Applied Mechanics and Materials Vols. 494-495

Abstract: In this paper, faced with the modeling problems of analysis and calculation for iron losses in variable-frequency motor under no-sinusoidal excitation, the author points out a method that the iron losses can be calculated under any magnetic field ,that is waveform-Harmonic analysis method. In consideration of the impact of Power supply harmonics, Core saturation and Skin Effect, the author proposes a new parameter -- Harmonic Loss Correction Factor. From the comparisons between the prototype test results and the theoretical results show that this method has high accuracy and strong feasibility.

Abstract: Power quality is getting worse with the extensive application of nonlinear loads, and active power filter technology is the effective way to settle the problem. This paper introduces the basic theory and the sorts of active power filters at first. Then the key technologies of active power filter are discussed in detail. Finally, based on some problems about current situation of active power filters, the directions of its development are analyzed in this paper.

Abstract: Due to excitation inrush current, no-load transformer accesses system can cause different degree of voltage sag. Therefore presents a method to estimate voltage sag caused by closing no-load transformer. Firstly, accord to the point of saturation magnetic flux and transformer core general single value curve equation to establish general nonlinear magnetization curve. Use the linear features of saturated magnetization curve segment to estimate the maximum inrush current and calculate the maximum depth of voltage sag. According to the magnetic flux decay time to estimate the duration of voltage sag. Simulate closing no-load transformer in a 10kV distribution network, and compare the simulated result with the calculated result. The results show that the proposed method is validity and accuracy.

Abstract: The reliability of Sampling and Transmitting Units (STU) are of great significance in power electronic systems. In order to reduce the sampling interruption, an FPGA-based and optic-isolated communication unit is proposed. The design philosophy and highlights of this method are described in detail. The sampled data is transmitted and received in digital mode in the STU. This unit realizes multi-channel sampling and supports simultaneous decoding of multiple fibers. It is pointed out that applications of this unit have practical value and excellent performance in isolation and transient properties in complicated power electronic systems. Waveforms and propagation delay between two nodes are presented by experimental result. The feasibility of the system design is shown through capacity calculations.

Abstract: This paper discusses the effect of power supply and power conversion structure on system operating efficiency of an EV charging station. The system efficiencies of two EV charging stations (ECS), AC bus (ABECS) and DC bus (DBECS), are evaluated by a simulation analysis. The effect of power conversion structure is investigated by an analytical model constructed in MATLAB. Based on the battery characteristics, we build an energy loss model of various components of EV charging stations with different topologies including distribution transformer, power cable and charger with different conversion structure. Using this model, the system operation efficiencies of charging stations equipped with an AC or a DC supply bus are compared. The comparative results for both power supplies, acquired by the appropriate MATLAB/Simulink simulations, are presented.

Abstract: We use Thevenin battery model and Kalman filter algorithm to online estimate lithium-ion battery pack state of charge (SOC) in this paper. In order to improve the accuracy of the model we use least square method and Dual Kalman filter (DEKF) algorithms to identify the parameters of model. The battery model can reflect the true state of internal battery well. The principle of Kalman filter algorithm is introduced. The relevant battery testing laboratory is designed. The algorithm has better accuracy when online estimate SOC and adapt to the environment well from experimental results. Finally, the convergence and robustness of DEKF algorithm are verified. It solves the problems that initial estimates are not accuracy and cumulative error.

Abstract: Experimental studies have shown that Acoustic Emission (AE) signals generated by the polluted-insulator discharge contain information of discharge energy. To extract the frequency characteristics of AE signals in polluted-insulator discharge, algorithm combining the empirical mode decomposition (EMD) and fast fourier transform (FFT) is used. Through a great many of artificial contamination experiments, the AE signals in different contamination discharge stages are collected, and the frequency characteristics can be extracted by the method presented in this article. The results show that the frequency characteristics of AE signals can be effectively extracted by the proposed method, which gives the right corresponding relationship between frequency characteristics and the polluted-insulator corona, partial and arc discharge. It also provides technical support for monitoring the intensity of polluted-insulator discharge and the change of external insulation status. The method for extracting AE signal frequency characteristics proposed in this paper has been applied to on-line monitoring of polluted-insulator external insulation status and good results have been achieved.

Abstract: The paper analyzed the influence of rotor parameters changing for the induction motor vector control, and an adaptive identification method for rotor parameters was proposed. Based on Lyapunov stabilization theory, design method of adaptive identification discipline was expatiated. The model of rotor parameters adaptive identification under induction motor vector control was completed using Matlab/Simulink. The simulation results demonstrate the feasibility of the proposed method, and it can be taken as the theory and practice reference for improve the orientation bias for vector control system.

Abstract: Model-Based Design (MBD) method is applied to power electronics device software development to overcome the problem of low efficiency in manual programming. The concept of Model-Based Design and several common development platforms are introduced. Based on tools in Simulink, an on-board charger control software is developed. Meanwhile the hardware platform, the model building, the model validation and the automatic code generation are also described. Experiments are carried out in the hardware platform to verify the correctness and feasibility of the codes.They are helpful for the software development of power electronics equipments.

Abstract: Very fast transient overvoltage (VFTO) is very dangerous for the transformer which is directly connected to gas insulated substations (GIS). At the same time, due to the continuous increasing of operating frequency in the power system, under the high frequencies of the transmission line calculation and simulation process, it is necessary to consider the frequency-dependent properties of the parameter. In order to study the voltage distribution in transformer windings under VFTO, a new Lumped parameter model which takes into account the fractional characteristics is proposed, named fractional lumped parameter model (FLP). The model divides each turn of transformer windings into proper sections, whose parameters are all lumped parameters. Finally it shows the correctness and validity of the model through the comparation of the experiment datas and simulation results.