Grid-Following Voltage Source Converter With a PLL-Less PI Passivity-Based Controller for Unbalanced Grid Conditions

Actual voltage-source converters (VSCs) advocate flexible and fast controls, low-voltage ripple levels at the dc-link, and grid compliances for operating under imbalanced grid conditions. To counteract these needs, this investigation focuses on proposing a straightforward passivity-inspired controller structure that facilitates the reference signals' generation to appropriately and quickly regulate grid currents and dc voltage ripples under unbalanced conditions, complying with the harmonic standard (ANSI/IEEE Std 519) thanks to the mitigation of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{2}\omega$</tex-math></inline-formula> oscillation. Since the proposal works on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abc</i> reference frame, this prevents the use of a phase-locked loop, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abc/dq0/abc</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abc/<inline-formula><tex-math notation="LaTeX">$\alpha \beta$</tex-math></inline-formula>/abc</i> transformations, and it reduces the computational burden in the prototyping stage. The results in both real-time simulation and experimental testbed confirm the controller's effectiveness for working under imbalance grid conditions greater than 35% of voltage drops in one or two phases, operating with low 2<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\omega$</tex-math></inline-formula> oscillations, and providing reactive power control. Besides, the controller is featured for settling back the voltage reference in less than 40 ms, guaranteeing voltage ripple levels below 5%, and fulfilling the harmonic standard since it reaches a total harmonic distortion maximum of 2.9%. Also, the passivity-based controller is characterized for reducing the computational burden by 73% compared to the widely used conventional, ensuring a lower computational cost than other approaches that use <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> control as a basis.