| In order to deal with the great pressure caused by the energy shortage, environment pollution and climate warming, the development and application of the renewable energy such as wind power and solar energy power generation has entered a rapid development stage, and has become an important foundation and development direction to promote the adjustment of energy structure and support the construction of a new type of environmental friendly urbanization in the Chineses field of energy.With the increasing grid-connected new energy power capacity and the operation of low voltage ride through (LVRT), the complicated fault current and different power generation mode of the new energy sources brings many new problems and challenges to the traditional relaying protection and fault analysis on the power gird, and the safe and stable operation of power grid and power supply reliability has been affected seriously. In this condition, with the support of the Natural Science Foundation of China, according to the technical characteristics of the new energy sources centralized connected and distributed connected to the power grid, the dissertation implements a theoretical research and simulation analysis on the fault analysis method and relay protection principle of the high-voltage power grid and low-voltage distribution network with new energy sources, respectively. The research results in this paper are of important theoretical and practical significance for the safe and reliable operation of the power grid, and the safe operation and efficient utilization of renewable energy sources.The analysis for the fault current characteristics of the new energy sources are the basis work in relay protection and fault analysis of the power grid. According to the operating principle and the influence for external power grid by different kinds of renewable energy sources, the new energy sources can be divided into two types:generators of doubly-fed type(such as doubly fed induction generator, DFIG) and inverter-based generators (such as inverter interfaced distributed generators, IIDGs). For inverter-based generators, the fault current characteristics research has been very depth because of its simple structure and operation mode. For generators of doubly-fed type, its special structure and complicated transient characteristics, especially under the asymmetric fault conditions, the fault current characteristics of the DFIG are related to low-voltage through control strategy and there are a lot of control strategies. Hence, the dynamic response of the ac/dc/ac converter and diversified control strategy result in much more complicated fault current characteristics of the DFIG which are difficult to analyze. In order to address this issue, the unified analysis method in the fault currents of the doubly-fed induction generator is studied. Firstly, the mathematical model of the DFIG under the asymmetric fault conditions is proposed. Then, the equivalent models of inner rotor current control loop are established by considering the dynamic response of a rotor-side converter (RSC) and the notch filters, and the simplified calculation models of rotor fault current are established. Then, the unified fault current analytical expressions of the DFIG are obtained, which is applicable for different control strategies. Finally, the theoretical analysis results have been verified by simulation examples in PSCAD/EMTDC.The fault analysis of the power grid is a vital foundation for relay protection setting calculation, grid operation and control, and the selection of electrical equipment. The complexed fault current characteristics of new energy sources make the conventional short-circuit calculation method can be no longer applied for the power system with penetration of new energy sources. Hence, a novel fault analysis method of the power grid with new energy sources is studied. Firstly, the short-circuit calculation model of different new energy sources are established according to the LVRT control strategy of the corresponding new energy sources. Based on it, a novel fault analysis method of the power system with new energy power plant based on the symmetrical component method and a novel fault analysis method of the unbalanced distribution network with decentralized renewable energy sources are proposed, respectively. Finally, the validity and effectiveness of the proposed fault analysis methods have been verified by simulation cases.With the large-scale new energy power plant centralized connected to the power grid, the versatile operating conditions and complicated fault current characteristics of the new energy power plants make the performance of the relay protection deteriorate greatly and cannot satisfy the safe operation requirements of the power system.Based on this, take the actual wind farm for example, the performance of tradition protection, such as current protection, distance protection, line differential protection and transformer protection, are comprehensive evaluated. For the problems of fault phase selector and current protection in practical application, an improved voltage phase selector is proposed, which is based on the comparison of superimposed amplitude between phase voltage and line voltage. Moreover, an improved setting principle and calculation method of the current protection is also proposed, which is applied on the collector line of new energy power plants. A variety of simulation tests shows the effectiveness and validity of the proposed protection schemes.New energy sources decentralized connected to the smart distribution network is an important development direction for the application of large-scale renewable energy sources. Nevertheless, it has brought many new problems and challenges for the traditional protection and automatic reclosing technology in distribution network. In order to address this issue, the influence of the new energy sources in the traditional distribution network protection and automatic reclosing technology are comprehensive studied. Based on it, according to the development of smart distribution network, the networked protection system in distribution network is studied based the fault information within the protection zone. Firstly, the construction mode of the networked protection system is proposed. Then, according to the fault information within the protection zone, the centralized decision-making of the networked protection system is applied in the central unit. It can be realized the main protection and backup protection function, and can also be meet the isolated island operation requirements of the new energy sources. In addition, the problem of the asynchronous reclosing and the frequently out of operation of the new energy sources can be prevented by the proposed automatic reclosing scheme.The reasonable networking mode and bandwidth scheduling scheme of communication system has important influence on the performance of the networked protection system, and it is the key technical problems of the networked protection system need to be solved in the engineering application. The network modes of the distribution network communication system are proposed in this paper based on Ethernet passive optical network (EPON) technology. Then, according to the quality of service (QoS) requirement of different traffic classes, an improved weighted interleaved polling with adaptive cycle time (IW-IPACT) algorithm is proposed. In addition, to evaluate the real-time performance of the IW-IPACT algorithm, the upper bound for the packet delay of each traffic class was derived by using the network calculus method. Simulation results show that the bandwidth utilization and delay performance of higher and lower priority traffic were significantly improved by the IW-IPACT scheme, which means the requirement of each traffic service in smart distribution networks especially the real-time requirement of relay protection can be satisfied by the EPON.At the end of this dissertation, the research work and results are summarized and the directions of further research are pointed out. |
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