Analytical Dual-Sequence Current Injections Feasible Region of Weak-Grid Connected VSC Under Asymmetric Grid Faults

Abstract

For phase-locked-loop synchronization (PLL-Syn) based Weak-Grid connected Voltage Source Converter (WG-VSC) system under asymmetric grid faults, published works mainly focus on existing of equilibrium point and small signal stability, which cannot address PLL-Syn transient stability problems. For the first time, we have proposed an analytical solution to the question of “ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Whether the WG-VSC system can reach to a new available equilibrium point (EP) of fault-on state from original EP of pre-fault state without loss of PLL-Syn transient stability under asymmetric faults?</i> ”. Dual-sequence current injections feasible region (CIFR) of WG-VSCs in positive and negative sequence current injection space is defined firstly. Then, by considering <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PLL-Syn transient stability constraint, Maximum available current constraint, and PCC Voltage constraint</i> , an analytical expression of CIFR has been obtained. Finally, experiments results based on detailed switching model in RT-BOX hardware-in-loop platform have been provided to verify the CIFR constructed in this paper. It should be noted that the work of this paper can not only address PLL-Syn transient stability problems of WG-VSC system under asymmetric faults, but also can pave the way for asymmetric fault ride-through control considering transient stability constraints.