Search

— In this article, the finite-element method is used to study the impact on a generator's electromagnetic torque by the position and level of a rotor winding interturn short circuit. The rules involving changes to the exciting current and the reactive power of generators are analyzed under the given adjustment patterns. The results of this study show that the saturability of ferromagnetic materials reduces the torque undulations that occur during the rotor winding interturn short circuit fault and that it improves the static stability of generators. Both the simulation experiment and the real case of a rotor winding interturn short circuit demonstrated that when a rotor winding interturn short circuit happens in a turbine generator, the generator can maintain its static stability by adjusting its state variables. This results in an increased exciting current and a decreased reactive power. The analytical method described herein allows accurate prediction of the change limits of the exciting curren...

In some important industrial applications, motor bus transfer often takes place in order to guarantee the reliability and stability of the power supply. However, in the adverse condition, the stator transient currents of motor are very considerable during bus transfer. A thyristor-based control method, which can suppress the stator inrush currents, is presented for the motor soft transfer between sources. Under the implementation of the method, the phase-sequence of the stator windings connected to power source would be BC-ABC-AB-ABC-CA-ABC-. In order to study the complicated transition process between two-phase and three-phase connection, an analytical method is employed in this paper since it is more rapid and efficient than the numerical simulation when the rotor speed is nearly invariant. Then, a group of consistent mathematic models based on space vector is proposed for the alternative transient, especially for three different asymmetrical transient of motor with two-phase connection. Thereafter, the analytical method is detailed for the asymmetrical transient. The results of analytical calculation for two cases are shown and compared with field test and numerical simulation respectively. And the accordance of results verifies the validity and effectiveness of the proposed analytical method and transient models.

A direct type multilevel current source inverter (CSI) and its closed-loop strategy are studied in this paper. In the three phase static symmetric axes (a, b, c), parameters on the AC side of the three phase five-level CSI are time-variant AC variables, which is a difficult point in the designing of control system. So a direct current control method based on the synchronous rotational axes (d, q, 0) is proposed. This strategy transforms AC variables in the three-phase static symmetric axes into direct values in the synchronous rotational axes (d, q, 0), so the problem of controlling the AC variables is transformed into adjusting the direct values. This control strategy has little influence over changes of system parameter, it suit well with linear system and nonlinear system. Simulations are carried out with software PSIM to confirm feasibility of the proposed control method.

The locomotive battery requests its testing system special requirements of excellent DC charge/discharge current which is sensitive to the fluctuation of the voltage. It also needs a fast transfer speed between charge and discharge state. Simple converters without appropriate filter can't meet the requirement mentioned above. The decay of the Chebyshev filter increases fast with frequency in the stop-band. As a low-pass filter, it avoids the influence to DC component when filtering low order harmonics. It is very benefit in filter design for bidirectional converters. But the traditional theory for filter-order design is based on the decay of not only stop-band but also pass-band, and the latter is not important in DC filter design. This paper extracts an equation of filter-order design for bidirectional converters which care more on the decay in stop band and introduced a method for enhance the response speed between bidirectional transitions. The theoretical deduction and simulation proved the practicability of the methods.

As the structure of generator is complex, and the saturated magnetic field is nonlinear, it is difficult to use generator's mathematic model to calculate field current directly, and then hard to use the deduced method to identify rotor interturn short-circuit fault, the computation time is long, and the computation precision is not good, so it is difficult to diagnose online. We proposed a new Radial Basis Function Network (RBFN) in this paper, it is two levels iteration clustering algorithm. This method overcomes the shortcomings that other algorithm have, it can compute the nerve unit number, center and width of RBSN implication layer automatically, and the clustering result is more reasonable, consequently increase the precision of RBSN. In condition of not adding any equipment, using actual measured inactive power, active power and terminal voltage etc. electric parameters of QFSN-300-2 generator as input, and in virtue of self-adaptive RBSN to identify generator field current, combining rotor inter-turn short-circuit fault diagnosis model to identify rotor inter-turn short-circuit fault online, it is faster than simply use generator mathematic model, and has high precision. After certification, the result is: comparing to the traditional diagnosis model, it increases the diagnosis precision and speed greatly, and satisfies the need of online identification.

Generator vibration characteristic and electric characteristic are analyzed when the rotor winding inter-turn short circuit fault has happened. First, the generator parameters of air-gap magnetomotive force, air-gap magnetic permeability and magnetic flux density on the fault are calculated, and the frequency characteristic of imbalance pull acting on rotor and that of pulsating magnetic pull acting on stator core are analyzed, then the rotor and stator radial vibration characteristics are gotten, which are that rotor vibration of fundamental frequency will increase, and stator vibration of second power frequency will decrease for one pair of poles generator. Next, the electric characteristic is analyzed, which is that the second harmonics circulating current between the stator winding parallel branches will increase when the fault occurs. Synthetically considering the vibration and circulating current characteristics, a method of the rotor winding inter-turn short circuit fault diagnosis, based on compositive characteristics of generator vibration and stator current, is developed. Finally, the vibration and circulating current of a type SDF-9 generator is measured in the laboratory to verify the theoretical analysis presented above.

This paper describes a direct phase control scheme for unity power factor three-phase Buck type rectifier modulated with space vector PWM method (SVPWM). The advantages of the developed system are low harmonic distortion in ac supply currents, nearly unity power factor over wide operating scope, easily realization. The theory analysis and modeling method are introduced first. Second, the control scheme and implementation based on FPGA is put forward. Finally, the characteristics of the developed rectifier are tested from experiments. It is proved from simulation and experiments that the developed rectifier, using direct phase control scheme, has good dynamic and static performance though the PWM frequency is rather low.

According to the system model of three phase current-source PWM rectifier in the d-q synchronous reference frames and based on nonlinear differential geometric theory, the geometric condition to apply the nonlinear differential geometric techniques is analyzed, the nonlinear control of current source PWM rectifier is proposed, which achieves decoupled control of d axis and q axis component of ac current. The stabilization of zero-dynamic is analyzed, and a state feedback controller cascade to inner current loop is designed to control the zero dynamics. Simulations show that the proposed control strategy can achieve better dynamic and static character. (6 pages)

Because of the wide application of power electronics equipments, harmonic pollution to power system caused by these nonlinear loads is increasingly severe. With the advantages such as simple structure, lower cost and so on, passive power filters (PPF) is the most wide used harmonic suppression device at present. To plan PPF optimally, optimizing targets including effect of harmonics suppression, original investment and reactive power compensation must be met, but traditional design of PPF is based on experience or consideration of part of economical and technical targets, so the optimal solution can't be acquired. Simulated annealing algorithm (SAA) is a random optimal-solution searching algorithm based on Monte Carlo iteration solution strategy. Began from a initial temperature, random search is progressed among solution space by adopting the metropolis sampling strategy with probability kick character, the sampling process is repeated with the temperature falling, at last, the global optimal solution is acquired. In this paper, four optimal sub-target functions are constructed then the general optimal target function is constructed as the linear weighted sum of the four sub-functions and is solved by SAA. The validity of the method is tested by experiment result, which shows that a better general character of PPF in accordance with the optimizing targets can be presented

Through calculating the generator parameters of air-gap magnetomotive force, magnetic permeability, magnetic flux density, stator winding parallel-connected branches electromotive force distribution, the characteristics of the stator winding parallel-connected branches circulating current are analyzed. The results discover that the second harmonics circulating current will increase when the rotor winding inter-turn short circuit fault occurs, and the fundamental circulating current will increase when the stator winding inter-turn short circuit fault or the air-gap eccentricity fault occurs, neither being strongly affected by the imbalance fault Considering the differences of the circulating current characteristics caused by different generator faults, a method of generator fault diagnosis, based on the stator winding parallel-connected branches circulating current characteristics, is developed. Finally, the circulating current of a type SDF-9 generator is measured in the laboratory to verify the theoretical analysis presented above.

Based on the multiloop model presented previously, the transient simulation of stator winding inter-turn short circuit fault (SWITSCF) in induction motors, as well as the relevant experiments, has been completed. By thoroughly analyzing the simulation results under a variety of conditions, this paper draws a conclusion that stator negative sequence apparent impedance is the most reliable fault feature with satisfactory sensitivity for the SWITSCF detection. Meanwhile, the experiment results clearly indicate that, for an actual motor operating on site, stator negative sequence apparent impedance is fluctuating with time to a certain extent, as would deteriorate the detection reliability/sensitivity. As a result, the low-pass-filtered stator negative sequence apparent impedance is chosen as the fault feature to reliably and sensitively detect SWITSCF in induction motors. The experiment results demonstrate that this technique is valid and effective for the SWITSCF detection.

This paper emphasizes to develop a hybrid detection scheme for induction motor broken rotor bar fault, taking into account the intrinsic asymmetry, air-gap eccentricity and rotor misalignment of induction motors. Firstly, numerical simulation and related experiments of broken rotor bar fault have been performed successfully. Secondly, a series of principles and methods, which assure the sensitivity and reliability of broken rotor bar fault detection in practice, are generalized and revealed, based on thorough analysis of simulation and experimental results. Finally, a hybrid scheme to detect broken rotor bar fault, which blends continuous subdivision Fourier transform, self-adaptive filter, rotor slot harmonics based slip estimation and detection threshold self-tuning technique perfectly, is proposed in this paper. Fault detection instances in laboratory demonstrate that the presented scheme is valid and effective.

In this paper, the advanced H/sub /spl infin//-optimization control theory is concretely applied to the controller design of power quality regulation equipments. A novel control method of waveform tracking compensation control based on H/sub /spl infin// model matching technology is proposed for the first time. In addition, the control principle and physical essence of this method are profoundly expatriated. Moreover, the H/sub /spl infin// standard control block diagram and the state space expression of model matching system are given. This H/sub /spl infin//-optimization control method, which has both strict mathematical basis and explicit physical meaning, can be used not only for realizing the optimal design to improve control precision, but also for assuring the designed closed-loop control system to be internally stable. This study establishes the well-knit theoretical basis for improving the compensation control characters of power quality regulation equipments. By adopting this method, the dynamic tracking compensation optimization control of voltage and current waveform can be conveniently implemented, and its validity has been testified successfully.

The stator temperature monitoring is very important in order to ensure the safe and economy operation of turbo-generator. Thus, the paper researches the stator thermo-hydraulic model on generator's load varying with accordance with the transfer theory and fluid mechanic theory, deduces cooling-water temperature distribution in hollow strands along axial direction in detail, and disperses the solid and cooling-fluid temperature model with equivalent thermal net method to obtain non-linear equations about temperature. The solid and cooling-fluid temperature equations are solved simultaneously in order to obtain the stator 3D temperature field. In the end, the paper calculates the stator temperature field and relationship between temperature of different position with time about QFSN-220-2 turbo-generator. The results show the presented model and calculation method to be correct

Stator and rotor vibration characteristics of generator are analyzed when the rotor winding inter-turn short circuit fault and the imbalance fault occur. The rotor vibration of fundamental frequency increases and the stator vibration of second frequency decreases when the rotor winding inter-turn short circuit fault occurs. But when the imbalance fault occurs, the rotor vibration of fundamental frequency increases and the stator vibration of second frequency increases too, so the stator vibration characteristics are different from that of the rotor winding inter-turn short circuit fault. Considering the differences of the stator vibration, a new diagnosis method of rotor fault, based on stator and rotor vibration characteristics, is developed. Comparing to the traditional method that only considering the rotor vibration signals, the rotor winding inter-turn short circuit fault and imbalance fault can be effectively diagnosed. Finally, the vibration data of a type of SDF-9 generator are measured in the laboratory to verify the theoretical analysis presented above

The paper presents a method of space vector pulse width modulation (SVPWM) based on DSP for permanent magnet synchronous controller in radar servo system. It discusses the control method of SVPWM and indicates its advantages in PMSM drive. The paper also presents how the parts of hardware has been selected to perform field oriented control function in order to implementing controller for PMSM. At last it gives out the results of simulation and tests, and it validates that the controller we designed and developed can meet the demand in radar servo system

A dynamic model and simulation method of turbo-generator by reluctance network model is presented. The reluctance network model is based on the analogy between magnetic and electric circuits, and each tooth, yoke and slot of generator is expressed one of magnetic conductor cell, its main advantages are to take into the rotor movement and core saturation effects, with a good compromise between calculation time and accuracy of results. Then the generator status differential equations based on the reluctance network model are developed, whose parameters are stator winding branch current, stator reluctance, rotor reluctance, air-gap reluctance, and rotor magnetomotive force. Finally, it is applied to the study of the rotor winding inter-turn short circuit fault of turbo-generator, and main results are presented and compared to experiments

This paper aims to the detection of stator winding inter-turn short circuit fault (SWITSCF) in induction motors. Firstly, the multi-loop mathematical models of squirrel cage induction motor, YN, Y or D connected, under the conditions that the motor is healthy/faulty with stator winding inter-turn shorts, are developed. Secondly, the transient simulation of SWITSCF as well as the related experiment is completed. By thoroughly analyzing the simulation and experiment results, a series of interesting highlights to guarantee the sensitivity and reliability of the detection scheme for SWITSCF have been revealed explicitly. Furthermore, a novel detection method for SWITSCF, which takes the filtered value of stator negative sequence apparent impedance as the fault feature, is presented. Experiment results demonstrate that it is effective

The stator-rotor-hybrid fault in squirrel cage induction motors, which means that rotor bar breaking fault and stator winding inter-turn short circuit fault occur simultaneously, has been investigated based on the motor multi-loop model. The results indicate that the features of rotor bar breaking fault and stator winding inter-turn short circuit fault always interlace and interact to some extent. The detection method, which is only suitable for single fault, may lead to a misinterpretation. In this paper, the stator-rotor-hybrid fault feature of rotor bar breaking and stator winding inter-turn short circuit has been summarized and the mutual relationship of the two types of fault has been disclosed by thoroughly analyzing the simulation and experiment results. As establishes an important theoretical foundation for joint detection of rotor bar breaking and stator winding inter-turn short circuit fault

This paper develops a sensitive and reliable detection scheme for broken rotor bar fault in induction motors, taking into account the intrinsic asymmetry, air-gap eccentricity and rotor misalignment. Firstly, numerical simulation along with related experiments of broken rotor bar fault are performed successfully. Secondly, by thoroughly analyzing the simulation and experiment results, a series of interesting highlights, which could help improve the sensitivity and reliability of broken rotor bar fault detection in actual field, are revealed explicitly. Finally, a novel scheme to detect broken rotor bar fault, which perfectly blends continuous subdivision Fourier transform, self-adaptive filter, rotor slot harmonics based slip estimation and detection threshold self-tuning technique together, and thus possesses high-sensitivity and high-reliability, is proposed in this paper. Fault detection instances in laboratory demonstrate that the presented scheme is valid and effective.

The early diagnosis of rotor winding inter-turn short circuit fault is one of the most difficult problems in the operation of large synchronous generator, and a diagnosis method based on excitation current harmonics is described. Through analyzing air-gap electromagnetism characteristic on the fault, it is got that armature reaction magnetic field nonsynchronously rotates with rotor when harmonics' times and the poles' pairs of generator satisfy a certain relation, so additional harmonic current is induced in rotor winding, and gives the additional harmonic equation, which is the function of air-gap excitation magnetic field harmonic frequency, poles' pairs of generator and rotor mechanical revolution. Finally, practically acquires the excitation current of MJF-30-6 generator on the rotor winding inter-turn short circuit fault, the results of verification show that the theory analysis is right, and points out that the amplitude of additional excitation harmonic current can reflect the rotor inter-turn short circuit fault extent.

The most significant difference between the ac-exited generator and the traditional synchronous generator is the adjustable speed. A detail analysis of the static state stability of the ac-excited generator is present. The stability of the ac-excited generator is limit not only by the static state stability limit as synchronous machine but also by the breakdown torque as asynchronous machine. The relation between static state stability limits and rotor speed is derived from the mathematic model, thereby the law of static state stability at any speed is presented and these have been tested by dynamic physical simulative experiment.

Multilevel PWM inverters have become the development trends of medium-voltage and high-power motor adjustable-speed drives (ASDs). Harmonic analysis of medium-voltage ASD output voltage is described first in this paper. Through lots of simulation and experimental results, the frequency spectrum characteristics of multilevel PWM voltage waveforms are concluded. It offers the academic fundamentals for the filter design. The use of an L-R-C filter is a simple and efficient method to mitigate the voltage surges effects. The filter parameters are related to the harmonic components of ASD output voltage and cable length. Furthermore it makes some problems more serious with the increase of motor capability. On the basis of considering some problems synthetically such as fundamental voltage drop, active power loss, current harmonics and resonance, this paper presents the parameter choice formulae that can be applied to medium-voltage and high-power ASDs output filter design.

This paper aims to the detection of stator winding inter-turn short circuit fault in induction motors. Firstly, the numerical simulation of stator winding inter-turn short circuit fault is accomplished. Secondly, this paper points out that the stator winding apparent impedance angle can be viewed as the fault feature, and moreover, the lagging stator winding, adjacent to the faulty stator winding with inter-turn shorts, possesses the largest apparent impedance angle variation among the 3-phase stator windings, as allows to identify the faulty stator winding. Finally, the relevant experiments have been carried out, and the results obtained clearly validate the detection strategy. The further work will focus on refining the detection strategy and applying it to the industrial site.

This paper reviews briefly the typical methods to extract the feature signal of the inter-turn short circuit fault in the stator windings of induction motors, and points out that the phase difference of the stator three-phase winding current is more preferable than the others, as the fault feature signal. Moreover, a novel feature signal of the inter-turn short circuit fault is derived, and the corresponding extraction scheme, i.e., the voltage-current cross-correlation approach which is based on the cross-correlations of the stator three-phase voltages and currents, is presented in this paper. The proposed scheme is immune from the asymmetry of the three-phase power voltage sources, and thus superior to the other methods. The validity and effectiveness has been demonstrated by a series of experimental results.

The radial basis function network (RBFN) is one of artificial neural networks (ANNs) applied widely. A new adaptive RBFN algorithm, named the two level iteration cluster algorithm, is put forward, which can calculate automatically RBFN parameters with samples, and overcomes the conventional algorithm's shortcoming where the hidden layer neuron number must be given in advance. In addition, a new generator vibration fault diagnosis method based on a stator and rotor vibration spectrum eigenvector is presented. Using practically acquired MJF-30-6 generator vibration data in three conditions of normal operation, rotor excitation winding short circuit and stator winding fault, the results of verification show that the method has higher diagnosis precision than the conventional method based on rotor vibration spectrum eigenvector.

This paper analyzes generator stator vibration frequency spectrum characteristic and correlation dimension characteristic based on phase space reconstruction of fractal theory, when generator is in three conditions of normal operation, rotor excitation winding short circuit and stator winding fault. The results show that rotor excitation winding short circuit and stator winding fault resemble stator vibration frequency spectrum, but three conditions have a different correlation dimension. So a new method of generator vibration fault diagnosis based on correlation dimension and artificial neural network (ANN) is proposed, which selects the stator vibration correlation dimension for the input vector of ANN, and practically acquired MJF-30-6 generator data for learning samples. The results of verification show that the method can identify efficiently three generator conditions.

In this paper, a new method of stator winding blocking fault diagnosis based on artificial neural networks (ANN) has been proposed. At first, the characteristic of blocking fault is analyzed, and the temperature distribution in all kinds of faults is calculated, which made the one-to-one corresponding relationship mathematics model between the temperature-rise of each stator winding measuring points and the different faults founded. Then the neural network is trained, which can identify the. blocking fault position and the serious level, and the real-time example is adopted to verify the method.

The stator winding inter-turn short and rotor bar breaking are both frequent faults in squirrel cage induction motors. The previous work is inclined to detect one single fault, in other words, to detect the stator winding inter-turn short circuit or rotor bar breaking fault, separately. Hence there exists the misdetection probability due to the inter-influence of them. To solve that problem, this paper addresses the joint detection of the two faults. Firstly, this paper completes the numerical simulation by utilizing the multi-loop mathematical model. Secondly, some creative and interesting conclusions, which depict explicitly the inter-influence of the stator winding inter-turn short and rotor bar breaking faults, have been drawn based on the thorough analysis of the simulation results. Finally, a series of tests verify the necessity and effectiveness of the joint detection, which reduces the misdetection probability to a great extent. Further work will focus on refining the joint detection and applying it to the industrial site.

On analyzing the influence of rotor slip influence potential on exciting current as asynchronous operation of asynchronous synchronous generator, the relation of static state stability limit with slip is clarified. Thereby the law of static state stability of asynchronous synchronous generator at any rotation rate is revealed in this paper.