Configuring cogging torque compensation granite devices. Cogging torque from 2ndorder solution the secondorder solution gives much smoother results, although the peak cogging torque is roughly the same around 9 mnm. Feb 23, 2016 cogging torque is a function of position. Reduction of cogging torque in permanent magnet mo tors. Influence of design parameters on cogging torque in.
Jul 17, 2018 cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a permanent magnet pm machine. Identification and analysis of lowfrequency cogging torque component in permanent magnet machines devon r. Reduction of cogging torque, harmonics in pm bldc motor. Variation of peak cogging torque with slot number in 2pole motor.
As a result of inclination of stator slots with angle. It arises from the rotor permanent magnet interacting with the steel teeth on the stator. A novel method for cogging torque reduction in permanent. Minimization of cogging torque in permanent magnet motors.
Cogging torque target and design of motor for eps 20060120 this project studied a dc brushless motor for an eps system that would not cause control performance to decline even when the vehicle was operated with a low steering angle at high vehicle speeds. Identification and analysis of lowfrequency cogging. These speed ripples are induced by parasitic torque. A study of cogging torque reduction methods in brushless dc motor teeradej srisiriwanna1 and mongkol konghirun2, nonmembers abstract the cogging torque is undesirable e. Tooth pitching is applied to a separate phase mpm in order to reduce the most prominent harmonics present in a threephase mpms cogging torque. In other words, when the poles of the rotor line up with the teeth of the stator, a force is required to break the attraction, and this force is referred to as cogging torque. Research on reducing cogging torque in permanent magnet synchronous generators 231 where np1 is periodicity of tcog curve on a slot pitch, and z1 24 stator slots.
Since it is the shape of the rotor poles and the stator configuration that primarily determine the torque characteristic, this paper focuses on designing the iron and magnet rotor poles as well as the base of the tooth shape in. Torque analysis of magnetic spur gear with different. It is because of the high forces during acceleration1. Nm p 1 vector of the pulsating torque estimate nm r 1 vector of the estimated mean torque nm. This torque is position dependent and its periodicity per revolution depends on the number of magnetic poles and the number of teeth on the stator. Study of cogging torque in surfacemounted permanent magnet. Cogging torque is the torque produced by the shaft when the rotor of a pm generator is rotated with respect to the stator at no load condition. Cogging torque results in torque as well as speed ripple. Abstract the necessity of indepth learning of cogging detent torque for mainly undergraduates is discussed with particular attention to its method and tools. It can be observed that skewing stator slot opening has a significant effect on the magnitude of cogging torque curve. It can be said that the proposed method can reduce the cogging torque more e. Cogging torque reduction in a permanent magnet wind turbine.
Cogging torque is an inherent characteristic of pm generators and is caused by the geometry of the generator. Due to the cogging torque, the effect such as torque ripple and unbalanced magnetic force arises. It can be seen that the coging torque is nearly eliminated with the reduction of 99. This paper presents two methods that use a position. Gieras, fellow, ieee abstractthis paper discusses the approach to analytical calculation of the cogging torque in permanentmagnet pm brushless motors. Shahgholian surfacemounted permanent magnet pm is a wellknown structure in pm machines. Mar 29, 2016 obviously, the cogging torque results from the combined influence of the interaction of each individual magnet with each individual tooth. Whats the difference between cogging torque and torque. It is important to reduce the cogging torque in a pm generator, because.
The cogging torque on a pmsg is constant and produces zero work 7. Table ii factor c for typical 2pole brushed pm motors with overlapping windings all edges of magnets would face slot openings. Pdf how to reduce the cogging torque of the integrated propeller motor is. Ma university of sheffield, sheffield, uk this paper proposes a novel cogging torque mitigation method for modular permanent magnet pm machines with flux gaps in alternate stator teeth. Maxwell stress tensor for cogging torque and radial pressure calculation.
Pdf this paper deals with the finite element estimation of cogging torque oscillations that occur in. Pdf analytical approach to cogging torque calculation in pm. It is also verified that the period of the waveform is 6 degrees. Cogging torque measurement, moment of inertia determination. Pdf the paper discusses the approach to analytical calculation of the cogging torque in pm brushless motors. Reduction of cogging torque in permanent magnet motors. However, in order to get an optimal machine design the cogging torque should be minimized. Such a technique is performed for the reduction of cogging torque in bldc motors 5. While other methods exist to compensate for currentbased torque ripple mutual or reluctance torque, none have addressed cogging torque, except by adding expensive force sensors. Cogging torque is a product of the magnetic interaction between the poles of the rotors permanent magnets and the steel laminations of the stators teeth. Skewing for both cogging torque components in permanent magnet machines devon r.
To improve the result of a programmed reference current waveform, a calibration 1. The values of cogging torque obtained before and after changing the slot opening width are given in table 1. Cogging torque is an undesirable component for the operation of such a motor. Cogging torque in permanent magnet motors and generators is characterized by a torque ripple.
Cogging torque ripple minimization via positionbased. But the magnitude of the results is too large and the pitchvalue graph is not quite what i would expect. A method for reducing cogging torque of integrated. Examination of 2 reveals that cogging torque can be represented as a fourier series so it is a summation of harmonic sinusoids. To achieve a smooth output torque, compensation for the cogging torque is added to the control scheme. Pdf methods for reducing cogging torque in permanent. The pole number, slot number, and number of periods corresponding to the four curves are shown in table 2. Understanding the distinctions among torque ripple, cogging. The advantages of such a motor are that it is free of cogging, has efficient cooling, and has low inductance. Pdf finite element analysis of cogging torque in low speed. The n cog is the first cogging torque harmonic and has a significant effect on the level of cogging torque. Analytical prediction of cogging torque for interior.
Also since magnets are on the surface of rotor, air gap can be large and effective and saliency effect is minimized. Influence of design parameters on cogging torque in permanent. Cogging torque minimization of surfacemounted permanent magnet synchronous machines using hybrid magnet shapes brahim l. Dec 24, 2017 hello whenever in motor stator teeth and rotor teeth is in equal number then one strong alignment force is experienced between them and due to that one strong alignment torque is going to induced, which is in the opposite direction of the operatin. Pdf a method for reducing cogging torque of integrated. Influence of pole and slot combinations on cogging torque in. Torque ripples are caused by the interaction of the rotor permanent magnets with the ferromagnetic pole pieces i. Torque ripple is defined as the variance of the torque of the energized motor with a constant current. Cogging torque reduction in surfacemounted permanent magnet. Finite element method fem and other numerical methods are used for cogging torque calculation in many papers 6,7, and proper combination of the number of polesnumber of stator slots 8, skewing. Cogging torque reduction in permanent magnet machines.
This goes back to the holding cogging ratio is there a general rule on this ratio or does it differ on a product by product basis. As a result, many studies have been carried out on the prediction and minimization of cogging torque. Cogging torque and torque ripple in a directdrive interior permanent magnet generator article pdf available in progress in electromagnetics research b 701. Conclusions the cogging torque of a motor, due to attractionrepulsion cycles caused by the interactions of. Pdf minimization of cogging torque in permanent magnet. A study to determine design parameters with statistical. In further work is planned to select and develop the. Cogging torque in permanent magnet motors and generators is characterized by a torque ripple that usually pulsates at a characteristically high. The cogging torque waveform after changing the slot opening width obtained through fea is shown in figure 6. Chikouche1, kamel boughrara2,andrachidibtiouen2 abstractthis paper deals with the magnet pole shape design for the minimization of cogging torque in permanent magnet synchronous machines pmsm. It is especially prominent at lower speeds, with the symptom of jerkiness. For this reason, the cogging torque causes noise and vibration in pmsgs especially at low speeds and the direct drives applications. Low cogging torque design of permanentmagnet machine.
Cogging torque minimization of surfacemounted permanent. It is important to reduce the cogging torque in a pm generator, because cogging torque affects selfstart ability and produces noise and mechanical vibration on wind turbines. Cogging torque mitigation of modular permanent magnet machines g. This paper presents finite element fe analyses results that show a previously unaddressed low. Low armature reaction and capability of standing high power load can be achieved by choosing the slotted surface pms in machines. In order to eliminate the cogging torque theoretically, it is very important to investigate the equations which define it. Pdf cogging torque and torque ripple in a directdrive.
Cogging torque calculations for a novel concept of a transverse flux linear freepiston generator alija cosic. Permanent magnet motors are generally used for eps but a reduction of cogging torque in these motors is one of the challenges we face to ensure safe and comfortable vehicle handling. Pm locating for cogging torque reduction in a singlephase surfacemounted pm motor jawad faiz, a. This paper presents the method for reducing cogging torque in surfacemounted. Cogging torque in permanent magnet motors and generators is characterized by a torque ripple that usually pulsates at a. Understanding the distinctions among torque ripple, cogging torque, and detent. Anticogging algorithm brings out the best in your hobby. Reduction of cogging torque in dual rotor permanent magnet. The waveforms of cogging torque within the rotation of one slot pitch with different combinations are shown in fig. Identification and analysis of lowfrequency cogging torque. In the most fundamental form cogging torque can be represented as hanselman 1994.
Obtained cogging torque values are relatively high, but there are many techniques of reducing them 1819202122232425 26. Pdf critical evaluation of cogging torque in bldc motor. In some granite devices drives ioni pro family on the time of writing there are options to adjust compensation current by few parameters. The suggested is the optimization of an anisotropic ferrite magnet shape and magnetization. Feb 26, 2018 having a quick look at cogging torque, measuring it and looking at its effects at speed. I need a stepper that has the highest possible holding torque when power is on and smallest possible cogging detent torque when power is off. The higher n cog is, the lower the resulting cogging torque should be. Stepper motor holdingcogging torque ratio electrical.
Cogging torque measurement, moment of inertia determination and. Now the cogging torque waveforms of inner and outer air gaps were different. Cogging torque has been analyzed to be reduced by slot skewing. Magnetic field evaluation of sidebyside packed ultra. Indepth learning of coggingdetenting torque through. Methods for reducing cogging torque in permanent magnet synchronous motors. Experimental results show that the application of tooth pitching to these machines can reduce the cogging torque and back emf harmonics significantly. In practice, cogging torque cannot be easily eliminated, but it can be greatly reduced 1. Analytical and fem approach to reduce the cogging torque. Study of cogging torque in surfacemounted permanent. The experimental tools developed include a cogging torque tester, variableskew rotors for a dc motor and a threephase hybrid stepping motor having a special rotor construction to eliminate certain harmonic components of cogging torque. Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a permanent magnet pm machine.
To analyse that, we shall make the assumption that the magnetic circuit is linear unsaturated, which is a reasonable assumption at no load, to allow the use of the superposition principle. The predicted cogging torque curve against measured points for the skewed case is also shown in fig. This cogging torque is calculated using the virtual work method vwm as shown below. Reduction of cogging torque and emf harmonics in modulated. Influence of pole and slot combinations on cogging torque. The experimental tools developed include a coggingtorque tester, variableskew rotors for a dc motor and a threephase hybrid stepping motor having a special rotor construction to eliminate certain harmonic components of cogging torque. Reduction of cogging torque in permanent magnet machine. The cogging torque stems from the interaction between the rotor permanent magnets pms and the stator teeth 6. This paper presents the method for reducing cogging torque in surfacemounted permanent magnet synchronous motor spmsm. The authors derive magnetic field solutions, force relations and commutation laws for. The free piston energy converter can be used in many different areas e.
Pm locating for cogging torque reduction in a singlephase. Cogging torque reduction methods oleg kudrjavtsev, aleksander kilk tallinn university of technology estonia kudrjavtsev. However, in slotted motors, cogging torque, which may affect the control accuracy, is produced as a result of the interaction between permanent magnets and armature. Cogging torque reduction in surfacemounted permanent. It is not possible to make g as zero because some amount of airgap flux is needed for the alignment and reluctance torque components for driving. A number of studies on cogging torque calculation and minimization can be found. It also depends on the rotor pole design, and stator pole design, and pole angle, and pole spacing. Cogging and torque ripple questions are common and many times, difficult to answer.
In traditional machines with no cogging torque reduction. These effects are caused due to the connecting wires between the slot windings 6. Influence of design parameters on cogging torque in permanent magnet machines 409 fig. Critical evaluation of cogging torque in bldc motor with various techniques article pdf available in international journal of automation and control 73. The cogging torque is formed in the air gap as a force and can be calculated from the stored energy in the air gap. These torque fluctuations cause vibrations, noise and speed fluctuations. One of the properties of the electric motor used, is the presence of cogging torque. Cogging torque mitigation of modular permanent magnet. Cogging torque mitigation of modular permanent magnet machines. In the free piston energy converter the cogging torque is not of relatively high importance. It can be used as an index to identify the level of cogging torque. In this method a 2d finite element model of a bldc motor which includes the effect of connecting wires was developed.
In practice, however, the cogging torque cannot actually be eliminated, but it can be reduced zhu et al 2003. How to reduce the cogging torque of the integrated. Cogging torque is produced predominantly as a result of fringing fields in the magnet interpole and slot regions 5, a typical cogging torque waveform being shown in fig. Abstract the necessity of indepth learning of coggingdetent torque for mainly undergraduates is discussed with particular attention to its method and tools. Torque decreas rapidly with the increase of the air gap length. The cogging torque is also a source to the tooth vibrations and motor noise. Cogging torque compensation feature in drive that aims to make motor torque production more uniform and ideal. It can be shown that in a motor having full polepitched magnets the instantaneous cogging torque is zero when a the interpole axes. I am then steping the rotor around to see the value at different pole pitches. So in these kinds of applications, cogging torque is of important concern. Cogging torque calculations for a novel concept of a. Skewing for both cogging torque components in permanent. Considering the limitation of manufacturer and installation the suggested air gap length is between 0.
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