I was talking with some friends about control technology and made the observation that over the last decade the progress in the control field has been really amazing. Particularly, the processor technology that is available for controlling electric motors is operating 1000 times faster than the control platforms of a decade ago. We look at events in nanoseconds, not microseconds.
Increasing the control system’s frequency response is not signficant in itself. But it does mean that software can be applied to problems that are more subtle in the operation of a particular system. Observation of the phase relationship between the rotor and stator in an electric motor is now commonplace in 3 phase systems. Algorithms for optimizing this relationship dynamically are also commonplace to adjust the power factor or reduce energy consumption in inertial loads like fans.
But this is not where the big energy gains will come from. These improvements are smaller and more incremental.
Variable speed motors are systems that are made up of electric motors and power electronic systems. Both are subject to losses in the form of heat. In the motor bulk magnetizing of the stator, phase loss due to load, and copper losses due to the construction methods used are common.
Better metallurgy is needed to reduce losses associated with magnetizing the stator core. The steel industry has attempted to address this issue, but the high cost of exotic alloy laminations prevents the advanced materials from becoming widely used.
Copper loss is improved in the segmented stator, but this manufacturing technique is most often found in more expensive servo motors, even though analysis suggests the cost is lower. This may have to do with scale effect, since the servo motor world runs at much lower volumes than the AC motor world.
The other major dependency in the speed control is the power semiconductor. The costs for power devices are falling and performance is improving.
So where are the big efficiency gains going to come from?
The control system strategy. If the application is not well regulated you might be able to get a big increase in efficiency by measuring things more carefully. In a cooling tower changing from a +/- 10 degree thermostat to a +/- 1 degree thermostat allowed me to implement a control system that reduced the energy consumption sufficiently to pay for the equipment in less than two years.
No new technology motor, nothing special about the variable frequency drive. Just what was available at the time. The big difference was the strategy. Measuring what was important and organizing everything in the control system to achieve our objective.
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