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Saturday, 12 February 2011 15:30

The evolution of the variable speed drive -- past and future

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The use of power semiconductors to vary frequency to control the shaft speed of an electric motor is now five decades old. Since electric motors and support systems are almost everywhere where people need to accomplish work, and since there are clear benefits in the efficient and smart application of computerized speed control, there has been, and remains, ample economic incentive in this market to innovate. This is an high-level overview of drives evolution, broken into six phases, five looking backwards, and one looking forward.

Today, the market is at a critical inflection point. While most makers and users of machines have embraced the idea that drives, in some form, are a must for nearly every motor, as energy and labor costs rise and new application challenges emerge, the new mega trend -- smart everything -- comes clear. Here's why:

Drive Systems
Drives have their roots as a better, more capable and flexible alternative to a switch or a soft-start (a less disruptive switch) for a motor. Early adopters in the 1980s needed motor speed control for process reasons, and systems - sensors, switches, computers and infrastructure - were adapted and rigged to make way for the drive to do this speed control job. But systems were highly complicated and expensive, so only a few could justify the investment. The market was mostly about large motors and complex processes.

Integrated Control
Seeing a larger potential market, systems designers quickly responded, adapting new architectures and sensing and control schemes into common, integrated control approaches. Redundancies, like extra switches, valves and sensors were eliminated. Control components were made more compatible. By lowering overall costs by reducing the number of connections for power or data and the size and complexity of the system, designers, integrators and OEMs were able to bring speed control to a larger audience, albeit one with a sharp focus on process.


Software Sensing
The game changed as computing costs plummeted while processing power and bandwidth took off. Sensors and wire were replaced with software and circuit boards inside of the drive. Vector control and other integrated torque control systems eliminated feedback loops and components, buss, electric infrastructure, boxes, and made drive systems easier and more accessible to more people and more applications. Architects began to select drives for energy ROI, and within a period of about a decade, nearly every new commercial HVAC fan came into view as a candidate for drive control.

Embedded Control
The first decade of the 21st century has machine OEMs of all specialties looking at direct, on-board computerization of the machine, for various reasons. At the basic end of an innovation spectrum, embedded drives are the natural next step in the quest for component reduction, and the first to do it well in their market always has a clear cost advantage. In the middle, we can find sophisticated, OEMs that are finding new ways to connect their machine products with their service offer through the drive. At the farthest end of the spectrum, we find core drive components -- power semi-conductors, processors and I/O, adapted to energize new motor architectures, like the permanent magnet motor. Here, drives essentially disappear into the machine, while still doing the critical work of speed variation.

Smart Grids and Machines
Back to our "critical inflection point." Change is coming faster then ever. The current trend toward miniaturization leading to invisibility is accelerating. The new factor is the smart grid. We're not at a place where the system is collapsed, completely. A smart and flexible machine will tap into a cloud of power and information, interpret signals in a coordinated dance with its peers, delivering precise motion into a cloud of work. The digital motor is one that produces the most work at the highest quality and flexibility, with the least attention, and by using the lowest possible amount of energy and resources for the effort. Here, it's important to understand the the smart grid is poorly named. It's not the grid that is smart, it's that all machines on it are smart, dare we say, self and network and process aware, in ways that were unimaginable 50 years ago, when this all began.

In summary, hindsight shows that drives have captured a larger role in linking electricity to work and information networks, while, ironically perhaps, they are getting smaller and closer, until they virtually disappear into the machine. When the do, then power delivery, information delivery and environment will change in ways that are unimaginable today.

 

Read 2577 times Last modified on Monday, 14 February 2011 09:16

3 comments

  • Comment Link Publisher Monday, 14 February 2011 07:23 posted by Publisher

    You need only look at a computer power supply to find a clear example of miniaturization in power conversion. The same is happening in drives, with active topologies and increased frequency. But, this is not a schematic - it's a representation of components and their connections.

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  • Comment Link PowerNut Monday, 14 February 2011 07:04 posted by PowerNut

    Where are transformers and filters in your scematic

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  • Comment Link WallaceNeyhart Saturday, 12 February 2011 17:15 posted by WallaceNeyhart

    Excellent insights. But why are these still so many panels -- bypass and control boxes, being built?

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