Narrowband Powerline Communication—Applications and Challenges—Part II
PLC TransceiversWhatever the type of modulation used, a PLC transceiver includes a few basic blocks. Different solutions use various levels of integration of these components, from full-digital modems with external discrete components to highly integrated systems-on-chip.
The core of each transceiver is the modem itself, which usually implements the Physical and Data Link layers, according to the OSI model. Modulation-demodulation, error correction, media access control are among the major functions performed at this level. A processing unit is responsible for networking, protocol, and application-specific functions. At the other side, transmitted and received signals are processed, in digital and analog form; the main operations include filtering and amplification. The interface with the power lines is made via a capacitive or inductive coupling circuit, which also provides galvanic isolation and protection against line voltage disturbances. The design of the analog front-end is related to the channel characteristics, such as amplitude and frequency of line voltage, wiring style, location, potential disturbances, applicable regulations, etc.
PLC transceivers must be able to cope with the channel electrical impairments and must meet the regional regulations for EMC. In most power line installations, high transmission power is required so that the transmitter be able to drive an adequate amount of signal into low impedance loads. Excellent receiving sensitivity is necessary in order to receive highly attenuated signals. High noise immunity, error detection and correction mechanisms enable data reception with low signal-to-noise ratio. Media access control and adjustable communication frequency allow sharing the medium and adapting to channel conditions.
Narrowband PLC: Where and howNB-PLC finds applications wherever there is electrical wiring, from utility power grid and distributed renewable energy systems to homes and buildings, public lighting, and plug-in electric vehicles. There is also a large variety of custom applications involving AC, DC or un-powered lines, like fireworks control, emergency lighting, dive data management, submersible water pumps – to mention just a few. Each implementation has its own challenges that mainly depend on the channel characteristics and market requirements. We’ll review the main areas of application for NB-PLC and we’ll discuss typical implementation challenges and specific solutions to consider.
Home and building automation
Home and building automation is one of the primaries markets for narrowband PLC. By eliminating the need to install new wiring, PLC transceivers allow easily creating smart automation systems in homes, hotels, offices, commercial and institutional buildings. Energy savings, greater comfort and safety are only a few benefits. Typical implementations include lighting control, load shedding, heating and cooling systems, energy monitoring, fire detection, etc.
The main PLC challenges in home and building environment are the high density of loads, which produce both signal attenuation and noise, and split-phase or three-phase wiring topology, which results in additional signal loss. Typical solutions include:
- Line filters. Built into PLC devices or as stand-alone equipment, they help preventing noise and signal attenuation from critical appliances (for example, High Pressure Discharge lighting, fluorescent light electronic ballasts, refrigerators, computers, etc.).
- Phase-couplers. Connected near the breaker panel, they are usually used to allow PLC signals travel between phases.
- Repeaters. Typically associated with phase-couplers, these devices are helpful in large locations. A coupler-repeater detects data signals upon one phase and repeats them on all phases of the power line system.
Clean energy management
A more recent market for NB-PLC is in the distributed renewable energy systems. Generating electricity from many small energy sources is a modern alternative to traditional large generation plants. The use of renewable distributed energy is growing rapidly, as it allows reducing distribution losses, improving security of supply, lowering pollution, and cutting customer electric bills. Data transfer between energy production devices (like solar panels or wind turbines), inverters and gateways is required for the management of distributed generation systems and for reliable integration to the power grid.
There are two approaches for managing solar or wind energy today:
- Using large single inverters that convert the DC voltage from several PV solar panels or wind turbines into AC energy.
- Using small micro-inverters that perform the DC to AC conversion at each individual source.
In single inverter topologies, the PLC signals are sent on the DC line between individual sources and inverter. The main challenge here is typical high attenuation from inverter’s input capacitors. A possible solution is the use of inductive coupling instead of capacitive coupling. Inductive couplers are based on specialized current transformers that are connected in series on the communication channel. They allow injecting a PLC current signal instead of a voltage on the line, and avoiding the signal attenuation caused by low parallel impedance of the inverter’s capacitors.
In micro-inverter topologies, the communication is performed on the AC line between each micro-inverter and in-home gateways or displays. The challenges here are typical to indoor power lines, i.e. multiple phases and possible high density of loads. Consequently, similar techniques to those find in home and building automation applications can be applied, including line filters, phase couplers, and signal repeaters in larger locations.