Search

Traction power fluctuations have economic and environmental effects on high-speed railway system (HSRS). The combination of energy storage system (ESS) and HSRS shows a promising potential for utilization of regenerative braking energy and peak shaving and valley filling. This paper studies a hybrid energy storage system (HESS) for traction substation (TS) which integrates super-capacitor (SC) and vanadium redox battery (VRB). According to the characteristics of the traction load under actual operating conditions, an energy management strategy with fixed-period control (FPC) is proposed, which fully leverages the periodicity and regularity of HSRS operation. To achieve the optimal size, economic feasibility is selected as the optimization objective, which is fully assessed in terms of Net Present Value (NPV). The optimization constraints are formulated in which the Discrete Fourier Transform (DFT) is performed for power allocation between SC and VRB. Besides, an improved mutation-based particle swarm optimization (IMBPSO) is proposed to efficiently solve the optimization and enhance convergence performance. Finally, combined with the measured traction load data, the effectiveness of the FPC energy management strategy is verified and the optimal scale of the HESS is provided.

Increasing railway traffic and energy utilization issues prompt electrified railway systems to be more economical, efficient and sustainable. As regenerative braking energy in railway systems has huge potential for optimized utilization, a lot of research has been focusing on how to use the energy efficiently and gain sustainable benefits. The energy storage system is an alternative because it not only deals with regenerative braking energy but also smooths drastic fluctuation of load power profile and optimizes energy management. In this work, we propose a co-phase traction power supply system with super capacitor (CSS_SC) for the purpose of realizing the function of energy management and power quality management in electrified railways. Besides, the coordinated control strategy is presented to match four working modes, including traction, regenerative braking, peak shaving and valley filling. A corresponding simulation model is built in MATLAB/Simulink to verify the feasibility of the proposed system under dynamic working conditions. The results demonstrate that CSS_SC is flexible to deal with four different working conditions and can realize energy saving within the allowable voltage unbalance of 0.008% in simulation in contrast to 1.3% of the standard limit. With such a control strategy, the performance of super capacitor is controlled to comply with efficiency and safety constraints. Finally, a case study demonstrates the improvement in power fluctuation with the valley-to-peak ratio reduced by 20.3% and the daily load factor increased by 17.9%.

The rational use of regenerative braking energy for urban rail transit trains directly affects the voltage safety of the traction power supply system and the electric braking function of the train. It is also of great significance for the implementation of train traction energy saving. This paper proposes a scheme of train regenerative braking ground absorbing device based on super-capacitor energy storage. It adopts multiple modular Buck/Boost DC conversion topology to realize bidirectional control of electric energy and stabilize the secondary utilization of traction network voltage and regenerative electric energy. According to the scheme of this paper, the energy storage device was developed and verified in the engineering of the Guangzhou Line 6 main line traction substation. The test indicators have met the design expectations.

The accuracy of wind speed forecasting is related to the wind power scheduling. When large-scale wind power connected grid, it also affects the stability of the grid. This paper applies time series model and Back Propagation (BP) neural network model to predict wind speed. Finally, a combination model of time series and BP neural network is proposed. In the combination model, the inputs of BP neural network are made up of historical data and residual errors calculated by time series model. The model can be more accurately in the short-time wind speed forecasting. And then shows an actual example.

In the design of high-speed railway's traction power supply system, the choice for exterior power supply concerns many factors, and is a multi-criterion decision problem. In this paper, the principle of analytic hierarchy process (AHP) based on rough set theory and group decision-making is presented. An index system of exterior power supply evaluation is then constructed. Through independent decision making of each expert and the definition of the attribute significance based on the weighted sum, the weight values of alternatives is obtained and ranked, the quantitative description of decision process is realized and the optimum scheme for exterior power supply is determined. Taking an under construction high-speed railway for example, the availability and reasonableness of the proposed method is demonstrated.

The problem of urban rail train energy saving control with specified running time is a typical multi-constrains, non-linear optimization problem. By applying minimum principle to differential motion model of trains, the energy saving control strategies are obtained. An approach for optimizing problem based on variable-length real matrix coding multi-population genetic algorithm (MPGA) is presented. The train running is simulated by a multi-particle simulator considering complicated line conditions and influence of train length. The GA chromosome consisting of a variable-length two dimensional real matrix represents the train control sequence. A variable length operator based on annealing selection is introduced to enhance global search performance. Fitness sharing keeps population's multiplicity. Multi-population parallel search improves convergence rate and evolution stability. The correctness and advancement of the optimization control method have been validated through the simulation platform of train operation.

This paper presents a method of GPS differential positioning based on pseudorange. Both the generation and encoding of differential data based on pseudorange and differential data transmission protocol based on Interne are mainly discussed in the paper. An improved communication protocol is proposed which can decrease the transmission quantity without changing the differential positioning accuracy. The comparison between original data and coding data and the improved coding data are tested by instantiations. Experimental results show the modified coding method decrease the transmitted data amounts compared with the point positioning. When there are more than 9 satellites, the transmission quality acquired by this advanced communication protocol is only 70 percent of the RTCM protocol and the accuracy of the differential position is greatly improved.

In view of the facts that complexity of life distributions of the parts, classical exponential distributions can't truthfully and profoundly portray it due to inconsideration depreciation behavior impacts in process of the elements life, therefore, under many situations, the acquired results do not accord with objectivity. However, once deviating from the assumption of the exponential distributions, quantitative analysis of the stochastic life will face difficulties. Therefore, in accordance with the characteristics of phase-type(PH) distributions of its approaching all distributions in nature, the paper applies the rough function concept to construct the PH distribution function sets called the upper approaching and the lower approaching sets, the upper approaching function set is those smallest distribution functions whose lives are bigger than practical life, the lower approaching distribution function set is those largest distribution functions whose lives are smaller than practical life, the boundary between them is a measurable domain of practical life distributions. The section is created in [0,+infin) by PH distribution function classes, after a larger number of the elements lives are tested and processed, the life distributions of the tested elements only rely on its location in the boundary. Obviously, the lower approaching function sets are those PH distributions that all tested elements lives are bigger than their lives, and the upper approaching function sets are those PH distributions that all tested elements lives are lower than their lives, the remained PH distribution classes can more accurately approach practical life of the elements. The paper forecasts the life distributions of the elements by using of mixed Erlang distribution, a sort of PH distribution function classes, research results show that the method is simple and flexible, and is an instruction idea for evaluation of life or life distributions of the elements, and relatively more accurate than conventional ways based on exponential distributions, and more robust

This paper presents a wavelet based commutation failure (CF) detection technique in HVDC system, and selects the suitable mother wavelet. The different properties of wavelets are analyzed in detail. It is shown that the orthogonality, regularity, moments, and symmetry of a wavelet function may affect the CF detection to some extent, and the critical factor is the moments of the mother wavelet. Discrete Wavelet Transform (DWT) has executed respectively on normal sinusoidal voltage signal and alternative voltage record with CF in Tianguang HVDC project. The transform result shows that DWT by Daubechies wavelet function with high vanishing moments is a cogent tool for CF detection in HVDC system.