Electronic Design
LED Lighting And The Smart Grid Hold Promise

LED Lighting And The Smart Grid Hold Promise

So where is the power market headed? For a better idea, get out your calendar and take a look at some recent and upcoming conferences. If they’re any indication, LED lighting, the Smart Grid, and energy harvesting all are destined for growth in the near future (see “Energy Harvesting: Coming Soon To An Application Near You”). And if these events don’t persuade you, perhaps some industry partnerships will offer some compelling evidence.

The Global SMART GRID
Here in North America, media reports of Smart Grid (Fig. 1) developments (usually consumer revolts over bills, “meter noise” in baby monitors, and the dire effects of radio waves) would lead one to think that the Smart Grid was only about smart metering and that it was exclusive to this hemisphere. In fact, we’re part of a global phenomenon. Savvy North American companies are partnering around the planet, trying to profit from the opportunities.

With China’s energy use set to double every 10 years, the country’s chief power distribution company, State Grid Corp., is looking to have an operational smart grid by 2020. Last year, China spent more on building out the grid and making it smarter than on power generation. Overall, building a modern grid will mean spending a lot of money—as much as $10 billion a year through 2020, according to one U.S. analyst.

General Electric is partnering with the city of Yangzhou (population 4 million) in China to build a smart grid “demonstration center” to be completed by 2015. By the end of the initial demonstration phase, there will be a 100,000-square-foot lab with wireless-enabled smart meters, home energy management systems, and smart appliances.

The point of the center is to sell those smart appliances to the Chinese top brass as well as to the Chinese public, keeping ahead of the country’s demand for energy as its middle class grows in purchasing power and numbers.

Meanwhile, just over a year ago, IBM announced an agreement with ENN Group, a Chinese energy provider, to form a joint venture focused on “intelligent energy.”

How can designers get involved in this growing market? One way might be the 1st China International Smart Grid Technology and Equipment Exhibition (Smart Gridtec), May 5-7 at the Shanghai New International Expo Center (SNIEC), held concurrently with the China Smart Grid Forum.

Speakers will address intelligent network technology standards, distributed energy, smart power distribution automation, intelligent homes and buildings, electric vehicle charging stations, and similar topics.

Just as South Korea has invested in its national broadband infrastructure to position itself as a broadband leader, it also has started spending what is expected to amount to at least $15.8 billion on building out a smart grid infrastructure with a target date of 2016.

Beyond that, Korea’s government-backed Smart Grid Institute has said the government and industry plan to spend more than $24 billion by 2030. South Korea’s smart grid roadmap includes private and government investment of $6.16 billion on technology and $18.05 billion on infrastructure.

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One pilot project is underway on the island of Jeju, south of Seoul, with 10 of Korea’s top telecom and broadband firms, including LG, SK Telecom, KT, KEPCO, GS Caltex, and Hyundaiare, getting set to build out the infrastructure there. The companies hope to exploit what they learn in the world market. The Jeju consortium has said that it is shooting for 30% of the global smart grid pie.

India is the home of many brilliant engineers, concentrated in a few urban centers, and even more people with other kinds of skills spread across an enormous subcontinent with a challenging transportation and energy distribution infrastructure.

Although those engineers likely will play a big part in smart grid development, the larger effect of their efforts probably will be seen outside India. For example, IBM expects to benefit from any Indian innovations via another partnership, this time with the India Institute of Technology.

In many ways, Japan is the opposite of India. It’s small and homogeneous in population, and it has a well-developed, robust infrastructure. But like India, it also has good engineering schools that turn out smart graduates.

Internally, Japan is more committed to shrinking its carbon footprint than managing its limited resources, which makes sense in a country with a birth rate below replacement levels. Externally, the large Keiretsu (the vertically integrated interlocking business organizations that powered the Japanese “economic miracle” of the 1970s) appear eager to repeat their successes in consumer goods, now eclipsed by China, in the hoped-for smart-grid boom.

One factor that makes Asia different from North America and Europe is the size of its largest players, China and India, and the isolation between regions that results from their underdeveloped ground transportation infrastructure. Because of their size, it’s possible to wonder whether there’s enough copper and aluminum on the planet to wire China and India with a monolithic grid.

For instance, five years ago, the Chinese building boom had already increased the price of copper wire by a factor of five, yielding parity between synchronous ac motors and permanent-magnet motors, which in turn changed the way engineers have thought about driving motorized appliances and vehicles. There will certainly be other unforeseen consequences as the Smart Grid develops in different ways across Asia.

As with solar and nuclear power, Europe’s mild brand of state socialism has led to fast implementation that has in turn given the continent a technological lead over North America. But that’s not to say that there haven’t been glitches that mirror in a European way the deployment problems we have seen here.

According to one presenter at the IEEE Communications Society meeting at the National Institute of Standards and Technology (NIST) in Gaithersburg, Md., in October, Dutch citizens rebelled against smart meters when it became apparent the fine granularity of their reporting of daily energy use could be used by criminals to detect variations from normal patterns that would allow them to target specific residences for burglaries.

Nevertheless, for the moment, the Smart Grid is marching like Napoleon through Europe, with Italy the leader in the installation of smart meters. In fact, last July, Freescale Semiconductor announced the very first commercial IC that would allow appliances to autonomously decide when to operate, based on the Euros/kWh rate. The IC was specifically designed for the Italian market.

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The Europeans also have their eye on the potential solar and wind power (Fig. 2) that could be developed in the deserts of North Africa. Political issues aside, the technical challenge would be to get all that Saharan energy to European load centers. It would necessitate an HVDC transmission grid, which has already been dubbed the “SuperSmart Grid” (SSG). The SSG would supply the current HVAC distribution grid, and traditional ac grids would handle what broadband and cable TV companies call “the last mile.”

LED Lighting
In early December, a joint Arrow/Cree conference for Arrow customers included presentations and demonstrations from semiconductor vendors that offer LED drivers and dimmers, from power-supply manufacturers, and from one RF-control company that wants to turn streetlights and parking-garage lights off and on selectively. Overall, the conference pointed to four emerging trends:

LED performance (Fig. 3) characteristics are evolving so rapidly that the lighting product you design today could be obsolete before you recover your design investment. A talk about “future-proofing” your designs got a lot of attention from the audience.

• Whatever those performance characteristics are, we aren’t describing them accurately and consistently. Although you can’t go wrong with luminous efficacy (lumens/W), after that, characteristics (like LM-80) may not mean what you think they mean. LED makers will soon announce a mutually accepted set of consistent characteristics.

• It’s hard to differentiate semiconductor companies’ LED driver and dimmer chips. If you’re looking for winners, it’s a hard race to call at this point.

• Although LED lighting may look like just another electronics design business (i.e., LEDs are diodes; power supplies are essentially voltage converters or current sources; etc.), the companies that make the end products are different and that changes a number of factors in how the products must be marketed.

RAPID EVOLUTION
It is worthwhile to take a closer look at these trends. Starting with the issue of performance characteristics, although red, green, and blue LEDs still have a place in signage and scoreboards, high-brightness (HB) white LEDs captured the most attention at the Arrow/Cree event. As the terminology says, their virtues are their high brightness overall, or for any given power dissipation, and the color characteristics of their output.

Actually, their “whiteness” varies from unit to unit. So, Cree and other LED makers sort and bin them to allow lighting designers to mix and match bins to achieve the precise flavor of white they want. This binning follows a model developed in the 1950s for then-new fluorescents.

The bins are getting tighter month by month, though, making it easier to achieve a specified color with fewer LEDs. That’s a good thing, because those steady improvements in luminous efficacy mean fewer and fewer LEDs are needed to achieve a specified intensity of light output.

HB white LEDs work by combining blue-emitting LED diodes with phosphors that emit photons for different colors that add up to white light when mixed. According to Cree, most of the recent advances in HB white LED manufacturing arise from the techniques employed for depositing the phosphor so it will be struck by the maximum number of primary photons and will, in turn, radiate the maximum number of secondary photons in an optimum pattern.

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Just laying down a “glob” of phosphor on top of the diode junction isn’t a very good approach. Instead, an “optimum pattern” facilitates the use of lenses and reflectors in shaping the light from all the LEDs in the fixture.

PERFORMANCE CHARACTERISTICS
While presenters at the IEEE Communications Society meeting agreed that luminous efficacy was one satisfactory metric for characterizing HB white LEDs, they also said other characteristics were either misleading or poorly understood. The one that received the most disparagement was LM-80, which a lot of people (myself included) thought referred to the time it takes for an LED to age to the point where its output in lumens is 80% of its original light output. Not so!

LM-80 is essentially a test procedure the U.S. Department of Energy devised for its contest to develop a 60-W equivalent screw-in replacement for a standard incandescent light bulb. Apparently, when you start to try to apply it to individual LEDs, it isn’t easy to achieve consistent results, especially from manufacturer to manufacturer.

The good news at the conference was that the LED makers were close to releasing a comprehensive and consistent new suite of data-sheet characteristics that they all agree upon. Developed by the Illuminating Engineering Society’s (IES) TM-21 working group, the suite may be out as early as the first quarter of 2011.

DRIVERS AND DIMMERS
Merely driving LEDs is a fairly simple matter. You arrange them in series strings or in parallel, and then you arrange them to provide sufficient current, making sure that it’s shared evenly, with enough voltage to handle all the forward voltage drops in each string. For general illumination applications, it gets interesting when it’s time to get from the wall socket or the utility-pole transformer to the final dc power stage.

When a general lighting system requires a lot of power, then the first power-conversion stage, the ac-dc stage, gets interesting. While it’s a long way from the LEDs, the U.S. Department of Energy and the European Union have made it clear that they want it to exhibit a very clean power factor, which is difficult because of that darned capacitance on the output of the rectifier bridge.

This is approached in different ways. The EU’s IEC61000-3-2 specifies acceptable levels for the first 32 harmonics of the ac line frequency, while the DoE’s Energy Star program (which is voluntary but enforced by the buying power of the U.S. government) specifies a power factor of at least 0.7. On top of that, real customers for general lighting applications demand a minimum power factor of 0.9, so that’s what companies design for.

In turn, that requires a somewhat sophisticated flyback topology for the first stage, with operation in critical conduction mode. Subsequent stages of switching regulation, buck, boost, or buck/boost support a final stage that provides the drive to the string or parallel strings of LEDs.

This is generally a switcher also, but one vendor at the conference was using linear regulators. One of the vendor’s applications engineers said that this made it less expensive to achieve the required overall efficiency because the output stage could be designed to supply the full voltage needed by the sum of the string’s forward voltage drops while dissipating less than a volt in its own pass transistors.

Apart from that, all of the silicon vendors’ offerings at the conference appeared to resemble each other. When it comes to product differentiation, marketing personnel were quick to note that they had their own fabs or that they make switching FETs and diodes too.

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While those are valid responses from a supply-chain standpoint, they don’t say much about circuit-design innovation, company to company. That, in turn, suggests that companies are still staking out their turf in lighting applications.

There is more differentiation in dimmers—the circuits that can be used in a bulb or a ballast to accommodate old-fashioned triac dimming devices. (“Ballast” in general lighting terms seems to mean whatever electronics are required to get from the building ac supply to the LED fixture.) When you play with enough dimmer demos, you can notice some subtle differences.

Generally, they all work fine. But at the low end, some are smooth down to minimum light output (about 10% of full brightness, typically), and some exhibit hysteresis in turning on and turning off. For the most part, this manifests itself in the LED array sort of popping on suddenly at a brightness level noticeably higher than the level at which it turned off.

WHO’S THE CUSTOMER?
The engineers who design with LEDs, particularly the ones who design streetlights, architectural lighting, and vehicle lamps, are in a specialized sub-field of the profession. They’re concerned with high power levels, and they’re really concerned with heat dissipation. But unless they’re using RF for remote control, they’re dealing with low signal bandwidths and simple control loops that can be treated as state machines.

On the other hand, they also really care about esthetics, because they deal both with architects and with end users who have decided ideas about what the spaces they inhabit should look like. From the standpoint of companies that want to sell things that interface with LEDs, that last point suggests a new marketing environment that needs to be understood and catered to for sales.

Further, these customers and their customers live in a kind of brave new world, where engineering decisions are influenced not only by the laws of nature, but also by the regulations of government agencies and the efforts of energy utilities to create incentives for energy savings. In the long term, return on investment may be based as much on convincing energy suppliers that rewarding customers for choosing solid-state lighting in their new offices is more beneficial than rewarding them for using extra insulation.

In fact, a considerable amount of education may be involved in the sales pitch. For example, many people need some education before they comprehend that the advantage of LED lighting in many general lighting situations lies not so much in the luminous efficacy of the LEDs themselves, but in their ability to be turned on and off virtually instantaneously.

Most legacy outdoor lighting uses one form or another of discharge tube that takes a relatively long time to turn on. As a result, lighting systems that use them are designed to stay on all night. With LED fixtures, it’s possible not only to turn the total array on and off on-demand, it’s also possible to modulate the light output to different levels by turning on only some of the LEDs. This makes it possible to cut back on lighting in structures like parking garages (Fig. 4) for most of the night and bring it up to full power only when a motion detector or a suspicious guard calls for it.

According to energy-efficiency consultant Robert Seaman, who addressed the IEEE Communications Society conference, this approach has proven effective in crime control because the differential lighting tends to lead security personnel to locations where unauthorized presences have been detected.

The challenge, in dealing with organizations that offer subsidies to encourage energy saving, is to persuade them that saving energy by reducing the lighting in a multi-story parking garage is more effective and should have preference over putting more insulation in the walls.

Seaman’s point (and the point made by the city and utility energy scientists who followed him) was that the involvement of power utilities (private and public), as well as city, state, and federal governments, architects, ergonomists, and so forth illustrates is that there are probably far more stakeholders involved in making a lighting venture a success or a failure than there are in many other aspects of engineering design.

TAGS: Components
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