Electric motors are the workhorse of industry. Globally 20% of all energy generated is in the form of electricity. Electric motors consume 40% of all electricity. Electric motors are a big part of how things work, industrially and on the consumer level. Major and small appliance account for huge numbers of motors manufactured each year.
What is most surprising is that in slightly over 100 years of the electric motor being a part of our culture, progress seems very slow. It has taken decades of manufacturing clothes washer, for example, to migrate away from expensive 2 speed mechanical transmissions to the more modern belt and pulley solution. This is due in part to the low cost barrier created by the price point of the product. The other issue is the available motor technology.
Now it seems commonplace to talk about permanent magnet AC motors, in spite of the fact that they are a relatively recent development. The underlying magnetics were demonstrated years ago, but the fact of this motor design as a production product has been very recent. In the case of the washing machine, it became possible to manufactured almost the identical AC motor that has been in use for many years, but increase the available torque from that motor by adding permanent magnets to the rotor. The increase in the available torque and the ability to control the motor with the state of the art speed control technology made it possible to simplify the washing machine by creating an agitation cycle electronically in the motor controller.
Motor technology rarely changes without control technology. 40 year ago Jim Hendershot demonstrated the switched reluctance motor running with an early PC chip as a controller. The switched reluctance motor is another 3 phase motor variant with a ‘cold’ rotor, a rotor made of magnetic steel. The poles of the motor result simply from the shape of the steel, no rotor bars necessary, no casting process. Simple and durable. The combined system made possible a motor whose speed torque curve that was programmable. You could have high speed and low torque, or low speed and high torque with the change of a status bit.
当时控制器昂贵得多than the motor making the SR (switched reluctance) system impractical. Fast forward to the present, and switched reluctance control is possible on the same embedded processors used for every other type of motor control. The merits of this solution make no make it practical for some high volume applications.
Let’s see what the future brings.
Filed Under:Mechatronic Tips
