What is Variable Reluctance Stepper Motor & Its Working

When it comes to the enhancement of the industrial and engineering domain, motors hold crucial responsibility. The extensive utilization of motors has enhanced both power and controlling applications. With this huge prominence of regulating motors, the usage also getting increased day for every annual year. And stepper motor is a kind of control motor that operates on speed and position regulation having no use of a feedback loop. This phenomenon is termed as Open-Loop Control Motor. So, this article gives a clear description of one of the types of stepper motor and it is “Variable Reluctance Stepper Motor”. The below sections explain on this device working, the principle uses benefits and drawbacks.


What is Variable Reluctance Stepper Motor?

This is the most general kind of stepper motors. It holds the easiest design when compared with the other types of stepper motors. As the rotor section is non-magnetized, there exist no attractional forces in between the stator and rotor. Because of this, the variable reluctance stepper motor will not generate any detent torque.

The dynamic torque generation is too minimal but possesses a torque drop-off when the motor runs at high-speed rates. So, this variable reluctance motor is mostly applicable to the speed rates of medium to high. These motors also have a high range of noises, so suitable for scenarios where noise is not considered.

Principle

The fundamental variable reluctance stepper motor working principle is that it is dependent on multiple reluctance locations of the rotor device. When the stator phases receive the voltage signal and get excites, there will be the creation of a magnetic field whose axis lines are across the poles.

And now, when the rotor attempts to revolve in such a path that it gains low reluctance. This revolution corresponds that a position magnetic field axis created by the stator is the same as the axis that passes across the rotor poles (any two of the poles).

Variable Reluctance Stepper Motor Construction

Mainly, this device consists of a wounded stator and multi-teeth rotor sections. The stator windings are covered with an array of silicon steel coverings. In general, this is covered for three phases that are scattered in between the pairs of poles. So, the number of poles in the stator section is the same as the even multiple phases for those windings that exist are covered in the stator. In the below depicture picture, the stator has 12 similarly separated projection pole where every pole is covered

Variable Reluctance Stepper Motor Construction
Variable Reluctance Stepper Motor Construction

with an excitation coil. The three phases are then activated using a DC source through the support of solid-state switches. Whereas the rotor section has no windings and it is considered as a prominent pole type that is constructed of slotted steel coverings. Here, the stator teeth and the rotor’s projected teeth are of similar width, while the number of a pole in both these sections is different that offers the capability to start by itself and allows for motor rotation in two directions.

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Here, the relation between the stator and rotor poles corresponding to the three-phase variable reluctance stepper motor is given as

Nr = Ns ± (Ns/q)

Where ‘Ns’ corresponds to the number of stator poles


‘Nr’ corresponds to rotor poles

Working Scenario

The variable reluctance stepper motor working can be easily explained by considering three cases. Let us know the working of this device in detail. Consider the below figure.

The working is explained as the three windings X, Y, and Z are connected in a series way and they are energized one after another using the three switches S1, S2, and S3.

Scenario 1

When the power supply is provided across the edges XX1, by closing the S1 switch. As there are magnetic poles in between the XX1 windings, because of attractional force between the magnetic poles, the rotor attempts to accomplish a low value of reluctance position. So, the 1 and 3 rotor axis attempts to be in alignment with the XX1 poles axis.

Working Scenario 1
Working Scenario 1

Scenario 2

When the power supply is provided across the edges YY1, then there will be a modification in the stator poles magnetic axis. Now, the rotor attempts to accomplish a low reluctance direction in so creating the rotor movement. Here, 2 and 4 axis of the rotor poles gets so close to the YY1 windings. This creates rotor rotation and 2 and 4 rotor axis attempts to be in alignment with the YY1 poles axis. Hence, the rotor movement will move by 30 degrees.

Variable Reluctance Stepper Motor Scenario 2
Variable Reluctance Stepper Motor Scenario 2

Scenario 3

In the same way, when the ZZ1 windings are energized by S3 making XX1 and YY as dis-connected. The magnetic poles of the rotor axis attempt to be alignment with the axis of the stator. Hence, the rotor movement will move by 30 degrees, so there will be a total rotation of 60 degrees from XX1 to ZZ1.

Working Scenario 3
Working Scenario 3

With the successful execution of three phases in a corresponding manner, the motor finishes one revolution in 12 steps. And the rotor direction is based on the supply series provided to the stator phase. Then the torque generation that operates on the device has a direct proportion to the double of the phase current which is T α i2.

Advantages and Disadvantages

The advantages of a variable reluctance stepper motor are:

  • Enhanced acceleration rates
  • Easily operated and cost-effective
  • Quick dynamic response
  • The proportion of torque to inertia is more

The disadvantages of the variable reluctance stepper motor are:

  • Capacity is minimal when there are huge inertial loads
  • There will be a limitation on output power

This is all about the detailed concept of this device. This section has given an explanation of variable reluctance stepper motor working, uses, design, and the principle of operation. In addition, also know what the applications of the variable reluctance stepper motor and its usage in multiple domains are.

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