Integrating SMPS Control with Application Software

Electrical and computer engineers at North Carolina State University have developed a new technique for creating less-expensive, low-power embedded systems – the computing devices found in everything from thermostats to automobiles. Having a dynamic, responsive power converter is important because it allows the embedded system to be more energy efficient; the system can go to sleep, then operate quickly, then shut back down – and the power converter can adjust the flow of power accordingly. Digital control and software-defined power will be major topics at the 2015 Darnell's Energy Summit.

“Using our techniques, we’ve been able to create prototype systems with power converters that have a combination of energy efficiency and low cost that – as far as we’ve been able to tell – is unmatched by anything currently on the market,” says Alex Dean, co-author of a paper on the work and an associate professor of electrical and computer engineering at NC State.

“Our advance is that we’ve used design principles from real-time systems and incorporated the power converter software into the embedded system processor. These methods guarantee that the other software on the embedded system’s processor will not disturb the power converter’s correct operation,” Dean explains. “This eliminates the need for a separate processor or controller circuit on the power converter itself, which in turn makes the overall system less expensive.”

It also makes the embedded system smaller, lighter and more flexible. “Because the embedded system software and power converter software are using a shared processor on a single chip, it gives developers more coordinated control over both the system’s functions and related demands those functions may make on the power converter,” Dean says.

“In this research, we showed how to integrate SMPS control software into the MCU running application software, which reduces system cost while increasing the design space and flexibility for developers. Real-time system design methods are employed to ensure SMPS voltage regulation quality, while retaining the original embedded application behavior,” Dean continued. “Our methods apply to a wide range of software task schedulers, from simple interrupt-based foreground/background systems to sophisticated preemptive real-time kernels (RTOS). We also demonstrated our methods on a position-logging embedded system, with multiple voltage domains controlled in software, resulting in power savings.”

The researchers made two prototype converters using the new technique and compared them to dozens of other compatible power converters on the market – and found that none of the other converters could match the prototypes’ combination of low cost and high efficiency.

“Our second-best prototype had 90 percent efficiency – less than 10 percent of the energy was wasted,” Dean says. “Our best prototype had 95 percent efficiency. And both had component costs of about 50 cents. All other converters either cost more, were less efficient or both.”