Real-time digital power control increases system efficiency
While real-time control has typically fallen under the realm of microcontrollers, the latest MCUs are enabling new applications that use energy more efficiently.
Scratching the surface
Digital power is proving to be one of the primary differentiating technologies of the new millennium. Companies are facing rising energy costs, a heightened awareness of consumer and industrial electrical and electronic systems' power consumption, and the impact that this power consumption has. Engineers across all industries are being forced to not only consider power management and control earlier in their design cycles, but also devote more resources to reducing power consumption and increasing efficiency.
To grasp the significance of this drive to lower power consumption, consider that approximately two-thirds of the electrical load in industrial applications is consumed by electric motors. Although variable speed drives use only one-eighth of the energy of equivalent constant speed drives at light load, they only make up 5 percent of the industrial motors deployed today.
Put into perspective, this 5 percent conserves energy produced by 10 power plants and prevents 68 million tons of greenhouse gases from being emitted every year. With this type of energy-saving objective in mind, environmental regulators continue to improve energy efficiency by requiring motor-driven products to meet the stringent standards mandated by initiatives like ENERGY STAR, the Kyoto Summit, and the U.S. Department of Energy Part 430.
Recent advances in microcontroller (MCU) architectures are making it possible to implement even greater levels of power management and control in existing applications. Digital power electronics, or the control of power supplies via programmable embedded processor technology, can bring substantial savings to various applications including industrial motors, rectifiers, automotive control systems, commercial lighting, power supplies, backlighting for consumer electronics, and white goods (see sidebar).
Although designers today can introduce real-time control in systems that could not previously afford to focus on power efficiency, they must balance power management with other issues such as design complexity, flexibility, and system costs.
A better architecture
Implementing digital power control involves more than just increasing processing efficiency. While traditional MCUs offer the accurate, real-time interrupt handling necessary to implement robust control logic, these devices generally lack the internal architecture to perform complex control algorithms efficiently. For example, multiply instructions can take several cycles to execute. DSPs, on the other hand, can execute complex control algorithms within the narrow execution window of real-time control applications; however, in many instances, they do not support an internal interrupt infrastructure that can guarantee real-time responsiveness.
While many of today's MCUs and DSPs provide some level of digital power electronics, most lack the integration and processing capacity to do so cost-effectively. As a result, implementing the high-frequency, high-accuracy control algorithms required for digital power electronics requires a separate processor as well as several external components, increasing system complexity and cost.
Next-generation real-time MCUs address the increasing pressure for engineers to improve performance and power efficiency by combining the real-time control capabilities and power efficiency of traditional MCUs with the high-performance and math capabilities of DSPs (see Figure 1).
This approach helps bring power efficiency to cost-sensitive control applications within a single microcontroller, such as the 32-bit, real-time Texas Instruments Piccolo MCU, which bridges the efficiency/cost gap with new features.
One such feature is a programmable control law accelerator that provides a system performance boost for processing math-intensive control loops, thus freeing main CPU cycles for other tasks such as communication and diagnostics. Integrated, application-specific, control-optimized peripherals enable these next-generation microcontrollers to acquire and drive higher-resolution signals without overburdening the CPU, further improving accuracy and efficiency (see Figure 2).
Advances in real-time control microcontrollers allow these devices to manage several control loops while simultaneously implementing multiple levels of digital power electronics, thus providing a number of unique benefits.
Digital control systems are continually being improved to achieve greater efficiency that will lower cost per kW. Variability in load conditions and operational requirements makes it important to select the right controller for the system – one that provides high performance, integration, and flexibility. Real-time MCUs allow designers to adaptively tune and calibrate their systems based on real-time diagnostics.
For example, in a variable frequency air conditioning unit, a single 32-bit real-time MCU can precisely control two electric three-phase motors as well as perform power factor correction calculations. Currently required in approximately 30 percent of the world's markets, including Europe, China, Japan, and India, power factor correction improves the load's efficiency to capitalize on the utility's power.
Higher accuracy and reliability
High-resolution pulse-width modulation, on-chip analog comparators, and computational bandwidth further improve control loop performance and provide the output accuracy needed for full digital control at high switching frequencies. Real-time component measurement facilitates compensation for component aging and drift. In addition, having the key functional block integrated within the real-time MCU reduces the amount of system components and thus increases system reliability.
Improved system integration and management
All loop control, sequencing, and system management can be handled by a single controller. This integration eliminates the need for multiple converters and stand-alone components, greatly improving the resulting architecture. On-chip communication peripherals simplify interfacing and allow direct system monitoring and reporting.
For commercial and industrial lighting applications, LED technology can bring up to 50 percent higher energy efficiency when compared to traditional high-pressure sodium lamps. Thirty-two-bit MCU-based LED control systems offer intelligent current control and easy system networking to minimize system complexity as well as the cost of managing color mixing and temperature control required for white LED systems.
In addition, many real-time MCUs offer performance and integration to implement power-line communications. One use of power-line communications is for street light networks that allow cities to pinpoint power outages and centrally manage and adjust lighting based on time of day or traffic and weather conditions. According to a 2008 study prepared by Robert Grow, director of government relations for the Greater Washington Board of Trade, the 10 largest metropolitan areas in the United States could reduce annual carbon dioxide emissions by 1.2 million metric tons – the equivalent of taking 212,000 vehicles off the road – and save $90 million a year by switching to more efficient lighting such as LED or intelligent street light networks for their roads.
Lower system cost
Real-time MCUs are optimized for embedded applications, offering smaller packaging that requires less PCB space and optimized peripherals. Fewer components and simpler hardware design mean lower manufacturing costs and complexities in addition to accelerated product development.
Another aspect of decreasing system costs is reduced development time and complexity. It is imperative that developers have access to a mature development environment backed by a comprehensive ecosystem of resources that reduces learning curves and design cycles. Tools such as TI's Piccolo-based controlCARDs cut tools costs down to $49 and can be leveraged across a wide variety of application development kits for digital power, DC/DC, and AC/DC applications.
Real-time control offers greater system efficiency and precision through the implementation of advanced algorithms for industrial, consumer, and automotive applications such as solar power micro-inverters, LED lighting, white goods appliances, and hybrid automotive batteries. Real-time MCUs are helping launch new applications as well as bringing better power efficiency to existing applications at lower system costs.
Rather than bear the cost of adding a second processor to implement power conversion control, a single real-time MCU's combination of performance, optimized integrated peripherals, flexibility, and modular low-cost design tools enables impressive digital control capabilities that will drive the future of power electronics.
Keith Ogboenyiya is product manager for C2000 32-bit microcontrollers at Dallas-based Texas Instruments, where he is responsible for product definition and positioning, customer design engagements, business development, and customer support for the C2000 product line. Keith has experience in microcontroller and DSP applications at TI, providing technical and commercial knowledge of the industrial and automotive semiconductor market requirements and system-level understanding in a variety of applications. He received his BSEE from Georgia Institute of Technology.
Zhen Yu is end-equipment team manager for 32-bit microcontrollers at Texas Instruments, where he is responsible for end equipment market and business development strategies and priorities for the 32-bit MCU product lines. Zhen also has experience as an applications engineer and business development manager and was responsible for applications and business development for the C2000 product line in Asia and worldwide. He received his BS and MS degrees from Beihang University in Beijing, China, and his PhD from Washington University in St. Louis, Missouri.