Abstract:As the requirements of economical operation and reliability on power grid are enhanced gradually nowadays, the existing under frequency load shedding (UFLS) scheme is not quite fit for the modern power system that integrates high wind power. In this paper, the impacts of high wind power penetration on the UFLS are discussed thoroughly. A novel adaptive load shedding (LS) scheme is presented taking the high wind power penetration into account. In the proposed scheme, the equivalent inertia constant (EIC) is calculated accurately to improve the power deficit accuracy so as to reduce the error of LS. The dynamic correction of power deficit is able to solve the negative effects of the wind power output random reduction/the wind generator tripping. Besides, the locking criterion is capable of avoiding the influences of the wind power output random increase on the LS, thus cutting down the LS costs and even preventing the frequency overshoot. Moreover, in terms of the LS parameters setting, the coordination of the low frequency protection of the wind generator and the frequency threshold is addressed. The location and capacity model of LS, which is based on the load characteristics, can ameliorate the frequency recovery process. Finally, the validity and robustness of the proposed scheme are verified in the simulations on the IEEE-39 bus system with high wind power penetration.

Coordination polymerization of styrene (St) using molybdenum pentachloride supported by phosphite ligand in the presence of metal organic compound was studied for the first time. The types of phosphite and co-catalysts significantly affected the catalytic activity of the molybdenum (V) (Mo(V)) active center and the number-average molecular weight ( Mn) of the resultant polymer. Among the examined catalysts, tri(nonylphenyl)phosphite (TNPP) ligand and AlOPhCH3( i-Bu)2 as co-catalyst provided the polymer with highest yield (up to 87.1%), metallocene as co-catalyst provided the polymer with highest Mn (up to 5.32 × 105). The effect of [P]/[Mo] molar ratio on catalyst activity of the polymerization was discussed and the structures of Mo·TNPP complexes were preliminarily studied by infrared (IR) and ultraviolet spectroscopies. Besides, the polystyrene (PS) samples synthesized through bulk polymerization and solution polymerization were characterized by gel permeation chromatography, IR, carbon 13 nuclear magnetic resonance, and differential scanning calorimetry, respectively, and the results indicated both of the PS had high molecular weight (approximately 105) and atactic structure. All these results demonstrated that Mo(V) catalyst system was very effective for St polymerization.

The matching characteristics of wind power output and nuclear power peak shaving are studied and the influence of coordinated dispatching of wind power and nuclear power on peak shaving flexibility and cost of the power grid is analyzed. Taking the lowest total operation cost of the system as the objective and considering the operation constraints, peak shaving cost of nuclear power units and the abandoned wind cost, a multi-power dispatching model for power system is proposed. In addition, in order to accurately optimize the output of nuclear power, a method of subdividing the peak shaving depth of nuclear power to linearize the constraint of nuclear power peak shaving is proposed. The analysis of example shows that the multi-power dispatching model considering the coordinated operation of wind and nuclear power has a high operation economy and can significantly reduce the amount of wind abandonment. The daily load tracking mode can be used for the participation of nuclear power units in daily peak shaving and the feasibility and necessity of coordinated wind-nuclear dispatching are verified.

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This paper proposes an active power control strategy for wind farms based on high-precision prediction technology. The aim of this study is to improve the absorptive capacity of large-scale wind farms, reduce network loss and promote the operation economy of wind farms. The strategy divides the active power dispatching into four layers. Based on the constraints of the safe operation of the power grid, the corresponding objective function and power allocation method for each layerare given. The result of this study shows that the strategy proposed can effectively improve the operation economy of the power grid and promote wind power consumption. Compared with the traditional control strategy, the proposed control strategy can well deal with the actual situation of large power fluctuation, and reduce the number of wind turbine start-up and shutdown.