DSPs, MCUs or Mixed Signal FPGAs in motor control? Making the choice.

Mike Thompson

December 09, 2008

Mike ThompsonDecember 09, 2008

Electric motors convert electrical energy into mechanical motion. These motors are broadly categorized into two main categories: DC (Direct Current) and AC (Alternating Current). In turn, each of these categories comprises numerous sub-types, each offering unique capabilities and each targeted toward a specific range of applications.

Today, electric motors are ubiquitous, appearing in a seemingly-infinite variety of applications, including residential (refrigerators, fans, washers, pumps...), commercial (heating, cooling, ventilation...), and industrial (actuators, robotics systems...).

Consider the "How It's Made" program on the Science television channel, for example. A typical installment shows a product being processed by multiple actuators, manipulators, and robotic systems. As the product wends its way through the factory, it may be "touched" by hundreds of motors.

Few people, however, realize just how many motors there actually are and their impact on the environment. In fact, over 20 million motors are produced every day around the world, which equates to more than 7 billion new motors each year.

Furthermore, experts estimate that motors consume over 50% of the total energy production in the United States. In 2005, for example, the US consumed over 4,000 billion KWh (kilowatt hours) of electrical power, a staggering 2,000 billion KWh of which was consumed by electric motors.

The power output of electric motors is measured in horsepower (HP), where 1 HP equates to approximately 750 watts. Electric motors may be broadly categorized as small (less than HP), medium (1 to 99 HP), and large (100 HP and up). Some electric motors can be extremely large; NASA and Boeing use 60,000 HP electric motors in their wind tunnels, for example.

The larger motors tend to be the most efficient, because they are constructed from the ground up with efficiency in mind. The theoretical maximum efficiency for a motor is around 95%, and the larger motors typically achieve 93 to 94% efficiency.

Unfortunately, for every large electric motor there are tens of thousands of smaller ones, the vast majority of which are highly inefficient. The efficiency of small AC motors, for example, can be as low as 50%. What does this mean? Well, if a motor is only 50% efficient, then only half of the power it consumes is being converted into useful work; the other half is burned off as heat, which means each motor is actually acting like a small (or not-so-small) radiator.

This can add up to a huge amount of energy in an industrial setting like a factory, which actually receives a "double whammy." This is because it is now necessary to provide cooling systems to remove the undesired heat, and these cooling systems use ... you guessed it ... yet more inefficient electric motors.

Users are becoming increasingly conscious of the rising cost of energy and the effects of technology on the environment. Also, there is ever-increasing pressure for greater efficiency from environmental regulators, and motor-driven products are more-and-more being required to meet the stringent environmental standards mandated by regulatory initiatives like Energy Star, the Kyoto Summit, and the U.S. Department of Energy Part 430.

One solution is to add intelligent load-matching and variable speed control, which can increase efficiency by anywhere from 14 to 30%. Implemented broadly, electronic motor control could result in savings of as much as 15% of the total electric power used in the US. This equates to an annual reduction in energy consumption of as much as 300 billion KWh, thereby saving $15 billion and reducing greenhouse gasses by more than 180 million metric tons a year. When extrapolated on a worldwide basis, the potential savings are staggering.

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