Torque In Permanent Magnet Motors Research Articles

Analysis of Cogging Torque of Permanent Magnet Motors Under Mixed-Eccentricity and Manufacturing Tolerances

Analysis of Cogging Torque of Permanent Magnet Motors Under Mixed-Eccentricity and Manufacturing Tolerances

Optimal design and control of permanent magnet assisted dual rotor motor

As high-performance motors, permanent magnet motors are widely used in a wide range of applications. It has become a consensus to mine reluctance torque in permanent magnet motors. The combination of permanent magnet motors and reluctance motors to generate higher output torque is one of the hotspots in motor research. A dual-rotor motor can be formed by connecting a coaxial connector or a concentric end disk, which can make the motor generate higher torque. However, although the motor torque has been improved, the cogging torque still affects the output torque of the motor. This paper describes a method to reduce the cogging torque of the permanent magnet rotor of the permanent magnet-assisted double rotor motor. By analyzing the motor power equation, it is concluded that the pole arc coefficient, the thickness of the magnetic steel, the length of the air gap, and the slot width of the stator have four influences on the teeth. For the parameters of the slot torque, the upper and lower limits of the parameter value are obtained according to the size of the motor. A certain parameter is taken as a fixed value, and the remaining parameters are uniformly valued. Use parametric scanning to determine the optimal value range of the parameter, and use Maxwell for parameterization. Simulation and analysis show that the cogging torque of the motor is reduced by 90% and the torque ripple is reduced by 50%. In order to simplify the motor control system, this paper designs a fuzzy controller based on granular functions, and the fuzzy rules of the fuzzy controller are to perform feature sampling and fit the response function, eliminating fuzzification and defuzzification, improving the response speed of fuzzy control, and simplifying the control system.

Research on the influence of trapezoidal magnetization of bonded magnetic ring on cogging torque

Abstract In this article, the influence of trapezoidal magnetization method on cogging torque of permanent magnet motor is studied. First, the structure is analyzed by analytical method to explain its mechanism of reducing cogging torque. Then, in order to verify the effectiveness of the formula, a six-slot four-pole motor is introduced for finite element analysis. Through comparison of the original structure motor, the magnet skew structure motor, and the trapezoidal magnetic pole structure motor, it demonstrates that the trapezoidal magnetic pole structure motor can effectively reduce the Cogging torque and does not produce additional axial electromagnetic force. Finally, a magnetizing fixture with a trapezoidal magnetic pole structure is made to magnetize the magnetic ring. The magnetized magnetic ring is installed on the motor, and the Cogging torque, Back EMF, etc., are tested. The test results are in good agreement with the simulation results. This method can be used to optimize the cogging torque of the permanent magnet motor.

Refined modeling and experimental verification of a torque motor for an electro-hydraulic servo valve

The Permanent Magnet Torque Motor (PMTM) is the key electro-mechanical conversion device in an Electro-Hydraulic Servo Valve (EHSV). In this work, a refined model of a PMTM is developed, considering the non-working air-gaps between the upper or lower yoke and the armature, the fringing effect at the limiting holes, and the nonlinear permeability of soft magnetic material. Based on the refined model, the influences of various factors on the calculation accuracy of the magnetic flux at the pole surfaces of the armature and the output torque are investigated. For verifying the validity of the refined model, a Finite Element Analysis (FEA) of the PMTM is conducted, and a test platform is constructed. Compared with existing models, the refined model can better reveal the intrinsic mechanism of the PMTM, and its calculations are more consistent with the FEA results. The experimental results of the armature deflection displacement show that the refined model can accurately describe the output characteristics of the PMTM.

Research on a Limit Analytical Method for a Low-Speed Micro Permanent Magnet Torque Motor with Back Winding

The conventional permanent magnet torque motor (PMTM) is slotted on the inner surface of the stator core. When the size of the stator core is small, the winding coils are difficult to embed into the slots. To solve the problem, a novel PMTM is presented, which is slotted on the outer surface of the stator core. As a result, the winding coils can be conveniently embedded into the slots from the outer surface of the stator core. The novel structure of the PMTM with back winding (BWPMTM) is introduced, and the advantage of the novel structure is analyzed. Furthermore, this paper proposes a limit analytical method to solve the optimal parameters of the motor which comprehensively considers four constraints: no-load back electromotive force (EMF), torque, temperature and slot space factor. The optimal parameters of the motor are directly solved to maximize torque density within the constrained range. This method avoids repeated iterative processes and greatly reduces the amount of calculation for PMTM design. Electromagnetic performance and thermal performance are analyzed based on the finite element model (FEM). Finally, the building of a prototype and the experimental results obtained with it are discussed. The rationality of the novel structure and the limit analytical method are verified.

Optimization of cogging torque in permanent magnet motors based on parameter sensitivity and Kriging model

The weakening of cogging torque in permanent-magnet synchronous motors brings about the problem of low efficiency optimization. To solve this problem, an optimization-simulation scheme for the response surface model based on the parameter sensitivity screening is proposed. A surface-mounted motor having 12 poles and 48 slots is used to obtain the law of the influence on cogging torque caused by multiple electromagnetic parameters. Additionally, the Spearman correlation is used to analyze significant factors that affect the cogging torque. The sample is collected by an OSF optimal space filling design. A Kriging model is applied to construct the relationship between the cogging torque and significant factors, and to modify the model accuracy. The multi-island genetic algorithm is used to find an optimal solution to the cogging torque. The results show that the result of the finite element analysis after optimization only has an error of 1.5% compared with the predicted value of the pseudo model, which is 62% lower than the initial value. Therefore, the sharp reduction in cogging torque in the motor verifies the effectiveness of the optimization scheme.

PM Torque Motor With Armature Teeth Made by Oriented Silicon Steel Sheet

For the advantages of oriented silicon steel sheet (OSSS) with better magnetic permeability in the rolling direction, this paper proposes a permanent magnet (PM) torque motor with armature teeth made by OSSS. This paper introduces the influence of unequal tooth width on the winding factor and the width calculation method of the armature teeth tip top, and analyzes the torque performance improvement by OSSS. In the end, based on testing the B-H waves of OSSS, the flux linkage, back electromotive force, rated torque and overload torque of three motors with different structure or material are compared by finite element software. The results show the proposed motor can increase the torque density and overload ability.

Multi-Objective Optimization Design of Permanent Magnet Torque Motor

Permanent magnet torque motor (PMTM) is widely used in aerospace, computer numerical control (CNC) machine tools, and industrial robots with many advantages such as high torque density, strong overload capacity, and low torque ripple. With the upgrading of industrial manufacturing, the requirements for the performance of torque motors have become more stringent. At present, how to achieve high output torque and low torque ripple has become a research hotspot of torque motors. In the optimization process, it is necessary to increase the output torque while the torque ripple can be reduced, and it is difficult to get a good result with the single-objective optimization. In this paper, a multi-objective optimization method based on the combination of design parameter stratification and support vector machine (SVM) is proposed. By analyzing the causes of torque ripple, the output torque, efficiency, cogging torque, and total harmonic distortion (THD) of back electromotive force (EMF) are selected as the optimization objectives. In order to solve the coupling problem between the motor parameters, the calculation formula of Pearson correlation coefficient is used to analyze the relationship between the design parameters and the optimization objectives, and the design parameters are layered ac-cording to the sensitivity. In order to shorten the optimization cycle of the motor, SVM is used as a fitting method of the mathematical model. The performance between initial and optimal motors is compared, and it can be found that the optimized motor has a higher torque and lower torque ripple. The simulation results verify the effectiveness of the proposed optimization method.

Theoretical research on magnetization and demagnetization process of electrohydraulic servo valve with permanent magnet torque motor

The magnetization and demagnetization process of electrohydraulic servo valve with permanent magnet torque motor is the last manufacturing process of electrohydraulic servo valve before its service, which has a significant effect on the output characteristics and magnetic stability of both torque motor and electrohydraulic servo valve. However, the previous studies mainly focus on the static state of the magnetic circuit instead of the changes of the magnetic steel’s states while operating magnetization and demagnetization process of torque motor, which causes many issues such as the unpredictability and inaccuracy of magnetization and demagnetization process. In this paper, a set of theoretical models are proposed to describe this entire magnetization and demagnetization process more accurately aiming at this issue. Firstly, a detailed magnetic circuit mathematical model of permanent magnet torque motor before demagnetization is established according to two kinds of magnetic circuits. Secondly, different from the existing research, in this paper, taking the variety of internal reluctance and magnetomotive force of magnetic steel into consideration, an equivalent method is presented by dividing the B-H curve of the magnetization and demagnetization process into several segments. Finally, the finite element method is used to verify the accuracy of the proposed mathematical model. The research results show the proposed model can accurately calculate the magnetic flux density of magnetic steel at any time and even the air gap’s magnetic flux and the output torque after the magnetization and demagnetization process. This research can help to design the magnetization and demagnetization process such as demagnetizing current to make sure the toque motor meets the requirements, which has an important guiding significance to design and conduct the magnetization and demagnetization process of electrohydraulic servo valve with permanent magnet torque motor.

Current Harmonics Controller for Reduction of Acoustic Noise, Vibrations and Torque Ripple Caused by Cogging Torque in PM Motors under FOC Operation

This article presents an effective algorithm to reduce acoustic noise, vibrations and torque ripple caused by cogging torque in three-phase Permanent Magnet (PM) motors under Field Oriented Control (FOC) operation. Cogging torque profile is suitably included into q-axis current reference, which must be then precisely tracked in order to mitigate acoustic noise, vibrations, torque ripple and speed ripple caused by cogging torque. Conventional FOC structure has been extended by a Current Harmonics Controller (CHC) to achieve precise control of dq current harmonics for all operation speeds, which is crucial to reduce impact of cogging torque and increase performance of electric drive with PM motor. Effectiveness of proposed control technique is experimentally verified by vibrations and acoustic noise measurements.

Self-Aligning Limited-Angle Rotary Torque PM Motor for Control Valve: Design and Experimental Verification

This study investigates the design and characterization of a permanent magnet torque motor with a limited operating range. The design method and configuration that satisfy the range and torque at a specific applied current were determined. The motor was designed and analyzed through finite element analysis. This motor was then fabricated, and an experimental setup was constructed to measure the torque at various rotation angles and different currents. Approximate values were obtained by comparing the finite element and measured results, and the characteristics of the limited-angle rotary torque motor obtained through the analysis were verified.

Cancelation of Torque Ripples in PMSM via a Novel Minimal Parameter Harmonic Flux Estimator

This paper presents a novel approach for treating the harmonic torque in permanent magnet motors at selected harmonic orders. The method is based on the online estimation of the motor harmonic flux. For this purpose, a novel minimal parameter harmonic flux estimator (MPHFE) is developed. The MPHFE is formulated such that the inductance, resistance, and stator current and its derivative are not necessary for the estimation of the harmonic flux. This was achieved by forcing the harmonic current to zero through the combined action of a field-oriented controller (FOC) and a feedforward controller. Subsequently, the harmonic flux can be obtained directly from the estimated harmonic back EMF without the involvement of other motor parameters. Finally, the estimated flux is used in conjunction with a comprehensive model of the motor harmonic torque to determine the stator current compensation for eliminating the torque harmonic. Experimental results presented from a permanent magnet motor confirm the theoretical claims in this paper as well as demonstrate the effectiveness of the proposed method to reduce the magnitude of the harmonic torque significantly.

Identification and Suppression of Unbalanced Magnetic Force and Cogging Torque in Permanent Magnet Motors With Magnetic Field Distortion

Permanent magnet (PM) induced vibration is one of the major concerns for PM motors. This work aims at the identification and suppression of the vibration source from magnetic field distortions caused by magnet/slot combination, uneven-magnetization, and magnet shifting. Modulation method is employed to predict the relationships between parameters and unbalanced magnetic force (UMF) and cogging torque (CT). Motivated by the magnetic field periodicity and structure especially air-gap symmetry, a new concept of equivalent magnet (EM) wherein one or more real magnets are defined as an imaginary one is introduced to help predict the unexpected force harmonics normally lower than magnet number, and rotation-frequency is used to present unified interpretation on magnetic force regarding the three distortions. The results imply that the relationships are determined by magnet/EM/slot combination including their greatest common divisor (GCD). Compared with CT, the UMF is more sensitive to the uneven-magnetization and magnet shifting. Like ideal motors, if the GCD is greater than unity, the UMF is eliminated, but the CT is not simply via altering the combination. The results also show that magnetic forces for the same EM/slot combinations share similar behaviors regardless of specific magnetic field details. The results can be utilized to suppress undesirable force, or inspect magnetization and installation status by monitoring force frequency and its amplitude, or gain vibration suppression by magnet's selective assembly. The modulation method, EM concept, and main findings are successfully verified by the finite element method (FEM) and comparison with the existing results in the literature. Main contribution of this work is the unified explanation on the relationships between the three distortions and unique force behaviors, especially the prediction on those unexpected harmonic forces.

The use of shaping face of pole in rotor as a component of molding cogging torque in Permanent Magnet motor in selfbreaking systems

In the paper the results of analysis concerning magnetic circuits with shaping flux density in motor with permanent magnets have been presented. In the research FEM Method has been applied. All simulations used to compute flux density, forces, and torques have been performed in the program Ansys. The application of this method in self-loocking PM Motors was discussed in authors' previous publications. The simulations showed differences in work of machines with density system. It can be used as the way to increase the desired drives parameters values.

A NEW ANALYTICAL DESCRIPTION AND FEA VALIDATION OF AN EFFECTIVE METHOD TO REDUCE THE COGGING TORQUE IN SM-AFPM MOTORS

So far, several methods to reduce the cogging torque of permanent magnet motors have been introduced. Implementation and evaluation of these methods have usually been done on radial flux types of motors. Nowadays, as axial flux permanent magnet motors have more advantages over radial ones, they are more attractive. Therefore, in this paper analytical modeling and calculation of the most effective method impact in reducing the cogging torque in axial flux permanent magnet motors will be studied. In fact, in this method the radial edges of the magnets will be curved to have a significant impact on reducing this unwanted component. This paper introduces a new concept to model this method. Finally, the accuracy of the proposed method will be verified by finite element analysis.

Development and Experimental Study of Magnetic Property for Servo Valve Torque Motor

Torque motor is an electrical-mechanical converter of servo valve, is bridge which connects the electrical devices and hydraulic devices, is one of key components of servo valve. The permanent magnet torque motor is studied in this paper. As key parameters of design of servo valve, the magnetic property of torque motor determines magnitude of the electromagnetic torque. At present, many manufactures of servo valve pays more attention on the test of integral servo valve. The design of torque motor also bases on experience, lacking of specialized tool for torque motor test. This paper described the principle of magnetic property of the test, developed a test system for magnetic characteristics, and established the relationship between the electromagnetic torque and current control current, and the relationship between output angular displacement and control current.

Development and Experimental Study of Dynamic Characteristics for Servo Valve Torque Motor

Torque motor is the electrical - mechanical converter of servo valve, is the bridge connecting electrical devices and hydraulic devices, is one of the key elements of electro-hydraulic servo valve. The main object of study of this paper is moving iron permanent magnet torque motor. The dynamic characteristics of torque motor are the key parameter to measure the overall performance. At present, the research of most of manufacturers emphasize on the test of integral valve servo valve. Torque motor is also designed to mimic the structure and size of foreign-based valve, lacking of system understanding for characteristics of servo valve. Early in the design, people cannot effectively control the overall performance of the torque motor products. There is large performance difference with a larger group of torque motor, producing serious waste. This paper describes the principle of dynamic characteristics test, establishes a test system of dynamic characteristics for torque motor, accurately obtain nature frequency and bandwidth of torque motor on the test bench which we have established before.

Application of Taguchi Experiment Design for Decrease of Cogging Torque in Permanent Magnet motors

Application of Taguchi Experiment Design for Decrease of Cogging Torque in Permanent Magnet motors

Desired Compensation Adaptive Robust Control for NC Rotary Table Direct Drive Rotary Feeding System

For the characteristics of direct drive NC rotary table servo system using ring permanent magnet torque motor being influenced by varying of external disturbance, parameters varieties and load disturbances, the desired compensation adaptive robust position controller based on projection algorithm is designed to achieve high performance and parameters estimation. The desired compensation adaptation law based on projection algorithm for uncertainties off-line estimation is calculated by desired information only to achieve high requirement of the servo system of the ring permanent magnet torque motor. Compared with adaptive robust controller, the controller can reduce the effect of measurement noises. Therefore the process of uncertainties estimation is faster and the estimators are more accurate. Simulation result shows that the designed method enables the system to be better in robustness in general.

Design of Digital Controllers for Permanent Magnet Torque Motors

The design of control system can be divided into two steps. The plant has to be converting into mathematical model form, so that its behavior can be analyzed. Then an appropriate controller has to be design in order to get the desired response of the controlled system. In this paper, the linear model of a Permanent magnet torque motor (PMTM) is considered and three controllers, digital PID controller with two forms of positional and velocity, a deadbeat controller and pole placement controller method are designed and due to a comparing between their, the best controller for this kind of plants will be chosen.