## 2 Literature Review
### Gap in the Research Related to Influence of Supply Voltage Distortion on Supraharmonics Emission
However, these tests also ignore the issue of low-frequency emissions from the distorted supply voltage. In turn, in article [24], the authors outlined the third line of considerations. Based on tests carried out with the use of LED light sources and compact fluorescent lamps, the authors confirmed that the share of non-intentional emission introduced into the network by these loads might be greater than the results of emission tests carried out under the conditions of emission tests of loads following EN 61000-3-2 standard. Although the authors observed emission in the frequency band 2-40 kHz, it should be assumed that this phenomenon might also apply to other frequency ranges. In each of the three lines of the problem consideration presented above, it can be shown that the aspect of the harmonic content in the supply voltage, in the range 0-2 kHz, as the potential origin of the increased level of non-intentional emission of the electrical devices, in the range 2-150 kHz, has not been (as of yet) sufficiently investigated. Many works investigate the impact of selected supply voltage parameters on current harmonics up to 2 kHz. Many works also present current supraharmonic emissions of different electrical devices, but are usually investigated under sinusoidal supply voltage. This work is focused on the non-intentional emission of the selected electrical devices under non-sinusoidal supply voltage conditions and their impact on power line communications. In [27; 31], authors attempted to assess the influence of the voltage curve distortion in the form of a flattening of the peak of a sine wave, which corresponds to an increase in the harmonic content factor. The authors of these works, using the example of lighting devices, assessed the harmonic content during parallel operating the devices. The authors demonstrated, among other findings, that new electronic equipment based on active power factor correction (PFC) shows a qualitatively different dependence of harmonic emissions on the degree of distortion (flattening) of the supply voltage concerning loads without PFC. The influence of voltage distortion on the differences in work efficiency between compact fluorescent lamps (CFL) and light emitting diode (LED) light sources in the low and high-frequency range was described in [17]. The tests were carried out for three scenarios: sinusoidal voltage, flat-top distorted voltage (total harmonic distortion in voltage THDV about 3%), and pointed-top distorted voltage (overswing) (THDV about 4% in accordance with IEC 61000-4-13), which were used to power a group of 142 lamps manufactured in 2009-2016 (69 CFL sources and 73 LED sources). These lamps worked in various ranges of rated power (CFL range up to 46 W, LED range up to 17 W). A frequent phenomenon is also the secondary emission of the load, which is understood as the part of the current of the tested load that is not derived from its primary emission, but is transferred by parallel connections from another load. The research results presented in [9; 17; 18; 21] indicate that, due to the use of various input systems of loads, including EMC filters, and due to the phenomenon of secondary emission from the parallel operation of loads, the share of higher frequencies in the supply current at the point of common coupling (PCC) point might be smaller than would result from the emission of individual loads. It has been observed that in the case of supraharmonic emissions above 2 kHz, some frequency components of the currents are closed by the input circuits of neighbouring loads and some of the frequency components of the currents are closed by the supply and neutral circuits. The issue of secondary emission is also present in the considerations concerning the influence of loads' operation on the narrowband PLC transmission. In [23], authors indicate selected disturbances originating from loads connected to the LV network, which may affect the transmission efficiency in the range of 0-2 kHz and 2-150 kHz.