The thing about the electronics industry is the incredibly consistent economies of scale. The more volume that is produced the lower the price gets. The economy of scale also has the ability to change the economics of complementary technology. So as the electronic components for motor control continue to fall in price, the impact not only measurable in the products that we are familiar with, it also makes possible innovations that have been impractical because of cost.
Among these, the venerable Switched Reluctance motor appears to be having a resurgeance. SR motors have a number of unique features that were expected to transform many electric motor applications. Among which, the motors can be programmed on the fly to produce dramatically varied speed/torque profiles. One of the large targets was transmissionless washing machines. The motor and controller could be programmed to run a low speed high torque profile for agitation and then programmed to a higher speed lower torque output for spin cycle.
Another feature of the SR motor is in the manufacture of the rotor. The rotor does not use magnets or windings. A stamped laminate structure with salient poles is all that is needed. Less complex, read “lower cost”, than an alternating current rotor.
So let’s review, a motor with programmable power output, and potentially lower cost than traditional AC or any permanent magnet variant. So where’s the hitch?
At the time, the controller requirement were extremely high performance. So the available processor technology was very expensive. The power electronics needed were typically three phase, although many variations of phase and rotor pole count are possible. But regardless of the exact implementation, the power electronic cost of 20 years ago which made AC inverters very expensive, also made the SR motor control very expensive.
So fast forward 20 years, where processor power is cheap and power electronics continue to follow the economies of scale that have brought us, for example, the $99. inverter. Algorithms for control are widely available and custom motor control code can be written by a larger population of engineers. So a couple of possibilities are now created;
SR motors unique performance and potential low cost of manufacture are now attractive for many applications. Development teams in many industries are dusting off the old textbooks and checking out this fascinating technology.
The nature of software programmable motor applications is changing what kind of performance and cost we can embed in a wide range of products and processes. This trend will continue to expand what is possible.
Like Moore’s law for semiconductors, the electronics industry will drive innovation in some unexpected ways.