Disturbance and Signal Filter for Power Line Communication

: Today, to use home automation, intelligent home controls or remote controls in the ofﬁce, electronic equipment is moving away from wireless communication in favor of Power Line Communication (PLC). In the standard PLC solutions, the corrections that result from error transmissions are based on complex digital modulation methods and algorithms for validating the transmitted data without paying attention to the causes of the errors. This article focuses on the implementation of a ﬁltering system for interference and signals in the 120–150 kHz band (CENELEC band C), which is injected into the network by transmitters. Such a ﬁlter separates the desired signal from the interference that is occurring in the network, which can result in communication errors. Moreover, when used properly, the ﬁlter can be used as a subsystem separation element. The paper presents the requirements, design, construction, simulation and test results that were obtained under actual operating conditions. It is possible to use less complex methods for correcting errors in transmission signals and to guarantee an improvement in the transmission rate using the proposed ﬁlter system.


Introduction
Power line communication systems have been used for various purposes within a broad range of fields, including telephony [1], street lighting controls, intercoms [2] and power transmission systems for almost 100 years [3,4]. Currently, Power Line Communications (PLCs) have a wide range of applications in smart grids [5,6]. The smart building market is in an early stage of its development and has great potential for future growth. According to the report "Smart Building Market Industry Analysis, Size, Growth, Trends, Segment and Forecast 2016-2021" that was prepared by MarketsandMarkets, the value of this market will increase from 7.26 billion dollars to 36.40 billion dollars by 2021 and the expected annual growth rate will be 38% [7]. The idea of an intelligent building has already taken root in developed Asian countries and in the USA, and its rapid development in Europe is also predicted. The fact that this trend is supported by a European Union policy is not without significance and the promotion of energy efficiency and pro-ecological solutions, including intelligent constructions, has been mentioned among the priorities for the coming years [8][9][10][11]. As the current market for intelligent home management systems is heavily dominated by companies that only fast response time, its filters and matching circuits are less expensive, and its processing needs are significantly less demanding-simple encryption and the possibility of defining its own MAC layer. The end application was defined as a power line communication home automation system in which short frames (commands) are exchanged between the nodes and for which the effective range and fast system response time is critical. Autonomous nodes are distributed in the system, and therefore a small form factor and low power consumption must be guaranteed. Inexpensive nodes and accompanying elements are also desirable. Therefore, a low-frequency narrowband power line communication opened for end-user applications with defined medium access control and advantageously without any protocol-dependent MAC was selected as one of the possible application scenarios.
In this case, a ready-made STEVAL-IHP005V1 development board with an ST7540 was used to perform the PLC communication tests. The line coupling interface was modified to allow the ST7540 device to transmit and receive on the AC mains line using the available FSK and PSK [25,26] modes within the European CENELEC EN50065-1 standard C band, which is specified for home network systems with the mandatory access protocol CSMA/CA. Customized software was developed for the STM32 microcontroller, which was included in the reference design in order to make it more flexible and suitable for use as a standalone smart PLC node [27].
Currently, many electric energy receivers are strongly non-linear. Unfortunately, these types of receivers often add disturbances to the power supply network in the frequency band that is used for PLC communication [28]. Under certain circumstances, these may interfere with system communication, thereby leading to delays in executing a command. In extremely unfavorable cases, they can prevent communication completely. One of the ways to avoid such problems with a connection is to create an appropriate communication protocol using the appropriate modulation for the signal transmission [29][30][31][32]. Unfortunately, in many cases [33], the application of even the most sophisticated communication protocol does not solve the problems connected with the transmission of a useful signal. An additional element of such a system operating using PLC technology should be a filter that separates the undesirable signals (noise, interference, disturbances, signals from other PLC network) from the desired signal in the transmission medium. There are many EMI filters [34,35] on the market, but only few fulfill PLC specific requirements. Usually, PLC EMI filters are relatively large and expensive three-phase filters that are intended to be placed in an electrical switchboard next to the main electricity switch. The cost and form factor of the available PLC EMI filters means that they are not suitable for distributed PLC home automation systems. What is more, in the event that the disturbance source is located after the EMI filter, the communication frequencies are vulnerable to disturbances. An example of such a disturbance source that is located inside the PLC network might be the LED power supply or a fluorescent lamp that is controlled by the home automation system.
There is a need for a compact, single-phase, low-current (5 A), cost-effective filter for the distributed PLC home automation applications that work in CENELEC band C. The main goal is to filter a disturbance source inside the home grid as well as to filter a disturbance source that is located near the communication node.

Filter Design
From the point of view of the application of a given electronic system, the basic task of filters is to suppress the undesirable component frequencies that may occur in the control signal. Filter systems are divided into different groups by considering the appropriate criteria. One of the most important of these divisions is the frequency band that is to be suppressed by the filter. Thus, there are different filters-low-pass, high-pass, band-pass including broadband and narrowband (selective) and band-stop-that suppress the signals in a specific frequency band [36]. Other criteria that are considered in the classification of the filters are, for example, the shape of the frequency characteristics: the amplitude and phase, the type of elements that are used and the technology in the system execution. Another important feature of a filter is its level. Filters at I, II and higher levels are used when the higher the filter level, the steeper the edges at the ends of the frequency response are and the frequency response (amplitude) is ideal (rectangular).
The article will focus on the design of an LC filter with chokes in the longitudinal branch and capacitors in the transverse branch as is shown with a diagram in Figure 1a. The role of the inductors is to increase the impedance for a high frequency differential mode component (current or voltage) and the capacitors constitute a low impedance path for differential disturbances at Terminals B 1 and B 2 . In addition, the LC parameters were selected so that the resonance frequency was smaller than the 133 kHz communication frequency that had been selected for the purposes of the study and were of an inductance L = 66 µH and a capacity C = 200 nF, respectively. The influence of the change of the inductor parameters was also taken into account [37][38][39]. The impedance characteristics as seen from Terminals A 1 , A 2 and Terminals B 1 , B 2 are shown in Figure 2. For the communication frequency f com = 133 kHz, the impedance module was Z AA = 49.17 Ω and Z BB = 6.71 Ω. Such impedance values effectively contribute to the filtering of high frequency disturbances in the communication band when the source of the disturbances is connected to Terminals B 1 , B 2 . The article will focus on the design of an LC filter with chokes in the longitudinal branch and capacitors in the transverse branch as is shown with a diagram in Figure 1a. The role of the inductors is to increase the impedance for a high frequency differential mode component (current or voltage) and the capacitors constitute a low impedance path for differential disturbances at Terminals B1 and B2. In addition, the LC parameters were selected so that the resonance frequency was smaller than the 133 kHz communication frequency that had been selected for the purposes of the study and were of an inductance L = 66 μH and a capacity C = 200 nF, respectively. The influence of the change of the inductor parameters was also taken into account [37][38][39]. The impedance characteristics as seen from Terminals A1, A2 and Terminals B1, B2 are shown in Figure 2. For the communication frequency fcom = 133 kHz, the impedance module was ZAA = 49.17 Ω and ZBB = 6.71 Ω. Such impedance values effectively contribute to the filtering of high frequency disturbances in the communication band when the source of the disturbances is connected to Terminals B1, B2.  The paper will focus on an analysis of an LC filter with a structure as is shown in Figure 1b. Figure 1c presents parasitic resistance occurring in L and C. These values are dependent on the components and magnetic materials being used [38]. The solution uses two chokes with the toroidal core DTMSS-20/0.033/8.0-V with the inductance L1 = 33 μH (which gives inductance L = 66 μH) with an allowable current of 8 A and a resistance for the direct current of 15.9 mΩ (total RLdc = 31.8 mΩ). Two WIMA MKS 100 nF/630 V capacitors with a capacity of 100 nF were used. The filter schemes with a view of the printed circuit are shown in Figure 3.  The article will focus on the design of an LC filter with chokes in the longitudinal branch and capacitors in the transverse branch as is shown with a diagram in Figure 1a. The role of the inductors is to increase the impedance for a high frequency differential mode component (current or voltage) and the capacitors constitute a low impedance path for differential disturbances at Terminals B1 and B2. In addition, the LC parameters were selected so that the resonance frequency was smaller than the 133 kHz communication frequency that had been selected for the purposes of the study and were of an inductance L = 66 μH and a capacity C = 200 nF, respectively. The influence of the change of the inductor parameters was also taken into account [37][38][39]. The impedance characteristics as seen from Terminals A1, A2 and Terminals B1, B2 are shown in Figure 2. For the communication frequency fcom = 133 kHz, the impedance module was ZAA = 49.17 Ω and ZBB = 6.71 Ω. Such impedance values effectively contribute to the filtering of high frequency disturbances in the communication band when the source of the disturbances is connected to Terminals B1, B2.  The paper will focus on an analysis of an LC filter with a structure as is shown in Figure 1b. Figure 1c presents parasitic resistance occurring in L and C. These values are dependent on the components and magnetic materials being used [38]. The solution uses two chokes with the toroidal core DTMSS-20/0.033/8.0-V with the inductance L1 = 33 μH (which gives inductance L = 66 μH) with an allowable current of 8 A and a resistance for the direct current of 15.9 mΩ (total RLdc = 31.8 mΩ). Two WIMA MKS 100 nF/630 V capacitors with a capacity of 100 nF were used. The filter schemes with a view of the printed circuit are shown in Figure 3. The paper will focus on an analysis of an LC filter with a structure as is shown in Figure 1b. Figure 1c presents parasitic resistance occurring in L and C. These values are dependent on the components and magnetic materials being used [38]. The solution uses two chokes with the toroidal core DTMSS-20/0.033/8.0-V with the inductance L 1 = 33 µH (which gives inductance L = 66 µH) with an allowable current of 8 A and a resistance for the direct current of 15.9 mΩ (total R Ldc = 31.8 mΩ). Two WIMA MKS 100 nF/630 V capacitors with a capacity of 100 nF were used. The filter schemes with a view of the printed circuit are shown in Figure 3.

Insertion Loss Filter
In order to determine the insertion loss of the topology LC the filter in Figure 1, filter impedance was measured as a function of the frequency using an Agilent 4294 A Impedance Analyzer in a frequency range of 40 Hz to 2 MHz. Figure 1c shows the parasitic resistances of the reactors and capacitors, which, due to the impedance analyzer measurements, led to the determination of the actual parameters as a function of the frequency. The measurements were taken for Figure 3 of the filter. The filters for the SMD inductors were not analyzed because they had a different substitute pattern in which significant self-capacitances of the inductor winding were revealed. Using the toroid core revealed a relatively low self-capacitance of the inductor winding, and therefore, these inductors were taken into consideration for the filter design. Figure 4 presents the frequency characteristics of inductance L and resistance RL of the inductors as well as the capacitance C and resistance RC of the capacitor. The inductance of the inductor was practically constant as a function of frequency, but the capacity of the capacitor changed significantly. According to the LC filter equivalent parameters, the insertion loss was determined from Terminals A1, A2 and from Terminals B1, B2. Both insertion losses were determined analytically for circuits as is shown in Figure 5. The insertion loss was defined as in Equation (1) (1)

Insertion Loss Filter
In order to determine the insertion loss of the topology LC the filter in Figure 1, filter impedance was measured as a function of the frequency using an Agilent 4294 A Impedance Analyzer in a frequency range of 40 Hz to 2 MHz. Figure 1c shows the parasitic resistances of the reactors and capacitors, which, due to the impedance analyzer measurements, led to the determination of the actual parameters as a function of the frequency. The measurements were taken for Figure 3 of the filter. The filters for the SMD inductors were not analyzed because they had a different substitute pattern in which significant self-capacitances of the inductor winding were revealed. Using the toroid core revealed a relatively low self-capacitance of the inductor winding, and therefore, these inductors were taken into consideration for the filter design. Figure 4 presents the frequency characteristics of inductance L and resistance R L of the inductors as well as the capacitance C and resistance R C of the capacitor. The inductance of the inductor was practically constant as a function of frequency, but the capacity of the capacitor changed significantly.

Insertion Loss Filter
In order to determine the insertion loss of the topology LC the filter in Figure 1, filter impedance was measured as a function of the frequency using an Agilent 4294 A Impedance Analyzer in a frequency range of 40 Hz to 2 MHz. Figure 1c shows the parasitic resistances of the reactors and capacitors, which, due to the impedance analyzer measurements, led to the determination of the actual parameters as a function of the frequency. The measurements were taken for Figure 3 of the filter. The filters for the SMD inductors were not analyzed because they had a different substitute pattern in which significant self-capacitances of the inductor winding were revealed. Using the toroid core revealed a relatively low self-capacitance of the inductor winding, and therefore, these inductors were taken into consideration for the filter design. Figure 4 presents the frequency characteristics of inductance L and resistance RL of the inductors as well as the capacitance C and resistance RC of the capacitor. The inductance of the inductor was practically constant as a function of frequency, but the capacity of the capacitor changed significantly. According to the LC filter equivalent parameters, the insertion loss was determined from Terminals A1, A2 and from Terminals B1, B2. Both insertion losses were determined analytically for circuits as is shown in Figure 5. The insertion loss was defined as in Equation (1) (1) According to the LC filter equivalent parameters, the insertion loss was determined from Terminals A 1 , A 2 and from Terminals B 1 , B 2 . Both insertion losses were determined analytically for circuits as is shown in Figure 5. The insertion loss was defined as in Equation (1) AT(dB) = 20 log Electronics 2019, 8, 378 6 of 17 For the insertion loss that was measured from terminals B to A, the scheme is shown in Figure 5 applies.   Voltage V 1 is the voltage that occurs on the standard resistor R w = 50 Ω in a case in which there is no filter in the system (Figure 6a); and V 2 is the output voltage on a standard resistor in a case in which the analyzed LC filter is connected between the R w resistors (Figure 6b).
For the insertion loss that was measured from terminals B to A, the scheme is shown in Figure 5 applies.   According to Figure 6, the following dependences on the voltages V 1 and V 2 can be determined as follows: where Z C = 1 jωC + R C ; Z L = jωL + R L , thus Equation (3) can be rewritten into Equation (4): For the insertion loss that was measured from terminals B to A, the scheme is shown in Figure 5 applies.
Voltage V 1 was the same as in the previous case V 1 = V S /2. Voltage V 2 was determined according to Equation (5) and the filter insertion loss is given as Equation (6). where Z LCR = (Z L +R w )Z C Z L +R w +Z C thus the filter insertion loss is given as Equations (4) and (6) are simplified to the same form, which means that the insertion loss of the filter on the side of Terminals A and B are equal and can be described by Equation (7). The characteristics of the insertion loss are presented as the frequency function in Figure 7.
Equations (4) and (6) are simplified to the same form, which means that the insertion loss of the filter on the side of Terminals A and B are equal and can be described by Equation (7). The characteristics of the insertion loss are presented as the frequency function in Figure 7.
As can be seen in Figure 8, the insertion loss for the 133 kHz frequency that was determined was about 16 dB. Figure 7 shows the characteristics of the filter insertion loss along with the insertion loss of the lossless filters with different inductances and capacitances as a function of the frequency. The   As can be seen in Figure 8, the insertion loss for the 133 kHz frequency that was determined was about 16 dB. Figure Figure 9 shows the filter insertion loss characteristics of the LC filter together with the ideal characteristics that were obtained for filters with different capacitance values with the assumption that C = 200 nF for 0.1C, 0.5C, C, 2C and 5C. With such insertion loss characteristics for the frequency f = 133 kHz, they were 0.9, 9.3, 15.4, 21.6 and 29.7 dB. Based on the actual characteristics, it can be seen that this solution is ideal for frequencies up to 350 kHz. The reason for the discrepancy between the actual insertion loss characteristics and the ideal characteristics was a decrease in the capacitor capacitance for the frequencies above 350 kHz (Figure 4), while the inductance of the chokes in the frequency range from 40 Hz to 2 MHz remained practically constant. The developed filter is a differential filter and the insertion loss for this filter will never be high as is the case with a common filter in which the common currents component are small.  seen that this solution is ideal for frequencies up to 350 kHz. The reason for the discrepancy between the actual insertion loss characteristics and the ideal characteristics was a decrease in the capacitor capacitance for the frequencies above 350 kHz (Figure 4), while the inductance of the chokes in the frequency range from 40 Hz to 2 MHz remained practically constant. The developed filter is a differential filter and the insertion loss for this filter will never be high as is the case with a common filter in which the common currents component are small.  Figure 9 shows the filter insertion loss characteristics of the LC filter together with the ideal characteristics that were obtained for filters with different capacitance values with the assumption that C = 200 nF for 0.1C, 0.5C, C, 2C and 5C. With such insertion loss characteristics for the frequency f = 133 kHz, they were 0.9, 9.3, 15.4, 21.6 and 29.7 dB. Based on the actual characteristics, it can be seen that this solution is ideal for frequencies up to 350 kHz. The reason for the discrepancy between the actual insertion loss characteristics and the ideal characteristics was a decrease in the capacitor capacitance for the frequencies above 350 kHz (Figure 4), while the inductance of the chokes in the frequency range from 40 Hz to 2 MHz remained practically constant. The developed filter is a differential filter and the insertion loss for this filter will never be high as is the case with a common filter in which the common currents component are small.

Thermal Testing of the Filter
If the designed filter is applied next to the disturbance source, it might be exposed to difficult operating conditions such as a constant maximum current flow and poor air circulation. Therefore, heat tests were carried out at a rated current equal to 5 A. The solutions used elements whose rated currents exceeded a 5 A r.m.s. value. The tests were carried out with a load consisting of a set of power supplies with LED lighting that were connected in parallel with a fluorescent lamp and additionally with a thermoregulator with a thyristor voltage controller with an applied phase control. The sum of the currents of the load for the tests was set at 5.4 A. The measurements were performed at an ambient temperature of 19.3 °C. The temperature was measured using a ThermoGear G-30 InfReC thermal imaging camera and a universal meter with an APPA-305 temperature measurement. In each case, the temperature sensor was attached to the surfaces. Therefore, the value from the meter with the temperature sensor was taken as the actual value. A thermal camera was used to determine the points with highest temperature as well as the temperature distribution. In the case of a filter with toroidal throttles, the temperature at a current of 5.4 A in the steady state was 44 °C. The photograph from the thermal camera with the toroidal choke ( Figure 10) for the steady state after heating the filter elements with the 5.4 A current indicated the

Thermal Testing of the Filter
If the designed filter is applied next to the disturbance source, it might be exposed to difficult operating conditions such as a constant maximum current flow and poor air circulation. Therefore, heat tests were carried out at a rated current equal to 5 A. The solutions used elements whose rated currents exceeded a 5 A r.m.s. value. The tests were carried out with a load consisting of a set of power supplies with LED lighting that were connected in parallel with a fluorescent lamp and additionally with a thermoregulator with a thyristor voltage controller with an applied phase control. The sum of the currents of the load for the tests was set at 5.4 A. The measurements were performed at an ambient temperature of 19.3 • C. The temperature was measured using a ThermoGear G-30 InfReC thermal imaging camera and a universal meter with an APPA-305 temperature measurement. In each case, the temperature sensor was attached to the surfaces. Therefore, the value from the meter with the temperature sensor was taken as the actual value. A thermal camera was used to determine the points with highest temperature as well as the temperature distribution. In the case of a filter with toroidal throttles, the temperature at a current of 5.4 A in the steady state was 44 • C. The photograph from the thermal camera with the toroidal choke ( Figure 10) for the steady state after heating the filter elements with the 5.4 A current indicated the temperature distribution on the individual elements. From this, it can be seen that the highest operating temperatures in the filter were observed in the inductors because they conducted the entire load current. However, their operating temperature remained relatively low. temperature distribution on the individual elements. From this, it can be seen that the highest operating temperatures in the filter were observed in the inductors because they conducted the entire load current. However, their operating temperature remained relatively low.

Verification of the Correct Operation of the Developed Filter
The measurements were carried in five variants. The schematic of the measurement system is shown in Figures 11-15 where: the AC source symbol together with yellow noise symbol represents real-life power grid connection, F-the designed filter, EMI-Schafner interference attenuation filter EMI FN 3256 [40], TPLC-transmitter (switch) of the PLC communication system, RPLC-communication system executive (receiver) and ChX-probe connection voltage differentials to the respective oscilloscope channels. The voltage spectra were measured using the FFT function. The scale of x: 50 kHz/div and y: 10 dB/div was set and the offset was x: 0 Hz and y: −30 dB. The load consisted of: -At the end of the supply line: 3 × 12 V/100 W halogen power supplies (each one) and 2 × 12 V/50 W halogen bulbs (each one); -In the middle of the power line: 1 × fluorescent lamp 2 × 36 W with an electronic ballast.

Verification of the Correct Operation of the Developed Filter
The measurements were carried in five variants. The schematic of the measurement system is shown in Figures 11-15 where: the AC source symbol together with yellow noise symbol represents real-life power grid connection, F-the designed filter, EMI-Schafner interference attenuation filter EMI FN 3256 [40], T PLC -transmitter (switch) of the PLC communication system, R PLC -communication system executive (receiver) and ChX-probe connection voltage differentials to the respective oscilloscope channels. The voltage spectra were measured using the FFT function. The scale of X: 50 kHz/div and Y: 10 dB/div was set and the offset was X: 0 Hz and Y: −30 dB. temperature distribution on the individual elements. From this, it can be seen that the highest operating temperatures in the filter were observed in the inductors because they conducted the entire load current. However, their operating temperature remained relatively low.

Verification of the Correct Operation of the Developed Filter
The measurements were carried in five variants. The schematic of the measurement system is shown in Figures 11-15 where: the AC source symbol together with yellow noise symbol represents real-life power grid connection, F-the designed filter, EMI-Schafner interference attenuation filter EMI FN 3256 [40], TPLC-transmitter (switch) of the PLC communication system, RPLC-communication system executive (receiver) and ChX-probe connection voltage differentials to the respective oscilloscope channels. The voltage spectra were measured using the FFT function. The scale of x: 50 kHz/div and y: 10 dB/div was set and the offset was x: 0 Hz and y: −30 dB. The load consisted of: -At the end of the supply line: 3 × 12 V/100 W halogen power supplies (each one) and 2 × 12 V/50 W halogen bulbs (each one); -In the middle of the power line: 1 × fluorescent lamp 2 × 36 W with an electronic ballast.                  Additional tests without EMI filters were carried out. The schematic of the measurement system is shown in Figures 14 and 15. Voltage waveforms and voltage harmonics spectra for the two variants configurations is shown in Figure 17.
Based on the results of the measurements (Figures 16 and 17 and Tables 1 and 2), it was found that: • non-linear type receivers and power supplies weakened the communication signal of the developed system significantly due to the capacitive filter in the input circuits of the power supplies; • the developed filter significantly improved the communication signal level of the developed system in each of the considered cases; • comparing the results for f 1 and the measurements for the variant at U CH1 and U CH2 , the difference in the signal levels at the input and output of the filter was about 5 dBV; however, it must be added that it is difficult to interpret this difference as an insertion loss because sources of interference were present on both sides of the filter; • by comparing the results for f 2 and the measurements for the variant at U CH1 and U CH2 , the difference in the signal levels was about 20 dBV; • adding a fluorescent luminaire in the middle of the model circuit line introduced additional disturbances; these disturbances occurred in the immediate vicinity of 133 kHz, which is used for the transmissions in the developed system; • it is reasonable to also use the filter for devices that are not controlled by a home automation system that has all types of power supplies installed in the immediate vicinity of the operating system; however, such receivers introduce disturbances that may interfere with the transmissions of the developed system; • by comparing the relevant cases, a significant reduction of interference at the level of 5 dBV and an improvement of the signal with a transmission frequency of 133 kHz at the level of 20 dBV can be observed, which proves the need to use correctly designed filters for communication in a PLC; • the use of an EMI filter at the input of the system also resulted in a very strong insertion loss of the communication signal of the developed system, due to the large capacity of the EMI filter; • obtained attenuation level is sufficient to filter both disturbances and communication signals around 133 kHz; • with specific filter applications, an independent communication subnetwork can be created (before and after designed filter), such application might be advantageous for PLC home automation system throughput and response time;  Additional tests without EMI filters were carried out. The schematic of the measurement system is shown in Figures 14 and 15. Voltage waveforms and voltage harmonics spectra for the two variants configurations is shown in Figure 17. Based on the results of the measurements (Figures 16 and 17 and Tables 1 and 2), it was found that: • non-linear type receivers and power supplies weakened the communication signal of the developed system significantly due to the capacitive filter in the input circuits of the power supplies; • the developed filter significantly improved the communication signal level of the developed system in each of the considered cases; • comparing the results for f1 and the measurements for the variant at UCH1 and UCH2, the difference in the signal levels at the input and output of the filter was about 5 dBV; however, it must be added that it is difficult to interpret this difference as an insertion loss because sources of interference were present on both sides of the filter; • by comparing the results for f2 and the measurements for the variant at UCH1 and UCH2, the difference in the signal levels was about 20 dBV; • adding a fluorescent luminaire in the middle of the model circuit line introduced additional disturbances; these disturbances occurred in the immediate vicinity of 133 kHz, which is used for the transmissions in the developed system; • it is reasonable to also use the filter for devices that are not controlled by a home automation system that has all types of power supplies installed in the immediate vicinity of the operating system; however, such receivers introduce disturbances that may interfere with the transmissions of the developed system;

Statistical Tests Used to Verify the Correct Operation of the Filter in a Model System
In order to verify the correct operation of the filters in the model system, a series of statistical tests were performed with different topologies of the model system. Nonetheless, the topology was always based on the layout shown in Figure 13. In each case, the same board, ST7540 configuration, software, 20-byte frame and transmission scheme were used. The transmission scheme was a series of 50 switches ON and 50 switches OFF commands that were sent with one second delay in between transmissions. A carrier frequency of 132.5 kHz was used with a 2.4 kHz frequency deviation (131.348 kHz for "1" and 133.626 kHz for "0") and 2400 Baud. To improve the robustness, Manchester coding was used. The Forward Error Correction (FEC) technique was used as the error correction mechanism. Situations of correct switching without the need for error correction (CS), correct switching after FEC correction (with FEC) and unsuccessful switching (US) were observed. The series of tests was performed for the following topologies of the model system: • TEST1-an EMI filter was connected at the model system input and a fluorescent lamp with a power supply system was connected in the middle of the wires, while LED lighting systems with power supply units, a fluorescent lamp and LED lighting were connected behind the proposed filter system (Figure 13). • TEST2-an EMI filter was present at the input of the model system and a fluorescent lamp with a power supply system was connected in the middle of the wires, LED lighting systems with power supplies worked as the receiver, a fluorescent lamp with no filter was connected and LED lighting was connected with the proposed filtering system ( Figure 12). • TEST3-an EMI filter was present at the input of the model system, while LED lighting systems with power supplies and a fluorescent lamp with a power supply system worked as the receiver and the receivers were connected with the proposed filtering system ( Figure 18). • TEST4-an EMI filter was present at the input of the system, while the receiver was used to work with the LED lighting systems with the power supplies and a fluorescent lamp with a power supply system and the receivers operated without the proposed filtering system ( Figure 19). power supplies worked as the receiver, a fluorescent lamp with no filter was connected and LED lighting was connected with the proposed filtering system ( Figure 12). • TEST3-an EMI filter was present at the input of the model system, while LED lighting systems with power supplies and a fluorescent lamp with a power supply system worked as the receiver and the receivers were connected with the proposed filtering system ( Figure 18). • TEST4-an EMI filter was present at the input of the system, while the receiver was used to work with the LED lighting systems with the power supplies and a fluorescent lamp with a power supply system and the receivers operated without the proposed filtering system ( Figure  19).

Figure 18.
Connection schematic of the model with an EMI filter while LED lighting systems with power supplies and a fluorescent lamp with a power supply system working as the receiver, the receivers were connected with the proposed filtering system (TEST 3).

Figure 19.
Connection schematic of the model with an EMI filter while LED lighting systems with power supplies and a fluorescent lamp with a power supply system working as the receiver, the receivers were connected without the proposed filtering system (TEST 4).
Based on the statistical tests that were performed (Table 3), the following can be concluded: • in the case of the switch OFF tests, there were more problems with the transmission and cases in which there was no response to the signal from the transmitter more often. This was because the receivers generated interference that hindered the reception of the signals; • the absence of additional filters in the system made it practically impossible to control the receivers when connecting in the middle of wires or as a controlled receiver of the fluorescent lamp (TEST2 and TEST4); • in the case of an EMI filter and the use of the developed filters, full system efficiency was obtained from the point of view of controlling the receivers. power supplies worked as the receiver, a fluorescent lamp with no filter was connected and LED lighting was connected with the proposed filtering system ( Figure 12). • TEST3-an EMI filter was present at the input of the model system, while LED lighting systems with power supplies and a fluorescent lamp with a power supply system worked as the receiver and the receivers were connected with the proposed filtering system ( Figure 18). • TEST4-an EMI filter was present at the input of the system, while the receiver was used to work with the LED lighting systems with the power supplies and a fluorescent lamp with a power supply system and the receivers operated without the proposed filtering system ( Figure  19).

Figure 18.
Connection schematic of the model with an EMI filter while LED lighting systems with power supplies and a fluorescent lamp with a power supply system working as the receiver, the receivers were connected with the proposed filtering system (TEST 3).

Figure 19.
Connection schematic of the model with an EMI filter while LED lighting systems with power supplies and a fluorescent lamp with a power supply system working as the receiver, the receivers were connected without the proposed filtering system (TEST 4).
Based on the statistical tests that were performed (Table 3), the following can be concluded: • in the case of the switch OFF tests, there were more problems with the transmission and cases in which there was no response to the signal from the transmitter more often. This was because the receivers generated interference that hindered the reception of the signals; • the absence of additional filters in the system made it practically impossible to control the receivers when connecting in the middle of wires or as a controlled receiver of the fluorescent lamp (TEST2 and TEST4); • in the case of an EMI filter and the use of the developed filters, full system efficiency was obtained from the point of view of controlling the receivers. Figure 19. Connection schematic of the model with an EMI filter while LED lighting systems with power supplies and a fluorescent lamp with a power supply system working as the receiver, the receivers were connected without the proposed filtering system (TEST 4).
Based on the statistical tests that were performed (Table 3), the following can be concluded: • in the case of the switch OFF tests, there were more problems with the transmission and cases in which there was no response to the signal from the transmitter more often. This was because the receivers generated interference that hindered the reception of the signals; • the absence of additional filters in the system made it practically impossible to control the receivers when connecting in the middle of wires or as a controlled receiver of the fluorescent lamp (TEST2 and TEST4); • in the case of an EMI filter and the use of the developed filters, full system efficiency was obtained from the point of view of controlling the receivers.

Conclusions
Today, PLC communication is being used more and more to implement home automation solutions as well as in intelligent homes and remote controls for electronic equipment. In the standard solutions, corrections resulting from error transmissions are based on complex digital modulation methods and algorithms for validating the transmitted data without paying attention to the origin of the errors. In this article, we have focused on the implementation of a filtering system for interference in the 120-150 kHz band that is introduced into the network by receivers. Such a filter separates the desired signal from the interference that occurs in a network, which can result in communication errors. An additional advantage of the developed solution is the ability to provide physical signal separation between two PLC sub-systems (before and after the filter system). This approach might possibly make the response faster and increase the throughput of PLC sub-systems. The entire project cycle was presented beginning with specifying the requirements, through the design, simulation, execution and testing under operating conditions. All of the tests were carried out in real life working conditions with an additional load and the validity and impact of using the EMI filter on the efficiency of information transmissions in the PLC was considered. Through these efforts, it was shown that by using an appropriate filtering system, it is possible to use less complex methods of error correction in the transmission of signals, thus enabling an increase in the transmission speed. In addition, due to the reduction in the complexity of the corrective methods, it is possible to use the computed savings in the capacities to implement other important functionalities or to improve the transmission security without affecting the transmission delay and user experience.