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The lowdown on power line communication

Posted: 02 Jan 2012 ?? ?Print Version ?Bookmark and Share

Keywords:Power line communication? cables? Narrowband? Broadband?

In order to avoid costly downtime due to overloading, the data center would prefer to over-design the system 每 operate the UPS at low loads, at the cost of energy efficiency. From the above curve, it is evident that the UPS is not working in its most efficient range.

Now consider a PLC-enabled system as shown in figure 3. The UPS, PDU, PSU and Network devices can communicate with each other via PLC. Consequently, at every stage in the power distribution, the device will have a clear map of power topology downstream and upstream from it. For ex. UPS 1 'knows' that it provides power to PSU 1 of Network device 1 and 2. Now, since the devices connected to it are visible, their power requirements are known precisely, and hence the load of the UPS can be safely increased to an optimum level.

Figure 3: Power PLC-enabled power distribution topology in a data center,

Thanks to PLC, UPS overloading, battery failure and circuit breaker failure will be reduced, or diagnosed prior to downtime. Thus, introducing PLC in such power distribution architectures will not only increase efficiency of the system, but provide many other benefits including ease of diagnostics and redundancy in communication for mission critical data centers. And all this, without the messy wiring that data centers dread.

LED control
One of the predictions for the energy sector in the next decade is the gradual phasing out of incandescent bulbs and their replacement by LEDs. LEDs offer an advantage over both CFLs and incandescent bulbs in being fully dimmable, having a longer lifetime, being mercury free, and providing options for adjustable color temperature.

The problem: Take for example, the case of street lighting. A city spends 30-40% of its budget on illuminating the city. The old system of street lighting makes no provision for dimming of lights, color temperature control or intelligent switching. Moreover, workers are hired for maintenance patrol 每 i.e. detecting and reporting failed street lights. Very often, streetlights are repaired after complaints are lodged. Millions of dollars could be saved and millions of tons of carbon emissions could be reduced with minor adaption in the streetlight usage pattern.

The solution: Now consider a street lighting system which is PLC enabled 每 say, every LED street light has a PLC device mounted on it. This would allow for monitoring and control of each streetlight. The advantages of such a system are numerous.

???According to time, traffic, weather and other factors, the street lights can be turned off/dimmed as optimally as possible. This could generate energy and cost savings in excess of 40%〞a huge number for any city. A corresponding reduction in carbon emissions is results 每 thus helping cities comply with Kyoto protocol guidelines. Additionally, dimming will increase the lifespan of the LED lamps 每 thus providing another benefit.
???Lamps, which reach the end of their life cycle can be replaced before they fail, with reduced maintenance costs.
???Information of mortality cycle, energy consumption and other factors can be sent to the remote monitoring site 每 and this used to diagnose problems.
???With the appropriate solution, color temperature of the streetlights can be dynamically adjusted 每 providing better aesthetics and safety.
???Moreover, all this is done with no additional wiring, no need to dig up roads or build towers 每 PLC is the most suitable and affordable solution for such an application.

Challenges
PLC, of course has its challenges. Firstly, Power lines were not designed to carry data, and actually behave as low pass filters. Modeling the PL channel is difficult 每 it is a very harsh and noisy transmission medium, frequency-selective, time varying, and is impaired by colored background noise and impulsive noise. Thus maintaining signal integrity over power lines requires robust signaling techniques and hardware. Secondly, the structure of the grid differs across and within countries and the same applies for indoor wiring practices. There is no universal standard either for PLC or the grid; steps to ensure interoperability of devices need to be taken. Thirdly, questions are being raised today about the digital security of personal information that is sent over the power lines because these can be tapped into. Thus establishing privacy safeguards and equally important〞convincing the public of these is another large-level issue that is being addressed. Lastly, PLC faces competition from other means of communication〞both wired and wireless, and ultimately the choice of technology will be decided by a mix of cost, complexity, and feasibility. Today, the major competing technologies to narrowband PLC are Zigbee, Wi-Fi, GPRS and RS-232.

Conclusion
In the above article, we introduced Power Line Communication, both as a technology and as a market. The various types of PLC, modulation schemes, standards, and frequencies in use today were discussed. Finally, we presented the various applications of PLC 每in energy generation, the smart grid, data-center power distribution networks, and, in LED lighting. Finally, the challenges of PLC were briefly emphasized.

We have seen how, in its current applications, PLC has added intelligence into previously dumb power networks. And this is just the tip of the iceberg. With the increased emphasis on developing PLC technology and standards, we can be confident that in the future, power line communication will continue adding smartness to our lines.

To download the PDF version, click here.


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