PLC technology – Powerline communication

How does CPL (Powerline communication) work? What are the benefits of this technology?

One can easily find products communicating in radiofrequency. This means of communication is not particularly appropriate in older homes. Why ? Just because thick walls absorb electromagnetic signals and make it impossible to control from one room to another or from one floor to another.

Powerline communication t allows communication over very long distances, from one stage to another, or from one room to another even through thick walls. The PLC can be used wherever the radio frequency does not work.

How do we communicate ?

There are two main uses: low frequency (from 3Khz to 150KHz) for data transmission in low bit rate but long range ( >3km see our article on this subject ) and high frequency (from 1 to 100MHz) for transmission in broadband but reduced range. These latter frequencies are widely used for the transmission of an Internet connection via the electrical network but suffer from problems of disturbances inherent in the frequencies used. The more frequent we go, the more we will be sensitive to disturbances and attenuations. Another factor strongly attenuating the carrier current signals are differential circuit breakers and all devices with a ground connection.

Electronically, the signal will be injected or received via capacitive coupling. Behind the capacitor will be present only the carrier frequency.

This shows how this can work, the 50Hz will be completely filtered by the coupling capacitor. The filter composed of the capacitor and the choke will make it possible to roughly filter the carrier current signal which will then be refined through passive and active filters. To emit the signal will come out of the microcontroller and will be amplified before being filtered to be injected on the lines of the sector. The diode is just there to prevent any overflow of the input voltage protecting all downstream stages.

How does PLC work ?

The principle of the powerline communicaiton is based on the following principle. We will superimpose an electrical signal on the existing cables. By way of example, below, a 2.5 KHz carrier on a 50Hz signal with an amplitude 5 times less than the amplitude of the fundamental signal.

At low frequencies, emission levels and frequencies on the network are standardized and fixed by CENELEC (European Committee for Standardization in Electronics and Electrical Engineering). This organization sets 4 usable frequency bands:

Band Fréquency Use
CENELEC A band Spectrum from 3KHz to 95 KHz. Reserved for electricity suppliers.
CENELEC B band Spectrum from  95KHz to 125KHz. All applications, no collision management.
CENELEC C band Spectrum from 125KHz to 140KHz. Domestic networks with collision management (CSMA/CA)
CENELEC D band Spectrum from 140KHz to 148.5KHz. Alarms and security systems without collision management

CENELEC also defines the maximum emission level, it is 122dBuV, ie 1.26Vrms. This level is therefore negligible and completely invisible on the 230V main. Wattlet products use the CENELEC B band as the X10 but at several carrier frequencies around 110KHz.

In high frequency, the standards change, the standards used are governed by the IEEE. Two main standards are used in the HomePlug AV and IEEE 1901. Carrier frequencies in the order of 1 to 30 MHz make it possible to obtain a theoretical throughput of the order of 200 Mbit / s to 600 Mbit / s on a 230 V cable with a theoretical range Maximum on a bare cable of maximum 200m. Beyond 30Mhz up to 100Mhz, we talk about BPL (Broadband Power Line). In this case, a twisted pair or a coaxial cable is generally used. The communication range can then 500m or 1km. Between 1 and 100 MHz, we use nearly 4000 different frequencies. If one or more frequencies are attenuated, the flow rate is therefore not greatly influenced.

Another technology called BPL-MIMO (Multiple-Input / Multiple-Output) makes it possible to considerably increase the throughput by using the earth as a data conductor. This technology has been widely used by Devolo in dLAN pro 1200 products for example. (1200 Mbit / s in three-phase + earth)

Powerline Solutions ?
This CPL technology inevitably makes one think of the X10, a solution released in the 70s and which has had good days with the first lovers of home automation.

This aging industrial standard suffered from some disadvantages: no immunization algorithm to deal with electrical disturbances on power lines (ignition of an appliance, attenuation by the washing machine ...), extreme slowness (1s per order) No acknowledgments, complexities of implementation and programming, problems of certification ...

With Wattlet products all factors of failure were taken into account . They use the latest modulation / demodulation circuits on the power grid recently introduced thanks to the Smartgrid (including the now famous Linky meter).

Comparison Wattlet versus X10 :

 

X10 Wattcube by Wattlet
Frame time 1s 50ms
Programming By coding wheels or by programmer With a badge
Immunization against disturbance None 5 algorithms to protect and restore the signal in case of error
Frame error rate Depending on the environment 1/40million
Communication range Depending on the environment > 3Km
Ackowledgement No Yes
Modulation Carrier presence or absence FSK (Frequency Shift Keying)
Carrier frequency 120KHz 110KHz*

*Several frequencies around 110Khz

Other technologies used by some manufacturers include:

- In One by Legrand

- X2D by Deltadore

These relatively popular products use low frequencies but do not have specific algorithms to immunize against electrical disturbances. Wattlet products are not compatible with these technologies but can coexist on the same electrical network.

What are the disrupters?

In high frequencies, PLC sockets or CPL adapters (D-link, LEA, Netgear, Freeplug, Devolo ...) are often installed next to equipment that disturbs the PLC signal, such as:

- Television
- Amplifier
- Computer
- Printer

There are also other devices that can reduce the carrier current:

- Washing machine
- Chaudière
- Oven
- Differential circuit-breaker (see list of compatible circuit-breakers)
- Circuit Breaker

Where does the disturbance come from?

Disturbances come from three distinct sources:

- Devices with a ground connection

- Non-conforming CE equipment

- Differential switches and circuit - breakers. (see compatible switch / circuit breaker list)

Almost all these devices have one thing in common, they have a connection to the earth (Schuko plug). To reduce the disturbances emitted on the electricity grid, manufacturers are obliged to add electrical components called capacitor X or Y. These components will greatly contribute to reducing the level of disturbance and allow manufacturers to be able to sell their products on The European market. (Standards for CE marking). On the other hand, these electronic components will decrease the carrier current signal if they are close to the PLC transceivers.

The non-CE-compliant devices will emit significant disturbances and will constantly come jamming the transmitted signal. If no algorithm is used, part of the received carrier current signal will be systematically lost. This type of problem is often encountered in power supply units for mobile phones or small power supplies for household appliances. In case of doubt, always try to disconnect these appliances and check that the appliances controlled by PLC module works better.

Circuit breakers and differential switches will attenuate the carrier signal if the carrier current passes through. The internal technology of these equipments contains what is called an inductor or a coil. This element will slightly attenuate the carrier current (# 2 below)

How to avoid these disruptions?

There are several alternatives to reduce the impact of these disrupters:

-The first diagnosis is to find the source of disturbances, so it will be necessary to disconnect device by device to find the source of the problem.

- The easiest solution is therefore to keep as far as possible devices with a connection to the earth. Simply adding a bit of cable between the TV and the power strip, for example, will greatly attenuate the impact of the disturbances.

- Another solution is to use a CPL filter. Generally it is simply an electronic component called inductance that will somehow simulate a significant length of cable and thus decrease the impact of disturbances.

- If the carrier current is to pass through the switchboard via circuit breakers and residual current circuit breakers, the transmitter and the PLC receiver should be tested under the same circuit breaker as far as possible. Alternatively, a phase coupler can be added which will short-circuit the differential switches for the carrier current. ( See our article )

- Use Wattlet products!

 

Wattlet products fully utilize the benefits of this unparalleled technology. The addition of signal correction algorithms and unparalleled programming ease in an extremely small size offers a complete system for renovation or new.

 

More information:

Brochure Wattlet

Product Catalog