Asynchronous motors are important loads in power systems. Motor performance has a great influence on a power grid, especially during the motor transient process such as voltage recovery after a grid fault cleared. In this paper the voltage-sag caused by motor dynamic is analyzed and an estimated formula is deduced on the system parameters to the degree of voltage sag. Then the phenomenon of delayed voltage recovery is simulated based on a power system model via MATLAB/SIMULINK to show the influence of system and motor parameters to the degree of voltage sag and low voltage dwell time.

ABSTRACT:Vibration reduction is a hot research field on switched reluctance motor (SRM) in recent years. This paper presented a new type rotor tooth with slot on each side. By rotor profile changed, the direction of air gap flux density was altered on surface of rotor and the radial magnetic flux density would be decreased as well as the tangential flux density increased. As a result, the reduced radial force wave would depress the vibration. Meanwhile the slotted rotor would improve the torque performance of SRM. Based on 2-D finite element analysis, it was confirmed that the new type rotor could reduce the peak value of the radial force wave as well as the torque ripple rate and it was researched that how the slot dimensions influence the simulation results. Then the optimal slot parameters for the prototype motor were ascertained. Finally two 5.5kW, 1000r/min, 12/8 SRM prototypes were designed and produced to conduct a comparative experiment. It is proved that this method could reduce the vibration of SRM validly with little reduction of efficiency.

A kind of 5MW Permanent Magnet Synchronous Generator (PMSG) is designed in this paper, which structure and main parameters is determined through the analysis of key design technology of PMSG. By combining the analytical method and finite element method (FEM) to analyze the factors influencing the cogging torque, several methods are obtained to reduce the cogging torque, so as to optimize the structure of the 5MW PMSG. Through the analysis of the PMSG by using the finite-element analysis (FEA) software, the cogging torque, rated electromagnetic torque ripple, voltage waveform distortion rate and rated power all comply with the design requirements. At last, demagnetization under the condition of sudden short-circuit is analyzed.

The electrical machine using induced excitation system is a kind of brushless self-excited machine with low cost and high reliability, the induced excited machine would provide high power density at high-speed. But the low efficiency of the excitation system limits the development of this kind machine. Based on traditional excitation system, an improved construction induced excitation system is proposed in this paper. Adaptive control method is used to control the current direction in the stator auxiliary winding to replace constant DC excitation, the input current can change its direction according to the position of the rotor, the result is that all of induced currents at work in excitation system. Position sensors are fixed on the rotor and the stator field winding currents can synchronize with the rotor position according to the signal of the sensors. Experiments with the proposed structure are performed and compared with those of the traditional induced excitation system one. The results show that the new structure can improve the excitation system efficiency and reduce the cost.

This paper presents the development of a new induced excitation system in the synchronous generator. The induced excitation system is a relatively new type of brushless and exciterless machine, which offers an excellent balance between cost, reliability, power density, and high-speed capability. Aiming at the low efficiency problem of the construction of excitation system, this paper presents an improved construction method for excitation system. The result showed that it has superiority in effect.

Based on rotating coordinate system a mathematical model of permanent magnetic doubly fed induction generator (PMDFIG) is established; the control strategies for grid-connection of PMDFIG under the conditions of steady state operation and power grid voltage dip are analyzed, and steady state and dynamic models of PMDFIG are built. Results of steady state simulation show that different from traditional doubly fed induction generators, the capacity of excitation frequency converter can be decreased, and the over current in rotor and stator during disturbance of power grid can be suppressed while PMDFIG is adopted. The effectiveness of the proposed control strategy under small voltage dip of power grid is verified by dynamic simulation results.

The switched reluctance motor (SRM) has a very simple structure and a wide speed range. Its speed performance and the system stability are very excellent. But it involves complex electromagnetic interaction and parts of its magnetic path could be deeply saturated. As a result, the nonlinear magnetization characteristic of the switched reluctance motor is difficult to accurately simulate. This article proposed a nonlinear analytical model of SRMs based on the given structural parameters in Matlab environment, using the fast nonlinear method and the fast nonlinear simulation method. The simulation programming is compiled in Matlab-language. The simulation results show that the nonlinear model can produce satisfactory. The simulation speed is fast; especially it can realize real-time simulation of the new design.

To avoid unexpected equipment failures and obtain higher accuracy in diagnostic for the predictive maintenance of induction motors, online monitoring system plays an important role to improve the system reliability and availability. Condition monitoring of the large motors is usually accomplished in the industry using vibration analysis. Using traditional techniques such as capacitive and piezoelectric accelerometers, to monitor the vibration would have been influenced by the impact of the electromagnetic interference. Fiber Bragg grating sensors are increasingly used because of the non-electricity signal measurement. In this paper, the online monitoring system for motor vibration using fiber Bragg grating sensing technology is studied.

The novel high efficiency single-phase induction motor has three series-connected stator windings which connected with two capacitors, which can operate almost symmetrically with single-phase supply with higher efficiency and smaller volume than the normal single-phase motor with same rated power. Based on the symmetrical components method and the stator circuit structure of the novel single-phase induction motor with three-phase symmetrical windings and two capacitors, the balanced operation condition of the motor is deduced and the actual-variable transient simulation model of the motor is constructed in a-b-c stationary reference frame. The transient performance of the motor are simulated, and the variation patterns of capacitors to start-time, torque, and speed are presented, which are important to the design of the motor. The performance tests are done on the proposed motor and the three-phase induction motor. The simulation results from the model agree well with the experimental investigations. To improve the starting performance, starting method with two additional capacitors is proposed, and verified by simulated results. To reduce the number of starting capacitors, a new starting method with one additional starting capacitor is proposed and verified.

This paper provides a novel permanent magnet motor with composite-rotor for flux weakening. The rotor consists of two segments with different permanent magnet materials. One kind of permanent magnet material has very high coercive force and high remanence, thus a strong air gap magnetic field could form; the other has low coercive force, thus tf-axis current pulse could demagnetize it easily. The structure and operation action are proposed and the magnetization process is analyzed. Simulation by finite element method expresses the results at different flux weakening state, showing effectiveness of the magnetization models.

Electromagnetic vibration is produced by radical exciting force waves acting on iron cores of permanent magnet motors.A new method to reduce no-load exciting force waves for PM motors was proposed based on the eccentric permanent magnet pole.Expressions of Fourier transform coefficient for magnetomotive force of eccentric permanent magnet were deduced and the relationship between the amplitude of the exciting force wave and the eccentric distance was obtained.Investigation results showed that the main exciting force wave can be reduced through suitable selection of the eccentric distance.The spectrum of main exciting force waves were obtained with Fourier transform,and the finite element method results verified the effectiveness of the presented method.

The dynamic performance of the permanent magnetic dc motor (PMDM) would deteriorate with the supply which unable provides directs current. The operational performance would change and the spark was brought out on the commutator. Experiments were performed to analysis the worse of the commutation. The factors influencing on commutating on PMDM were presented based on the experimental results, and improvement of commutating is also presented.

在对变压器绕组的频率特性进行分析的基础上,根据小波变换和傅立叶变换的特性,综合运用这两种变换对信号进行处理,提出了一种新的对大型电力变压器绕组内部的局部放电进行精确定位的方法.现场模拟试验表明,该定位方法正确可行.