IPM Traction Machine With Single Layer Non-Overlapping Concentrated Windings

In this paper, an interior permanent-magnet traction drive machine with single layer non-overlapping concentrated stator winding is analyzed. In the single layer winding design, the number of stator slots and a winding factor are specifically considered. Moreover, the effect of varying the coil pitch on the winding factor and torque pulsations is investigated. A new calculation method is proposed, whereby the constant torque and field-weakening speed characteristics of the machine drive can be predicted using torque and flux linkage functions. The measured and predicted field-weakening performance of a 150-kW direct traction drive machine is presented.     

Optimal flux weakening in surface PM machines using fractional-slot concentrated windings

A design approach is presented for achieving optimal flux-weakening operation in surface permanent-magnet (SPM) synchronous machines by properly designing the machine's stator windings using concentrated, fractional-slot stator windings. This technique makes it possible to significantly increase the machine inductance in order to achieve the critical condition for providing wide speed ranges of constant-power operation. The conditions for optimal flux weakening can be achieved while simultaneously delivering sinusoidal line-to-line back-electromotive-force waveforms and low cogging torque. A closed-form analytical model is described that can be used to design SPM machines to achieve optimal flux-weakening conditions. This technique is applied to design a 6-kW SPM machine that achieves constant-power operation over a wide speed range. Performance characteristics of this machine are compared using both closed-form and finite-element analysis.     

Electric Drive for an In-wheel Fractional-slot Axial Flux Machine

This paper describes the electric drive for an in-wheel fractional-slot axial flux machine,designed for achieving a wide flux-weakening operating region.By using a slotted stator with fractional-slot windings and additional cores enclosing end windings,the axial flux machine reaches a wide constant power speed range.The machine is designed for increasing flux-weakening capability while obtaining low harmonic back-electromotive force and low cogging torque.A 10 N.m axial flux machine exhibiting 3 to 1 flux-weakening speed range has been built.A flux-weakening controller,able to maximize the output torque in the flux-weakening region,is designed and implemented.The goodness of both design and control algorithm is proved by experimental tests.However,such a fractional-slot machine has not only advantages.Rotor losses are very high,and they have to be properly considered during the design process.     

Cogging Torque Reduction and Optimization in Surface-mounted Permanent Magnet Motor Using Magnet Segmentation Method

One of the main challenges in permanent magnet electrical machine design is cogging torque reduction. In this article, the magnet segmentation method is used for cogging torque reduction. For this end, each surface permanent magnet is divided into eight parts, and a symmetrical structure with equal angular widths and considering the angular gaps between them is used for minimizing a number of optimization parameters. In this article, three optimization algorithms—response surface methodology, genetic algorithm, and particle swarm optimization—are used to determine the optimal values of optimization parameters. Finally, the result is obtained that the optimum values of response surface methodology are more efficient than of those of the genetic algorithm and particle swarm optimization in cogging torque reduction, because the objective function of the response surface methodology is cogging torque that is calculated using the finite-element method, whereas the objective function in the genetic algorithm and particle swarm optimization is based on the analytical methods. However, the main objection of the magnet segmentation method is the simultaneous reduction of average torque with cogging torque.     

Slot Numbering and Distributed Winding Effects Analysis on the Torque/Current Spectrum of Three-phase Wound-rotor Induction Machine Using Discrete Modeling Method

Smooth torque production by induction machines is an improbable phenomena that is taken into account only in classic and ideal studying methods. In this research, slot numbering and also non-sinusoidal winding function effects are studied for a three-phase wound-rotor induction machine, which is addressed for the first time, and a new formula is introduced for calculating the spectral components of machine torque and current. To reach this aim, mathematical modeling of the air-gap function is proposed, and a discrete time modeling of the machine is introduced to study the effects of space harmonics on the torque/current spectral. To study the mentioned phenomena, in the first part, the winding functions are considered as ideally sinusoidal and the behavior of simulated machines is investigated based on the winding function approach and numerical method analysis. Two certain formulas are introduced for the spectral components of torque ripple and stator currents according to the slot numbers, rotor speed, and number of machine poles. In the second part, slot opening effects are neglected and non-sinusoidal windings are considered for obtaining the same results. Finally, considering both effects, model validation is confirmed by a finite-element-based method, and the introduced method is proven.     

基于有限元方法的双定子永磁同步电机齿槽转矩研究

永磁电机不通电时永磁体与有槽电枢铁心之间相互作用,产生齿槽转矩,引起低速永磁电机起动困难.为了有效地削弱低速双定子稀土永磁同步电机齿槽转矩,在目前国内外永磁电机齿槽转矩研究基础上,建立了低速双定子稀土永磁同步电机齿槽转矩的解析表达式,针对表达式中影响齿槽转矩大小的一些因素,利用有限元方法进行了仿真分析,得到了影响齿槽转矩大小的变化规律,为电机最优设计提供重要依据.     

新型数控转台双转子永磁环形力矩电机设计

为提高电机转矩密度,研究了一种直接驱动式新型数控转台双转子永磁环形力矩电机,以适应数控机床作业空间有限的要求。定子绕组采用串联背绕的绕线方式。采用近极槽数的特殊集中分数槽绕组解决了电机多极数,低转速情况下电机极、槽配合的矛盾。通过有限元分析方法对电机性能进行分析计算,电机保持较高的绕组系数,验证了电机具有较高的转矩密度,说明了所述设计方法的合理性和有效性。     

Design and Control of an Axial-Flux Machine for a Wide Flux-Weakening Operation Region

This paper describes the strategy to design and control an axial-flux (AxF) surface-mounted permanent-magnet machine for achieving a wide flux-weakening (FW) operating region. By using a slotted stator with fractional-slot windings and additional cores enclosing end windings, the AxF machine satisfies the specification of a wide constant-power speed range. The design procedure is presented for increasing FW capability while obtaining low-harmonic back electromotive force and low cogging torque. This technique is applied to design an 8-Nldrm AxF prototype machine that exhibits about 3 : 1 FW range. To the aim of exploiting full capability of the machine, an FW controller is designed and implemented. This controller utilizes the voltage difference between the current regulator and the output voltage, limited by a voltage source inverter. With this method, the output torque in the FW region is higher than that achieved using the conventional FW method based on the voltage-magnitude feedback. The goodness of both design and control algorithm is proved by experimental tests on a prototype.     

Effect of stator chording and rotor skewing on performance ofreluctance synchronous machine

Low torque ripple in electrical machines is generally required to reduce acoustic noise and mechanical resonance vibration. To design for low torque ripple, however, affects the average torque and the power rating of the machine. In this paper, the effect of stator winding chording and rotor skewing on the average torque, power factor, and torque ripple of the normal laminated, internal flux barrier rotor reluctance synchronous machine is investigated. The two-dimensional finite-element time-step method together with the basic machine equations are used in the analysis. It is shown that to design, in general, for low torque ripple and minimal effect on torque rating of the reluctance synchronous machine, full-pitch stator windings must be used, the rotor must be skewed by a stator slot pitch, and a low number of stator slots must be avoided     

Direct torque control for brushless doubly-fed machines

Work has illustrated the potential benefits of brushless doubly-fed machines in adjustable speed drive applications. While it has been shown that the drive is open-loop stable over a wide speed range, the resultant steady-state and dynamic performance characteristics are far from optimum. Thus, a closed-loop controller is desirable to achieve competitive drive performance. The controller proposed here is applicable for general purpose industrial drives in the medium to high power range. The nature of the doubly-fed machine, with two separate sources of excitation, only one of which is controllable, rules out field-oriented control strategies applied to conventional induction machines. However, the concept of direct torque control based on instantaneous error shows promise for this machine geometry. The present paper extends the concept of predictive torque control for induction machines to the doubly-fed machine. The controller calculates the value of converter voltage which leads to desired changes of flux and torque. Once the voltage is determined, conventional algorithms, such as space vector pulsewidth modulation (PWM), can be used to generate the inverter switching function     

Design of a Switched Reluctance Machine for Extended Speed Operation

This paper presents results from a design study on the feasibility of employing high-efficiency switched reluctance (SR) machines in minimal hybrid-electric vehicles. The application requirements are presented and highlight the constraining influences of the vehicle drive-line topology on the machine design. The benefit of continuous phase current excitation is reported for the first time, demonstrating that constant power at an extended-speed operation can be realized with a higher number of phase winding turns per pole than would otherwise be achieved with conventional discontinuous current control. Thus, the torque/Ampere capability, when operating at or below base speed, is not as significantly compromised, an important consideration for the power inverter rating and, hence, drive system cost. The design procedure and simulated results are validated by measurements from a prototype machine. The results demonstrate the potential of SR technology for high-performance low-cost automotive applications, which often combine arduous environmental and volumetric constraints. In addition, the results highlight the benefits of continuous current control for extended-speed operation.     

Optimization Design and Direct Torque Control of a Flux Concentrating Axial Flux Permanent Magnet Motor for Direct Driving System

Optimization design and direct torque control (DTC) of a flux concentrating axial flux permanent magnet motor (AFPMM) are presented in this paper, which leads the AFPMM to exhibit high torque capability at low-speed and wide speed operation range for direct driving system. Firstly design parameters and manufacturing materials which affect the output performances of the motor are discussed, and then based on finite element analysis (FEA) and response surface methodology (RSM), slot and pole number combinations, and structure dimensions are optimized. Furthermore, a novel DTC based on stator flux linkage tracking is introduced, which combines maximum torque per ampere (MTPA) control and field weakening (FW) control. Independent H-bridge inverter is used to enhance the voltage limit and enlarge the speed operation range. A prototype AFPMM is fabricated on the basis of the optimum model, and experimental measurements are conducted to verify the usefulness of the proposed optimization design and control methods.     

实现感应电机宽范围最大转矩控制的电流优化策略

针对广泛应用于数控机床主轴驱动系统中的交流感应电机,提出了一种新的宽范围运行的电流优化控制策略。根据感应电机在不同速段的转矩特性,充分考虑逆变器的输出电压限制、电机本体的电流约束条件及最大转差频率限制,以输出最大转矩为目标,得出了全速范围内的最优电流控制轨迹和感应电机宽范围转矩输出最大化的电流优化分配指导原则。在此基础上,设计了一种工程实现算法,依据电机实际运行的状态变量实现恒转矩区、恒功率区与恒电压区的快速平滑过渡,完成了对最优电流控制轨迹的逼近。实验结果证明了提出方法的有效性,可以实现感应电机宽范围运行的最大转矩输出,并且使系统具有较快的动态响应性能。     

开关磁阻电动机直接转矩控制的研究

直接转矩控制(DTC)在交流电机驱动系统中是一种较完善的控制理论.事实证明它能很容易的控制电机的转矩和转速,并能减小转矩脉动.但是以前通常认为交流DTC方案不能应用于非正弦激励的SR电机.将直接转矩应用到开关磁阻电机的控制上,解决了SR电机转矩脉动问题.仿真及实验结果表明,这种控制策略不但可以有效地抑制SRM转矩脉动,同时控制简单、实时实现时只用低成本的微处理器即可.     

Nonlinear adaptive state-feedback speed control of a voltage-fed induction motor with varying parameters

An adaptive nonlinear-state-feedback speed control scheme of a voltage-fed induction motor has been developed in which the control of torque and flux is decoupled. The inputs to the control algorithm are the reference speed, the reference flux, the measured stator currents, the measured rotor speed, the estimated rotor flux, and estimates of the rotor resistance, stator resistance, and load torque, which may vary during operation. The controller outputs are the reference stator voltages in rotor-flux rotating reference frame. An accurate knowledge of the rotor flux and machine parameters is the key factor in obtaining a high-performance and high-efficiency induction-motor drive. The rotor flux is estimated using the induction-motor rotor-circuit model. Although the estimated rotor flux is insensitive to the stator-resistance variation, it does depend on the rotor resistance. A stable model reference adaptive system (MRAS) rotor-resistance estimator insensitive to stator-resistance variation has been designed. Stable stator-resistance and load-torque MRAS estimators have also been developed. These estimators have been developed to constitute a multi-input-multi-output (MIMO) decoupled-cascade structure control system. This simplifies the design problem of the estimators for a stable operation from a MIMO design problem to a single-input-single-output (SISO) design problem. The continuous adaptive update of the machine parameters and load torque ensures accurate flux estimation and high-performance operation. Simulation and experimental results are presented to verify the stability of the induction-motor drive in various operating modes.     

Robust sliding mode control and flux observer for induction motor using singular perturbation

This paper proposes a sequential methodology for designing a robust adaptive sliding mode observer for an induction motor drive using a two-time-scale approach. This approach is based on the singular perturbation theory. The two-time-scale decomposition of the original system of the observer error dynamics into separate slow and fast subsystems permits a simple design and sequential determination of the observer gains. In the proposed method, the stator currents and rotor flux are observed on the stationary reference frame using the sliding mode concept. The control algorithm is based on the indirect field oriented sliding mode control with an on-line adaptation of the rotor resistance to keep the machine field oriented. The control–observer scheme seeks to provide an asymptotic tracking of speed and rotor flux in spite of the presence of an uncertain load torque and an unknown value of rotor resistance. The validity for practical implementation has been verified through computer simulations.     

Modern improvement techniques ofdirect torque control for inductionmotor drives - a review

Conventional direct torque control (DTC) is one of the excellent control strategies available to control the torque of the induction machine (IM). However, the low switching frequency of the DTC causes high ripples in the flux and torque that leads to an acoustic noise which degrades the control performances, especially at low speeds. Many direct torque control techniques were appeared to remedy these problems by focusing specifically on the torque and flux. In this paper, a state of the art review of various modern techniques for improving the performance of DTC control is presented. The objective is to make a critical analysis of these methods in terms of ripples reduction, tracking speed, switching loss, algorithm complexity and parameter sensitivity. Further, it is envisaged that the information presented in this review paper will be a valuable gathering of information for academic and industrial researchers.     

Uncontrolled generator operation of interior PM synchronousmachines following high-speed inverter shutdown

Interior permanent magnet (IPM) synchronous machine drives are vulnerable to a special fault mode when gating is suddenly removed from the inverter switches during high-speed operation. The resulting IPM machine operation as a generator in combination with an uncontrolled rectifier must be properly understood and accounted for in the machine design to avoid damage to either the machine or inverter. An approximate closed-form solution is derived in this paper which relates the resulting machine phase current (and torque) to the IPM machine parameters, the DC-link voltage and the rotor speed. The resulting operating characteristics are particularly interesting for IPM machines that have been designed with inductance saliency ratios greater than 2 (i.e., high-saliency machines). The validity of the approximate solution is confirmed using dynamic simulation results, and the implications of these results for the machine designer seeking to minimize or eliminate the impact of this undesired operating mode are thoroughly discussed     

Dual-rotor, radial-flux, toroidally wound, permanent-magnet machines

A novel machine family-dual-rotor, radial-flux, toroidally wound, permanent-magnet (RFTPM) machines-is proposed in order to substantially improve machine torque density and efficiency. After the principles of operation, configurations, and features are discussed, the machine design and optimization guidelines are given. A prototype has been designed, built, and tested. The measured torque density of the prototype, which well matches the design value, is almost three times of that of the induction machine with the same power of 3 hp and speed. Meanwhile the efficiency is still kept high and the material cost is kept low by using ferrite magnets. Three novel approaches are proposed to reduce the cogging torque in the RFTPM machines, whose validity is verified by finite-element analysis results and experimental measurements.     

内置式永磁电机齿槽转矩的分析研究

内置式永磁电机因其高转矩及能量密度,在许多高性能装置中得到广泛应用.但永磁电机结构的特殊性,转子永磁体和定子齿槽之间相互作用产生的齿槽转矩会引起振动和噪声,同时齿槽转矩会降低速度和位置控制系统的低速时的性能.研究了一种内置式结构永磁电机的齿槽转矩,其转子磁极永磁体分段.根据分析可知,在相同的等级及尺寸条件下,永磁体分段的内置式永磁电机(SIPMM)比传统非分段内置式永磁电机(IPMM)的齿槽转矩低得多,然后利用有限元软件Maxwell 2D计算分析比较了SIPMM与IPMM的齿槽转矩.此外,还分析了两种不同转子结构的内置式永磁电机的齿槽转矩情况.