A Zero Harmonic Distortion Grid-Forming Converter for Medium Voltage Islanded Microgrids

Grid-forming converters in islanded microgrids face power quality problems due to disturbing loads and possible resonance issues caused by multiple electronically interfaced systems. In addition, grid-forming converters require complex control, filters or topology structures. The present work proposes the application of the Zero Harmonic Distortion Converter (ZHD) as a grid-forming converter due to its inherently sinusoidal voltage source characteristic without the need for capacitive filtering elements that negatively impact costs, efficiency, size, and can originate resonance conditions. These features are achieved by the harmonic cancellation in a three-winding transformer along with harmonic elimination using the Selective Harmonic Elimination Pulse Width Modulation (SHE PWM). Simulation, hardware-in-the-loop, and experimental results show the ZHD converter setting voltage and frequency to an islanded microgrid, delivering sinusoidal voltage waveforms respecting the IEEE 519 harmonic limits, even in the presence of nonlinear loads.