Synchronous machine field time constant regulator

The purpose of a field time constant regulator for a laboratory model synchronous machine is described. The design and test results described show that it is possible to adjust the field transient time constant over a range that is adequate enough to model synchronous machines over a very wide range of sizes.     

Effects of Spin-Up Rate on Internal Resonance in a High- $Tc$ Superconducting Bearing System

This paper investigates the transient behaviors of a rotor passing through resonance in a high- $Tc$ superconducting bearing system. Such a low-damping multidegree-of-freedom system, which is subjected to nonlinear force, can show complex dynamical behaviors, in which energy transfer occurs between modes through nonlinear coupling. Our numerical and experimental results show that, in a system of a high-$Tc$ superconducting bearing, internal resonance can occur even in transient cases where the rotor passes through resonance. The effects of the internal resonance and also the effects of the spin-up rate on the transient dynamics of the rotor have been examined and clarified by changing the period of increasing voltage applied to a direct-current motor for rotating the rotor.      

High-performance decoupling control techniques for various rotatingfield machines

This paper presents a comparative study of different field-oriented rotating-field machines, including squirrel cage induction machines, series-connected wound rotor induction machines, and synchronous machines. Evaluation of various field-oriented rotating-field machines for high-performance applications is presented. The concept of torque linearization and decoupling control is studied and compared for the various field-oriented motors. Computer simulations, experimental results and space phasor diagrams are employed to illustrate the dynamics of decoupling control for the various field-oriented-control (FOC) systems. The control complexity and parameter sensitivity of various FOC drive motors are compared     

Anisotropy Comparison of Reluctance and PM Synchronous Machines for Position Sensorless Control Using HF Carrier Injection

Position sensorless control of reluctance and permanent magnet synchronous machines at zero and low speed is possible using HF voltage injection and proper demodulation. The so-called saliency position, which is tracked by the HF sensorless scheme, is different from the actual rotor position: the difference contains both offset and rotor-position-varying components, which may be explained by carefully considering the HF behavior of the machine and the effect that fundamental excitation and rotor position have upon it. This paper gives insight into the HF behavior of synchronous machines and serves as a practical guide for implementation of stable and robust position estimation at zero and low speed.      

Decoupling control of induction motor drives

The decoupling control of induction machines is investigated. Three different schemes for decoupling-control methods based on stator flux, airgap flux, and rotor flux field regulation are developed. The control dynamics of each scheme are outlined and studied. Simulation results are presented to verify that these schemes provide decoupling control with excellent dynamic behavior. The transient and steady-state relationships between slip frequency and torque, under constant stator flux, airgap flux, and rotor flux operations, are simulated and compared. The sensitivity characteristics of the three methods of flux-control, machine fed by impressed currents and voltages, are also compared and studied. A prototype torque-drive system is implemented to demonstrate the decoupling control of a squirrel-cage induction machine     

Induction motor speed estimator and synchronous motor positionestimator based on a fixed carrier frequency signal

A speed and position estimator, based on the introduction of a constant-frequency carrier signal (400-1000 Hz) in AC motor stator currents has been developed. Speed and position are estimated through the detection of irregularities in the rotor and, hence, the results are independent of machine parameters. These irregularities generate amplitude oscillations in the currents generated by the high frequency carrier, which are proportional to the rotor position. At the same time, the frequency of these amplitude modulations is proportional to machine speed. In induction machines, the amplitude of these signals is too low to estimate position accurately. However, special electronic circuits, designed and implemented with analog multipliers and filters, have permitted measurement of very low speeds with high precision. Computer simulations and some experiments have been carried out, and they have shown that it is possible to measure speeds as low as 20 r.p.m. In the case of salient-pole synchronous machines, the method is useful to measure rotor position due to the high irregularities produced by the poles, which are easily computed because of the important amplitude variations detected in the high frequency carrier     

Staged Fault and Laboratory Tests on a Cable Pair Protection System Designed to Serve Power Stations

Cable pairs entering power stations may be subjected to ground potential rise (GPR) and/or induction of several thousand volts during power system faults. A cable protection system designed to give a high degree of reliability is described, and the results of staged fault and laboratory tests are discussed. An analysis of neutralizing transformer transient performance shows how the transformer's behavior during fault conditions is determined by its volt-time capability.     

Measurement of rotor load angle of synchronous machines

A measurement system is presented in which an almost immediate and permanent record of steady-state or transient values of rotor load angles of synchronous machines may be obtained utilising an ultraviolet recorder.     

复阻抗法验证凸极同步电机双反应理论研究

本文从同步电机电感和电枢反应磁势出发，推导单相交流供电在转子静止且无励磁时纯直轴、纯交轴，以及一般电枢反应状态下的电压方程和复阻抗，确定验证双反应理论的复阻抗关系，从而通过实验测量验证双反应理论的有效性。该方法也可以作为同步电机电感参数测量方法，有助于深入理解双反应理论和同步电机运行规律。     

大型同步电机交交变频调速系统对电网的谐波影响分析

针对热连轧机组中同步电动机主传动的交-交变频调速系统,定量分析了同步电机负载经由交交变频器对变压器供电网侧产生的谐波影响.分别对不同的负载参数、变压器原副边电感量和变流装置的进线电抗器参数的情况进行了仿真分析.同时,对大型多组交交变频器移相组合式供电进行了数据移位方式仿真.并且对交-交变频器和交-直-交变频器所产生的谐波干扰进行了对比分析.仿真结果表明调节变压器原副边电感量再结合移相组合式供电的方法可以有效地降低大型同步机负载对供电网侧的谐波干扰,并使得总谐波率在各相中分布趋向均衡.     

A new driving scheme for synchronous rectifiers: single windingself-driven synchronous rectification

Single winding self-driven synchronous rectification (SWSDSR) approach is a new driving circuit that overcomes the limitations of the traditional driving schemes, becoming an interesting alternative to supply new electronic loads such as microprocessors. Traditional self-driven synchronous rectification (SDSR) technique has shown very good performance to improve efficiency and thermal management in low-voltage low-power DC/DC converters, however it can not be extended to the new fast dynamic, very low voltage applications. SWSDSR scheme is based on an additional winding in the power transformer (auxiliary winding). It allows for maintaining the synchronous rectifiers (SRs,) on even when the voltage in the transformer is zero, which is impossible to do in traditional self-driven approaches. It also makes it possible to drive properly the SRs even in very low voltage applications, 1.5 V or less. Coupling of the windings strongly affects the performance of the SWSDSR technique. The influence of the coupling between the different windings is analyzed through simulations of different transformers designed for the same application. Models of transformers are generated with a finite element analysis (FEA) tool. Goodness of the SWSDSR scheme is validated through experimental results     

Linear electric machines—A personal view

The history of linear motors is a history of shape. Once having departed from the cylindrical geometry of rotating machines, a wider world of three-dimensional design becomes possible. Linear induction motors dominate the field of linear drives to the same extent as does the rotary induction machine in relation to more complicated adjustable-speed motors. It is therefore thought appropriate to devote only one section to linear motors other than induction. A fairly full treatment of electromagnetic levitation is also included together with a treatment of oscillating machines. Perhaps the most important features are the division of electrical machines into two classes which are termed "magnetic" and "electromagnetic" and the "topological explosion" which is at present taking place in linear motor design. Some linear machines are already well established on a commercial basis but the vast bulk of recent inventions still remain to be exploited.     

基于小波和能量特征提取的旋转机械故障诊断方法分析

轴承和转子系统在旋转机械中是非常关键的部件,小波包对振动故障信号的特征提取是对于旋转机械故障诊断的关键.针对传统的软、硬阈值量化方法在阈值常数偏差和不连续的问题,设计一个可调参数改进的连续函数以用来量化阈值.对于旋转机械转子常出现故障采用振动信号的小波包分解、去噪然后进行小波包能量特征提取.     

对比分析法在“电机学”课程教学中的应用

本文针对"电机学"课程性质,通过分析学生在课程学习中存在的问题,提出对比分析法在课程学习中的应用。该方法有助于培养学生对电机基本理论的理解能力,并且能够提高学生分析问题、解决问题的能力。这种方法贯穿课程学习的始末,在直流电机、变压器、异步机和同步机这四类通用电机中都能用到。实践证明,这种教学方法的应用能达到较好的教学效果。     

Optimization of a synchronous reluctance machine for a sensorless drive with a wide field-weakening range

For more than one century, electrical machines have been utilized for electrical drives. Nowadays, in most applications the electrical machine is fed by an inverter. Three types of machines are available for such purposes: the asynchronous induction machine, the permanent magnet excited synchronous machine and the synchronous reluctance machine. Reluctance machines represent an alternative to the other types when utilized in high-performance drives with a wide speed range. Due to the rotor saliency, these machines have an inherent suitability for a position-sensorless control. The parameters of a 5 kW machine with a maximum speed of 8000 rpm are evaluated by means of nonlinear finite element analyses. With regard to an application in a high-performance drive with a wide field-weakening range and a position-sensorless control scheme, the characteristics are calculated for the conventional reluctance machine as well as the reluctance machine with additional permanent magnets in the rotor. The comparison of the characteristics of the conventional reluctance machine and the permanent magnet assisted reluctance machine clearly shows the improved performance in terms of electromagnetic torque and power factor due to the interior permanent magnets. Thereby, the suitability for the application in position-sensorless drives due to the high effective saliency is preserved.     

Control and performance of a doubly-fed induction machine intendedfor a flywheel energy storage system

A large-capacity low-speed flywheel energy storage system based on a doubly-fed induction machine basically consists of a wound-rotor induction machine, and a cycloconverter or a voltage-source pulse width modulation (PWM) rectifier-inverter which is used as an AC exciter. Adjusting the rotor speed makes the machine either release the kinetic energy to the power system or absorb it from the utility grid. Thus, the machine has the capability of achieving not only reactive-power control, but also active-power control based on the flywheel effect of the rotating parts. This paper proposes a new control strategy for a doubly-fed induction machine intended as a flywheel energy storage system, which is characterized by the combination of vector control and decoupling control. The control strategy enables the induction machine to perform active-power control independent of reactive-power control even in transient states. The validity of the theory developed in this paper, along with the effectiveness and viability of the control strategy, is confirmed by computer simulation. In addition, this paper discusses a transient behavior of a magnetizing current in the induction machine     

Some electromagnetic aspects of coreless PCB transformers

In this paper, some EMI aspects of using coreless PCB transformers are addressed. Based on the antennas theory, the radiated power of a coreless PCB transformer is estimated and found to be negligible. The electromagnetic field plot of a power electronic circuit using a gate drive circuit isolated by a coreless PCB transformer has been recorded. The major radiated EMI source in the frequency range of 30 MHz to 300 MHz is found to be the copper tracks of the power circuit, where switching transients occur, rather than the coreless PCB transformer. Coreless PCB transformers essentially operate at relatively low frequency (8 MHz in this case) by near-field magnetic coupling. Experimental results have confirmed that the application of coreless PCB transformer in gate drive circuit will not impose any serious EMI problem on the power electronic circuit     

Development status of rotating machines employing superconducting field windings

Superconducting rotating machines have looked promising since multifilamentary niobium-titanium (NbTi) superconductors became available in the mid-1960s. Both dc homopolar and ac synchronous machines were successfully tested from the 1970s to the 1990s. Three different 70-MW generators were recently demonstrated by the SuperGM project in Japan. However, economic considerations with respect to competitive cost combined with the requirement for liquid helium cooling did not make these machines commercially attractive. On the other hand, high-temperature superconductors (HTSs) can operate at much higher temperatures (30-40 K), providing much larger thermal margin and simpler cooling systems. This refrigeration advantage has provided new impetus to the development of such machines for commercial applications. In the last few years, a number of superconducting rotating machines with HTS field windings have been demonstrated and several projects are currently transitioning to advanced development stages. HTS machines with ratings from a few kilowatts to several megawatts have been demonstrated in the United States and Europe. Currently, large high-torque ship propulsion motors, large generator prototypes, and synchronous condensers are under development and are expected to be commercially available in the next few years. Prospects for improved life cycle cost, smaller size, less weight, and higher efficiency benefits are providing incentives for the development of these larger rating HTS machines. This paper reviews the past and recent progress on the worldwide development of industrial-grade superconducting rotating machines utilizing low-temperature superconductor and HTS field windings and provides an outlook on the benefits and opportunities of this new technology.     

A high-performance sensorless indirect stator flux orientation control of induction motor drive

A new method for the implementation of a sensorless indirect stator-flux-oriented control (ISFOC) of induction motor drives with stator resistance tuning is proposed in this paper. The proposed method for the estimation of speed and stator resistance is based only on measurement of stator currents. The error of the measured q-axis current from its reference value feeds the proportional plus integral (PI) controller, the output of which is the estimated slip frequency. It is subtracted from the synchronous angular frequency, which is obtained from the output integral plus proportional (IP) rotor speed controller, to have the estimated rotor speed. For current regulation, this paper proposes a conventional PI controller with feedforward compensation terms in the synchronous frame. Owing to its advantages, an IP controller is used for rotor speed regulation. Stator resistance updating is based on the measured and reference d-axis stator current of an induction motor on d-q frame synchronously rotating with the stator flux vector. Experimental results for a 3-kW induction motor are presented and analyzed by using a dSpace system with DS1102 controller board based on the digital signal processor (DSP) TMS320C31. Digital simulation and experimental results are presented to show the improvement in performance of the proposed method.     

Design and analysis of a novel wound rotor for a bearingless induction motor

The traditional squirrel-type bearingless induction motor (BIM) suspension winding generates induced current in its squirrel-cage rotor and affects the phase and amplitude of the suspension force. Based on the analysis of the spatial distribution of torque winding magnetic field and suspension winding magnetic field, a new type of wound rotor BIM is designed. Different from the squirrel-cage rotor, the wound rotor uses a special method of embedding a set of coils at any symmetrical four rotor slot positions, so as to only induce the torque winding magnetic field. The induced current, air-gap magnetic density, magnetic field line distribution, suspension force as well as electromagnetic torque of the traditional squirrel-cage motor and the new wound motor are analysed by Maxwell finite element calculation. The results show that the designed new wound BIM can not only effectively suppress the induced current of suspension winding, eliminating its influence on the suspension force, but also has a better starting performance.