For many years, magnetic reluctance motors were typically overlooked in favour of induction or permanent magnet designs. Yet now, nearly two centuries since the invention of the first reluctance motor, the synchronous reluctance motor (SynRM) is unlocking ultra-premium IE5 efficiency levels. ABB UK managing director, David Hughes, explains how we arrived at this point, and what it means for motor-driven applications both now and in the future…

Reluctance motors have come a long way. The first switched reluctance motor was invented all the way back in 1838 and was initially designed to propel locomotives. Unlike common brushed DC motor types, in a switched reluctance motor power is delivered to windings in the stator rather than the rotor. The idea, however, was unfortunately doomed to failure – the motor was highly complex for its time and, rather than utilising the power electronics that we have today, it relied on mechanical switches to energise the windings, which could not operate fast enough to generate anything more than very slow speeds.

Then, in the 1920s, the synchronous reluctance motor was invented. These use a specially designed cageless rotor, eliminating rotor losses. A magnetic field is generated inside the motor, which is guided through low reluctance paths. The field is rotated, which in turn pulls the rotor around to generate torque. The switched reluctance motor initially suffered from a lack of effective speed control. 

It was not until the 1970s, with the emergence of fast-switching electronics within variable speed drives (VSDs), that the synchronous reluctance motor was able to finally come into its own and reach performances comparable to that of conventional induction and permanent magnet motors.

Getting up to speed

Even then, the synchronous reluctance motor was still, for many years, widely considered uneconomical due to its complexity and cost. Furthermore, VSD technology had not yet evolved sufficiently to handle the complex needs of the motor, as the drive needed to be capable of switching the frequency of the supply current thousands of times per second to control the magnetic field effectively. It was only in the early 21st century that both the VSD and the synchronous reluctance motor had both developed to a point where they were finally able to effectively combine in successful operation together and deliver the required performance at an affordable cost.

The emergence of the modern synchronous reluctance motor came in 2011, when ABB launched its IE4 SynRM product. Since then, the technology hasn’t looked back, and today they are among the most efficient motors available on the market at a price comparable to equivalent induction or permanent magnet motors, often with a better return on investment and lower cost of ownership.

Today, the ABB SynRM combines the performance of permanent magnet motors with the simplicity and user-friendliness of induction motors. The rotor contains no windings which means there are virtually no power losses. It also contains no rare earth materials or magnets, which makes maintenance similar to an induction motor, and is a more sustainable option compared to other motor types.

The next chapter in the evolution of electric motors

In 2019 ABB launched its IE5 SynRM ultra-premium motor, representing a major leap forward in the efficiency capabilities  of electric motors. The IE5 motor offers up to 40% lower energy losses, as well as significantly lower energy consumption and CO2 emissions compared to an equivalent IE3 induction motor.

By optimising the motor and drive package, ABB can maximise efficiency levels, offer accurate motor control and give excellent reliability over the product’s lifecycle. Furthermore, the motor drive package is suitable for a wide range of applications, based on both constant and variable torque.

What’s next for the SynRM?

As recently as a decade ago the limit for energy efficiency was IE4, and the concept of IE5 was merely theoretical. With the ABB SynRM now capable of IE5, further energy saving opportunities are now available. With motors accounting for 45% of all electricity consumed by buildings and industrial applications, if each of these was upgraded to an IE5 SynRM, the energy and carbon savings would be vast, and have major implications for the UK government’s target of achieving Net Zero carbon emissions by 2050, as well as other targets for individual industries and sectors.