Current Error Based Compensations for VSC Current Control in Weak Grids for Wind Farm Applications

Controlled transition bridge converter: Operating principle, control and application in HVDC transmission systems

“…5(a) experiences sudden collapse when the dc or active power being transmitted exceeds 85% of the rated power. It is worth emphasizing that this problem is well known when the voltage source converters operate in weak ac system and extensively investigated [38,39]. But this is beyond the scope of this paper.…”

A Less-Intrusive Approach to Stabilize VSC Transmission Against Highly Variable Grid Strength

“…Since PLL was regarded as the cause of negative damping in weak grids [17][18], intensive researches have been carried out to mitigate the impact brought by PLL [19][20][21][22][23]. The corresponding approaches can be categorized into two types: 1) tuning the parameters of a PLL [22] [23]; 2) modifying the structure of PLL [19] [20]. By reducing the gains of a PLL in weaker grids, the former type can effectively improve system damping when the grid condition is fixed or known; however, its robustness is undermined with unknown grid strength, especially during a fast-developing event, e.g.…”

“…fault isolation. By adding extra compensation or modifying the closed-loop design of a PLL [19] [20], the latter approach can be designed with better damping against SCR variations. However, the absence of effective reactive power dispatching and voltage control scheme limits the operational margin [21].…”

“…Known as "var/volt" droop, reactive power/voltage droop can provide automatic voltage support [22]; nevertheless, its coupling effect with electromagnetic damping has been overlooked and therefore not adequately investigated. Further, for most studies reported, stability analysis is based on a presumed equilibrium point [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], but how it is reached has not been explicitly explained.…”

Machine learning based impedance estimation in power system

“…The increasing penetration of power electronic converter interfaced distributed energy sources into the power grid, introduced new challenges to the monitoring, protection and control of the system [1]. The high amount of converter interfaced sources impacts the stability of the system, especially in a weak grid with high inductive impedance [2][3][4][5][6]. The knowledge of the grid impedance at the connection point of the converter to the grid (PCC) is essential for improving the control strategy and overall grid stability by either changing the control action or re-tuning the controller [7].…”