基于极弧系数选择的实心转子永磁同步电动机齿槽转矩削弱方法研究

齿槽转矩的削弱是永磁电机的难点和研究重点之一。为削弱实心转子同步电动机的齿槽转矩，文中提出了一种基于能量法和傅立叶分解的的解析分析方法，给出了能明确表达齿槽转矩与设计参数关系的齿槽转矩解析表达式，据此研究了极弧系数对齿槽转矩的影响。在此基础上，提出了极弧系数的最佳确定方法。根据该文给出的方法，可以方便地得到不同极数和槽数配合时的最佳极弧系数，进而削弱齿槽转矩。最后利用有限元法对其进行了验证，证明文中提出的方法是正确有效的。     

Selection criteria of induction machines for speed-sensorless drive applications

Induction motors, both three and single phase, are used extensively for adjustable-speed drives' applications. These machines are structurally very robust and are a primary source of motive power and speed control where DC machines cannot be used. For closed-loop control of these machines, sensorless speed estimation is usually preferred. Among the current estimation techniques available for speed-sensorless induction motor drives, speed measurement based on rotor-slot-related harmonic detection in machine line current happens to be a prominent one. While these harmonics can be strong in certain kinds of machines, some other machines may exhibit very weak rotor slot harmonics that can be obscured by noise. Skewing, slot shapes and types, structural unbalances, etc., also have a prominent effect on the detectability of these harmonics. This paper attempts to investigate this problem based on the interaction of pole pairs, number of rotor bars, and stator winding. Although the analysis and experimental results have been mainly provided for three-phase squirrel-cage induction motors, single-phase and slip-ring induction motors have also been addressed. Further, it has been shown that eccentricity-related fault detection could also be easily accommodated with this kind of speed detection technique at no or negligible extra cost when certain motors are selected.     

OPTIMIZATION OF DUAL SPEED INDUCTION MOTORS

ABSTRACT

Design optimization of single-winding dual speed and double-winding dual-speed three phase induction motors is attempted. The choice of independent variables and the specification of the performance requirements for these two types of motors are discussed. The formation of an objective function end the various steps involved in the minimization process are explained. It has been shown that comprehensive computer programs can be developed to design optimum dual speed motors of any pole ratio with any stator coil span and winding connection.     

大型无换向器电机技术

大型同步电机经过变频器与电网连续，采用转子磁极位置反馈信号进行闭环控制的无换向器电机技术，可使大型同步电机实现具有直流电机无级平滑调速，目前最大单机容量已发展到100MW，极限容量为250MW，在电力及传动行业具有广阔的应用前景。     

Load Sharing of Dual Motor Grinding Mill Drives

Relatively small slowly varying shaft position and velocity variations superimposed on the normal running speed of dual drive grinding mill motors can cause individual motor torque variations which disturb load sharing. The magnitude of load or torque unbalance is a function of the magnitude of the mechanical variation, the type of motors used, i.e., induction or synchronous, the number of motor poles, and the ratio of the gear connecting the motors to the load. When the magnitude is large enough to be of concern, it can be compensated for through motor secondary or field controls. How the causative factors relate, how dual drive motors should be specified for purchase are discussed, and a compensating load sharing controller for dual drive synchronous motors is described.     

A new generalized high‐frequency voltage injection method and mirror‐phase estimation method for sensorless drive of salient‐pole PMSMSs

This paper proposes a new generalized high‐frequency voltage injection method for sensorless drive of salient‐pole permanent‐magnet synchronous motors. The injected high‐frequency voltage has a unique spatially‐rotating elliptical shape, with the amplitudes of both the major and minor axes varying with the motor speed, and can be designed by selecting a design parameter. The high‐frequency current caused by the injected voltage, which has information on the rotor phase to be estimated, is speed‐independent, that is, is not affected by the motor speed at all. Consequently, the rotor phase can be estimated in a wide speed range from zero to the rated speed. By selection of the design parameter, the properties of the high‐frequency current can be adjusted appropriately to the associated motor‐drive system consisting of a motor and an inverter. As a versatile phase estimation method for estimating rotor phase using the high‐frequency current, the “mirror‐phase estimation method” is reconstructed and reproposed. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(3): 67–82, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20803     

不等齿顶宽间隔绕组对直接驱动转台电机转矩特性的影响

为了满足直接驱动数控转台对低速大转矩电机的要求,研究并设计了一种基于极槽数相近结构的不等齿顶宽间隔绕组多极永磁同步电机。多极电机保证了转台具有较低的额定转速。极槽数相近结构不仅可以提高绕组短距系数,更能有效地降低电机的齿槽转矩波动。间隔绕组和不等齿顶宽结构的配合设计最大化了定子齿磁链和绕组系数,从而有效地提高了电机的转矩密度。另外,还采用解析计算方法分析了不等齿顶宽结构对齿槽转矩波动和谐波绕组系数的影响。从有限元软件ANSYS计算结果和实验结果可以看出,样机的齿槽转矩波动小于额定转矩的1%;与等齿宽电机相比,不等齿顶宽结构有效地提高了电机的平均转矩,证明了所提出设计方法的正确性和有效性。     

Effects of momentary voltage dips on the operation of induction andsynchronous motors

Simplified stability calculations of induction and synchronous motors on voltage dips are presented. The voltage dip withstand characteristics of induction and synchronous motors rated at the same horsepower and driving the same inertial loads are calculated. The motor characteristics influencing stability are: the type of motor selected (synchronous or induction); the pull-out torque of synchronous motors and the breakdown torque of induction motors; a constant excitation controller or an excitation boost on voltage dips for the synchronous motors; load and motor inertia; and load characteristics. Synchronous motors are not suitable for fast autoclosing or bus transfer, although these can be autoresynchronized. Transient torques and current surges must be considered when induction motors are connected for fast bus transfer. Due to varying power systems, motors and load characteristics, and much interaction between these, an analysis of avoiding a shutdown on voltage dips has to be performed on a case-by-case basis. This may include a computer-based study. The stiffness of the power system in relation to motor loads, the probable type of faults and fault clearance times, and motor protection and controls are some other concerns requiring an analysis in this context     

A Cycloconverter?Synchronous Motor Drive for Traction Applications

An electric drive suitable for traction is described consisting of a cycloconverter and a synchronous motor. Essentially, the same system can be used with either single-phase or three-phase input with frequencies around 50-100 Hz. The motor speed range is not limited by the input frequency. The cycloconverter thyristors are commutated by the source voltage at low motor speed and by the motor electromotive force (EMF) at higher speed. The transition between the two regions is smooth and automatic. Only 16 low- switching speed thyristors are required for the single-phase input system. The short time overload capability of this drive at low speed is excellent, and full range regenerative, as well as dynamic braking, is readily accomplished. Compared to dc motors occupying the same space, three-phase ac motors, both synchronous and induction, offer higher output power, higher efficiency, and the elimination of brush and commutator maintenance. Compared to inverters, cycloconverters have higher efficiency and lower cost and weight.     

Field Weakening Alternative

The most common machines for traction are induction and PM synchronous machines. The latter are efficient and small, but they are more expensive and less rugged than induction machines. Fault behavior is easier to manage with an induction machine. For induction machines, the back electromotive force vanishes rapidly when the stator voltages are removed. As shown later, the efficiency of a rerated induction machine can compete with that of a PM machine when both are operated over a wide speed range. The size of any electromechanical device is related to the internal force it generates. It is important to recognize that the size and mass of a motor in a traction system are based on the target torque level. Any induction machine can support a wide frequency and speed range. When operated by an inverter, the name- plate frequency rating of the motor becomes meaningless, as it can be operated at arbitrary speed by adjusting the inverter fundamental frequency. By keeping the voltage-to- frequency ratio constant, the flux level in the machine is constant, meaning that nominal torque can be obtained at any given frequency that supports this constant ratio. The speed and output power of the machine then change linearly with frequency. It works within reason, as long as physical limits on the currents (overheating) and the flux densities (core or tooth saturation) are maintained. According to the National Electrical Manufacturers Association (NEMA), the admissible maximum operating speed for a general-purpose induction machine is twice its synchronous speed.     

Characteristics of a permanent magnet type bearingless motor

Super high-speed and high-power electric machines are required for turbomolecular pumps and spindle drives. High rotational speed and high power drives can be achieved with bearingless motors. In this paper, a bearingless motor with the principles of permanent magnet type synchronous motors is proposed. High power factor and high efficiency can be expected in permanent magnet type bearingless motors. The proposed bearingless motor is a 4 pole permanent magnet synchronous motor, in which additional 2-pole windings are wound together with 4-pole motor windings in stator slots. With currents of 2-pole windings, radial magnetic forces are produced to support a rotor shaft. Principles of radial force production of surface-mounted permanent magnet bearingless motors are analyzed mathematically. It was found that radial forces are efficiently produced by employing thin permanent magnets on the surface of rotor iron core. A test machine was built in order to measure inductance functions as well as relationships between voltages and currents     

Optimum pole configuration of variable speed AC induction motors

Sometimes a user who is familiar with fixed speed AC induction motors may specify a variable speed AC requirement with a preconception of the number of motor poles. This is appropriate in the case of an application where the motor will be run “across-the-line”, and is expected to run at the same speed and load as provided on inverter operation. If, on the other hand, “bypass” operation is not required, a more optimal choice of motor designs might be available. For example, an application requiring 3000 or 3600 RPM operation would demand a two-pole motor design if bypass (at 50 or 60 Hz) must be provided. However, when bypass is not required, it is often the case that a smaller motor can be provided in a four-pole design (utilizing 100 or 120 Hz base frequency) compared to a two-pole configuration. Another aspect of applying adjustable frequency power supplies to AC induction motors is that it allows an essentially infinite number of possible “base speeds”, including base speeds in excess of 3600 RPM. In this paper the author discusses the number of poles required for fixed speed AC motors, DC motors, and adjustable frequency AC motors. Motor performance issues are also discussed     

Optimal current control methods of a non‐salient pole hybrid field‐synchronous motor for energy‐efficient and wide speed‐range operation

This paper proposes new practical optimal current control methods for a newly emerging class of non‐salient pole synchronous motors with hybrid rotor fields by both permanent magnet and winding. In practical situations with limited voltage, the extensively used permanent magnet synchronous motor hardly achieves an ideal performance that allows simultaneously both low‐speed high‐torque and wide speed‐range operations, due to its constant magnet field. Hybrid field synchronous motors (HFSM) have recently emerged to achieve ideal performance as practical motors with controllable hybrid rotor field. For HFSM, the same torque can be produced by a variety of currents due to nonlinearity between torque and currents. Consequently, appropriate determination of a set of stator and rotor current commands plays a key role in achieving possible energy‐efficient and wide speed‐range operation. Proposed methods determine the current commands corresponding to a given torque command such that total winding copper loss due to stator and rotor currents can be minimized if the exact solution exists; the best approximate torque can be produced if no exact solution exists. The determined current commands are optimal in the sense of energy efficiency or degree of approximation in wide speed‐range operation under voltage limit. New real‐time recursive algorithms searching the optimal current solution are also given. The proposed methods are analytical but practical, and their usefulness is verified through experiments. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(1): 70–83, 2006; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20156     

New block diagrams using vector signals in the general frame of reference for AC motors with stator core losses

This paper presents new block diagrams for induction and synchronous motors with stator core losses such as eddy‐current and hysteresis losses. The proposed block diagrams succeed in realizing simple and clear configurations with physically meaningful vector signals, which are helpful for understanding motor electromagnetic mechanism and useful for designing controllers for them. Vector signals, which are defined in the general reference frame, are utilized as transfer signals between blocks. The proposed vector‐signal block diagram in the frame can be directly and easily reduced to the one in such a specific frame as a stationary or synchronous frame simply by adding certain constraints to it. Shown are three configurations for induction motor, two for synchronous motors including permanent magnet cylindrical motor, permanent magnet salient‐pole motor, and reluctance motor. © 2001 Scripta Technica, Electr Eng Jpn, 138(2): 59–70, 2002     

Sensorless controls of salient‐pole permanent magnet synchronous motors using extended electromotive force models

In this paper, we propose a new mathematical model for synchronous motors and a sensorless control method based on it. To control permanent magnet synchronous motors, knowledge of rotor position and velocity are necessary. Heretofore, expensive sensors have been used to detect rotor position information. Although many sensorless control methods based on the electromotive force (EMF) have been developed for non‐salient‐pole permanent magnet motors, they cannot be applied for salient‐pole motors without approximation because of complications in the mathematical model; this is turn may lead to problems of instability. To solve this problem, we propose an extended electromotive force model for synchronous motors. The proposed model has a simple structure, making position estimation possible without approximation. Experimental results show that the proposed model and method are valid. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(3): 55–64, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10257     

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.     

Stator-flux-oriented sensorless induction motor drive for optimumlow-speed performance

For high-performance AC drives, the speed-sensorless vector control of induction motors has received increasing attention from the standpoints of cost, size, noise immunity, and reliability. This paper presents the speed- and voltage-sensorless drive of vector-controlled induction motors for general-purpose drive applications. The rotor speed is determined by the difference between the synchronous angular frequency and the estimated slip angular frequency, which is estimated by the detected stator current and the stator-flux reference. To improve the low-speed drive characteristics, accurate applied-voltage calculation is proposed under considerations of the compensations for the quantization error in the digital controller, the forward voltage drop of switching devices, and the dead time of the inverter. The experimental studies show the improved drive characteristics     

Synchronous and Reluctance Motors in Position Servo Loops

At the present state of the control art, it is economical to replace dc motors in servo systems with ac synchronous and induction motors, in spite of the generally more complex circuitry induction motors, in spite of the generally more complex circuitry required by the ac principle. This report deals with synchronous motors that rely on shaft position reference to fit them into high-performance position feedback systems. It is shown analytically that any synchronous motor, including the reluctance motor, becomes a direct replacement for a converter driven dc motor if the phase voltages are the result of properly modulated shaft resolver outputs.     

Rapid parameter determination for induction motor analysis and control

This paper describes the implementation of a rapid online parameter determination method for three-phase induction motors. The technique is based on data sampling during a normal run-up-to-speed test. The method has been refined such that even the normal locked-rotor and synchronous speed data are measured during the run-up test. Furthermore the technique takes into account rotor parameter variations with frequency due to skin effect (mainly due to double-cage or deep-bar rotor), and other nonlinear imperfections such as heating and main flux path saturation. Moreover, the monitoring system, capable of identifying three-phase RMS voltage and current, power, power factor, and speed within one or two sampling periods of less than a few hundred microseconds each, can be used for condition monitoring of any three-phase electrical drive system and can be permanently or temporarily connected to such a system for diagnosis.     

A comparison between the axial flux and the radial flux structures for PM synchronous motors

The aim of this paper is the comparison of the axial flux (AF) structures versus the conventional radial flux (RF) structures for permanent-magnet synchronous motors. The comparison procedure is based on simple thermal considerations. Two motor typologies are chosen and compared in terms of delivered electromagnetic torque. The comparison is developed for different motor dimensions and the pole number influence is put into evidence. The paper reports the complete comparison procedure and the related results analysis. The obtained results show that, when the axial length is very short and the pole number is high, the AF motors can be an attractive alternative to the conventional RF solutions.