Performance analysis of single-phase line-start permanent-magnet synchronous motor

Single-phase line-start permanent magnet (LSPM) synchronous motors have always been far less amenable to detailed computer-aided performance analysis compared with three-phase LSPM synchronous motors. The main reason is the lack of an accurate mathematical model of the motor characteristics arising from the unbalanced stator field and the rotor saliency. However, there is great potential for these types of motors to replace conventional single-phase induction motors in many domestic applications on account of their higher efficiencies when properly designed. In this paper, a new model that is applicable to both synchronous and asynchronous operation of the motor is proposed in which the parameters can be readily obtained by the two-dimensional (2-D) static finite-element method (FEM). It includes both the forward and backward rotating magnetic fields. It can be used to analyze the torque versus slip characteristics and predict the steady-state performances of the motor quickly with reasonable accuracy. The model has also been extended to simulate the transient start-up process and other dynamic performances. The models are suitable for the initial design and optimization of the motor geometry because of its low run-time overheads. Experimental results have verified the practicability of the models.     

Starting characteristics of direct current motors powered by solarcells

The authors deal with the calculation of the starting to rated current ratio and starting to rated torque ratio of the permanent magnet, separately, series and shunt excited motors when powered by solar cells for the two cases where the system includes a maximum-power-point-tracker (MPPT), and without an MPPT. Comparing these two cases, one gets a torque magnification of about three for the permanent magnet motor and about seven for other motor types at rated design insolation. The calculation of the torques may assist the photovoltaic system designer to determine the advantage of including an MPPT in the system as far as the starting characteristics of the DC motors are concerned     

切向永磁电机转子整体斜极方法及其对转矩脉动的影响

切向结构电机谐波含量丰富,转矩脉动较大,转子斜极可有效降低电机转矩脉动。文中针对切向结构永磁电机,使用不分段转子整体斜极方法来抑制电机的转矩脉动,并通过有限元分析软件对比了对称结构与斜极结构的各种性能表现,并试验验证了转子斜极结构能够有效改善电机的转矩脉动。     

Analysis of torque developed in axial flux, single-phase brushless DC motor with salient-pole stator

An analysis of the torque developed by a single-phase disc brushless permanent magnet motor with salient-pole stator is presented. The machine represents a new family of brushless disc motors with the starting torque issue appearing to be most challenging. To produce a starting torque, the permanent magnets on one of the rotor discs are distributed nonuniformly. However, this significantly distorts a shape of the cogging torque versus rotational angle characteristic which, in turn, affects a waveform of the overall torque. A three-dimensional (3-D) finite-element model is used for the purpose of determining of angular variations of the torque developed by the motor. To find how the torque varies with time, a model of the source-inverter-motor circuit is developed. A simulation study on an influence of the commutation angle on the electromagnetic torque is also a subject of this paper. The results obtained show that the motor performance can be improved by a proper selection of the current commutation angle to reach the maximum efficiency. The simulation results are in good agreement with measurements obtained from a prototype motor.     

Asynchronous performance analysis of a single-phase capacitor-start, capacitor-run permanent magnet motor

This work presents a detailed analysis of the asynchronous torque components (average cage, magnet braking torque and pulsating) for a single-phase capacitor-start, capacitor-run permanent magnet motor. The computed envelope of pulsating torque superimposed over the average electromagnetic torque leads to an accurate prediction of starting torque. The developed approach is realized by means of a combination of symmetrical components and d-q axes theory and it can be extended for any m-phase AC motor - induction, synchronous reluctance or synchronous permanent magnet. The resultant average electromagnetic torque is determined by superimposing the asynchronous torques and magnet braking torque effects.     

Torque ripple analysis of a PM brushless DC motor using finite element method

Three-phase permanent magnet brushless DC motors are widely used. As a function of the rotor position, the torque produced by these machines has a pulsating component in addition to the DC component. This pulsating torque has a fundamental frequency corresponding to six pulses per electrical revolution of the motor. The shape of the torque waveform and, thus, the frequency content of the waveform can be influenced by several factors in the motor design and construction. This paper addresses the various factors that influence the torque waveshape. It is shown that in addition to the basic induced electromotive force (EMF) waveshape, the magnetic saturation in the stator core, and the accuracy in the skewing are also key factors in determining the torque waveshape. Computer simulation using finite element technique has been conducted to study the torque waveform. Simulation results successfully duplicated the torque waveforms measured in experiments under different excitation currents.     

Control-based reduction of pulsating torque for PMAC machines

Control methods in torque pulsating reduction for surface-mounted permanent magnet motors are discussed in this paper. The pulsating torque is a consequence of the nonsinusoidal flux-density distribution caused by the interaction of the rotor's permanent magnets with the changing stator reluctance. The proposed control method is estimator based. To assure parameter convergence, Lyapunov's direct method is used in estimator design for the flux Fourier's coefficients. A novel nonlinear torque controller based on flux/torque estimate is introduced to reduce the influence of the flux harmonics. The influence of the cogging torque is considerably reduced at lower motor speed using the internal model principle and adaptive feedforward compensation technique. The overall control scheme and experimental results are also presented     

An observer-based robust adaptive controller for permanent magnet synchronous motor drive with initial rotor angle uncertainty

An observer-based robust adaptive nonlinear position and speed tracking controller is developed for a permanent magnet synchronous motor with initial rotor angle uncertainty. The unknown initial rotor position is treated as a constant motor parameter in the development of the controller. An incremental encoder, which provides relative position variation of the rotor, is used along with stator current signals to achieve stable control. However, the controller does not require the knowledge of motor parameters and it only assumes friction, external disturbances, and model uncertainties are bounded. By using state observers, the measurement of acceleration and load torque, which is required usually in the nonlinear controller design with high tracking performance, is avoided. The stability of the control system and tracking convergence are guaranteed using Lyapunov theory. Finally, the stability and efficacy of the proposed drive system are verified by experimental results.     

Modeling of effects of skewing of rotor mounted permanent magnetson the performance of brushless DC motors

A method for computation of the parameters and performance of permanent-magnet brushless DC motor drives is developed in which the concept of skewing is implemented through the geometries of permanent magnet mounting on the rotor and not through the usual skewing of the armature slots. This technique of permanent-magnet mounting eliminates the 2-D axial symmetry in the resulting magnetic fields. This difficulty is overcome by the use of multiple cross-sectional 2-D finite-element field computations, coupled with a concept of an artificial mutual-coupling inductance between the armature phase windings and the rotor-mounted permanent magnets for induced EMF and torque computations. The computed induced EMF waveforms, motor phase winding current waveforms, and other performance characteristics are found to be in excellent agreement with test data obtained using a 1.2 hp, 120 V brushless DC motor drive system     

Design features and protection of valve actuator motors in nuclearpower plants

A status report on an effort of the Working Group IEEE-NPEC-SC4.7 is presented and the performance requirements, selection, design, and protection of valve actuator motors (VAMs) commonly used as components in direct gear driven valve actuator assemblies in nuclear power plants are discussed. VAMs are short-time-rated, high torque-to-inertial ratio motors. The actuator manufacturer selects the performance parameters for the VAM based on the maximum thrust required by the valve for tight shutoff. Since valve actuators require a high starting torque, the rating system begins with the assignment of nominal starting torque. The requirement of minimum frame size dictates a minimal (running) torque and a minimum run time. Design features of the VAM leading up to its design as a short-time-duty rated motor are described and compared with a continuous-duty motor designed to NEMA MG1. The unique features of the speed-torque characteristics and performance at varying voltages and temperatures are described     

Sensorless direct torque control for salient-pole PMSM based on extended Kalman filter fed by AC/DC/AC converter

In this paper, a new sensorless interior permanent magnet synchronous motor (IPMSM) drives method with extended Kalman filter (EKF) for speed, rotor position and load torque estimation is proposed. The direct torque control (DTC) technique for permanent magnet synchronous motor (PMSM) is receiving increasing attention due to the important advantages of the low dependence on motor parameters when compared with other motor control techniques. The Kalman filter is an observer for linear and non-linear systems and is based on the stochastic intromission, in others words, noise. The PMSM is fed by an indirect power electronic converter which is controlled by a sliding mode technique. The simulation tests performed for different operating conditions have confirmed the robustness of the overall system; and it is shown that the sliding mode technique has successfully minimized the different harmonics introduced by the line converter.     

A novel high power density permanent magnet variable-speed motor

A novel polyphase, multipole, permanent magnet (PM) motor which possesses high power density, high efficiency and excellent controllability, yet can be produced by conventional fabrication techniques, is proposed. The basic operating principles, design features, performance analysis and control system are described. The experimental results for a 5 kW, 1500 RPM prototype PM motor and its comparison with other types of motors such as switched reluctance motors and induction motors are given. This motor also has superior dynamic performance     

Analytical model for permanent magnet motors with surface mounted magnets

This paper presents an analytical method of modeling permanent magnet (PM) motors. The model is dependent only on geometrical and materials data which makes it suitable for insertion into design programs, avoiding long finite element analysis (FEA) calculations. The modeling procedure is based on the calculation of the air gap field density waveform at every time instant. The waveform is the solution of the Laplacian/quasi-Poissonian field equations in polar coordinates in the air gap and takes into account slotting. The model allows the rated performance calculation but also such effects as cogging torque, ripple torque, back-EMF form prediction, some of which are neglected in commonly used analytical models.     

不同工况下3.3 MW永磁直驱风力发电机电磁场仿真分析及损耗修正

文章设计了一台3.3 MW外转子表贴式永磁直驱风力发电机,并对其电磁性能及短路故障情况进行了有限元仿真分析。首先,得出了这台电机在额定工况下的转矩和磁密分布等结果,以及在相间绕组短路和三相绕组短路两种情况下电机转矩、电压和电流等曲线的变化情况;然后,通过三维静磁场仿真,探究了电机定子的径向通风道结构对二维有限元仿真的影响程度,并对铁耗进行了修正;最后,通过电磁场-温度场的耦合迭代仿真,考虑了温度场影响下的电机内部材料特性的变化对电机损耗结果的影响。     

小型风力发电机电磁设计特点

文章分析了小型风电机组用的永磁同步发电机的电磁设计特点,并与其他普通永磁电机区别,详细介绍了永磁同步发电机各个电磁参数的特点以及对发电机性能的影响。重点介绍永磁同步发电机定子、转子设计的特点,对不同的极数与槽数的配合进行对比分析,总结降低齿槽转矩的规律。     

A direct torque-controlled interior permanent-magnet synchronous motor drive without a speed sensor

This paper reports results of further investigation of the so-called direct torque control (DTC) technique to an interior permanent magnet (IPM) synchronous motor drive. This torque control technique for IPM motors requires no dq-axes current controllers and coordinate transformation networks. A completely sensorless IPM motor drive with DTC, which uses a new speed estimator from the stator flux linkage vector and the torque angle, is presented. It is shown that including the torque angle in the estimation process results in a far more accurate transient speed estimator than what is reported in the existing literature.     

Comparison of the nature of torque production in reluctance andinduction motors

The nature of torque production is different in reluctance and inductance motors. One significant difference occurs in a reluctance motor that has nonsalient stator punching and a salient motor. When the flux per pole is small in such a motor, the torque can still be high, as long as the rate of energy change with respect to the rotor angular displacement at the rotor pole fronts and pole ends is high. A theoretical foundation to improve the torque capability of reluctance motors is provided. Effects of saturation and stray-load loss are also studied. Experimental results show agreement with theoretical conclusions     

Commutation torque ripple minimization for permanent magnetsynchronous machines with Hall effect position feedback

A permanent magnet synchronous motor (PMSM) with sinusoidal flux distribution is commonly commutated using discrete rotor position feedback from Hall sensors. A commonly used stator current excitation strategy used in such a system is a six-step current waveform. Application of sinusoidal current waveforms is shown to produce smooth torque in the PMSM. This paper shows how a pseudo-sensorless rotor position estimator may be used with Hall sensors to provide sinusoidal current excitation in place of six-step currents to reduce the torque ripple associated with the six-step strategy. Performance evaluation of the rotor position estimator in a PMSM drive is provided through simulation     

Analysis of flux distribution and core losses in interior permanentmagnet motor

The interior permanent magnet (IPM) motor with its robust rotor construction, hybrid torque production nature and flux-weakening capability is suitable for electric vehicle applications when wide speed and torque range is required. At high-speed operations, core losses become an important issue because they affect efficiency and raise operating temperatures. This paper discusses the results of two-dimensional finite element analysis into the relationship between flux distribution and core losses in the IPM motor. The analysis is further supported by flux measurements using search coils installed in an experimental motor. Three methods of predicting the core losses in IPM motor are also investigated. These methods are the empirical formula method, finite element computed waveform method and the search coil induced voltage method     

Torque behavior of one-PhasePermanent-magnet AC motor

This paper presents a detailed comparative study of two starting and running methods for a single-phase permanent magnet synchronous motor, equipped with a squirrel-cage rotor. The analysis of the motor performance is realized for a pulse width modulated (PWM) inverter fed motor and for a capacitor-start, capacitor-run motor. The developed approach may be extended to any 1-phase ac motor-induction, synchronous reluctance or synchronous permanent magnet.