Applied Mechanics and Materials Vols. 341-342

Abstract: A variable speed engine generator set for an isolated power system is investigated to reduce fuel consumption and emission than conventional fixed speed engine generator. An inverter incorporated with the variable speed gasoline engine generator set can improve dynamic characteristics under a sudden load change, and power quality, fuel consumption, and emission of pollutants can be improved remarkably. The superiority of a fuzzy neural network control to the engine speed and a digital PID controller to the inverter is verified by the experimental results.

Abstract: The article describes how to use MCU that the latest low-cost of ATMEL SAM3 series to achieve the ideas and implementation methods of smart grid collector, and elaborates the specific programs from hardware to software implementation process. The schemes has the advantages of low-cost, high-performance, and high-reliability and meets the actual needs of hardware resources, the demanding requirement of cost-performance and reliability in the power industry, and now it has been applied in the National Grid collector.

Abstract: Cell imbalance is one of the key factors that limit the capacity and power of battery energy storage systems (BESS), especially the large lithium-ion battery packs. To deal with the unbalancing problem, an effective balancing circuit is required, so is an optimal balancing strategy. In this paper, an optimal strategy for cells balancing has been presented. Contrary to the conventional balancing algorithms which base on instantaneous voltage or state-of-charge (SOC) no matter what the cause of imbalance is, the proposed strategy is targeted to different imbalance situations. Four cases of cell imbalance have been analyzed and the balancing effects of different algorithms are discussed. The simulation results show that the proposed strategy improves the performances of battery packs, including the usable capacity and maximum power.

Abstract: The random variation of wind speed causes active power and reactive power injection of large-scale wind base to fluctuate constantly, this in turn leads to voltage fluctuation and unqualified voltage amplitudes of this area. This article proposes quantitative voltage control to solve this problem. Firstly, analyze the reason and characteristic of voltage fluctuation in large-scale wind base. Then apply sensitivity method to derive voltage/reactive power sensitivity coefficient matrix; this matrix is the product of two special matrices, one is symmetric and the other is diagonal. It can be demonstrated that the symmetric one has a relatively bigger value at the diagonal line; combined with the diagonal one, several simple conclusions can be obtained. According to the conclusions, quantitative voltage control flow can be established. In addition, operating mode of wind turbine generator is taken into account in the simulation process. Simulation results of IEEE 9 nodes system and an actual system demonstrate the validity of proposed measures.

Abstract: Characteristics of ultracapacitor and classic model have been introduced in this paper. Due to its superior performance, ultracapacitor is used for hybrid energy storage system with lead-acid battery. The performance and potential application of hybrid energy storage system have been elaborated, which make some contribution to the promotion and application of energy storage technology.

Abstract: Accurate short-term wind power forecasting has important significance to safety, stability and economy of power system dispatching and also it is a difficult problem in practical engineering application. In this paper, by use of the data of numerical weather forecast, such as wind speed, wind direction, temperature, relative humidity and pressure of atmosphere, a short-term wind power forecasting system based on BP neural network has been developed. For verifying the feasibility of the system, some experiments have been were carried out. The results show that the system is capable of predicting accurately the wind power of future 24 hours and the forecasting accuracy of 85.6% is obtained. The work of this paper has important engineering directive significance to the similar wind power forecasting system.

Abstract: Microcomputer relay is a kind of intelligent devices used for detecting and protecting power system. Whenever, it quickly calculate whether the power system is wrong or not on the basis of the fundamental and harmonics detected from power system, And according to the calculating results to obviate the troubles, among them, the fundamental and harmonics acquired accurately in time is the most important part of the power system protection process. The basic principle of d-q fundamental and harmonics voltage detection is presented and on this basis a fundamental and harmonics detection method of presumption the transformation frequency is put forward. The results of the theoretical analysis and MATLAB simulation indicate that the d-q method in this paper can precisely detect the voltage and frequency change of the power system in time, whether the distortion voltage or not in three-phase power system .

Abstract: Uses cost-benefit analysis theory, combined with analytic hierarchy process, set up the cost benefit analysis index system for hebei province, Quantitative study the present situation and problems of photovoltaic power generation enterprises in hebei, then put forward the development countermeasures, which can make Hebei find suitable mode for their own photovoltaic development according to their characteristics.

Abstract: Traditional methods of AC/AC converters have general drawbacks: output voltage is lower than input voltage, the input side THD is poor and output voltage frequency is lower than input voltage frequency by using voltage regulation method and cycloconverters. We introduce the novel approach - DC-modulated AC/AC converters in this paper, which successfully overcomes the drawbacks. Simulation and experimental results of the DC-modulated AC/AC converter are the evidences to verify our design. These methods will be very widely used in industrial applications.

Abstract: This paper described the ship power system digital simulation technology is object-oriented simulation technology, it adopts the modular design and layered structure, among them, the modular design to enhance the simulation agility and scalability, and hierarchical structure is in reducing modeling workload at the same time greatly improve the simulation efficiency. Therefore, this technology in the ship power system digital simulation field has high practical value and broad application prospect.