC system,and analyzes the operating principle,control strategy,power reversal and the fault ride-through characteristics,so that it can provide a theoretical basis for the FBMMC-IH-HVDC project.Firstly,the paper builds the mathematical model of FBMMC-IH-HVDC system,analyzes its structure and operating principle,proposes the corresponding modulation strategy,sub-module trigger control strategy,capacitance voltage equalizing control strategy,circulating current restraining control strategy and the loss reduction control strategy,and designs the corresponding controllers.Secondly,the paper analyzes the controllability of FBMMC-IH-HVDC system,proposes the station-level control strategy,and designs the controller.For LCC side,the paper proposes the control strategy;for FBMMC side,the paper builds the dynamic model based on the dq coordinate,designs the basic controller.Thirdly,the paper analyzes the fault ride-through capability of the FBMMC-IH-HVDC system.Compared to other hybrid HVDC mode,it don't need to disconnect the line until the reaction of the mechanical switch AC breaker,so that it can prevent the fault current from increasing and prevent the scope of fault from expanding,thus greatly improving the safety and reliability of the system.Finally,the paper analyzes the power reversal characteristics of the FBMMC-IH-HVDC system.The paper designs an improved method of reversing the power which is suitable for the FBMMC-IH-HVDC system.And with the proposed method,the system can reverse the power under the no power-down mode,thereby reducing the impact on the power reversal of the system.