永磁同步电动机电抗参数研究

永磁同步电动机电抗参数是电机性能分析和优化设计的重要依据.由于永磁同步电动机转子磁路结构多种多样,与普通同步电机有很大差别,电抗参数用现有计算方法难以计算准确,不仅导致延长研制过程、加大研制费用,而且使设计优化和性能仿真缺乏科学依据.本文利用ANSOFT软件对永磁同步电动机的交、直轴电枢反应电抗参数进行计算,计算结果与试验测试结果吻合较好,在此基础上总结出永磁同步电动机电抗参数的变化规律,为永磁同步电动机设计提供了依据.     

变频空调负荷虚拟同步机化改造及其参与微网互动调控

为了提高微网系统运行的安全稳定性,充分发掘海量空调负荷资源的可调潜力,从而增强负荷响应自主性,在对空调压缩机电机控制电路改造的基础上,提出了一种变频空调负荷虚拟同步机群参与微网调频的控制方法。首先对变频空调压缩机电机进行负荷虚拟同步机控制改造,建立其控制模型;然后将空调压缩机电机进行聚合等值,便于其参与微网互动调控;接着建立了变频空调负荷虚拟同步机群参与微网互动的控制架构;最后提出变频空调负荷参与微网一次和二次调频的策略,并通过对变频空调负荷虚拟同步机群控制仿真,验证了负荷虚拟同步机化改造能够有效提升空调负荷参与调频的能力。     

10 Mvar超导同步调相机总体电磁设计

高温超导同步调相机具有响应速度快、同步电抗小等优异的无功补偿性能,本文介绍和分析了10 Mvar高温超导同步调相机的总体电磁设计。该调相机的额定电压和电流分别为11 kV和525 A,定子采用无磁性齿水冷绕组。励磁绕组采用10 mm宽的REBCO高温超导带材绕制而成,工作温度为30 K,采用冷氦气冷却,额定空载电流为375 A,气隙磁密1.4 T。空载时REBCO绕组上的最大磁密为3.05 T。对阻尼屏蔽层的分析表明其存在一些相互矛盾的特性,需要更为深入的设计。为分析无功补偿特性进行了简单的电路仿真,当满载励磁电流为428 A时,该超导调相机可实现10 Mvar的无功输出。     

变频调速异步电动机设计研究

由于采用变频器供电,变频调速异步电动机的设计与普通工频供电的异步电动机的设计存在一定差别,采用普通的异步机进行变频调速时,电机性能很难达到最佳。文章从电机本体出发,总结了变频调速电机的设计特点,阐释了不同控制方式下变频调速系统的总体设计思想,以及改善系统运行性能时的变频调速的整体设计和优化策略。     

永磁同步电动机驱动系统的故障工况分析

研究了逆变器供电的永磁同步电动机驱动系统在故障状态下的运行特性 ,仿真分析了PWM逆变器开关元件断路、短路故障工况下的电流及转矩波形 ,通过对故障状态下的电流及转矩波形特征的分析可进一步实现驱动系统的故障检测与诊断。     

旋转超导电机发展现状

大容量旋转超导电机在风力发电、舰船驱动等低速直驱应用领域具有广阔的应用前景。依据是否采用低温耦合传输装置实现低温冷却介质的传输和励磁功率的输入,将旋转超导电机分为动态密封和静态密封超导电机两类。分析了动态密封超导电机的常用定子、转子结构形式及其优缺点。针对静态密封超导电机,以转子分段式磁通切换结构、场调制双定子结构、单体励磁分极式结构等典型拓扑为例,揭示了其能够实现冷却系统静态密封形式的本质原因。最后,对两类超导电机面临的超导励磁绕组失超这一共性问题进行了探讨,从电机本体结构层面,给出了静态密封超导电机抑制电枢反应磁场对超导线圈影响的策略和方法。     

基于定子谐波电流的六相永磁同步电动机双电机串联系统的仿真

电压型逆变器驱动多相电机运行时,虽然降低了转矩脉动,但却在定子绕组中出现了明显的低次谐波电流.抑制多相电机定子谐波电流的方法是串联电抗滤波器,电抗器与多相电机定子绕组电磁结构类似,使在多相电机中不产生旋转磁场的谐波电流在滤波电抗器中产生旋转磁场来抵抗谐波电流.据此提出一种新颖的两电机串联驱动系统,将电抗器换作一台多相电机,使谐波电流在这台电机中产生旋转磁场输出转矩,并且实现对两台电机转矩的独立控制.以双Y移30°六相永磁同步电动机(PMSM)为例,对两电机串联驱动系统建立数学模型并进行了仿真分析,仿真结果验证了串联驱动系统的可行性.     

无轴承永磁同步电机的转子磁场定向控制研究

无轴承永磁同步电机由于功率密度大、转矩脉动低等优良特性受到了高度重视。文中针对一类表面贴装式无轴承永磁同步电机，详细推导出径向悬浮力表达式，建立了准确的数学模型。针对电磁转矩和径向悬浮力之间耦合的特点，采用了基于转子磁场定向的控制策略来实现这类无轴承永磁同步电机的非线性解耦控制。实验证明了该控制算法的有效性。该控制算法对插入式转子结构和内装式转子结构的无轴承永磁同步电机的控制系统设计具有一定的借鉴作用。     

Synchronous Machines Adapted for Six Step Converters–Part II: Experimental Evidence

ABSTRACT

An investigation has been carried out to evaluate converter driven synchronous machines including a machine which is specially adapted for use with converters. The adapted machine has been designed so that the internally generated voltage is tailored to produce a desired current waveform when the machine is driven by a six step voltage source inverter. In this manner, the energy flows associated with commutation are supplied by electromechanical means. In the specific example presented, an armature current waveform is produced which is congrument with the applied armature voltage.

A short design study has been carried out which compares a conventional machine and an adapted machine of similar volume under converter driven operation. The rating of the adapted machine is slightly better than the conventional machine, although both are derated compared to the sinusoidal operation of the conventional machine.The adapted machine has a significantly improved power factor as well as smaller armature currents and reduced variations in shaft output power. Because of the reduced requirements for reactive power and armature current, it is expected that a simpler converter could be utilized. In addition to the design study, an experimental program has been carried out to demonstrate that the adapted machines will operate as predicted. An experimental machine in the 6 kw range was constructed and tested in a variety of conditions. The results of the experimental work agreed well with predicted behavior.     

Steady-state performance of a line-start synchronous reluctance motor with capacitive assistance

This paper sets forth the steady-state performance analysis of a connection scheme that improves the power factor and torque with a lower magnetizing current for a line-start synchronous reluctance motor. The machine stator winding is split into two equal halves, one connected to the mains and the other connected to a balanced capacitor. Performance of the machine is improved if the capacitor value is such that the winding to which it connected operate at or very close to resonance in the d-axis. Current in both windings contributes positively to torque production and external control circuitry is not required. Steady-state equations arising from the d–q model gives a direct insight on the operating limits and how this capacitance aids the machines torque and power factor by boosting its direct axis reactance while the quadrature axis reactance remains fairly constant. An equivalent circuit is also deduced from the steady-state equations from which an explicit expression for input impedance of the new machine can be derived. Conditions for unity-power factor at varying load conditions are also examined. A comparison with conventional single-winding synchronous reluctance motor is given. Such comparison is fair because both machines have the same amount of copper and iron. Experimental results are provided to validate the analytical results.     

Natural Commutation of Current-Source Thyristor Inverters by Cage-Rotor Induction Machines

A new type of brushless cage-rotor induction machine has recently been developed [1]-[3] which is capable of providing enough counter electromotive force (EMF) when interfaced with a current-source inverter (CSI) to naturally commutate the thyristors in a high-voltage dc-link adjustable-frequency converter. The basis of this system is that by stator electromagnetic design, the induction motor may have the terminal characteristics of a dc-field synchronous machine yet still retain the torque and constructional features of a conventional induction machine. Four-quadrant operation has been demonstrated on 35- and 150-hp cage motors, and most important, leading power factor operation of the entire unit at full load is compatible with high power natural commutation of thyristor inverters. The single rotating machine has two distinct and different stator pole-pitches which must be excited from a common CSI. The analysis determines the magnitude of the CEMF available from the asynchronous condenser winding and the consequent operation of the machine in both natural commutation and in a dc-link current pulsing mode for startup.     

谐波分量对异步电机性能的影响及抑制方法

晶闸管逆变器作为异步电动机的供电电源时,输出的电压和电流中含有丰富的谐波,对异步电机的运行性能会产生显著影响,主要表现在功率损耗增加、效率和功率因数下降等,传统脉宽调制(PWM)方法虽然可以消除低次谐波的影响,但整体效果不理想。通过谐波对定子及其他电机参数影响的具体分析,提出了以电机总损耗最小为目标函数,并根据各种损耗系数随频率变化情况与逆变器晶闸管开关元件切换次数的关系,确定载波比,对传统PWM进行优化策略设计方案。试验结果表明,优化后的方案可有效抑制谐波影响。     

用于抑制多相异步电动机定子谐波电流的电抗滤波器

电压型逆变器驱动多相异步电动机运行时,虽然降低了转矩脉动和转子谐波损耗,却在定子绕组出现了明显的低次谐波电流.在总结现有的方法基础上,提出一种新型的电抗滤波方法.电抗器采用和多相交流电机定子类似的电磁结构,适当调整绕组的分布,使在多相电机中不产生旋转磁场的谐波电流在滤波电抗器中产生旋转磁场.这些谐波电流在多相异步电动机中仅遇到漏电抗,在滤波电抗器中却遇到高值的耦合电抗,因而有选择地对定子中的显著谐波电流进行滤波.以六相移30°的绕组结构为例,对包括滤波器的多相异步电动机建立了数学模型并进行了仿真分析,仿真结果验证了电抗器的有效性.     

Machine parameters and performance of interior permanent magnet synchronous motors with different permanent magnet volume

Permanent magnet synchronous motors are widely used for several industrial applications. Some applications such as electric vehicles and compressor drives require a constant power operation. The operating limits and the constant power speed range deeply depend on the machine parameters. The relationships between the motor parameters and the operating performance have been theoretically examined. This paper examines the performances of the prototype synchronous motors, where the stator structure and the rotor structure of all motors are the same. The permanent magnets are inserted into the rotor slits and the volume of the permanent magnet is adjusted to control the magnet‐flux linkage. The effects of adding the magnet to the rotor on the machine parameters and the operating performance are examined based on the various experimental results. The prototype motor has flexibility as to speed versus power performance by adjusting the volume of the permanent magnet. The theoretical results with respect to the operating limits and the motor parameters are also confirmed experimentally. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 70–77, 2000     

Generalized analysis of operating limits on PM motors and suitable machine parameters for constant-power operation

Permanent magnet synchronous motors (PM motors) are widely used in industrial applications. Some applications such as electric vehicles and compressor drives require constant-power operation. The available maximum power under specified voltage and current constraints can be obtained by optimal current vector control, such as maximum torque control and flux-weakening control. The operating limits, however, strongly depend on the machine parameters. This paper examines the relationships between the machine parameters and the output characteristics. It is shown that the power-versus-speed characteristic depends only on the difference between the magnet flux linkage and the maximum flux linkage of the d-axis armature reaction. The maximum torque and the constant-power operating range are obtained as functions of this difference. The optimal machine parameters and the design of PM motors for constant power operation are discussed based on the overall analytical results and on analyses that takes into account both copper loss and core loss in light-load operation. © 1998 Scripta Technica. Electr Eng Jpn, 123(3): 55–63, 1998     

A brushless three-phase synchronous motor using the armature winding as both load and DC excitation winding

This paper presents a new brushless three-phase synchronous motor which has no exciter. The technique applied to the motor provides an effective way for conventional brushless synchronous motors to simplify the system configuration. The stator of the motor is equipped with a double-star connected armature winding which has two neutral points. The rotor is a cylindrical one, which is equipped with a two-phase field winding. The field winding is connected with shaft-mounted rectifiers. A dc voltage is applied to the two neutral points of the armature winding to obtain the rotor excitation when the motor is operated at synchronous speed. At that time. the armature winding acts as a stator dc exciting winding while also acting as a load winding. In this paper the principle and characteristics of the motor are described. and the experimental results are shown. It is confirmed that with a 2-kW experimental machine, the proposed motor has good performance. For example, by adjusting the stator dc current, this motor power factor can easily be controlled within a wide range.     

A Combined Frequency Converter for Soft Acceleration of Induction Electric Drives with Heavy Starting Conditions

The usability of a thyristor frequency converter with a supplementary controlled series compensator for soft starting of induction motors with high torque of inertia of actuating mechanisms is considered as an alternative to transistor converters. It is shown that the supplemental device, in the form of a transistor–capacitor convertor, can be considered as an adjustable capacitor, the equivalent capacitance of which can be varied from very large values (to a maximum of infinitely large) to some fixed minimum value. The voltage of an adjustable series capacitor provides the desired switching conditions of thyristor inverter, and the capacitive reactance ensures the compensation of reactive power consumed by the induction motor and thyristor inverter, reducing the current load of the motor and converter. The addition of a thyristor current converter with a controlled series compensator of reactive power in the form of a transistor–capacitor unit makes it possible to carry out a soft start of induction motors similar to the starting modes of synchronous machines. Simulation results confirming the achievement of the desired effect are presented. It is shown that the supplemental device in the form of transistor–capacitor converter is a robust system well adaptable to various conditions of electric-drive operation. The functional equivalence of a transistor frequency converter and thyristor frequency converter with a supplemental transistor–capacitor unit with a substantially lower cost of the latter makes possible a new mechanism for soft starting of powerful electric drives with induction motors under conditions of high torques of inertia of actuating mechanisms.     

System Design Method for a Load Commutated Inverter-Synchronous Motor Drive

In a thyristorized load commutated inverter synchronous motor drive system, the inverter relies on the back EMF of the synchronous motor to provide the reverse voltage for commutation. The level of the back EMF is a function of both the synchronous motor's field current and rotational speed. The inverter operating frequency is determined by the motor speed and number of pole pairs. For a fixed thyristor firing angle, an increase inmthe level of armature current decreases the available thyristor turn-off time due to overlap of the incoming and outgoing thyristor. This overlap time is a function of the commutating reactance of the synchronous motor. These factors, field current, motor speed, inverter frequency, and armature current, together with a thyristor turnoff time specification, set a maximum limit on the value of motor commutating reactance. The motor designer and inverter designer must perform a tradeoff study of these factors to arrive at a satisfactory drive system. The results are presented of an analysis that allows the synchronous motor reactance to be specified based on the other given parameters of the inverter-synchronous motor drive system. Test data are provided from a 20-kVA 500-1000 Hz load commutated inverter/ inductor type synchronous motor drive system. The effects of motor speed and field excitation on the operating condition of the drive are discussed.     

Development of a 70‐MW‐class quick response excitation superconducting generator

A superconducting generator is expected to be a next‐generation machine due to its many advantages over a conventional generator. Super‐GM has been promoting R&D of 70‐MW‐class superconducting model generators to verify the basic technologies required for the design and manufacture of a 200‐MW‐class superconducting pilot generator. Verification tests of the third model generator, quick response excitation type C generator, were finished in June 1999. The excellent characteristics as a superconducting generator were verified through the series of tests. We report main test results such as “open and short‐circuit test,” “loaded test,” “quick excitation test,” “negative‐phase sequence overcurrent test,” and “sudden short circuit test.” © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(1): 22–29, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10029     

Dynamic stability and optimal excitation control of doubly excited synchronous machine: Influence of load characteristics

This paper is concerned with the effects of connected loads on the optimal excitation control and dynamic stability of power systems, incorporating doubly excited synchronous generators. The system studied is made up of a generating unit with local load and a transmission line connecting the machine to an infinite bus.A number of operating conditions are examined, and different system parameters used in order to identify effects attributable to the regulators, tie-line reactance, and the characteristics of the local load. For purposes of comparison, corresponding results of dynamic stability studies are also presented for the system with a conventional synchronous machine.