In the last decade, the use of renewable energy has gained a meditative interest in a lot of applications, especially in-home applications, traction, and industrial systems. Consequently, this requires growing concerns on the reliability of the communications between the smart grid elements. The Power Line Communication (PLC) is considered as one of the most used techniques for the interface between the smart grid elements, as it uses the existing power cables in the system to provide data transmission capabilities. The use of the electrical cable infrastructure results in lowering the cost and providing a high data transition rate; however, a lot of problems could appear in the communication due to the presence of harmonics and conducted Electromagnetic Interference (EMI) in the power cables due to the increasing amount of devices utilizing switching frequencies (e.g. photovoltaic (PV) inverters, chargers for electric vehicles (EV)) in the frequency range of narrowband communication in CENELEC A band. Based on that, the interference in this frequency band can be divided into four types (A-D):
A. Interference between devices with communication
At which two or more devices that has communication features and they work together affect each other causing the increase in the bit error rate. As their interaction is intentional, these devices are designed to work with specific signal to noise ratio. Consequently, this type of interference is not considerable as it is not expected that they disturb each other in an unwanted way.
B. Interference of devices without communication by devices with communication
In this type of interference, the communication equipment (e.g: PLC) can has a great impact of the device without communication as shown on the figure below. This type of interference was stated in [1], For example the PRIME PLC industrial solution work between 42 and 88 kHz frequency band, in this case the PLC can effect of the loads that work with a switching frequency between this range and this may cause the malfunction of the working device and additional heating of internal components of the affected device, which can e.g. reduce its lifetime [2].As the signaling frequencies of PLC are usually above 20 kHz , the generation of audible noise is not an issue for interference type. However, the interference may exist in case of high frequency converter.
C. Interference of devices with communication by devices without communication
In this case, the victim is the communication device (e.g: PLC), the interference cause the decrease of the SNR below the level of noise-free communication, respectively, cause the presence of bite error and sometime failure of the communication .This could be happened for two reasons: the first is due to the low input impedance of the non-communicating device, which lead to the decrease on the level PLC Signal and the receiver will not decode the data accurately. The second reason is the non-intention emission generated by the device without communication which may lay down between the PLC frequencies working range. Depending of the location and the number of the EMI sources, the communication may fail in one or multiple communication devices in the LV network.
D. Interference between devices without communication
Interferences of type D always require at least one device with non-intentional emission. The interaction between devices is again mainly determined by their input impedance characteristic. High non-intentional emission levels combined with low input impedances of the affected equipment can increase the probability of interference significantly. However, if a disturbance finally occurs, depends mainly on the susceptibility of the affected devices. Main consequences of interferences between devices without communication are malfunctions, which are usually reversible, the emission of acoustic noise and additional heating of internal components. The effects based on the type of interference are shown in the table below.
| EFFECT | B | C | D |
|---|---|---|---|
| Additional heating | x | x | |
| Audible noise | x | ||
| Malfunction of equipment | x | x | |
| Malfunction of PLC | x |
The types of noise affecting PLC.
In this case, type C of interference is considered at which the PLC system is the victim. The noise produced by a lot of nonlinear residential work (in the scope of using the PLC in the smart meters applications) was divided into four categories:
1. Noise Synchronous with the 60-Hz Power Frequency
2. Noise with a Smooth Spectrum
3. Single-Event Impulse Noise
4. Nonsynchronous Periodic Noise
1. Noise Synchronous with the 60-Hz Power Frequency
This noise generated from the loads that use the silicon control rectifier (SCR) or solid-state devices like Triacs that work at the same fundamental frequency or multiple of the fundamental frequency. A good example for this type of load is the light dimmers [3].
2. Noise with a Smooth Spectrum
This noise is often created by loads on the line which do not operate synchronously with the powerline frequency. A universal motor, like one used in an electrical drill, is a good example. Such a motor has brushes that cause current switching at intervals which depend on the speed of the motor-the speed is controlled by the load.
3. Single-Event Impulse Noise
Lightning, thermostats, and other switching phenomenon cause such impulse noise. Capacitor banks being switched in and out for power-factor correction create impulse noise.
4. Nonsynchronous Periodic Noise
This type of noise generated by the mean of devices that use transistor or any switching electronic device that lead to continuous periodical noise, in most cases this electronic switching devices work in the frequency range between 10kHz to 100kHz and not synchronized with the fundamental frequency of the grid. Now days, a lot of residential devices working with SMPS and battery chargers that may generate this type of noises.
References:
[1] S. K. Rönnberg et al., “On waveform distortion in the frequency range of 2 kHz–150 kHz—Review and research challenges,” Electr. Power Syst. Res., vol. 150, pp. 1–10, 2017.
[2] CENELEC SC 205A, “Study report II, electromagnetic interference between electrical equipment/systems in the frequency range below 150 kHz, SC 205A/Sec0339/R,” 2013.
[3] D. Q. G. Lwv, F. Kduprqlfv, P. Zklfk, and L. V Lq, “AC Chopper Harmonic Magnitude in Narrowband Power Line Communication Frequencies,” in 2019 7th International Istanbul Smart Grids and Cities Congress and Fair (ICSG), 2019, vol. 1, pp. 3–7.