Reluctance motors

MACCON develops and supplies both switched reluctance (SR) as well as synchronous reluctance (SyR) motors.

Reluktance motors employ the magentic reluctance principle - the natural attraction of an electro-magnet to iron. SR motors have salinet stator and rotor poles. SyRmotors use a classical stator (AC/BLDC); the rotor is round but its inner structure contains paths of different reluctance, symmetrically distributed around the rotor.

The SR motor is working with the switched reluctance principle - an electromagnetical pole in the stator is attracting the iron pole of the rotor. The SR motor has got a different number of stator and rotor poles. Both the stator and the rotor are made of laminated iron. Each of the stator poles carries a coil.  Opponent poles are electrically connected together to form the south and north pair of one phase. The phase is energized by two electrical switches in one current direction. A continuous torque is generated by the correct switching of the phase currents according to the rotor position.

The most important characteristics of this technology can be summarized as follows:

  • Efficiency: The efficiency of SR motors is comparable to permanent magnet motors in all 4 quadrants. The values reach more than 85% in a wide range of operation. Compared to conventional AC induction motors the SR motors often have an advantage (especially in the middle speed range).
  • Controllability: The SR motor can be operated in all 4 quadrants. Due to the unipolar design the driving electronics is quite simple. To achieve less torque ripple some more sophisticated design is necessary.
  • Robustness and Reliability: The SR motor is as robust as conventional AC induction motors, since the rotor is pure iron. In case of a winding fault these motors are better protected than other motor technologies.
  • Audible Noise: The audible noise during operation is as good as other technologies; new lamination designs and driving algorithms promise further improvement.
  • Speed Range: The SR motor  can be operated over a wide speed range. In this characteristic it is similar to a vector controlled AC induction motor with constant torque at low speed and constant power at high speed.
  • Peak Torque: The SR motor offers a by far higher eak torque than an induction motor of the same size; but it cannot reach the value of a similar sized permanent magnet motor.
  • Power to Weight Ratio: Also here the SR motor has advantages over the AC induction motor. For a given power the SR motor is about 40% smaller and lower weight than the AC induction motor. There is no physical limitation for the power of SR motors; SR motors have been developed for a power range of 50W to 5MW!

MACCON is the leading supplier for SR technology in Germany. In case you have an application for this technology, please contact us.

We perform research and development to explore further possibilities for teh design and usage of SR motors in various applications. An example is the transversal-flux, reluctance machine.

Switched reluctance rotor (SRD Ltd.)
6/4 3-phase SR-motor (wikimedia.org)
Synchronous reluctance rotor