## 1 Introduction  
After the Paris climate agreement, all the EU countries committed to strict yearly targets in terms of CO2 emissions reduction, energy conservation, and the adoption of clean energy sources. Aiming to meet such ambitious energy sustainability goals, smart grid solutions have become more and more frequently adopted to effectively manage energy generation, transfer, and storage systems. With the expansion of the smart grid, communications between the increasing number of smart devices connected to the grid are essential, and any interruption or transmission error could lead to significant losses. In this context, Power Line Communication (PLC) is one of the most commonly used approaches for communication networks, as it does not require extra infrastructure for data transfer. Modern smart grid communication systems face several key challenges, primarily due to signal repetition, protocol incompatibility, and electromagnetic interference (EMI) [1]. Major contributors to EMI include switching-mode power converters [2, 3], LED lighting [4], and energy storage systems (ESS) [5]. Among these, switching-mode power convertersare particularly problematic, as they can significantly disrupt smart grid communication. Studies such as [6,7] highlighted how the conducted EMI from nearby equipment can impair Power Line Communication (PLC), sometimes causing smart meter malfunctions. This issue stems from the fact that both smart meters and switching-mode converters operate within the CISPR A narrowband frequency range (9-150 kHz), making them especially vulnerable to interference [8]. As a result, PLC system performance may degrade, leading to data transmission failures. A number of researchers have been investigating techniques to reduce the emissions of switching-mode converters. Some researchers proposed the utilization of power filters. However, this can be costly and require additional space [9,10]. A different approach proposes to reduce emissions of switching-based devices by modulating the switching signals by Spread Spectrum (SS) modulation techniques [11, 12, 13]. This approach is particularly attractive since it comes almost for free, with no need for additional circuits. SS modulations vary the switching pattern of power converters by spreading the EMI power over a definite frequency range. Based on the literature, many variables can be controlled in SS modulations, namely the switching frequency [14], phase shift [15], duty cycle [16], or a combination of them [17,18]. While the advantage of SS reduction in the measured emission peaks is clear, their practical effectiveness in reducing the interfering potential of switching signals is a more controversial matter. In particular, the influence of SS-modulated EMI on communication systems has been studied in many research studies, giving contradicting results. In [19], it is shown that the SS modulation has no advantage over the conventional modulation, and both modulation techniques have the same effect on the performance of the serial communication system. Other research shows that it is important to tune the SS parameters properly to avoid the spreading of emissions to levels that cause more transmitted data losses as presented in [20,21]. The shape of the generated EMI depends mainly on parameters like the modulation switching frequency, the bandwidth of the used SS modulation, the rate of change between frequencies, or the phase shift. Consequently, the behavior of the victim channel changes extremely with the chosen SS parameters setting. This paper investigates the effect of the buck converter while using SS modulation on G3-PLC performance. The Shannon capacity equation is used to evaluate the performance of the communication system under the SS-modulated EMI. The utilized SS in this paper is Random Carrier Frequency Modulation with Constant Duty cycle (RCFMFD), while controlling three variables (spreading factor, modulating signal profile, and modulating signal sampling frequency).