| Smart distribution grid, which consists of distributed generation, loadsand energy storage devices, can guarantee customers’ special requirementsabout the quality and security of the power supply, such as improving thepower reliability of loads, reducing the transmission loss, maintaining thevoltage of the grid, increasing the efficiency through using waste heat and soon. Microgrid is the very important manifestation of smart distribution grid.However, the fault feature of smart distribution grid is totally differentfrom traditional one; Therefore, study on improving the protection systemto adapt smart distribution grid is important to the reliable and safeoperation of distribution grid. This dissertation focuses on the protectionissues of distribution grid with distributed generations.The dissertation first considers a typical distribution generationtechnology, photovoltaic power generation. For common maximum powerpoint tracking (MPPT) control methods, the complexities of the structuresand the controlling effects cannot be balanced very well. Aiming at thisproblem, an argumentation about the application of maximum powertransfer theorem in the PV system is discussed and a solution on impedanceadaption is presented. And a new MPPT control algorithm which has theability of rapid self-optimization was proposed. The simulation model isestablished through MATLAB/Simulink. Comparing the improved controlmethod with some classic ones, the results indicate that the tracking effect ofproposed improved impedance adaption algorithm is better.The dissertation deeply analyzes different fault features of distributiongenerations, which affect protection systems. Based on proposedconclusions, a GOOSE-based adaptive directional interlocking scheme (GADIS) is proposed. The novel protection principle can changeinterlocking direction adaptively according to the fault position, exchangethe interlocking signals between relays using GOOSE, and minimize thefault clearing time with the coordination between the upstream anddownstream protections. The proposed principle is suitable for closed loopdistribution grid composed of several microgrids. It functions properlyboth in the islanded and grid-connected modes of the distribution grid.Furthermore, the dissertation studies starting and directionalcomponents of proposed protection scheme. Considering that there arepower sources with stochastic fluctuation and frequency offset during faultperiods in the smart distribution grid under the islanded mode, limitationbased on phasor protection theory is simulated. The dissertation proposesadaptive current protection, which is suitable for distribution grid with anytype of distributed generation, can measure impedence of power sourceson the back of protection relays. The dissertation proposes the theory ofstarting and directional components based on R-L model, which can avoidinfluences brought by frequency offset and fractional harmonics.Finally, aiming at the GOOSE-based adaptive directional interlockingscheme (GADIS), the implementation based on the cyber-physical energysystem (CPES) is proposed. First, the general CPES model of the smartdistribution grid is given which takes the Intelligent Component (IC) as theprimary unit. Next, the detailed physical as well as cyber models areconstructed for the circuit breaker IC based on IEC61131-3and IEC61850respectively, and a rule-based model mapping method is proposedaccordingly. Then, the configuration process of the whole CPES system isdesigned, which illuminates the fusion approach of the cyber and physicalsystems. The circuit breaker IC is simulated using RTDS, and the CPESsimulation system is constructed via connecting the ICs. Various faults inthe distribution lines and buses and abnormal conditions are simulatedusing RTDS. The simulation results tentatively demonstrates theadaptability and reliability of the proposed protection schema for the smart distribution grid in cyber-physical energy systems. |
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