A reluctance motor uses magnetic reluctance to generate torque, producing temporary magnetic poles on its rotor. It has high power density but generates torque ripple and noise at low speed. Advances in computer design tools have helped overcome design limitations and decreasing microprocessor costs provide adequate control. The stator and rotor are made of malleable magnetic material with protrusions that produce magnetic poles. The maximum and minimum magnetic reluctance positions generate torque. Commutation controls the motor’s behavior. A synchronous reluctance motor has equal stator and rotor poles, with low energy losses.
A reluctance motor is an electric motor that produces temporary magnetic poles on its rotor. It is so called because it uses magnetic reluctance to generate torque. The main advantage of this type of engine is that it typically produces a high power density for a given cost. The main disadvantage of this motor is that it tends to generate torque ripple at low speed, which produces noise.
The use of reluctance motors has traditionally been limited by the complexity of their design and method of control. Advances in computer design tools have helped overcome the design limitations of these engines. The decreasing cost of integrated microprocessors has provided these motors with adequate control at an acceptable cost. These microprocessors use parameters such as rotor position, current and voltage to control the motor.
The stator and rotor of a reluctance motor are composed of a highly malleable magnetic material, such as silicon steel. The stator and rotor contain numerous protrusions which produce magnetic poles. The rotor typically contains fewer poles than the stator. This prevents all poles from lining up at the same time, which prevents the motor from generating torque. The disparity between the number of rotor poles and the number of stator poles also reduces the torque ripple.
The maximum amount of magnetic reluctance occurs when one rotor pole in a reluctance motor is exactly between two stator poles. This position is also known as the fully misaligned position of the rotor pole. The least amount of magnetic reluctance occurs when at least two rotor poles align with at least two stator poles. This position is known as the rotor pole aligned position.
The stator pole produces a magnetic field which pulls the nearest rotor pole from a completely misaligned position to an aligned position, thus generating a torque. The stator’s magnetic field continues to rotate, pulling the rotor along with it. Most modern reluctance motors use commutation to control aspects of the motor’s behaviors, such as starting the motor, running it smoothly, and specifying its speed. Some variants of this type of motor are capable of using three-phase alternating current (AC) power.
A synchronous reluctance motor has the same number of stator poles and rotor poles. The holes in the rotor produce areas of low flux to achieve this equality between the stator and the rotor. This type of reluctance motor typically contains four or six poles. The energy losses of the rotor are much lower than those of induction motors because the rotor does not contain any electrically conducting parts.
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