## 3 Literature Review
While the majority of energy-efficient loads based on power electronics consume significantly less energy than their more antiquated counterparts, the authors of [12] emphasize that they are harmonic pollutants and produce relatively high conducted emissions compared with their power demand. Nonlinear electrical equipment causes an increase in harmonic emission in current, while the range above 2 kHz is relatively little known. Several researchers have begun to characterize the phenomenon of non-intentional conducted emission in the frequency range between 2 and 150 kHz, which is experienced by power system operators. The noise levels measured from CFLs, LED lamps, photovoltaic (PV) inverters, and electric vehicle (EV) chargers are shown in [45; 46; 47]. These noises are experienced by the efficiency of the power line communication (PLC) systems, which are considered as intentionally conducted emissions. As the frequency range used in the PLC is from 2 to 148.5 kHz (supraharmonics range), interferences in the communication channel are expected. Thus, as indicated in [48; 49; 50; 51] the presence of intentional and non-intentional emissions in low voltage (LV) networks is a growing problem and manifests itself, for example, with a malfunction of smart metering systems based on PLC transmission. The authors of [52] analyzed the conducted emission in the suprahramonic frequency range for a set of different LED lamps. Evaluating them is relevant because this type of lighting source has been dynamically developing. The researchers drew attention to the research methodology and examined the emissivity of single and parallel-connected selected devices. The results show that selected LED lamps do not meet EMC standards. Both types of peak and average values of emission are related to the permissible limits given in the standard EN55015 [21]. Three tested lamps from one manufacturer exceeded the permissible limits. These results were not repeatable for other manufacturers. In the case of group work of lamps generating significant electromagnetic disturbances, the lamp emitting the highest disturbances has a decisive influence on total emissivity. Hence, in the case of operation of these loads in a group, connecting lamps from different manufacturers in a common circuit gives a favorable (from an economical and radio-electric point of view) reduction of electromagnetic disturbance values up to 10 dB. However, the emissivity depends on the topology of an LED lamp, the converter used and power supply conditions. The authors of [43] analyze the harmonic and suprahramonic emission of individual LED and CFL lamps in three scenarios: sinusoidal waveform voltage, flat-top shape distorted voltage (total voltage harmonic distortion \(THD_{u}\approx 3\%\)) and pointed-top distorted voltage (\(THD_{u}\approx 4\%\)). The tests were conducted on a group of 142 lamps manufactured between the years 2009 and 2016 (69 CFL sources and 73 LED sources). These lamps work in various ranges of rated power (CFL range up to 46 W, LED range up to 17 W). For the operation of different, as well as for the same type of these lighting sources, clear differences in the current emission in the band above 2 kHz are noticed. Examining LED lamps supplied by a voltage other than sinusoidal in shape indicates that the level of unintentional emissions injected into the network in the frequency range of 30-95 kHz is greater than the emissivity measured during tests for equipment supplied with nominal voltage sinusoidal in shape. The research [53] characterizes the level of waveform distortion introduced by the connected step-by-step 1, 10, and 48 identical fluorescent lamps. The result shows that these are some of the most diffuse electrical loads that introduce significant waveform distortions in low-voltage distribution networks. As the number of connected fluorescent lamps increases, the characteristic effect of decreasing emissions in the total current drawn by these devices at low frequencies of 0-2 kHz is observed.