Many embedded developers, while attracted by the possible market opportunities represented by making their designs more power efficient and greener, hesitate because of the complexity they think is involved in programming or reprogramming their motor-control applications.
In his class at the Embedded Systems Conference Silicon Valley ” “Advanced Motor control algorithms for reducing power consumption of embedded applications (ESC-326)” – Christian Fritz of National Instruments spends a lot of time taking students step-by-step through some of the complexity of motor-control algorithm development.
However, he said, there are some preparatory steps that can be done before that daunting chore to improve the power efficiency of any motor-control design: 1) select the right high efficiency motor; 2) select the right size motor and 3) select the appropriate motor technology.
“In the face of economic uncertainties and increasing environmental concerns,” said Fritz, “many businesses are taking a look at how to make their operations more lean, efficient and environmentally friendly.
“Examining your electricity bill is a good place to start. The top consumers of electricity are HVAC systems, water heating, lighting, office equipment, and machinery.”
More specifically, he said, the motors within these machine are responsible for approximately two-thirds of the total electrical energy consumption in a typical industrial facility. Motors are everywhere—blowers, pumps, compressors, conveyors, machine tools, mixers, shredders, said Fritz, and more and a lot can be done to improve the efficiency and lower the operating costs of the electric motors.
Step #1: Select the right high efficiency motor
“The fundamental purpose of any electric motor is to convert electrical power into mechanical energy,” said Fritz. “A motor running at 50% efficiency is converting half of the electrical power into useful mechanical work at the motor shaft, while the rest is wasted.
“This makes the extra investment in efficient motors financially prudent since electricity costs make up 96% of the total life cycle costs of a motor, while the original purchase price and service/maintenance costs combined contribute only 4%.”
The first and most obvious solution to increasing motor efficiency is to replace it. When your older motors need service, he said, consider purchasing a new high efficiency model rather than refurbishing the old motor. “According to the U.S. Department of Energy (DOE),” said Fritz,”switching to a motor with a 4-6% higher efficiency rating can pay for itself in just two years if the motor is in operation for more than 4,000 hours a year.”
Step #2: Select the right size motor
A second fundamental component to improve energy efficiency,” he points out, is proper motor sizing. “The U.S. DOE estimates that 80% of all motors in the United States are oversized, causing businesses to pay a high price in wasted energy. “
Step #3: Select the appropriate motor technology
The type of motor chosen, he said, has a big impact on energy efficiency. For example, AC induction motors are low cost and can be operated without sophisticated controls, making them the workhorse for most household goods.
“They are usually operated in an open loop fashion for constant speed applications but can also be augmented with more sophisticated controls for use in applications requiring variable speed and torque.”
For low power applications, said Fritz, inexpensive stepper motors and brushed DC motors are popular due to the simple control circuitry necessary. “However, they provide somewhat lower energy efficiency and therefore higher operating costs,” he said. “Stepper motors are particularly inefficient, because they draw power even when stopped and they must be significantly oversized due to poor torque output at high speeds.”
The best bet for most appropriate technology for green uses, he said, are Brushless DC (BLDC) motors. “They are more costly but provide better energy efficiency and performance when controlled using advanced algorithms compared to AC induction motors,” said Fritz, “and they can scale up to serve very high power and high speed applications.
“Although AC induction motors still dominate the market, brushless DC motor adoption has quadrupled over the last five years to more than $1.2 billion USD according to the ARC Advisory Group.”
Helpful as these initial steps will be to improving the power efficiency of a design, in the long run nothing will help more, said Fritz, than getting into the details of the motor control algorithms used in a specific application and how to make them more efficient.
“Improving motor operating efficiency can produce significant energy and dollar savings and provide a rapid return on investment,” he said. “For example, a 5 percent efficiency increase on a 500 horsepower motor operated 8,000 hours/year could save over $12,000 and 170 kilowatt-hours of electricity each year per motor.
“When evaluating control system upgrades, keep in mind that energy costs are typically orders of magnitude higher than hardware costs over the lifecycle of the motor. “
Other classes on Green Technologyand Energy Conservation at the ESC Silicon Valley in San Jose,Ca., include:
If you want to learn more about this important topic, attendthe Panelon Energy Harvesting. Hosted by Patrick Mannion, EditorialDirector of TechOnline, it will include panelists such as TI's DaveFreeman,Perpetuum's Keith Albate, Eugene You of EnOcean, Steve Grady of Cymbetand University of Illinois Energy Harvesting Researcher PatrickChapman.