Search

Harmonic is an important factor threatening the safe and stable operation of HVDC system. This paper firstly analyzes the mechanism of harmonics caused by converter transformer. Then., the whole process that harmonics transfer back and forth between the AC system and DC system through the converter is studied by switching function method., which shows the frequency of harmonics is changed systematic after commutation. The analysis method of Harmonic Multi-infeed Interaction Factor for harmonic transmission characteristics in multi HVDC(DC/DC) system is proposed in this paper. Research shows the induced harmonic magnitude from remote DC converters are relative to the electrical distance. PSCAD simulations verify the methods and conclusions.

The waveform data recorded by fault indicators imply rich fault information, and effective information mining of the data can help grasp the distribution of line faults and make targeted measures in distribution networks. In this paper, a fault type identification method based on fault indicator data is proposed. With the consideration of fault indicators' characteristics, such as big error, low reliability of voltage measurement and saturation condition of measured current in short-circuit fault, the characteristics of waveform data in three-phase short circuit, phase-to-phase short circuit, phase-to-phase grounding fault and grounding fault are analyzed respectively. Based on the characteristics analysis, a multi-level fault type identification method is proposed, successfully identifying disturbance and fault, grounding fault and short-circuit fault, symmetrical short-circuit and unsymmetrical short-circuit, phase-to-phase fault and phase-to-phase grounding fault. The effectiveness of the fault type identification method proposed is verified by the field recording data collected by fault indicator. The method proposed in this paper provides a feasible method for the identification of fault type of distribution lines, and it can help master distribution laws of distribution network faults.

The wave-recording fault indicators widely used in distribution network provide a large amount of raw data which is used to judge the operation state of the distribution network. It is significant to improve the handling level of grounding fault. Firstly, This paper analyzes the invalid data of the existing transient wave-recording fault indicator. A preprocessing method of recording data, based on the characteristics of temporal and spatial distribution of recording start, was proposed. Then the tripping adaptability index is proposed which includes the probability of fault expansion, the loss of outage and the risk of personal injury. The fuzzy comprehensive evaluation method is adopted to evaluate the tripping adaptability of the current fault. Finally, based on the importance of load, an adaptive trip protection strategy for single-phase grounding fault in non-solidly grounding network is proposed.

Currently the issue of renewable energy related encourage policies, high penetration of renewable energy connect to the distribution network would lead to increased voltage levels, short circuit current increases, power supply reliability and power quality deterioration and other problems are particularly prominent. In the traditional distribution network, the uncertain factors that affect the voltage optimization result are the fluctuation of the load. The renewable energy integration represented by wind power and PV power not only changes the characteristics of the traditional distribution network power flow, but also because of its power electronic converter connection, making the distribution network voltage characteristics, whether steady or transient have brought significant changes, and then the distribution network voltage control has brought great challenges. To maintain the distribution network voltage level, how to set a reasonable control strategy for different renewable energy network connection situation makes the voltage in the distribution network be reasonably controlled and optimized to become an urgent problem to be solved. In order to achieve flexible control system supply voltage, improve the level of reactive power operation, and meet the demand of power users under the conditions of the initiative to network and renewable energy power generation operation optimization and control. In this paper, the voltage control problem of distribution network under the condition of large-scale renewable energy integration is studied. Firstly, the voltage characteristics of the distribution network under the uncertainty of renewable energy output are analyzed, and the voltage sensitivity analysis model of renewable energy connect network is established. On this basis, put forward renewable energy voltage control strategy, and finally a regional distribution network system as a case to verify the proposed method and strategy of correctness and effectiveness.