As to the cogging torque results obtained from measurements, finite element calculations, exact and approximate analytical modeling are compared with each other. Skewing for both cogging torque components in permanent magnet machines devon r. Pdf the paper discusses the approach to analytical calculation of the cogging torque in pm brushless motors. In this method, the desired torque decreases because less magnet. The rotor has 36 neodymium magnets in a nsnsns 6 pole configeration. In the range between 2 mm and 50 mm it has two peaks of cogging torque for in each cycle both at 7 mm and 42 mm width of rotor pole. The curves indicate that for an eightpole motor with a 9slot.
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. We proposed a method to reduce the cogging torque by optimizing the size of. In wind energy systems employing permanent magnet generator, there is an imperative need to reduce the cogging torque for smooth and reliable cut in operation. Cogging torque reduction in a permanent magnet wind. Torque a novel minimization method of cogging torque and. This paper presents two methods that use a position. So, key point in the motor design is minimizing the cogging torque and maximizing the. Cogging torque in permanent magnet motors and generators is characterized by a torque ripple that usually pulsates at a characteristically high. Various approaches of reduction the cogging torque were considered.
Understanding the distinctions among torque ripple, cogging torque, and detent. But the magnitude of the results is too large and the pitchvalue graph is not quite what i would expect. Variation of peak cogging torque with slot number in 2pole motor. As the rotor starts rotating, the reluctance in the air gap. The detent torque of pm motors is composed of cogging torque and friction torque. Cogging torque reduction in surfacemounted permanent magnet.
So in these kinds of applications, cogging torque is of important concern. Minimization of cogging torque in permanent magnet machines using the topological gradient and adjoint sensitivity in multiobjective design. 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. Dependence of fluctuation amplitude of the torque on width of stator slot opening is researched. Cogging torque in permanent magnet motors precision. In most cases, a classical meshing methodology is not sufficient and specific methodology must be used. Cogging torque reduction consists of manipulating the shape of the tooth torque waveforms so that the sum over all the stator teeth is as close to zero as possible. To improve the result of a programmed reference current waveform, a calibration 1. Reduction of cogging torque in dual rotor permanent magnet. 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 geometry of the loafshape pm is formulated and optimized to reach a design with a low value of the cogging torque. In this case, the cogging torque is times the cogging torque generated by each pole, where is the 1 pole number additive effect.
The paper presents an application of the topological derivative and continuum sensitivity analysis for the optimal design of the permanent magnet excited machines with the adjustable excitation. Cogging torque reduction methods oleg kudrjavtsev, aleksander kilk tallinn university of technology estonia kudrjavtsev. Incorporates exclusive highrigidity torque detection component configured in a vertical structure to reduce torquedetector bearing size, enabling detection of low torque levels of 0. Ways to overcome static friction and cogging torque when micropositioning the. As a result of inclination of stator slots with angle. Cogging torque in permanent magnet machines is a source of acoustic noise, vibrations and one of the reasons behind output torque ripple. The mutual dependency of armature geometry and magnetization pattern as to their influence on the cogging torque is discussed. This general expression, valid if the teeth and the magnets all are in their right position, will be useful to analyse the frequency components of the torque. Cogging torque reduction technique on ecore hybrid flux. Cogging torque reduction by increasing tooth tang radius in. 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. Abstract the necessity of indepth learning of cogging detent torque for mainly undergraduates is discussed with particular attention to its method and tools. Permanent magnet synchronous motor driver and control.
In this paper, an analytical calculation of airgap magnetic density is derived. Feb 23, 2016 anticogging algorithm brings out the best in your hobby brushless motors. Cogging is an undesirable characteristic of some permanent magnet motor designs. 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. In contrary with the conventional stator skew, this paper is concentrate on the. The generator was rotated at low rpm about 3rpm to measure the dynamic characteristics, acquired through a high speed data acquisition system. Whats the difference between cogging torque and torque.
Cogging torque is prime creator of torque ripple and it is one of the most important disadvantage of pmbldc motor which results vibrations in shaft and noise. What type of motor driver circuit should be used and how to dimension it in order. Using thinner magnets can also decrease the cogging torque, by 64%, though it is not sufficiently effective. Cogging torque results in torque as well as speed ripple. Tooth pitching is applied to a separate phase mpm in order to reduce the most prominent harmonics present in a threephase mpms cogging torque. As a result, many studies have been carried out on the prediction and minimization of cogging torque. From a practical point of view, effective elimination of cogging torque is never obtained due to fringing effects and.
This paper presents cogging torque and torque ripple analysis of a dd fscw ipmg which was designed to achieve goals i cogging torque torque and ii machine generated torque ripples torque. This paper presents the method for reducing cogging torque in surfacemounted permanent magnet synchronous motor spmsm. Torque ripple is defined as the variance of the torque of the energized motor with a constant current. Effect of relative slotopening shift on cogging torque.
In a perfect world, positioning axes would deliver the load to the desired location both rapidly and accurately. Most of the methods utilized for cogging torque reduction lead to motor structure complexity, increasing manufacturing cost and also influencing the output torque. Comprehensive analysis and evaluation of cogging torque in. It is the energy variation within a motor when there is no current in the windings. Cogging torque is produced in a permanent magnet machine by the magnetic attraction between the rotor mounted permanent magnets and the stator. It is one of the most important parameters of permanent magnet motors, which causes torque ripple, vibration and noise.
Variation on cogging torque cogging torque is generated by the interaction between the magnet edges and the stator teeth. Compensation of permanent magnet motors torque ripple by. The interaction between the stator slots and rotor magnets is called cogging torque. A novel method for cogging torque reduction in permanent. We are also now seeing a difference in ripple based on motor rotation. Many methods have been reported to reduce cogging torque. In this paper the applicability of reducing the cogging torque is considered. Cogging torque ripple minimization via positionbased robotics. Cogging torque reduction in a permanent magnet wind turbine generator pdf. The cogging torque of the generator was measured at zero excitation to determine cogging characteristics. The machine cogging torque is computed by the maxwell stress tensor. Reducing cogging torque in brushless motors machine design.
Magnets 2d static solver can be used to calculate this cogging torque waveform. 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. Skewing for both cogging torque components in permanent. 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. Cogging torque of electrical motors is the torque due to the interaction between the permanent. Cogging force reduction for tubular permanent magnet. Cogging torque makes a noise and vibration in the motor speed. Reduction of cogging torque in permanent magnet flux. Pdf cogging torque reduction for interior permanent. A novel cogging torque simulation method for permanentmagnet synchronous machines article pdf available in energies 412 december 2011 with 1,3 reads how we measure reads. Yim, cogging torque ripple minimization via position. Cogging torque minimization of surfacemounted permanent magnet synchronous machines using hybrid magnet shapes brahim l. Cogging torque can be reduced by proper selection of rotor permanent magnet arc as peak to peak value and shape of the cogging profile depends on the magnet pole arc and on the physical geometry of the magnet 6. Study of cogging torque in surfacemounted permanent magnet.
Methods to reduce the cogging torque in permanent magnet. It also depends on the rotor pole design, and stator pole design, and pole angle, and pole spacing. Cogging torque measurement equipment mea testing systems. Cogging torque reduction in surfacemounted permanent. Pulsating torque wave is generated if a magnet pole edge passes a slot opening. Pdf analytical approach to cogging torque calculation in pm. Cogging torque and torque ripple in a directdrive interior permanent magnet generator rukmi dutta, kazi ahsanullah, and faz rahman abstractthis paper investigates the cogging torque and torque ripple in high pole number interior permanent magnet generators, designed for directdrive applications. Cogging torque is generated when the sides of the rotor teeth line up with the sides of the stator teeth within the motor. Cogging torque reduction in permanent magnet machines.
The magnetic flux density is determined from the two. Influence of design parameters on cogging torque in permanent. Cogging torque reduction of interior permanent magnet. This paper analyzes various cogging torque minimization. Unfortunately, low inherent torque ripple motors are expensive.
Cogging torque is defined as the attractioninteraction of the magnetic poles to the teeth steel structure of the laminations within an unenergized motor. There are two positions of the rotor pole that will result in zero tangential force on a stator tooth. This will be illustrated by a few examples hereafter. This measurement was compared to another measurement. 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. First, a target for cogging torque was established to ensure that control performance did not decline at. Pdf drive motors, which are used in the drive modules of electric cars, are interior permanent magnet motors. The impact of slots with different sizes on the fourier coefficients of relative airgap permanence function is. Identification and analysis of lowfrequency cogging torque. For such motors, it has been a challenge for the designers to minimize the torque fluctuations which may cause vibrations, noise and speed fluctuations. Analytical and fem approach to reduce the cogging torque in. Matthews algorithm works by measuring the applied voltage or current needed to servo the rotor to each measurable encoder position in a full. Pdf effect of magnet segmentation on the cogging torque.
I am then steping the rotor around to see the value at different pole pitches. Understanding the distinctions among torque ripple, cogging. The obtained analytical model is used as the computational tool to find the dependence of the machine cogging torque on the pm geometry. Influence of magnet shaping on cogging torque of surface. Indepth learning of coggingdetenting torque through. An approximate closed form solution is derived therefrom. The cogging torque graph for both cycles possesses the same pattern of dropping ping pong ball. Pdf analysis of torque ripple and cogging torque reduction in. This is done by manipulating pm magnetization pattern and stator tooth geometry, alone or in combination. Experimental results show that the application of tooth pitching to these machines can reduce the cogging torque and back emf harmonics significantly. 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. At cedrat, the application team, thanks to its experience has developed methodologies to successfully compute. Configuring cogging torque compensation granite devices.
Table ii factor c for typical 2pole brushed pm motors with overlapping windings all edges of magnets would face slot openings. I think the difference in torque ripple based on direction should be a result of some sort of asymmetry in how we are driving the rotor. Cogging and torque ripple questions are common and many times, difficult to answer. The underlying goal of this approach is to compensate the cogging torque of a kinetic energy harvester keh with the optimized counter cogging torque of a. Cogging torque reduction of permanent magnet synchronous. 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. 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. The conclusion isthe wider opening of slot, the greater value of cogging torque. Cogging torque is an important issue in design of permanent magnet motors, especially in certain high accuracy applications.
All electrical motor designers know that the computation of cogging torque is a tricky task in 3d. Cogging torque minimization of surfacemounted permanent. Cogging torque mitigation of modular permanent magnet. Cogging torque ripple minimization via positionbased.
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. This paper presents the method for reducing cogging torque in surfacemounted. Its reduction is of prime importance in automotive and positioning applications. Report permanent magnet generator performance testing. So a driver takes the sticking and the road sense degrades. Cogging torque, also called detent torque, is from the interaction of the. The previous cogging torque mitigation methods are feasible because of the assumption that resultant cogging torque can by synthesized from the cogging torque produced by each individual slot opening 19. Cogging torque reduction by magnet pole pairing technique 108 2 physical background a pmsm machine has several magnet poles and several slots. It is especially prominent at lower speeds, with the symptom of jerkiness. 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.
Presents an approach to determine sources of cogging torque harmonics in permanent magnet electrical machines on the basis of variations of air. A study of cogging torque reduction methods in brushless dc motor. To achieve a smooth output torque, compensation for the cogging torque is added to the control scheme. The brushless dc motors are the one in several motors gaining popularity in industrial applications. There are several methods for the reduction of cogging torque such as segmented permanent magnet 1, ux barrier employed in rotor structure 2, the continuum sensitive analysis combined with the fem for.
The results of the investigation of the cogging torque in permanent magnet synchronous machines. 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. Reduction of cogging force is one of the main concerns of tubular permanent magnet linear motor tpmlm. The pulsations of the cogging torque harmonics are then multiples of, where. The brushless dc bdc permanent magnet motor studied here exhibits a cogging torque even without any excitations.
Stepper motor holdingcogging torque ratio electrical. Cogging torque, torque ripple and radial force analysis of permanent magnet synchronous machines a dissertation presented to the graduate faculty of the university of akron in partial fulfillment of the requirements for the degree doctor of philosophy mohammed rakibul islam. Several techniques are available in the literature for cogging torque reduction in both radial and axial flux machines. The main issues with this bldc motors are cogging torque and harmonics associated with it. In a permanent magnet generator, cogging torque is produced due to interaction of the rotor. This paper analyzes various cogging torque minimization techniques as applied to a permanent magnet machine used in an electric power steering system. These torque fluctuations cause vibrations, noise and speed fluctuations. In addition, an analytical calculation of cogging force is deduced by the energy method. 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. The goal of this exercise is to familiarize the user with the methods used to calculate the cogging torque. Cogging torque reduction in a permanent magnet wind turbine.
This paper presents finite element fe analyses results that show a previously unaddressed low frequency modulation of cogging torque ripple. The cogging torque is parasitic, it will block the primary rotation of the rotor, give. Cogging torque reduction in permanent magnet machines luke dosiek, studentmember,ieee, and pragasen pillay, fellow,ieee abstractthis paper examines two methodsmagnet shifting and optimizing the magnet pole arcfor reducing cogging torque in permanent magnet machines. As a consequence of high peak torque, both cogging torque and torque ripple are increased if no measures are taken to decrease them. Cogging torque in permanent magnet motors and generators is characterized by a torque ripple. The largest cogging torque waveform amplitude is the 12 slot in a family of curves for 6, 9, 12, and 15slot lamination motors.
After the study, the dependence of the cogging torque on the ratio of the opening width of the magnet to the pole pitch was revealed. So by shifting slots in specific ways, the cogging torque produced by. Pdf in this paper, two new methods for the stator skew are introduced. Cogging torque measurement, moment of inertia determination. 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. One of the properties of the electric motor used, is the presence of cogging torque. Pdf cogging torque reduction in brushless dc motors using. Gieras, fellow, ieee abstractthis paper discusses the approach to analytical calculation of the cogging torque in permanentmagnet pm brushless motors. Most often these machines are of synchronous type with permanent magnets and large polepair number. Cogging torque reduction by magnet pole pairing technique szilard jagasics, istvan vajda obuda university, becsi ut 96b, h1034 budapest, hungary jagasics. 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. Inwheel direct drive motors are placed inside drive wheels of electric vehicles and have to deliver large torque without any mechanical gear.
Pdf minimization of cogging torque in permanent magnet. Influence of design parameters on cogging torque in permanent magnet machines 409 fig. Interior permanent magnet synchronous machines show a good range of behaviours, which make these kinds of machines good candidates for an electromechanical energy conversion. Cogging torque is an undesirable component for the operation of such a motor. Study of cogging torque in permanent magnet machines. A study of cogging torque reduction methods in brushless dc motor 147 cogging torque by designing either magnet width or magnet length decreased. How to reduce the cogging torque of the integrated propeller motor is an important means to improve its noise performance because cogging torque is one of the key factors causing torque ripple. Cogging torque is due to the interaction between the permanent magnet of the rotor and the stator slots in permanent magnet machine. Cogging torque is an inherent characteristic of pm generators and is caused by the geometry of the generator. The first pm pole centred on tooth is a stable point. Reduction of cogging torque, harmonics in pm bldc motor. Indeed, the amplitude of this quantity is almost the same as the numerical noise. Cogging torque compensation feature in drive that aims to make motor torque production more uniform and ideal. Effect of magnet segmentation on the cogging torque in surfacemounted permanentmagnet motors.
Cogging torque has been analyzed to be reduced by slot skewing. It is an undesired effect that contributes to the machines output ripple, vibration, and noise. Outrunner generator with optimized cogging torque pattern. This is a bedinicole type window motor before adding the coils. Influence of design parameters on cogging torque in. Cogging torque reduction by magnet pole pairing technique.
Its also known in stepper motors as detent or no current torque. Pdf a novel cogging torque simulation method for permanent. A method for reducing cogging torque of integrated. The cogging torque is generated by attractioninteraction of the magnetic poles to the teeth steel structure within an unenergized motor. Reduction of cogging torque and emf harmonics in modulated. A method for measuring the pulsations of a torque is described. A high performance electrical drive needs a smooth torque waveform and a high torque to inertia ratio. In permanent magnet machines, the cogging torque caused by reluctance variations in the air gap. A study of cogging torque reduction methods in brushless. Reduction of cogging torque on brushless direct current motor with. The customer is reporting that the cogging and torque ripple are now worst than before when we used a 12 slot4 pole design. Cogging torque occurs in pm motors in the air gap between rotor and stator. Paper open access methods for reducing cogging torque.