This study presents a 'seek' and 'check' approach to determine the operating area of the modular multilevel converter based high-voltage direct current (MMC-HVDC) transmission systems. First, the equivalent circuit for analysing the operating area of MMC-HVDC systems is derived and the operating area is represented by discrete operating points. Then, three operating constraints are proposed according to the MMC operation principles, i.e. the voltage, current and voltage stability constraints. Therefore, the determination of the operating area is transformed into checking whether the operating point meets the proposed constraints. The case studies are performed on a oneterminal MMC-HVDC system under six typical short circuit ratios. The results show that the top boundary of the operating area is limited by the voltage constraint, and the bottom boundary of the operating area is limited by the current constraint. The influence of the third harmonic injection and the ac impedance characteristic on the operating area is also studied. Lastly, the validity of the 'seek' and 'check' approach is proved by time-domain simulation results.
B 2014, 'Analysis of significant factors on cable failure using the Cox proportional hazard model', IEEE Transactions on Power Delivery, vol. 29, no. 2, pp. 951-957. https://doi.
Abstract-This paper proposes the use of the Cox ProportionalHazard Model (Cox PHM), a statistical model, for the analysis of early-failure data associated with power cables. The Cox PHM analyses simultaneously a set of covariates and identifies those which have significant effects on the cable failures. In order to demonstrate the appropriateness of the model, relevant historical failure data related to Medium Voltage (MV, rated at 10kV) distribution cables and High Voltage (HV, 110kV and 220kV) transmission cables have been collected from a regional electricity company in China. Results prove that the model is more robust than the Weibull distribution in that failure data does not have to be homogeneous. Results also demonstrate that the method can single out a case of poor manufacturing quality with a particular cable joint provider by using the hypothesis test of p-value (5%). The proposed approach can potentially help to resolve any legal dispute that may arise between a manufacturer and a network operator, in addition to providing guidance for improving future practice in cable procurement, design, installations and maintenance.
Index Terms-power cable, cable failures, Cox ProportionalHazard Model, hazard function, influencing factors, covariate.
With the rapid development of intelligent buildings, a lot of researchers have found that it is difficult to establish mathematical model when the problem that energy-saving in water supply system of an intelligent building tank is focused, because that the outflow of the tank volume is volatile when the water is daily living water. In this paper, fuzzy control theory is used to establish a fluid level, and the fluid input flow rate to determine the amount of control, which to push the valve’s opening size and speed in order to control the water supply valve opening adjustment level, so that the liquid position of container maintains a constant, and the MATLAB software is used to verify the effect of fuzzy control system. The results show that in this fuzzy control system the benefits of economic operation of water supply can be ensured by ensuring a constant level of liquid.
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