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Ma W.,Guodian Nanjing Automation Co.
Dianli Zidonghua Shebei/Electric Power Automation Equipment | Year: 2011

For the increasing rate of wind generation capacity, higher requests are brought to the capacity of low voltage ride through for the wind generation on grid. Based on the grid connection guidelines of wind turbine, the operation of DFIG (Doubly-Fed Induction Generator) wind turbine during grid voltage sag is analyzed and it is proposed to apply Crowbar circuit in the protection of rotor excitation source and generator. The wind farm model is built with Matlab/Simulink to validate its effectiveness. Simulative results show that the circuit ensures the safety of system components by limiting the maximum current generated by the rotor circuit during voltage sags, and the AC excitation DFIG can operate in connection with grid to stabilize the grid voltage during fault.

Chen F.,Guodian Nanjing Automation Co.
Dianli Zidonghua Shebei/Electric Power Automation Equipment | Year: 2014

The behavior of distance protection under CT(Current Transformer) disconnection is studied and its influence is analyzed based on the fault-circuit resistance measured by the protection, which shows that the influencing factors are the direction of power flow and the position of faulty phase. At the power-source side, the grounding-fault distance protection tends towards the miss operation when the in-zone fault occurs in the leading phase relative to the phase of CT disconnection and towards the improper operation when the out-zone fault occurs in the lagging phase relative to the phase of CT disconnection, while it behaviors on the contrary at the load side. Combined with the method of CT disconnection detection, an adaptive grounding-fault distance protection scheme is proposed, which is theoretically analyzed and verified by the test. Suggestions are given on the CT circuit and protection configuration. ©, 2014, Electric Power Automation Equipment Press. All right reserved.

Chen D.,Guodian Nanjing Automation Co. | Xu L.,University of Strathclyde | Yao L.,China Electric Power Research Institute
IEEE Transactions on Power Delivery | Year: 2013

System control for dc microgrids with variable generations and energy storage is proposed in this paper. An autonomous three-level control strategy is proposed for dc microgrids with selective slack terminal(s) assigned to each operation level. The system operational status is acknowledged via the common dc voltage and the transitions between different operational levels are triggered by its variation. A four-terminal sample dc microgrid system with a grid-connected voltage-source converter, a wind turbine, an energy storage system, and dc loads are established and a specific control scheme is outlined to demonstrate the proposed strategy during various operating conditions, such as load step, generation fluctuation, islanding, grid reconnection, load shedding, and generation curtailment. The control strategy and the specific scheme are validated by experimental results conducted on a prototype dc microgrid system. © 1986-2012 IEEE.

Fang G.-Z.,Harbin University of Science and Technology | Yang C.,Guodian Nanjing Automation Co. | Zhao H.,Harbin University of Science and Technology
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2012

In view of the fences phenomenon, spectrum leakage and issues of slow identification and location and weak real-time performance caused by complicated computation that exist in the harmonic detection, a comprehensive harmonic detection method is presented based on FFT and wavelet packet transform. This method uses the excellent amplitude frequency characteristics of FFT to identify the harmonic component, uses the excellent time-frequency characteristics of wavelet packet to locate the time of harmonic occurrence and end quickly and selectively, at the same time extracts the contained harmonic component, so that it can reduce the computation and improve the real-time performance of the harmonic detection. Using Matlab to simulate the comprehensive harmonic detection method, it shows that the comprehensive harmonic detection method is more effective than the common detection methods.

Hu D.,Guodian Nanjing Automation Co. | Wo J.,Jinhua Electrical Power Bureau
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2010

Considering characteristics of eliminating hard cable circuits in smart substations, implementation of integrated virtual circuit system (VCS) based on network information sharing is proposed. IEC 61850 modeling is used to express design, and system integration, debug and configuration, running repair etc. are all achieved by automatic software tools according to the unified information. For VCS of smart substation it needs to suitably expand and improve IEC 61850 standard. GMRP should be applied to achieve automatically network multicast management, and design and system integration should be fully integrated. Common software of 3rd party may be developed based on the uniform standard, so virtual circuits are easily expressed, understood, implemented and maintained by each professional. Work of information repeat configuration is fully minimized so as to avoid man-made errors. © 2010 State Grid Electric Power Research Institute Press.

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