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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. There are multiple rotor positions within a revolution where the cogging torque is high.
What is cogging in motors?
The phenomenon of Magnetic Locking between the stator and the rotor teeth is called Cogging or Teeth Locking. Even after applying full voltage to the stator winding, the rotor of a 3 phase induction motor fails to start. This condition is known as Cogging or Magnetic locking.
Is cogging torque bad?
COGGING torque is defined as the attraction/interaction of the magnetic poles (typically on the rotor) to the steel teeth (typically on the stator lamination) within an un-energized motor. Cogging is a “bad thing”; if the machine will not rotate, it is of no use for a process.
What is cogging torque brushless motors?
The cogging torque is undesirable effect in the brushless dc (BLDC) motor, causing vibration and audible noises. It arises from the rotor permanent magnet interacting with the steel teeth on the stator. Therefore, this paper studies the various reduction methods of cogging torque when designing a BLDC motor.
How is cogging torque calculated?
There are several possible ways of measuring the cogging torque, for example, by using (a) conventional torque transducer; (b) strain gauge bridge based on the reaction torque on the stator; (c) torque observer based on the voltage and current measurements; (d) special torque transducer for cogging torque measurement.
What is cogging crawling?
because of Cogging motors do not accelerate at all, and crawling induction motors stop accelerating at part speed. Acceleration can also be limited by the torque output of the motor relative to the load torque at that speed. Crawling and Cogging is explain for Induction Motor below.
How do you reduce cogging torque?
The most effective way to reduce cogging torque is skewing of stator slots or rotor poles. It means skewing of one side of stator (rotor) core by few degrees in according to the other side of core (Fig. 7). The skewing allows to eliminate the cogging torque or to reduce it to minimum.
Why is torque ripple bad?
Torque ripples have bad effects on the synchronous motors if they cause speed oscillations which contradict with the advantage of the synchronous motors being have constant speed applications. Induction motors may suffer from torsional oscillations due to these torque ripples.
How can we reduce motor cogging?
Reducing the cogging torque Skewing stator stack or magnets. Using fractional slots per pole. Optimizing the magnet pole arc or width.
What causes torque ripple?
Dr. Nir Vaks: Torque ripple is created by harmonics in the electromagnetic torque, which exist in all electric machines regardless of type or design. The harmonics are created by non-idealities in the electromagnetic fields produced by the rotor and stator interaction.
What is detent torque?
Detent torque is the amount of torque (the measured ability of a rotating element, as of a gear or shaft, to overcome turning resistance), that must be applied to overcome the static equilibrium of the motor when it is in an state of rest and unpowered.
What is crawling in 3 phase induction?
Sometimes, squirrel cage induction motors exhibits a tendency to run at very slow speeds (as low as one-seventh of their synchronous speed). This phenomenon is called as crawling of an induction motor. This action is due to the fact that, flux wave produced by a stator winding is not purely sine wave.
What is cogging torque in Pmsm?
Cogging torque is the interaction between the flux of permanent magnets (PMs) and stator teeth. Another method to reduce cogging torque is performed by controlling energy in the PMSM [15]. PMSM with skewed rotor is discussed for cogging torque reduction [16].
How is motor torque measured?
To calculate load torque, multiply the force (F) by the distance away from the rotational axis, which is the radius of the pulley (r). If the mass of the load (blue box) is 20 Newtons, and the radius of the pulley is 5 cm away, then the required torque for the application is 20 N x 0.05 m = 1 Nm.
Why does crawling occur?
Reasons for Crawling in Induction Motor It can be caused due to the presence of space harmonics within the air gap flux. Air gap harmonics can be occurred because of the uneven sharing of the Stator winding. The difference in air gap reluctance can be occurred due to the slots in Stator & Rotor.
How can you avoid crawling of an induction motor?
The primary method of avoiding or minimizing these problems is to select an optimum number of stator and rotor slots and an optimum winding distribution scheme. In addition, it is helpful to select a skew angle for the rotor slots. The shapes of the slots can also be optimized to reduce flux wave distortion.
What happens if 5th harmonics is given to induction motor?
It will rotates in normal operation. Either short circuit or open circuit occurs. The sinusoidal components having frequency five times of fundamental are known as fifth harmonics. Hence induction motor will rotates in reverse direction because of reverse phase sequence of fifth harmonics.
Why is my RC cogging?
One common cause of cogging is that the startup current settings are not set appropriately. This is especially true in applications where startup occurs under load. Increasing the power going into the motor at startup can give the motor the ‘extra kick’ that it needs to avoid cogging.
What is torque ripple in SRM?
Torque ripple minimization of SRM drive High torque ripple is due to variation of machine co-energy, which in turn varies with the stator flux linkage, excitation current and rotor position. Thus by controlling the current profile and suitable selection of turn on and turn off angle will reduce the torque ripple.
What are the effects of torque?
Just as force is what causes an object to accelerate in linear kinematics, torque is what causes an object to acquire angular acceleration. Torque is a vector quantity. The direction of the torque vector depends on the direction of the force on the axis.
Which of the following affects torque ripple?
The frequency of the torque ripple is proportional to the motor’s shaft speed. At high motor speeds, the inertia of the motor and the load can smooth out the effects of torque ripple. And at low motor speeds, high-frequency torque ripple can be filtered out using feedback and parameters in the motor controller.
