Fault Identification And Protection Strategy Of AC Line Connected To New Energy Of Flexible DC System

The new energy connect to flexible DC system has unique advantages in the offshore wind power generation system.However,both ends of the transmission line are controlled electric power commutation equipment,resulting in the weak feed characteristics of both ends of the AC line,and the fault characteristics are very different from that of the traditional power grid.It is difficult to identify faults,while the safe and stable operation of the power grid faces serious challenges.Therefore,this paper takes the flexible DC send-off system of wind power plant station as the research object,which studies the fault protection method of collector line of wind power plant station and the protection method of send-off line of wind power plant station through flexible and direct send-off.The correctness and feasibility of the scheme in this paper are verified by simulation.The achievements of this paper are summarized as follows:This article proposes a comprehensive inverter,semi-inverter power supply and shortcircuit current calculation method of the dynamic characteristics of the phase and the dynamic characteristics of the phase-locking loop.First of all,the short-circuit current analysis expression of a single unit affected by the dynamic output characteristics of the lock phase loop is calculated;on this basis,consider the unity characteristics of the crew and establish a detailed model of the stations;then Different control of the unit’s interaction power is divided into interactive power between machines and the interactive power of the machine network.Further,consider the dynamic characteristics of the lock-up loop of the soft direct stream station control system after the failure occurs,and the sub-module casting principle of the sub-module,the current-voltage relationship of the soft direct stream station,and the constructing an equivalent instantaneous model of the AC side of the soft direct stream station EssenceIn response to the contradiction between the existing new energy field station collection wire protection selectivity and the coordination of the fans fuse fuse,this article proposes a field and set line protection based on the composite modular current difference factors.First of all,the unit transient model suitable for the combination of electricity line protection is established.On this basis,the 1-mode and 2-modal current expressions of the circuit circuit group gathered in the home line were obtained.Further,the structure of two-stage current current is constructed,and the model parameter variation principle of the model parameter of the internal and external scenes of the district is used to construct a composite modulus current differential factors to determine the direction of fault and the protection judgment of the current segment Ⅱ.Finally,the RT-LAB simulation results verify the accuracy of this method and are not affected by the transition resistance and frequency shift.In response to the problem of dual-end feedback from the route,this chapter proposes a kind of vertical protection principle suitable for new energy sources;the problem of neglecting the characteristics of the difference between the separation of the line of the line is caused.New energy field stations based on interactive power differences are sent to the protection judgment;first of all,the power of interaction between the on-site machine and the network interaction of the machine in the line area of the line area and the power of the machine network are studied.Then,based on the different diplomatic power in the area,the new energy field was constructed to send out the longitudinal linked protection solution to identify the back side of the area in the area and the back side of the new energy field.For the protective solution on the soft side,first based on the control strategy of the soft direct stream stream station control system after the failure,the equation group composed of multi-time section information is used to find the soft straight model equivalent inductance.Then,based on the differential structure of the internal and external failure model,the constructed protection judgment is established,and the logical amount information of the interactive direction is established to achieve fault positioning.Finally,the simulation results of the RTLab platform verify the correctness and effectiveness of this solution.