| With more distributed generations(DGs)integrating to the distribution network(DN),traditional DNs are evolving into active ones with more prominent grid-source contradictions.Overall,the incompatibility and mutual repulsion between the DN and the DG have hindered the upgrading of active DN to smart DN.Therefore,it is imperative to construct the strategy of power distribution system grid-source compatibility.Regarding the problems faced by grid-source compatibility,academia and industry have proposed many solutions.Among them,for fault scenarios,the protection capability of active DN for DG access has been greatly improved,but from the perspective of making full and effective use of DG,there is still a large space for mining and improving the coordinated control between grid and source.A key aspect of the smart grid vision is to be able to effectively use DG to improve power supply reliability and enhance grid resilience.It can be predicted that the power industry will adopt increasingly "smart" active DN solutions in the future.With the support of the National Natural Science Foundation of China,this paper sorts out and condenses the key common problems in the background of the technical requirements of MW doubly-fed wind turbines connected to 10 k V feeders,analyzes the compatibility of two from the perspective of wind turbine and DN,studies the theories and methods of turbine-grid coordination at all levels,and proposes "system-level compatibility strategy" to meet common technical requirements.It aims to solve the problem of mutual incompatibility and mutual exclusion between the MW double-fed wind turbine and the 10 k V feeder protection system,and lay a solid foundation for the upgrade of active DN to smart DN.The research works carried out and contributions are as follows:(1)A detailed analysis of the compatibility of doubly-fed wind turbine with feeder automation(FA): firstly,the control and operation characteristics of doubly-fed wind turbine are analyzed thoroughly,including basic physical structure,mathematical model,physical nature of doubly-fed wind turbine connected to grid,and the characteristics of doubly-fed induction generator(DFIG)internal potential under typical vector control strategy,DFIG electrical characteristics after power failure,and stability control,which provide basic understanding and beneficial enlightenment for the strategy research of doubly-fed wind turbine compatible with FA.Secondly,the most advanced intelligent distributed FA is selected as the research object on the grid-side,and its system structure,GOOSE communication mechanism and working principle are analyzed and explained in detail.Then,based on the deep understanding of the operation characteristics of the doubly-fed wind turbine control and the working principle of the intelligent distributed FA system,the compatibility of the two systems is analyzed from the perspective of global dynamic operation of grid and source,and a series of contradictions between the doubly-fed wind turbine and the intelligent distributed FA are pointed out.Furthermore,it analyzes and studies a suitable active distribution network protection scheme that introduces intelligent distributed FA and points out the main problems to be solved in this paper.Finally,the goal and basic mentality of the grid-source compatibility research of this paper are given,and feasible technical routes are pointed out.(2)A compatible strategy of doubly-fed wind turbine with FA based on discrete messages is proposed:Under the information conditions that intelligent distributed FA can support,based on the GOOSE normative message,a single doubly-fed wind turbine is connected to the "hand in hand" ring network with a typical intelligent distributed FA as an example,and a coordinated control strategy for doubly-fed wind turbine compatible with intelligent distributed FA is proposed to enable the doubly-fed wind turbine to operate without shutting down from the fault isolation to restoration by the intelligent distributed FA.The key to achieving this strategy includes two aspects: Firstly,a doubly-fed wind turbine islanding active synchronization control method(IAS)is proposed to support islanding and pre-synchronization control;Secondly,a grid-source coordinated control strategy based on GOOSE messages is proposed to make the doubly-fed wind turbine and FA intelligently compatible.It includes a remote synchronization method in which an IAS controlled doubly-fed wind turbine cooperates with the GOOSE channel to transmit the synchronization state,which is fundamentally different from the traditional synchronization method.In grid-source coordination,the doubly-fed wind turbine works in PQ control mode(including wind turbine control and GSC DC voltage control)when it is connected to the grid,and works in IAS control mode when it is islanded,and returns to PQ control mode after reconnecting to the grid.The state awareness is guaranteed by GOOSE message.A number of detailed time-domain simulation examples with complete scenarios have been established to verify the effectiveness of the proposed compatible strategy.(3)A compatible strategy of doubly-fed wind turbine with FA without grid-source communication is proposed: Under the condition of no communication between grid and source,based on the virtual synchronous machine control technology,a doubly-fed wind turbine adaptive control strategy(ACS)and a coordination technology are proposed to be compatible with the intelligent distributed FA action logic in ring distribution network.The ACS wind turbine control and GSC control adopt existing strategies,and RSC control adopts virtual synchronous machine technology.Firstly,a new DFIG virtual synchronous machine control structure(NVSG)that simulates the inertia/damping characteristics and excitation method of the synchronous generator is proposed to seamlessly switch the grid-connected/islanding modes.In-depth analysis of the proposed NVSG control/operation characteristics,including: grid-connected/islanding dual-mode operation characteristics,multi-unit network operation characteristics,current inner loop control characteristics,comparison with synchronous machine(SG)power angle characteristics,static/transient stability,frequency control characteristics,and based on frequency control characteristics,the principle of remote synchronization of doubly-fed wind turbine islanding under the condition of grid-source no communication is analyzed.Secondly,after considering the entire electromechanical coupling system of doubly-fed wind turbine,the ACS equivalent inertia/damping characteristics are analyzed in detail and a robust parameter configuration method is given.Then,based on the ACS,a grid-source communication-free coordination technology is proposed to make the islands of double-fed wind turbines safely connected to the grid.Finally,detailed simulation examples of ring distribution network with multiple doubly-fed wind turbines are established to verify the effectiveness of the proposed ACS and coordination technology to be compatible with intelligent distributed FA action logic in multiple scenarios.(4)A real-time simulation dynamic experiment platform is built and verified by experiments: Based on RTDS and OPAL-RT,a real-time simulation dynamic experiment platform is built and a cross platform communication channel based on UDP protocol is established.Based on the built dynamic experiment platform,the proposed compatible strategy of doubly-fed wind turbine with FA based on discrete messages is verified in different scenarios.The grid-source compatibility strategy proposed in this paper enables the doubly-fed wind turbine to not only run without shutdown in the scenario of intelligent distributed FA processing faults,but also makes the doubly-fed wind turbine experience a "temporary islanding" process,which,on the one hand,helps solve the problem of power quality/personal safety arising from unintentional islanding,and on the other hand,upgrades the traditional one-way power supply recovery mechanism from feeders to loads to the two-way power supply recovery mechanism from DGs and feeders to loads.Therefore,the potential of doubly-fed wind turbines has been further tapped,which not only improves the utilization rate of wind turbines,but also improves the reliability of power supply and enhances the resilience of the DN.In addition,the idea of grid-source compatibility proposed in this paper also has some enlightenment for the coordinated operation of other types of DGs and grid-side protection equipment. |
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