Applied Mechanics and Materials Vols. 380-384

Abstract: The disadvantages of two existing traction power supply modes are analyzed and advanced co-phase traction power supply system based on three-phase to single-phase converter is studied in the paper. Then, the chain model of network and the constant power model of locomotive are established. According to the above results, further analysis of the circulating-impedance and the feasibility study of droop control in this system are presented. The circulating-current analysis results of the advanced co-phase traction power supply system and the droop control of the system are given in the end of the paper.

Abstract: Due to its great potential value in theory and application, nonlinear control strategies of doubly fed induction generator (DFIG), especially passivity-based control (PBC) methods, have been a focus in the literature. A PBC strategy for DFIG with time-varying load torque to track flux and speed trajectories is proposed in this paper. The key point of this method is the identification of terms, known as workless forces, which appear in the dynamic equations of DFIG but have no effect on the energy balance equation of the closed loop. The speed of DFIG is estimated via an ANN estimator avoiding the use of mechanical sensors. PBC combined with ANN speed estimator not only reserves the advantages of PBC such as nonexistence of singularity, but also rejects the flux and speed tracking error caused by stator and rotor resistance variation. This algorithm simplifies the control structure and enhances the robustness of the control system. The feasibility and effectiveness is testified by the experimental results based on dSPACE.

Abstract: In order to help the transportation enterprises strengthen their competitiveness, this study proposed a digital photo frame which based on the ARM9 family processor chip S3C2440, Linux operating system and Qt/Embedded, trying to make it different from the traditional frames in terms of function, capacity and operability. It focuses on the hardware circuit and the pivotal part of software which can successfully realize playing many formats of photos like magic lantern by the touch screen and audio files. The result of the experiment shows that the digital photo frame designed in the thesis works steadily, and it is easy to operate as well as it has strong expansibility. By adding some applications to the digital photo frame, it can complete many other functions.

Abstract: To improve the disadvantage of DC-DC converter output voltage fluctuation when output current changes in wide range, a compensation circuit for improving DC-DC converter dynamic response was presented. The circuit was based on the theory of parallel or anti-parallel capacitor. A charged capacitor was paralleled when output current positive jumped. A charged capacitor was anti-paralleled when output current negative jumped. It worked when output current changed. So DC-DC converter dynamic response was improved and efficiency could be high in the same time. The simulation results proved that the effect of compensation circuit in improving the converter dynamic response and stabilizing the output voltage.

Abstract: Zvzcs-pwm inverter combines the advantages of ZVS-PWM inverter and ZCS-PWM inverter, it can solve the problems of switching loses and extra circulation. Furthermore, it is provided with less duty cycle loss, small parasitic oscillation of the secondary side and large load rage conducted by soft-switching. A conjoint system based on MCU and DSP can make full use of the advanced ability of the event management, data processing and computing speed, which improves accuracy and real-time digital control of arc welding power. This paper introduces design of main circuit and control circuit of arc welding power and the working process of the zvzcs-pwm inverter. The simulation with matlab demonstrates the feasibility of the design.

Abstract: As a new type of pulse width modulate converter,the input current of matrix rectifier consists of a great deal of high-frequency harmony current. The harmony has a bad influence on the net side. So a input filter is needed to eliminate it. Through the approach of Fourier transform, the harmony wave of the matrix rectifier is discussed, and the conclusion of the value of high-harmony and the induction in inverse proportion is deduced. The inactive power that the capacitance absorbe determines its value. The range of the resonance frequency determine the range of the induction. From above analysis a basic design of input LC filter of matrix converter is given. The input filter has been verified in the matlab/simulink and good performances are achieved.

Abstract: According to the power quality problems of micro-grid, this paper presents a control program of the Unified Power Quality Conditioner (UPQC) to improve the micro-grid power quality.The shunt side of UPQC is used to eliminate the harmonic current brought by nonlinear load into the micro-grid. And the conditioner series part is used to suppress distributed new energy generation intermittence. In the paper synchronous coordinate transformation is used to detect compensated components and tracking control method is adopted to control the converter. The simulation results demonstrate the effectiveness of the UPQC on improving the power quality of the micro-grid.

Abstract: in view of the current high rate of abandoned wind, photovoltaic power generation costs and wind-fire bundling mode, in the active power control of the wind of low load operation of motor fluctuations in the fire team leader, the subject in the study of wind power, photovoltaic power generation, power, battery energy storage based on the load response characteristic, design the scheduler, a wind and photovoltaic power plant active power scheduling for equipment, allocation of plant-level optimal load distribution system of the thermal power plant joint scheduling, in order to improve the stability of output of new energy, reduce the energy consumption of the whole network. At the same time, the wind and photovoltaic power plant energy storage system and wind farm output coordination problem is equivalent to a mixed integer programming problem to be solved, to simultaneously determine fans and solar panels and bear the load rate; for thermal power plant load distribution optimization design of the minimum unit involved in strategy reduces the effect of variable load, variable load on set pressure and high temperature parts life. This topic to some extent to improve the wind energy and solar energy utilization, helps to reduce the carbon fuel usage, has certain theoretical and practical significance.

Abstract: When fault occurs in power system, the duration of voltage sag is determined by the fault clearing time of the protection system. In order to describe the duration of voltage sag more accurately, the time characteristic of protection system is considered for stochastic assessment of voltage sag. Based on the traditional assessment model, the mapping relationship between the time characteristic of protection system and voltage sag frequency is established using fault positions method. The proposed method is applied to the IEEE-30 bus test system, simulation results show that the time characteristic of protection system has an obvious influence on the duration of voltage sag, and very serious errors will be produced if the time characteristic of protection system is ignored. The proposed method is simple, adaptive and practical, and it is of academic value and practical foreground.

Abstract: An inverter arranged in the photovoltaic generating system is required to be with higher working efficiency and lower degree of distortion on waveform. In this thesis, mathematic model of inverter has been given out through an analysis using the structure of two-level inverter, and then put forward a traditional PID control in combination with rerunning control for output waveform from an inverter. It has been proven through simulation effects that a better control precision for output waveform can be given out by this method.