| From Passive to Active Efficiency |
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The history and future of power management At a time when energy conservation is on everyone’s mind, designing for efficiency seems to be a basic fundamental, but for power engineers it has been a permanent quest driving an amazing level of innovation that started many years ago when transistors were made of Germanium and J.F. Kennedy declared in his speech delivered in 1962 at Rice University in Houston, Texas, “We choose to go to the Moon…” By Patrick Le Fèvre, Marketing Director, Ericsson Power Modules From that day, DC/DC power designers targeted energy efficiency as prime driver for new technologies, though despite very innovative new topologies, energy efficiency has been very much driven by components’ performances nowadays reaching a level of evolution that requires additional magic in order to walk the last mile. The following article honors those that brought men to the Moon and the thousands of power engineers that, in the secretion of their laboratories contributed to make DC/DC converters highly efficient, and recently, introduced new technologies such as digital power control and power management providing the missing link from passive efficiency to active efficiency. Passive beginnings From the early origins of DC/DC power conversion, energy efficiency has been an issue that power and components designers have addressed to improve products and systems’ performances. This became critical when systems’ reduced availability of space for power conversion, simultaneously requiring lower power dissipation and longer lifetime, when combined together require higher efficiency DC/DC power converters. Considering where we are today, it is wise to take a minute to look back into the power history to really understand the long road we’ve traveled, moving from <50% to over 96% efficiency and to realize today’s concerns are very similar to what the power electronics pioneers faced in their time. There are many good examples that illustrate the evolution of energy efficiency, but to start I would like to mention what I consider as being the first challenging project power supplies designers faced when designing DC/DC power solutions to power the Apollo Spacecraft. In those days, most of the DC/DC converters where designed for military applications and the average efficiency topped, at best, 40% resulting in very-high power dissipation. The Apollo program triggered the demand for ‘higher efficiency DC/DC converters’ and a young engineer named Nicholas G. Tagaris, who later formed DATEL, was one of the engineers to consider new ways of working and thinking out of the box to step-down the 28V internal bus while reducing power losses. The Apollo Spacecraft and especially the Lunar Excursion Module (LEM) required a new way to distribute energy throughout the space vehicle while preserving the precious energy delivered by the fragile batteries. Part of this project investigated in a new concept to create ‘integrated DC/DC converters’, ten years later to be known as ‘bricks’. However the real challenge for those guys, despite an almost unlimited budget, was to improve the efficiency of something already limited by the components and topologies available at the time, often just a push-pull switcher inherited from audio systems, post-regulated by a series of transistors ballast-connected in parallel - and to use a brand new emerging technology called integrated circuits. During that project, designers had to consider a number of constraints today’s engineers are also facing; “How to reduce energy consumption to the lowest level” and the answer was simple, switch OFF everything you don’t have a need for and turn it ON when it’s time. In 1969 energy management was already considered as a way to reduce power consumption but it has taken 40 years for this concept to find its way to become easily manageable at board level. When in July 20, 1969 the LEM landed on the Moon, DC/DC converters were in their early development phase but from that date, the electronics industry gradually implemented DC/DC board-mounted power sources in various equipments and push-pull post regulated by using linear regulators, step-by-step to be replaced by new topologies.
Figure 1: DC/DC efficiency curve Figure 1 illustrates the evolution of the efficiency curve throughout the years, but hidden behind the major steps, reflecting improvements brought about by new components, a very large number of technical improvements remain invisible. Starting in the late seventies, the telecoms industry adopted the bricks-concept and Ericsson’s PKA was the first BMP power module to break the standardized 60% efficiency that BMP modules performed at in those days. To break this limit, engineers had to introduce several major innovations embracing designing a new set of power controllers, using a ceramic substrate, new ferrites, faster diodes, and new switching topologies resulting in a product performing at 80% efficiency. As for many power supply companies, the adoption by the telecom industry of a new power distribution, the so-called ‘distributed power architecture’ has been the ignition point for intensive research to improve energy efficiency as illustrated in Figure 1. From below 50% when Neil Armstrong said famously: “one small step for man, but one giant leap for mankind” to over 93% in 2000, the improvement is significant but despite expectations we may have in new materials such as Oxide Carbide or Gallium Nitride and others, we could consider the way to reach >98% efficiency as complex and as difficult as bringing men to march; not impossible but very costly. Components and topologies will continue to progress but as illustrated in Figure 1, after having improved power-trains to the highest extent, by around 2006 the efficiency curve started to flatten, requiring engineers to consider other methods to improve efficiency and to move from passive efficiency to active efficiency. Active efficiency arrived Considering that powertrains have reached a state of the art level, that some limits inherent to components are difficult to exceed and that the market is not ready to pay for a little extra efficiency resulting from an experimental new generation of components or materials, DC/DC power modules’ efficiency curve started to flatten. As it was for Nicholas G. Tagaris when considering powering spacecraft Apollo, power engineers had to think out of the box, considering combining the best of what analogue has already achieved with the benefits of an emerging new technology, digital power control and management. DC/DC power converters are commonly designed to deliver the best performances at a certain point of operation that when in operation is not always the case. For example, recent studies from a datacenter have demonstrated under-utilization of power supplies, often being used at 25 to 35% of their capacity, which is outside the ‘optimized performance point’, resulting in poor efficiency and higher power losses. Introducing a technology that permanently monitors load and input voltage conditions in order to dynamically adjust switching parameters to reconfigure power supply parameters to real conditions, will result in optimized performances at any load condition, limiting power losses to the lowest extent (Figure 2).
Figure 2: Optimized DC/DC efficiency Also, the recent evolution of the distributed power architecture in migrating to a 12V intermediate bus voltage simplified the board designers’ task but as it has been debated in many forums, 12V might not be the most optimized voltage at any point of systems’ operation. Adding the possibility to adjust the bus voltage to suit load conditions, for example 9V when low utilization and 12V when full performance is required will result in an extra energy saving without adding cost (Figure 3).
Figure 3: Optimized bus voltage Combining digitally controlled DC/DC converters and systems energy management lifted board-mounted power solutions from passive efficiency to active efficiency, closing the gap between product and systems optimization. Conclusions Maybe not as ambitious as walking on the Moon but when designing systems with power efficiency in mind, new technologies such as digital power management and control will contribute to reduce energy consumption, and active efficiency is still only in its infancy. I’m convinced that technology will take men to Mars and further, but until then it will change the way systems’ architects consider DC/DC board-mounted power solutions that have now moved from passive to active status.To close, I refer to a sentence often used by Antoine de Saint-Exupery (1900 – 1944), who said: "We haven't inherited the earth from our ancestors; we borrow it from our children." |
