## 1 Introduction
The inverter needs to reject DC-link ripples, which represent harmonic disturbances from the grid, to produce a clean output. The system can reject grid harmonics through feed-forward cancellation or by using an adequate DC-link capacitor. The inverter controls the voltage reference, so external synchronization is not required, but phase and frequency synchronization with the grid-tied inverter can be useful when reconnecting. Virtual oscillator control and self-synchronization methods can be used to enable DC-link-based coordination between systems [10]. The modern distribution network adopts LVDC systems as flexible alternatives to AC systems because they support renewable generation and provide better energy efficiency and lower conversion losses. ETAP simulations demonstrated that LVDC architectures operating at 110 V, 250 V, and 320 V outperform traditional AC systems by delivering superior voltage drop performance and harmonic distortion reduction and power quality improvement [26]. The review of LVDC microgrids demonstrated their importance for urban applications and prosumer integration and decentralized energy systems [27]. The implementation of advanced power electronic interfaces boosts the functionality of LVDC systems within hybrid power grids. The technological advancement of power converter topologies for electric vehicles and microgrids has been documented in recent research, which demonstrates how multilevel, bidirectional, and modular converters serve as fundamental enablers for grid flexibility [28]. The combination of LVAC-LVDC-HVDC architectures has been proven to decrease energy losses while enhancing DER-rich network hosting capacity [29]. A bipolar modular multilevel DC-DC converter functions as a connection between MVDC and LVDC subsystems by providing galvanic isolation and self-balancing control for decoupled power flow [30]. The research investigated power transmission boundaries of back-to-back converter systems together with PLL dynamics effects on weak grid conditions [31]. The survey of DC microgrid protection identified fast communication-less fault management strategies as essential for improving reliability in modular LVDC architectures [32]. The IDBS-MPET proposes a multiport power electronic transformer structure with isolated LVDC ports and maximum power transfer capability through a single converter [33]. The SiC-based single-to-three-phase converter has been tested for rural LVDS environments to provide a three-phase power supply under nonlinear and unbalanced load conditions [34]. Research on multi-frequency AC/DC systems demonstrates that BTB and AC/DC converters can successfully control power transfer between grids with different frequencies through unified power flow models. The models include converter control strategies, system constraints, and voltage regulation to enable accurate and flexible operation in hybrid power networks [35]. The main objective of this research is to facilitate the integration and control of multi-frequency power in low-voltage networks through a back-to-back converter structure with a shared DC-link. The proposed system includes a grid-side inverter that feeds fundamental and harmonic components into the DC link and a load-side inverter that reconstructs a pure 50 Hz voltage for residential loads. The DVR generates harmonic components on purpose to enable power transfer between different frequency channels without disrupting sensitive end-users. The DC-link functions as a frequency-selective barrier to protect the load from upstream harmonic distortions while enabling total power transmission, including harmonic contributions through controlled conversion. The research demonstrates that LVDC systems, together with modular converter topologies and harmonically decoupled back-to-back interfaces, form essential building blocks for future multifrequency power transfer networks.