Due to the cogging torque, the effect such as torque ripple and unbalanced magnetic force arises. The main drawback of permanent magnet synchronous machines is the presence of cogging torque which is a result of interaction between rotor permanent. Cogging torque from 2ndorder solution the secondorder solution gives much smoother results, although the peak cogging torque is roughly the same around 9 mnm. The suggested is the optimization of an anisotropic ferrite magnet shape and magnetization. Cogging torque is the main hindrance in bldc motor, which results in direct impact on the performance of the permanent magnet pm motor. Cogging torque and torque ripple in a directdrive interior. Torque ripple is defined as the variance of the torque of the energized motor with a constant current. The main issues with this bldc motors are cogging torque and harmonic. Cogging torque reduction of permanent magnet synchronous. Cogging torque mitigation of modular permanent magnet machines g.
Rectangular rpm and sinusoidal spm permanent magnet shape. Finally, the optimal model, that is, st1p15, had been obtained. 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. Then new structures of rotors are proposed by adopting di. 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. Selecting as high a cogging frequency as possible is desirable as it reduces the amplitude of the cogging torque. Conclusions the cogging torque of a motor, due to attractionrepulsion cycles caused by the interactions of. Having a quick look at cogging torque, measuring it and looking at its effects at speed. Cogging torque reduction in a permanent magnet wind turbine. However, they are affected by the electric loading and magnetic saturation. Costa abstract evaluation and minimization of cogging torque in axial flux permanent magnet afpm machines become essential specially in direct drives for low speed applications.
Influence of pole and slot combinations on cogging torque. The maximum cogging torque for the three experimental machines is. Comprehensive analysis and evaluation of cogging torque in axial flux permanent magnet machines a. Pdf methods for reducing cogging torque in permanent. Influence of design parameters on cogging torque in permanent magnet machines 409 fig. Cogging torque reduction in permanent magnet machines. Analytical modeling of the cogging torque in permanent. The cogging torque analysis resul ts shown in figure 5 show that the cogging torque was 4. Cogging torque measurement, moment of inertia determination. The cogging torque waveform after changing the slot opening width obtained through fea is shown in figure 6. In this work, a method for mitigating the effects of the cogging torque is proposed, based on the use of a nonlinear automatic control technique known as feedback linearization that. Cogging torque lower than 0,5 % easy start easy and stable power control.
All books are in clear copy here, and all files are secure so dont worry about it. Directdrive torque motors have half the cogging torque. Experimental results show that the application of tooth pitching to these machines can reduce the cogging torque and back emf harmonics significantly. It can be seen that the peak value of the cogging torque for the proposed model 2 can be reduced by as much as 92. Cogging torque is produced in a permanent magnet machine by the magnetic attraction between the rotormounted permanent magnets and the stator. At cedrat, the application team, thanks to its experience has developed methodologies to successfully compute. Cogging torque profile of the lspms motor with normal rotor and also cogging torque of the lspms motor with shifted pms have been obtained from 2d fea and results are shown in fig. Cogging torque reduction in surfacemounted permanent. Table ii factor c for typical 2pole brushed pm motors with overlapping windings all edges of magnets would face slot openings. Cogging torque minimization of surfacemounted permanent.
Variation of peak cogging torque with slot number in 2pole motor. It arises from the rotor permanent magnet interacting with the steel teeth on the stator. Cogging and torque ripple questions are common and many times, difficult to answer. Presents an approach to determine sources of cogging torque harmonics in permanent magnet electrical machines on the basis of variations of air. In order to eliminate the cogging torque theoretically, it is very important to investigate the equations which define it. Pdf new cogging torque reduction methods for permanent. Reduction of cogging torque and emf harmonics in modulated. Influence of electric loading and magnetic saturation on. Reduction of cogging torque in dual rotor permanent magnet. Minimization of cogging torque in permanent magnet motors by.
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. Reduction of cogging torque, harmonics in pm bldc motor. An example of a rotorskewed structure used to reduce cogging torque of permanent magnet synchronous machines is evaluated and compared. The cogging torque is compared for the various designs of the rotor structures. Cogging torque reduction of permanent magnet synchronous motor. It can be shown that in a motor having full polepitched magnets the instantaneous cogging torque is zero when a the interpole axes. The period of a cogging torque can be expressed as. Cogging torque ripple minimization via positionbased. When measuring the cogging torque of a test motor from a qaxis current generated by a driving motor when bypassing a torque sensor and directly connecting the test motor to and driving the same with the driving motor, first the qaxis current of the driving motor operating without a load is measured separately under the cogging torque measurement conditions. One of the properties of the electric motor used, is the presence of cogging torque. Both the cogging torque and backemf are normally calculated at opencircuit conditions. In practice, however, the cogging torque cannot actually be eliminated, but it can be reduced zhu et al 2003.
Cogging torque is the torque needed to overcome the opposing torque created by the magnetic attractive force between magnets on the rotor and the iron teeth of the stator. A novel cogging torque simulation method for permanentmagnet. An exact analytical description of the magnetic field in idealized models of surface mounted permanent magnet motors is presented. Analytical modeling of the cogging torque in permanent magnet. Sometimes, squirrel cage induction motors exhibits a tendency to run at very slow speeds as low as oneseventh of their synchronous speed. Now the cogging torque waveforms of inner and outer air gaps were different. Cogging torque in permanent magnet motors and generators is characterized by a torque ripple that usually pulsates at a. This work addresses the problem of mitigating the effects of the cogging torque in permanent magnet synchronous motors, particularly brushless motors, which is a main issue in precision electric drive applications. Pdf analysis of torque ripple and cogging torque reduction. An analysis of the cogging torque of a dc motor and a new. Cogging torque computation and meshing for radial electrical. Pdf methods for reducing cogging torque in permanent magnet. Permanent magnet shaping for cogging torque and torque.
Because of this periodicity, cogging torque can be expressed as a fourier series t cog. Cogging torque profile is suitably included into q axis current reference, which must be then precisely tracked in order to mitigate acoustic noise, vibrations. The purpose of this paper is to study the existence and effects of cogging torque, and to present a novel, rapid, half magnet pole pair technique for forecasting and evaluating cogging torque. Cogging torque is defined as the attractioninteraction of the magnetic poles to the teeth steel structure of the laminations within an unenergized motor. Current harmonics controller for reduction of acoustic. Cogging torque reduction for interior permanent magnet. In the model, the maximum input current per phase was 10 a with 30 turns as shown in fig. In many machines, where permanent magnets are used, the effects due to cogging torque generated by permanent magnets pms aggravate the output characteristics of the machines. 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. Us20070018520a1 motorgenerator to reduce cogging torque. 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 cogging torque of the machine with symmetrical magnetic circuit the same size of gap between magnets was compared to the one of the asymmetrical machine. It is an undesired effect that contributes to the machines output ripple, vibration, and noise.
Due to the nonuniform distribution of the slots, the periodicity of the cogging torque waveform is half that for the. However, in order to improve their accuracy in their torque responses, the cogging torque and torque ripple phenomena should be mitigated to obtain better performance of the machine. There are multiple rotor positions with a revolution where the cogging torq. 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. A study of cogging torque reduction methods in brushless dc motor teeradej srisiriwanna1 and mongkol konghirun2, nonmembers abstract the cogging torque is undesirable e.
A compact machine, designed with strong permanent magnets and small air gap, tends to have high cogging torque 6. Methods for reducing cogging torque in permanent magnet synchronous motors. The new motors can produce a high s1 torque density and are available in a choice of stator and rotor lengths. One of a series of teeth, as on the rim of a wheel or gear, whose engagement transmits successive motive force to a corresponding wheel or gear. Analytical prediction of cogging torque for interior permanent.
This paper presents two methods that use a position sensor already present for servo motors to map cogging torque to rotor. An approximate closed form solution is derived therefrom. Influence of edge slotting of magnet pole with fixed slot. Here jacques saintmichel, scientific director for leroysomer, explains the theories behind cogging torque. An analysis of the cogging torque of a dc motor and a new technique of reducing the cogging torque. Cogging torque is generated when the sides of the rotor teeth line up with the sides of the stator teeth and the motor requires torque to break that attraction.
Reduction of cogging torque in permanent magnet motors ieee. 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. This article presents an effective algorithm to reduce acoustic noise, vibrations and torque ripple caused by cogging torque in threephase permanent magnet pm motors under field oriented control foc operation. Cogging torque reduction in line start permanent magnet. Such a technique is performed for the reduction of cogging torque in bldc motors 5.
The airgap reluctance varies periodically, thus causing the cogging torque to be periodic 9. It can be said that the proposed method can reduce the cogging torque more effectively compared to teeth pairing method alone. Indeed, the amplitude of this quantity is almost the same as the numerical noise. Cogging definition and meaning collins english dictionary. This paper presents two methods that use a position sensor already present for servo motors to map cogging torque to rotor position. To improve the result of a programmed reference current waveform, a calibration 1. Identification and analysis of lowfrequency cogging torque component in permanent magnet machines devon r. Pdf cogging torque reduction for interior permanent. Crawling and cogging both are particularly related to squirrel cage induction motors. The values of cogging torque obtained before and after changing the slot opening width are given in table 1. Cogging torque mitigation of modular permanent magnet. Cn104655339a coggingtorque test method for alternating. The magnetic flux density is determined from the two. It is especially prominent at lower speeds, with the symptom of jerkiness.
Cogging definition of cogging by the free dictionary. Study of cogging torque in permanent magnet machines. To achieve a smooth output torque, compensation for the cogging torque is added to the control scheme. The achievement of low and repeatable values of cogging torque probably is the major problem encountered in designing and manufacturing permanent magnet motors. Cogging torque is most commonly estimated from the air gap magnetic flux density distribution calculated from the virtual work principle using the energy stored in the air gap 27. 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. Contrary to this, a high np means the peaks of elementary torques are distributed along the slot pitch resulting in lower peak cogging torque but with higher fundamental frequency. The cogging torque and torque ripple of the generator can cause fatigue and stress in the mechanical structure of the turbine 5. Nums tmx directdrive motors have extremely low cogging torque. The invention relates to a coggingtorque test method for an alternatingcurrent permanentmagnet synchronous servo motor. A study of cogging torque reduction methods in brushless dc motor. Although finite element methods show that cogging cancellation is theoretically always possible, if the dimensions of.
It is also verified that the period of the waveform is 6 degrees. The predicted cogging torque curve against measured points for the skewed case is also shown in fig. Cogging torque results in torque as well as speed ripple. Pdf critical evaluation of cogging torque in bldc motor. Mar 29, 2016 obviously, the cogging torque results from the combined influence of the interaction of each individual magnet with each individual tooth. These effects are caused due to the connecting wires between the slot windings 6. As to the cogging torque results obtained from measurements, finite element calculations, exact and approximate analytical modeling are compared with each other.
Most of the methods utilized for cogging torque reduction lead to motor structure complexity, increasing manufacturing cost and also influencing the output torque. Cogging torque reduction of interior permanentmagnet. Whether the two mean the same thing, well, thats a matter for discussion. Cogging torque reduction methods oleg kudrjavtsev, aleksander kilk tallinn university of technology estonia kudrjavtsev. Analyzed motor the analytical calculation of the machines which present complex geometries is a very di. With this in mind, 24s22p would be an attractive option with its 264 cogging steps per rotation and 0. All electrical motor designers know that the computation of cogging torque is a tricky task in 3d. Reduction of cogging torque by various structures of rotor. Cogging torque has been analyzed to be reduced by slot skewing. Article pdf available in iop conference series earth and environmental science 1942. This research tries to find an optimal solution set of the pmsm with the aim of reducing the cogging torque while the output torque is not affected. A 140mmdiameter motor with an active length of 70mm can produce a peak torque of around 82nm at speeds up to 1,500 rpm, and a continuous stall torque of.
Identification and analysis of lowfrequency cogging. Cogging torque in a permanent magnet motor, which arises from the interaction of the rotor magnets with the steel teeth on the stator, can be reduced. But the magnitude of the results is too large and the pitchvalue graph is not quite what i would expect. It is important to reduce the cogging torque in a pm generator, because. Understanding the distinctions among torque ripple, cogging. Cogging torque reduction in a permanent magnet wind. It is shown that the slot and pole number combination has a significant effect on the. This paper aims to the improvement of permanent magnet shape in the popular permanent magnet synchronous machine pmsm is proposed in this paper in view to mitigate cogging torque magnitude and torque ripple. From the geometry, the detent torque seems to have a period of 7. Comprehensive analysis and evaluation of cogging torque in.
Cogging torque in a permanent magnet motor, which arises from the interaction of. Influence of design parameters on cogging torque in. Interior permanent magnet synchronous machines show a good range of behaviours, which make these kinds of machines good candidates for an electromechanical energy conversion. Many analytical cogging torque calculation methods have been proposed, e. Cogging torque is an inherent characteristic of pm generators and is caused by the geometry of the generator. Skewing for both cogging torque components in permanent.
In the most fundamental form cogging torque can be represented as hanselman 1994. Low cogging torque design and simplified modelfree. Pdf the paper presents the results of the study of the cogging torque in. 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. Cogging torque mitigation of modular permanent magnet machines. As shown the peak to peak cogging torque for lspms motor with uniformly distributed magnet on the rotor is calculated as 2. In most cases, a classical meshing methodology is not sufficient and specific methodology must be used. The fea results of the cogging torque reduction, output torque reduction and torque ripple reduction for varying the teeth edge length l is shown in figure 10. In this method a 2d finite element model of a bldc motor which includes the effect of connecting wires was developed. There appears to be general agreement that cogging torque and detent torque refer to the same phenomenon. Influence of design parameters on cogging torque in permanent. Read online cogging torque reduction for interior permanent magnet.
Critical evaluation of cogging torque in bldc motor with various techniques. Proof is hereby given that the cogging torque could be greatly reduced. Aalborg universitet an analytical equation for cogging. This phenomenon is called as crawling of an induction motor. Reduction of cogging torque, harmonics in pm bldc motor open. The paper presents the results of the study of the cogging torque in. Cogging torque is an important issue in design of permanent magnet motors, especially in certain high accuracy applications. It can be observed that skewing stator slot opening has a significant effect on the magnitude of cogging torque curve. The maximum cogging torque value appeared 6 times per period, and the peak to peak value was approximately 2. According to the coggingtorque test method, a servo driver is utilized to drive a tested motor to stably rotate at a lower rotating speed, an encoder is utilized to detect the speed and the position information of the motor, and the cogging torque of the motor can be.
In this paper the pms has various structures such as surface mounted, interior and buried permanent magnet. This paper presents the method for reducing cogging torque in surfacemounted permanent magnet synchronous motor spmsm. Cogging torque is an undesirable component for the operation of such a motor. Hence, the cogging torque and torque ripple could be minimized by the cutting edge length l fixed in 0. Download cogging torque reduction for interior permanent magnet. I am then steping the rotor around to see the value at different pole pitches.
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