Rebirth of an oldest Electric Motor: Switched Reluctance Motor

Updated: Jul 18

Switched Reluctance Motor – SRM is one of the oldest electric motor type and still remain competitive.


Switched-reluctance (SR) motors were developed in the 1800s, but Their optimum operation depends on relatively sophisticated switching control, something not economical during that time.

First recognizable reluctance machines were built over 180 years ago, most famously by Davidson as a traction drive for an electric locomotive in 1838.


It was just 7 years after law of electromagnetic induction by Michael Faraday in 1831. Inspired by Faraday's experiments and results, Robert Davidson produces various versions of Electric Motor and arranged exhibitions and demonstrations at different places which was first kind of magical exhibition of old age where people paid for tickets. Famous Scottish scientist James Clerk Maxwell also attained one of the exhibition at the age of 10 with his father.


The first reference to the term switched-reluctance was made by Nasar in a paper in the IEE Proceedings in 1969. The term became popular from the 1980s on-wards, through the efforts of the first commercial exploiters of the technology, Switched Reluctance Drives Ltd. Now known as Nidec SR drive: http://www.srdrives.com. Emotron AB (Helsingborg, Sweden)-a manufacturer of SR products since 1983. For a time, SRM powered Maytag Neptune washing machines.


The Tesla Model-3(AWD P100D), 2019. It uses an SR motor on the front.


Why again SRM?

Availability and reliability of sophisticated power electronics converter and latest control techniques are main reasons for the rebirth of SRM.

SRM provides many benefits because of their

  • Simple mechanical structure

  • Magnetless Brusless Motor


What Simple Mechanical Structure adds to Motor?

  • Reduce Cost of Manufacturing

  • Reduce Manufacturing Process Time

  • Lower inertia

  • Less weight

  • High Efficiency

  • Higher Reliability

What Magnetless Operation adds to Motor?

  • Reduce Material Cost

  • Reduces manufacturing complexity (unike magnet mounting process)

  • Improves temperature profile of motor (Performance of magnet is deteriorate with increase in temperature)

  • This is why SRM is capable of replacing BLDC in EV applications.

SRM Vs SRM Drive?

  • SRM always required position sensing arrangement, power electronics converter & controller even for fixed speed applications.

  • SRM can not run direct on supply unlike DC motor and Induction Motor.

  • Means it’s not SRM, but it’s always SRM Drive in application.

  • It is not good idea to compare SRM with Induction Motor, but one need to compare SRM drive with Induction Motor Drive (VFD).

  • SRM is not best alternative to Induction Motor in fixed speed application like fan, blower and pump.

  • But in variable speed application, SRM drive is more preferred.

Beside all major attractions, major issues of SRM are torque ripple and acoustic noise.


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