What Is a Switched Reluctance Motor?

A switched reluctance motor works through manipulation of electromagnetic forces. Reluctance motors, in general, depend on a process known as magnetic reluctance to produce torque. Motors designed this way often have significant advantages over other designs. Several disadvantages, however, limit the applications for which a switched reluctance motor might be best. Controlling this process can be challenging, but digital technologies assist with many of them.

These motors typically consist of a rotor, which is typically composed of iron, and electromagnets. These electromagnets are not on consistently. Instead, they switch on and off to establish poles in the ferromagnetic rotor. When multiple electromagnets around the rotor are switched in the proper sequence, torque is established and further propelled. When the starting torque is reduced by a soft starter, this method of producing torque is often considered highly advantageous.

One defining advantage of a switched reluctance motor is the relatively high power produced within generally compact designs. Compared to many others, reluctance motors are often considered much simpler because there are few moving parts aside from the rotor. Another advantage to these motors is that the sequence can often be reversed, possibly creating equal torque in both directions.

Despite these advantages, a switched reluctance motor is often noisy and too powerful for low-torque applications. Misalignment of the rotor or the switching sequence can lead to inefficiency, especially for more powerful motors. Increasing the power of these motors also means increasing the complexity of the switching sequence, which limits the ability to control them with mechanical or direct electrical control.

These design challenges often limit the applications for which a switched reluctance motor can be most useful. Early reluctance motors were often used in locomotives and other high-power applications. In the early 21st century, a switched reluctance motor might be used as part of an oil or fuel pump. It also might be used as part of a vacuum cleaner or large fan motor. Optimization is often a costly challenge, so a switched reluctance motor is often considered feasible only for high-volume or high-power applications.

Digital technologies can alleviate many of the challenges associated with optimizing these motors. Rather than depending on mechanical processes to ensure proper switching, computerized controls provide a buffer between direct power and electromagnetic control. Computers also can monitor the alignment of the rotor and magnets to optimize performance during operation. Overall efficiency also can be improved through a digital switched reluctance motor, which may increase the potential applications.