Version 2 2021-12-09, 13:24Version 2 2021-12-09, 13:24
Version 1 2021-06-15, 04:09Version 1 2021-06-15, 04:09
preprint
posted on 2021-12-09, 13:24authored byM A AwalM A Awal, Md Rifat Kaisar Rachi, Hui YuHui Yu, Iqbal Husain, Srdjan Lukic
A double synchronous unified virtual oscillator controller (dsUVOC) is proposed for grid-forming voltage source converters to achieve synchronization to the fundamental frequency positive- and negative-sequence components of unbalanced or distorted grids. The proposed controller leverages a positive- and a negative-sequence virtual oscillator, a double-sequence current reference generator, and a double-sequence vector limiter. Under fault conditions, the controller enables to clamp the converter output current below the maximum value limited by the converter hardware while retaining synchronization without a phase-locked-loop (PLL) regardless of the balanced or unbalanced nature of grid faults. Consequently, balanced and unbalanced fault ride-through can be achieved without the need for switching to a back-up controller. The paper presents the systematic development of the double-synchronous structure along with detail design and implementation guidelines. Validation of the proposed controller is provided through extensive control-hardware-in-the-loop (CHIL) and laboratory hardware experiments.