The Mechanisms Behind Powerline Communications
by Adam Warmington, Advanced R&D and Controls Product Manager
Powerline communications (PLC) enables the sending of data over existing power cables. In turn, with just power cables running to an electronic device, it is possible to both power up and simultaneously control/retrieve data. PLC is a highly flexible and reliable communications technology that has enabled power-grid control and automation for over 100 years. The technology has progressed and has found many more uses in different fields, including LED lighting. At Lumenpulse, we have developed a PLC technology called Lumentalk, which enables digital data to be transferred over AC wiring. Lumentalk turns regular electrical wiring into a stable digital\control network for DMX, DALI, 0-10V, or TRIAC dimming. In this article, we discuss how PLC can be used in combination with LED lighting to create dynamic lighting scenarios, etc. in installations to achieve previously unobtainable results while remaining cost-competitive.
What is PLC?
Powerline communications refer to a variety of different technologies used to pass data and power over the same conductors. Regardless of how power and data are transmitted, all PLCs are based on three simple steps:
Modulation is the process in which data is encoded onto a periodic waveform. The LED lighting industry is built on the concept of Pulse-Width Modulation (PWM). PWM is used as the controls signal for the brightness of an LED. At its most basic level, modulation is the manipulation of the properties of a periodic signal in a controlled method, allowing the receiving equipment to interpret the signal. Modulation in PLC is slightly more complicated than LED dimming but is still quite simple at its core. The modulation techniques developed by the radio and telecommunication industries can be applied to PLCs.
Demodulation is simply the inverse of modulation; however, the signal is modulated dictates how the signal will be demodulated. This means that when developing a PLC, the modulation scheme and the injection method are two primary tools that can be used to design a system for a specific purpose.
As mentioned in the introduction, Lumenpulse has developed a PLC suited explicitly for LED lighting applications, called Lumentalk. This includes all of the equipment needed to transmit and control the LED light fixture. To provide an example of a modulation scheme, let's look at the modulation technique used in FM radio. This modulation is called Frequency-shift keying (FSK); it uses a center frequency and then either increase the frequency or decreases the frequency to denote 1s and 0s. When you're listening to the radio in your car, the center frequency is the station you are tuning into. This digital information that is being modulated and transmitted contains all of the information required to produce the audio signals. When the modulated signal is received at the end device, it is demodulated. In the case of FSK, high and low frequencies are converted into high and low voltage values. The selection of the center frequency affects some of the properties of a PLC. A lower frequency, in general, will have the ability to travel longer distances. A higher frequency enables faster data transfer but decreases resilience to transmission line effects.
The next element of a PLC is injecting the modulated signal onto the medium. For Lumentalk, the medium is standard 120-277V AC power mains inclusive. Other PLCs are injected onto multiple phase powerlines or DC powerlines. For AC powerlines, some challenges arise due to the nature of the AC power waveforms. The AC power waveform creates the difficulty that the medium is always shifting. The voltage waveform is a sinusoidal centered around 0 volts. One way to deal with this issue is to wait until the AC waveform nears the zero-crossing point, and transmit the data then. Another method is to superimpose the signal waveform on top of the power waveform. The Lumenpulse Lumentalk system utilizes the later.
While more technically challenging, there are several significant advantages to superimposing the modulated data signal on to the power waveform. Zero-crossing systems are limited to a tiny portion of time when they can transmit data. The majority of the time, the system will be unable to transmit data. Superimposing the signal allows for data transmission regardless of the power waveform. Another advantage to superimposing the waveform is resistance to poor powerline conditions. Power systems can be a poor electrical environment for transmitting data signals, which can make zero-voltage referenced data transmission unreliable. Superimposing the signal removes the zero-voltage reference, which allows the system to be more resilient to poor power system conditions.
Limitations of PLC
Many communication systems rely on a predictable network to communicate reliably. Ethernet communications are the backbone of modern internet connections and require particular network conditions for communications to operate correctly. This is achieved within the Ethernet specification and implemented by manufacturers developing devices. Other systems analyze the network before communicating. All those strange sounds your computer used to make when connecting to dialup internet were the two devices analyzing the phone network. Cable boxes still do this today but use electrical signals rather than audio signals. The ideal PLC installation consists of a completely known electrical network. Achieving a known network for lighting controls is much more difficult. Each building is wired differently and is subject to a multitude of variables. Each device connected to the power network will affect all signal transmitted on the powerlines. Due to this, attention should be paid to all equipment connected to the Lumentalk enabled circuit to ensure a strong signal is achievable.
PLC as a Lighting Control System
Lumentalk is a PLC system that has been optimized for lighting control. The modulators, Lumentranslator, and Lumenlink, were developed to perform the functions of modulating data and injecting it onto the powerlines. These devices are capable of receiving a signal from a 0-10V dimmer, DALI controller, or DMX controller and converting it into PLC.
On the other end, the Lumenear is embedded in the LED fixture and receives the modulated signal. The Lumenear demodulates the Lumentalk signal and provides the final control signal to the lighting fixtures. The Lumenear communicates with the Lumentranslator or Lumenlink to identify itself. The Lumenear can be addressed as an individual device, or as a group to allow for flexible control solutions to be implemented.
Lumentalk does not perform a direct translation of DMX, DALI, or 0-10V into a PLC, but rather converts the transmitted information as closely as possible. The properties of PLC do not necessary allow for a direct mapping of each control input.
Theory in Action
When implementing controls for lighting installations, there is rarely a perfect solution. Lumentalk is a control protocol and another tool that can help achieve the desired amount of lighting control without having to install data cables. As a lighting manufacturer, Lumenpulse feels that Lumentalk is ideally suited for retrofit applications where running new data wires is not feasible. Lumentalk enables you to introduce modern lighting control over your existing electrical wires without having to install new cables, saving you time, money, and hassle. Many historic buildings have old, outdated lighting systems that need to be upgraded, but running the data wires needed for modern LED lighting controls is not feasible. An example of a PLC being used in the field is the lighting design of Muider Castle. The Muider Castle was constructed in 1280 and is an important historical attraction just outside of Amsterdam. The use of Lumentalk gave the Muider Castle the freedom to upgrade to RGBW without having to excavate the surrounding grounds and thus not exposing any of the castle's architecture to the possibility of damage with the addition of new cables and conduits.
Lumentalk helps protect an architecture's integrity during retrofits but can also be used for more modern settings. When it came to upgrading the lighting design of San Francisco's most famous street, Lumentalk enlivened Castro's Street Business District with color-changing, digitally programmed LEDs without having to tear up the road. This not only saved a great deal of money by not having to excavate, but it also kept the popular area and its businesses in business during the retrofit.
These are just a few of the many examples of how Lumenpulse's PLC, Lumentalk, has been changing the way dynamic lighting can be installed. Lumentalk has allowed such modern, exciting lighting to be a new driving force in projects where it just wasn't feasible from an economic or conservational standpoint in the past.