Power Electronics

Digital Power and Renewable Energy Spark Discussion at APEC

In the exhibits and conference sessions at the Applied Power Electronics Conference and Exposition (APEC 2006) last month in Dallas, two topics - digital power and renewable energy - stood out as being especially significant to the power electronics industry. With regard to the first topic, the industry is showing that the capabilities of digital power control are advancing faster than the industry’s consensus on which markets will benefit most from digital control. And concerning renewable energy, there is an increasing awareness of the need to develop power electronics systems that interface to renewable sources such as solar panels and fuel cells.

Demonstrations by Primarion and Power One highlighted the impressive capabilities provided by digital control. Certainly one of the most impressive features (which Power-One demonstrated) was the ability to optimize the control loop for a given set of passive components through an automatic software control function.

Another demonstrated digital advantage was the ability to program many control parameters on-the-fly, making it possible to use the same circuit design for multiple board designs. In this way, each converter circuit can be customized for a particular board. This function could be highly beneficial to smaller companies with limited manufacturing resources. It may also benefit OEMs, which according to information presented by Artesyn Technology’s Bob White during the plenary session, will probably take greater ownership of the power solutions for their products going forward.

The conference began with a plenary session presentation by Larry Kazmerski, director of the National Center for Photovoltaics, about the status of photovoltaic technology. While it’s no surprise to most engineers that solar cells have been the basis for a quiet revolution over the course of their 50-year existence, photovoltaics now represent a $10 billion market worldwide, according to Kazmerski. Furthermore, Kazmerski described the PV industry as being at a “tipping point,”meaning that PV technology is on the verge of widespread adoption.

In his presentation, Kazmerski ranked the various PV technologies according to the worldwide impact they will have when they reach maturity. Technology that will impact the industry over the next three years was described as “accelerated-evolutionary”, while technology that comes to market in the next 3 to 10 years was called, “disruptive”. Meanwhile “revolutionary” was the label given to PV technology that could be significant in the next 10 or 20 years and beyond.

Through these three stages of development, new technologies will be deployed that raise solar cell efficiency dramatically. Currently, there are solar cells available commercially that achieve conversion efficiencies exceeding 20%. A new technology on the verge of being released , lattice-matched multi-junction cells, will raise that performance to about 40%.

Efforts to efficiently harness light will be complimented with efforts to efficiently produce light, and many presentations at APEC addressed requirements for driving fluorescent and white LED light sources. This was apparent in both the presentation sessions and on the exhibition floor.

Just as with photovoltaics, white LEDs are becoming increasingly efficient, perhaps reaching a “tipping point” of their own by recently achieving performance parity with fluorescent lighting (see “ LEDs to Outshine Fluorescent Lamps,” Nikkei Electronics Asia, http://neasia.nikkeibp.com/neasia/001584 ). However, just as with fluorescent lighting, there will be several design challenges in driving LEDs, such as reducing current ripple.

Another component that seems to be receiving increasing attention from power electronics designers is the fuel cell. At least two of the paper sessionpresentations focused on the issues that arise when a dc-dc converter is supplied from a fuel cell. The complex impedance of a fuel cell causes difficulties at the input of a dc-dc converter, but this can be partially addressed by placing large capacitances in parallel with the fuel cell’s output. Also, keeping the frequency of the ripple current high, and the amplitude low is necessary to obtain the best performance from the fuel cell.

These applications are all quite interesting and show great promise. However, they should not obscure the greater-than-90% working efficiencies of the power electronics systems to which they interface, especially since the energy conversion efficiency in some of these emerging technologies is not yet even half of that.

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