• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer
  • Advertise
  • Subscribe

Motion Control Tips

Automation • Motion Control • Power Transmission

  • News
    • Industry News
    • Editor Blogs
  • Controls
    • HMIs
    • PC-Based Controllers
    • PLCs + PACs
    • Stand-Alone Controllers
    • Software
  • Drives
    • Servo Drives
    • Stepper Drives
  • Encoders
    • Absolute Encoders
    • Incremental Encoders
    • Rotary Encoders
  • Mechanical
    • Bearings
    • Brakes + Clutches
    • Belt + chain
    • Couplings
    • Gears + Gearing
    • Lubrication
    • Shock + Vibration Mitigation
    • Springs + Rings + Seals
  • Linear
    • Actuators
    • Linear Motors
    • Linear Encoders
  • Motors
    • AC Motors
    • DC Motors
    • Brushless Motors
    • Gearmotors
    • Piezo Motors
    • Servo Motors
    • Stepper Motors
  • Systems
    • Conveyors + linear transport systems
    • Gantries + Stages
    • Rotary Tables
    • Grippers + End Effectors
    • Robotics
  • Networks
    • Connections + Sliprings
    • Fieldbuses
    • I/O
    • Sensors + Vision
  • Resources
    • FAQs
      • Motion Casebook
      • Motion Selection Guides
    • Suppliers
    • Video
You are here: Home / FAQs + basics / How do switched reluctance motors differ from stepper motors?

How do switched reluctance motors differ from stepper motors?

September 1, 2017 By Danielle Collins Leave a Comment

Switched reluctance motors operate by switching currents in the stator windings in response to changes in the magnetic circuit formed by the rotor and stator. The stator of a switched reluctance motor contains windings, similar to a brushless DC motor, but the rotor is simply made of steel that is shaped into salient poles, with no windings or magnets. To avoid a situation where all the poles of the rotor and the stator line up simultaneously (and no torque is produced), switched reluctance motors have fewer poles on the rotor than on the stator.

switched reluctance motors
A typical 8/6, four-phase switched reluctance motor. Notice that when rotor poles 3 and 6 are aligned with stator poles B and B’, all other rotor poles are out of alignment with the stator poles.
Image credit: scienceprog.com

When the rotor and stator poles are out of alignment, the magnetic circuit between them has a high reluctance. As the stator pole pairs are energized, the rotor turns to align with the energized stator poles, which minimizes the reluctance of the magnetic circuit. This tendency of the rotor to move to a point of minimum reluctance produces what is referred to as reluctance torque.

Energizing of the stator poles must be precisely timed to ensure that it occurs as the rotor pole is approaching alignment with the energized stator pole. Unlike stepper motors, which can, and for most purposes do, operate in open-loop mode, switched reluctance motors require position feedback from an encoder or Hall effect sensors, to control commutation of the stator currents based on the precise rotor position.


This article provides an in-depth look at drive options for switched reluctance motors, and this article looks at how drive technologies could make switched reluctance motors more common in the future.


switched reluctance motors
Switched reluctance motor with 6 stator poles and 4 rotor poles. Notice that the stator poles protrude toward the rotor, and the rotor poles protrude toward the stator. This is known as a doubly salient pole design.
Image credit: chargedevs.com

Switched reluctance motors have fewer poles and a larger stepping angle than stepper motors. While stepper motors are typically chosen for positioning applications, where step integrity and high resolution are important, switched reluctance motors are used in applications where power density is a primary concern.

Because switched reluctance motors have rotors with no magnets or windings, they have lower inertia and can therefore achieve higher accelerations and speeds than motors with permanent magnet rotors, such as stepper motors. The lack of magnets on the rotor provides other benefits as well – including the ability to withstand higher temperatures (less cooling required) and simple, lower-cost construction than permanent magnet motors.

Another difference between switched reluctance motors and stepper motors lies in the stator construction. In a switched reluctance motor, there is no overlap of coils between successive phases – in other words, the phases are independent of one another. This means that if one or more phases fail, the motor will still be operable, although with reduced torque output.

The fact that both the stator and rotor have salient poles (referred to as a doubly salient design) means switched reluctance motors produce more audible noise than stepper motors. The primary source of noise is distortion of the stator due to radial forces that occur when the stator pole pairs are energized. The energized pole pairs are attracted to one another, causing radial forces strong enough to distort the stator.


Salient poles are simply magnetic poles that essentially “stick out” from the diameter of the rotor (or stator), towards the stator (or rotor).


Torque ripple is also a common issue with switched reluctance motors. While both switched reluctant and stepper motors exhibit torque ripple, this effect is minimized in stepper motors with a higher number of phases (5 phases versus 2, for example). In a switched reluctance motor, torque ripple can be reduced by using a higher number of poles in both the rotor and the stator, but this decreases the motor’s average torque output, requiring a tradeoff between torque production and acceptable torque ripple.

You Might Also Like

Filed Under: FAQs + basics, Featured, Stepper Drives, Stepper Motors

Reader Interactions

Leave a Reply

You must be logged in to post a comment.

Primary Sidebar

LEARNING CENTER

Design World Learning Center

Motion Control Handbook

“mct
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for Design Engineering Professionals.

RSS Featured White Papers

  • Robotic Automation is Indispensable for the Logistics Industry’s Continued Growth and Success
  • Reliable Linear Motion For Packaging Machines
  • Polymers Outperform Metals In Precision Gearing

Footer

Motion Control Tips

DESIGN WORLD NETWORK

Design World Online
The Robot Report
Coupling Tips
Linear Motion Tips
Bearing Tips
Fastener Engineering.
Wire and Cable Tips

MOTION CONTROL TIPS

Subscribe to our newsletter
Advertise with us
Contact us
About us

Copyright © 2025 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy | RSS