Control Performance Assessment of a Zero Harmonic Distortion Grid-Forming Converter in Islanded Microgrids

The world is currently witnessing a rapid transformation in the production and utilization of electrical energy. The traditional centralized generation model for electric power is swiftly evolving into a more decentralized system, known as Distributed Generation (DG), which incorporates renewable energy sources situated closer to end-users. This shift towards DG has paved the way for the emergence of grid-forming converters, which play a pivotal role in enhancing voltage and frequency stability within microgrids (MGs) and isolated applications. This transformation is primarily driven by the increasing prevalence of inverter-based energy resources. In isolated MGs, ensuring high power quality becomes a paramount concern due to the presence of potentially disruptive loads and the risk of resonance issues arising from the integration of multiple electronically interfaced distributed energy resources (DERs) and loads. This study focuses on assessing the performance of the Zero Harmonic Distortion (ZHD) control method when applied to grid-forming converters in both stand-alone and parallel operation modes. The distinctive feature of this converter lies in its inherent ability to generate a sinusoidal voltage source without the need for capacitive filtering components, which can adversely affect cost, efficiency, and size while potentially contributing to resonance problems. This is achieved through a judicious combination of harmonic cancellation within a three-winding transformer and the utilization of Selective Harmonic Elimination Pulse Width Modulation (SHE PWM) dismissing a closed-loop control structure. Simulation results presented in this work demonstrate the satisfactory performance of the ZHD grid-forming converter.