Applied Mechanics and Materials Vols. 385-386

Abstract: Large-scale wind power connected to the power system is a challenge to the traditional dispatch mode which is based on the accuracy of load forecasting and the accessibility of power, how to deal with the randomness and volatility of wind power has become a new problem facing the dispatch of power system. In this paper, an optimal power flow model with the goal of minimizing the total generation cost is established under the environment of generation market. Consider a variety of power supply in the system, the hydro and wind power should be preferentially used; Thermal power units bid for the capacity which is determined when wind power reach its maximum output at the minimum equivalent load time, and then whether the booting units can satisfy the load is checked at the maximum equivalent load time, if not, wind power will be curtailed to boot new thermal units until the load is met. Finally the example shows the feasibility of the dispatching strategies.

Abstract: Due to the lack of fossil fuels, people are paying more and more attention to renewable energy. Wind energy is one of the important renewable energy. Unpredictability and volatility of the wind source make the output power unstable, so we need to control the active Power. This paper uses fuzzy control method, and the simulation results show that fuzzy control method mentioned in this paper is better than the conventional PI control for Wind power, the nonlinear system. Based on the analysis of pitch control theory and control process, we design fuzzy pitch controller and its model. We simulates gust wind speed imitates, wind turbine control and verifies the effects of the blur pitch control in a constant speed and constant frequency wind power generation system. According to the results of the simulation, we know the pitch controller of fuzzy logic has a better effect on the active control of the generator of the wind power generation system.

Abstract: The six-phase transmission can improve the power transmission density of the transmission lines effectively, and save line corridor. To save the problem that the sensitivity of the traditional transformer backup protection is low in six-phase transmission system, a backup protection for six-phase transformer was proposed. An over-current protection criterion is proposed for interphase short circuit and opposite zero sequence over-current protection criterion is proposed for ground faults, based on the six-sequence components relationship, and the existence of six-sequence components in different fault types. Theoretical analysis and EMTDC simulation experiments prove that the scheme is feasible.

Abstract: Under partially shaded conditions, the P-U characteristic of the photovoltaic (PV) array is characterized by multiple peaks. The presence of multiple peaks reduces the effectiveness of the existing maximum power point tracking (MPPT) schemes, which refers only to the tracking of a single peak on the P-U characteristic. This paper proposes a novel method for the global MPPT. The new method starts at the starting voltage which is 80% of the open-circuit voltage of the PV array, and finds the first local maximum power point (MPP) using the perturb and observe (P&O) approach. Then the second search finds the next local MPP based on the P&O approach starting from the new starting voltage, which is determined by increasing the rate of slope of the current line at the first local MPP. The new algorithm follows this searching procedure until the global MPP is found. The new algorithm avoids searching the turning-point voltage between the two local MPP, and the voltage range swept is shortened significantly with the result of fast searching speed. Simulations validates that under partially shaded conditions the proposed new algorithm can track the global MPP with the fast tracking speed and the high precision.

Abstract: Analyzing stability of power system mainly relates to the model of machine, which can be simulated by two order and damping coefficient D (D represents mechanical damping and electrical damping), but there is no standard which can illustrate how much the damping coefficient D is. Usually power flow, excitation system, PSS and prime mover system affect the total damping largely, but have little impact on the electromechanical oscillation frequency. Firstly the paper theoretically proves the correctness of calculating electromechanical inherent frequency with system matrix. Secondly considering the damping ration characteristic of power system, the feasibility of estimating the electromechanical oscillation frequency with electromechanical inherent frequency is analyzed. With different models, the simulation results demonstrate that the electromechanical oscillation damping is affected very largely, but the frequency is affected little, which proves the effectiveness of the system matrix analysis method.

Abstract: Aiming at the problem that the failure history data available from wind turbine are scarce and often accompanied with a high degree of uncertainty, the risk assessment using traditional failure mode and effects anaysis (FMEA) may not be well-suited. A wind turbine risk assessment method based on modified FMEA is proposed. The method introduces grey theory into traditional FMEA and use the degree of relation to rank risk level. The method is then used to assess the risk of a 1.5MW wind turbine. It is proved that this method can rank the risks of main failure modes.The assessment results can be used as a support for risk based maintenance decisions.

Abstract: Permanent magnet synchronous motor (PMSM) is a system with multi-variable, strong coupling and nonlinear. It is difficult to establish its precise mathematical model, and the parameter optimization method of PMSM control system is subject to many limitations. Aiming at the design of PID tuning of PMSM control system, a chaos optimization method based on Logistic chaotic map is proposed to avoid the complex process of PMSM modeling and parameter optimization analysis. Results have shown that this method is simple and efficient with short response time and small overshoot after the parameter optimization.

Abstract: In this paper, the model of Buck Converter in DCM is built based on the theories of Hybrid Systems and Switched Linear Systems firstly. Then the output controllability of Buck Converter is studied and its sufficient and necessary condition is given. In the end, the simulation analysis and verification are provided. The research results indicate that the output of Buck Converter can be stabilized at the setting value when the condition of output controllability is satisfied, on the contrary, the output can't be controlled stably.

Abstract: Transformer is an important component of switch power supply system, the distribution parameters of the transformer affects the performance of switching power supply. This paper analyzes the simulation of transformer parameters, studies the effects of transformer leakage inductance and distributed capacitance ,and calculate it by using numerical analysis method. To ensure reliability of switch power supply , 2D modeling is used for the simulation of transformer in Ansoft Maxwell.

Abstract: Electric vehicle has aroused peoples concern with soaring energy crisis and environmental degradation. However, it has not been widely used due to some drawbacks, such as the short driving range, long charging time, frequent charging requirements and high price. In order to solve these problems, the roadway-powered electric vehicles (RPEVs) based on an inductive power transfer (IPT) has been proposed. In the segmented RPEVs system, efficiency and annual cost are affected by the track distance, tracks interval, number of tracks and installed capacity of each track, etc. Aiming to such problem, the nonlinear programming (NLP) model for segmented tracks planning of RPEVs system is studied in this paper. Meanwhile, the relationship between the system efficiency and the number of loads is analyzed as a cogent argument to the application of segmented tracks.