By employing a microcontroller to provide variable-speed motor control, design engineers can realize significant energy savings over standard on/off control and other benefits as well. Here's a look from the trenches at this growing trend from an applications engineer.
Just how big is the trend toward variable speed motor control? One way to answer that question is to look at the number of products that could benefit from variable speed motor control, from HVAC, dishwashers, washers and dryers, garage door openers, and lawn mowers to microwave ovens. While no one knows what percent of these applications are using variable speed motor control, the number is definitely growing. One reason is that these types of applications account for more than 70% of total U.S. energy consumption, which could all benefit from the energy savings possible through variable-speed motor control. Instead of having an appliance clunking on and off, as is the case with single-speed designs, variable speed adds an element of efficiency and noise reduction to the operation.
How has variable-speed motor control impacted today's product design? I'll give you a example: With a normal blender, you might have five or six buttons for speed selection, which is controlled by simply connecting the motor windings and without using any electronics. But by using a microcontroller, engineers are able to increment the speed so precisely that you get the right consistency for your pesto or your frozen margarita.
What are some other benefits? When engineers go to electronic control, they also gain the ability to add extra features, such as more precise timing in a washing machine cycle based on the type of load. Engineers are able to reduce the amount of wiring in that appliance, because they don't need to run all the switch wires down to the electronics. If they put their microcontroller in a panel with the switches that control the appliance, they can reduce the complexity of the wiring harness.
What kinds of things do engineers need to think about when they decide to incorporate a microcontroller into their design? When automakers started to add microcontrollers to their vehicles, they had to deal with issues like electronic noise, to make sure that the microcontrollers weren't going to be resetting themselves due to the noisy environment. Obviously the issues are going to differ with the application, but design engineers are going to need to think about things like heat and noise in their designs.
How are vendors making it easier for engineers to make the transition to variable-speed motor control? One way is by building motor control kernel technology into their microcontrollers. The kernel makes it simpler for the engineer to use electronics in his or her design because much of the work has already been done. The engineer just has to communicate with the kernel through a predefined user command, which is fairly easy to grasp. It shortens the whole design cycle because an engineer doesn't have to develop the whole algorithm from scratch.
Download Jon Burroughs's "Reference Design for Smart Air Handling" at www.designnews.com/smartair . He specifically developed it for air handling in an HVAC system. It also provides a useful example of simplified motor control for other induction motor applications.